Solar Impulse plane leaves Oklahoma for Dayton

An experimental, solar-powered aircraft took off from Tulsa in the midwestern US state of Oklahoma early Saturday, kicking off the latest phase of its record-breaking quest to circle the globe without consuming a drop of fuel. Swiss businessman Andre Borschberg, who has teamed up with adventurer Bertrand Piccard for the Solar Impulse 2 project, piloted the flight expected to last about 18 hours. The plane, which aims to promote clean energy technologies, departed at 4:22 am (0922 GMT) from Tulsa International Airport and was due to land at Dayton International Airport, Ohio, hours later, at 11:00 pm (0300 GMT Sunday), project organizers said. “The flight is part of the attempt to achieve the first ever Round-The-World Solar Flight, the goal of which is to demonstrate how modern clean technologies can achieve the impossible,” they said in a statement. “Watching Si2 silently lift off is beautiful. Science fiction in reality!” a logbook comment said on the project’s website. The journey kicked off in Abu Dhabi on March 9, 2015. Thanks to an inflatable mobile hangar, which can be packed up quickly and transported, Solar Impulse 2 can be sheltered at a variety of locations. The aircraft was grounded in July when its batteries were damaged halfway through its 21,700-mile (35,000-kilometer) circumnavigation of the globe. The crew took several months to repair the damage caused by high tropical temperatures during a 4,000-mile flight between Nagoya, Japan and Hawaii. The plane was flown on that stage by Borschberg, whose 118-hour journey smashed the previous record of 76 hours and 45 minutes set by US adventurer Steve Fossett in 2006. He took catnaps of just 20 minutes at a time to maintain control of the pioneering plane during the flight from Japan, in what his team described as “difficult” conditions. – How it works – The Solar Impulse 2, which weighs roughly the same as a family car but has wings wider than those of a Boeing 747, contains 17,000 solar cells that power the aircraft’s propellers and charge batteries. At night, the plane runs on stored energy. The typical flight speed is around 30 miles an hour, which can increase to double that when exposed to full sunlight. After crossing the United States, the pilots are set to make a transatlantic flight to Europe, from where they plan to make their way back to their point of departure in Abu Dhabi. Piccard, a doctor by training, completed the first non-stop round-the-world balloon flight in 1999. His teammate Borschberg is no stranger to adventure — 15 years ago he narrowly escaped an avalanche, and in 2013 he survived a helicopter crash with just minor injuries.
source:http://www.solarimpulse.com/

ees AWARD: Ten entries shortlisted for the energy storage industry’s innovation prize

For the third time running, the ees AWARD is set to be presented for outstanding solutions and innovations in energy storage technology. This year, the prestigious prize received a record number of submissions. Ten of these can now pride themselves on having been nominated as finalists.

The winner will be announced at the Innovation and Application Forum at ees Europe, the continent’s largest exhibition for batteries and energy storage systems, on June 22^nd, 2016.

The event takes place in parallel with Intersolar Europe, the world’s largest exhibition for the solar industry and its partners from June 22–24, 2016 in Munich.

Energy storage systems are an important cornerstone of the global energy transition. As volatile energy sources, such as solar or wind power, do not consistently generate electricity, batteries will ensure stability and supply safety in the power grid of the future by decoupling generation from consumption in private and commercial usage.

To celebrate the industry’s innovative strength, the ees AWARD pays tribute to outstanding products and solutions in the field of energy storage. Submissions ranged from new materials to innovations in the areas of production, systems technology, applications, second-use concepts and recycling.

Submission trends

The many submissions for the ees AWARD revealed several trends, such as a new generation of domestic storage systems. These use JH3 lithium-ion cells developed specifically for stationary batteries, and a special separator to guarantee the highest degree of safety. The finalists clearly demonstrate that wireless interfaces, for example smart meters and control options using Apps, are gaining in importance in the energy storage industry.

One submission succeeded in closing a gap in the inverter market: A transformerless, high-voltage inverter offering a high level of flexibility for both retrofit projects and new installations.

In general, flexibility and diverse fields of application are key topics in the industry. This is why storage devices, which can be used on and off-grid, or are available for both low-voltage (48V DC) and high voltage systems (400V DC), are amongst the finalists.

The industry has also been working on solutions to stabilize weak power grids. Submissions included technologies to establish microgrids (local, decentralized power grids) as active grid components, and solutions combining photovoltaics and wind power.

ees Europe award ceremony

The winners of the ees AWARD will be announced on Wednesday, June 22^nd, at ees Europe at Messe Muenchen. Their awards will be presented alongside the Intersolar AWARD at 4:30pm at the Innovation and Application Forum. Visitors have the opportunity to meet the finalists before then, as they will be holding short presentations about their submissions and will be on hand to answer any questions between 10:30am and 3:00pm.

An overview of the ees AWARD finalists

• Ampere Power Energy S.L. (Spain): Easily installed storage device with wireless connection to the smart meter and corresponding App.
  
  
• BOS Balance of Storage Systems AG (Germany): Additional lithium-ion batteries for energy storage systems based on led batteries extending the entire system’s life span through smart connections.
  
  
• Digatron Power Electronics GmbH (Germany): Improved battery tester efficiency using silicon carbide semiconductors.
• Ferroamp Elektronik AB (Sweden): Bidirectional inverter for different PV strings, batteries and DC consumers. A high-voltage DC nanogrid connects different producers, such as sun, wind and water, and minimizes transmission losses throughout the entire system.
• Green Power Technologies, SL (Spain): Storage solutions on a megawatt-scale, where various producers can be integrated to help stabilize weak power grids.
• LG Chem (Korea): New generation of domestic storage systems with high energy density using advanced cell technologies (JH3 cells).
• Morningstar Corporation (USA): Charge controller for a wide variety of storage technologies with 98% efficiency.
  
  
• SMA Solar Technology AG (Germany): A transformerless high-voltage inverter, this innovative battery inverter closed a gap in the inverter market and is ideal for retrofitting existing PV installations with storage devices.
• SOCOMEC (France): Storage solution which can be operated both in the grid and in standalone mode – ideal for use as a microgrid in off-grid regions.
• sonnen GmbH (Germany): sonnenCommunity connects decentralized renewable energy producers with storage system operators and consumers throughout Germany, enabling its members to remain completely independent of the public power grid.
• source:http://www.solarserver.com

SA Power Networks to conduct trial of combined solar PV and batteries

SA Power Networks (Adelaide, Australia), the operator of the South Australian electricity distribution network, will deploy about 100 Tesla Energy and Samsung batteries in Salisbury in Australia’s largest trial of combined solar and energy storage in an established suburb.

The unique trial will get underway in June 2016 and will test the benefits of combining solar and battery storage to avoid the need to build additional network infrastructure to meet growth in local electricity demand in an existing residential area.

“In the next few years we will need to act to meet localised demand growth in Salisbury,” said Paul Roberts, Manager Stakeholder Relations.

“We want to work with customers to avoid the need to invest in new poles and wires. Instead of building a new power line, we would like to see whether we can defer or avoid that by tapping into local solar PV generation and combining this with energy storage.”

Financial support in purchasing batteries, PV panels

In a once-only offer, eligible customers will receive significant financial assistance in purchasing batteries (and solar panels if required), and also are guaranteed a minimum USD 500 per annum in savings on their electricity bill.

“Combinations of solar PV, battery storage and grid connections are the future of energy provision. With the right settings and approach they will provide benefits for customers and to us as managers of the network and also help contain long–term network costs for customers.

source:http://www.solarserver.com

Intersolar AWARD: Finalists announced for the solar industry innovation prize

Complete with a new category and record number of submissions, this year’s Intersolar AWARD pays tribute to ground-breaking innovations in the solar industry for the ninth time in a row.

Joining the established Photovoltaics category is the category entitled Outstanding Solar Projects, which will this year make its debut on a global level. The new category recognizes outstanding projects from around the world that make an exceptional contribution to driving forward the solar energy transition.

The winners will be announced in an official ceremony on June 22^nd, 2016 at Intersolar Europe, the world’s largest exhibition for the solar industry and its partners. The exhibition takes place in Munich from June 22–24, 2016.

Highly regarded in the industry, the award serves as testament of the pioneering position held by finalists and winners in the market. This year, it was not only Intersolar exhibitors who could submit entries for the award – owners of solar projects were also eligible.

An Intersolar AWARD debut

This year, the prize was expanded to include a further category: Outstanding Solar Projects honors projects that drive forward the global energy transition.

The submissions are indicative of the wide range of areas in which solar energy can be used. From a power-to-gas plant to the installation of a microgrid in Bangladesh that supplies clean solar power to homes not fitted with their own PV installations, the projects that were entered highlight the wide range of potential solar energy applications. Especially pleasing was that many of the projects submitted do not require grants or subsidies, as they are economical and their investment costs will be recovered in just a few years.

Many initiatives have succeeded in generating power in their regions at a cheaper rate than power purchased from the grid. Numerous projects place particular emphasis on helping society. In addition to generating power, they also bring additional benefits to the regions in which they are installed.

One example is in India, where small villages have been given access to electricity for the first time, enabling locals to read and study in the evening using electric lighting. The submissions also show that numerous countries are now turning their focus to large-scale photovoltaic installations, some of which with double-digit megawatt outputs. These systems make a valuable contribution to the energy transition.

Increase in economic viability and reduction in production costs – the 2016 trends

This year once again, the established Photovoltaics category received a large number of submissions, ranging from a production facility for cell strings to solar modules, inverters, trackers and electronics and from roof integration and mounting systems to operation and maintenance products and services.

As in the past, many submissions aim to boost the economic viability of solar installations by increasing their efficiency whilst reducing production costs, thus accelerating the expansion of solar power generation around the world.

Award ceremony and short presentations by the finalists

The winners of the Intersolar AWARD in the categories of Photovoltaics and Outstanding Solar Projects will be announced in an official ceremony on June 22^nd at Intersolar Europe, together with the winners of the ees AWARD.

The finalists of the Outstanding Solar Projects catego

• Alpiq InTec Management AG (Switzerland): Investigation into creating an intelligent power distribution grid. The Gridsense smart-energy solution combines an energy management system for smart buildings with a smart grid control system that monitors and regulates grid quality.
  
• DHYBRID Power Systems GmbH (Germany): Installation of a PV-diesel hybrid system on Mustique Island in the Caribbean, saving almost 500,000 liters of diesel per year.
  
  
• Aquion Energy (USA): Construction of a residential smart grid in Bakken Hale on Hawaii with a 176 kW solar array and 1 MWh storage capacity. The project stands out with a new environmentally friendly battery system made from carbon, manganese oxide and saltwater. The saltwater-based electrolyte used does not contain any heavy metals or toxic chemicals.
  
  
• Jakson Engineers LTD (India): Electrification of a village in India, making it the first village in the state of Odisha to be powered completely by solar energy.
  
  
• ME SOLshare Ltd. (Germany): A microgrid in the Shakimali Madborkandi village in Bangladesh connects owners of solar home systems with neighboring households not fitted with their own PV installations.
  
  
• Modern Arabia for Solar Energy MASE (Jordan): Installation of 400 roof-mounted solar installations with a total output of 600 kilowatt peak (kWp), facilitating access to cleaner, cheaper energy for low-income households.
  
  
• Rajasthan Electronics & Instruments Limited (India): Installation of a PV power plant with an output of 1 megawatt (MW) at India’s Katra Railway Station, an environmentally sensitive area with high visibility due to the 10 million pilgrims who pass through the station each year.
  
  
• RWE Deutschland (Germany): Installation and operation of a power-to-gas demonstration plant with an output of 150 kilowatts (kW). The plant links the power grid, gas grid and heating network, while allowing excess energy to be converted into gas.
  
  
• S.O.L.I.D. (Austria): Most powerful solar cooling system of its kind in the world, located in Scottsdale, Arizona, USA. With a collector area of 4,865 m² and a cooling capacity of 1,750 kW, the system provides the air conditioning for a school with over 2,600 students.
  
  
• Schneider Electric SE (France): Photovoltaic installations and battery storage units fitted in 170 schools and 11 public health centers in Nigeria.
  
  
• SMA Sunbelt Energy GmbH (Germany): Construction of a hybrid power supply system comprising photovoltaic modules, battery storage units and diesel generators on St. Eustatius island in the Caribbean.
  
  
• TERRA TECHNOLOGIES (Senegal): Construction of a house made from local materials in Dakar, Senegal that covers all its power requirements using renewable sources of energy. Excess power is fed into the public grid.
  
  
• Umwelt Arena AG (Switzerland): Construction of a self-sufficient multi-family dwelling powered entirely by photovoltaics in Brutten, Switzerland. Excess power is stored in batteries or converted into hydrogen to be used as heat.

The following submissions have made it through to the final round in the Photovoltaics category:

• IBC SOLAR AG (Germany): Control system for solar-powered water pumps for use in agriculture.

• iLumen BVBA (Belgium): Easy-to-install PID box that regenerates PV modules damaged by potential induced degradation (PID) at night.
  
  
• LG Electronics Deutschland GmbH (Germany): Bifacial solar module with the ability to boost a system’s yields by more than 10% in an optimal installation environment.
  
  
• M10 Industries AG (Germany): Multi-tray stringer with the capacity to process up to 5,000 solar cells per hour, significantly reducing PV module production costs.
  
  
• MBJ Solutions GmbH (Germany): Module tester for production facilities which combines several quality tests, increasing the efficiency of final checks for manufactured modules.
  
  
• NEXTracker (USA): Technical, cost-effective package solution for PV ground-mounted installations, allowing projects to be installed efficiently as well as boosting yields and thus improving economic viability.
  
  
• Solar Data Systems, Inc. (USA): Components for monitoring the yield and operation of PV installations built into a standard metering device.
  
  
• SolarEdge Technologies (Israel): Highly efficient, compact inverter with innovative power electronics at less than half the weight and size of comparable standard devices.
  
  
• Sunpreme Inc. (USA): Bifacial solar module with integrated optimizer in an extremely robust design, enabling it to withstand even adverse ambient conditions.
  
  
• Weidmuller Interface GmbH & Co. KG (Germany): Innovative plug-in connector for DC cables that simplifies PV system cabling, considerably reducing cabling times and eliminating errors during the installation process.
• source:http://www.solarserver.com

Tata Power wins 100 MW solar PV projects in Karnataka, India

Tata Power (Mumbai), India’s largest integrated power company, on May 19^th, 2016 announced that the Company’s 100% subsidiary, Tata Power Renewable Energy Ltd. (TPREL) has won two grid-connected solar photovoltaic (PV) projects of 50 MW capacity each in Pavagada Solar Park in the Tumkur district of Karnataka.

The PV projects have been awarded under the Jawaharlal Nehru National Solar Mission (JNNSM) Phase-Il Batch-Il Tranche-l under “State Specific Bundling Scheme”.

TPREL has received the Letter Of Intent to develop the projects and will sign a 25 year Power Purchase Agreement (PPA) with NTPC Vidyut Vyapar Nigam Ltd.

“The two solar projects will add 100 MW of non-fossil fuel energy to our total generation capacity, thereby, significantly increasing our green footprint,” comments Anil Sardana, CEO & Managing Director, Tata Power.

“This move is line with the Government’s set target of 100 GW from solar energy by 2017. In the next 5 years, the Company plans to significantly add to its solar generation capacity.”

 source:http://www.solarserver.com

New study: Solar power could supply 27% of U.S. electricity demand in 2050

Solar power could deliver USD 400 billion in environmental and public health benefits throughout the United States by 2050, according to a study from the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and National Renewable Energy Laboratory (NREL).

“We find that an U.S. electric system in which solar plays a major role – supplying 14% of demand in 2030, and 27% in 2050 – would result in enduring environmental and health benefits,” said Ryan Wiser of Berkeley Lab’s Energy Technologies Area.

“Moreover, we find that the existing fleet of solar plants is already offering a down-payment towards those benefits, and that there are sizable regional differences in the benefits.”

The total monetary value of the greenhouse-gas and air pollution benefits of the high-penetration solar scenario exceeds USD 400 billion in present-value terms under central assumptions.

Focusing on the existing end-of-2014 fleet of solar power projects, recent annual benefits equal more than USD 1.5 billion under central assumptions.

Benefits of the Existing Fleet of Solar Projects

The study finds that the 20 gigawatts (GW) of solar installed as of the end of 2014 is already lowering annual greenhouse gases (GHGs) by 17 million metric tons, worth about USD 700 million per year if valued with a central estimate of the “social cost of carbon” – the Obama Administration’s estimate of the long-term damage done by one ton of carbon emissions. Over half of these benefits come from emissions reductions in California.

Benefits from a high-penetration solar energy future

Looking further ahead, with solar growing to 14% of demand by 2030 and 27% by 2050, the study finds GHG reductions of 13% in 2030 and 18% in 2050, compared to a scenario of no new solar.

These emission reductions are worth about USD 259 billion in reduced global climate damages based on central estimates, or 2.2 cents per kWh of solar.

source:http://www.solarserver.com

CSEM unveils new facilities at its solar PV center

On May 19^th, 2016 CSEM, the Swiss Center for Electronics and Microtechnology, has unveiled the new facilities at its PV-Center. The existing infrastructures have been extended with a cleanroom, module testing, and production laboratories covering over a thousand square meters.

This will allow researchers to continue the work begun three years ago and explore different avenues to develop solar energy for the benefit of the economy and society.

A number of personalities from the energy sector came to look around CSEM’s new photovoltaic (PV) facilities in Neuchâtel.

The addition of the 500 m² clean room and the 600 m² PV module testing and production laboratories means that the PV-Center is now fully operational.

The Center provides an extraordinary environment for the 50 people who work there. They benefit from optimal working conditions in which to improve and test the various photovoltaic technologies and expand their scope of applications.

Firmly industry-focused

“These new infrastructures are unique in Switzerland. With them, we will be able to help Swiss companies increase their competitiveness,” explains Christophe Ballif, PV-Center Director.

“Although solar energy is enjoying rapid growth, it is still far from being used to its full potential – in association with everyday objects, for example.”

The PV-Center was inaugurated three years ago and has rapidly forged itself a reputation that reaches beyond Swiss borders. It works to improve the performance of silicon cells using heterojunction technology (HJT) and has developed white and colored panels, a world first that has been a hit with architects.

Helping Switzerland reach its energy goals

“In the array of technologies developed by CSEM, photovoltaics are given special focus,” says Mario El-Khoury, CSEM's CEO.

“As this becomes more widespread, the world can dream of a cleaner future, where quality of life is maintained. This aspiration is a core value for our company.”

The work of Christophe Ballif and his team aims to boost the appeal of solar energy, an undertaking that will help the Swiss Confederation hit its energy targets. The Federal Council fully appreciates this, which is why it provides the Center with financial support.

The Center works with a range of industries and research laboratories in Switzerland – including the EPFL (the Swiss Federal Institute of Technology Lausanne) photovoltaic laboratory in Neuchâtel, known as the PV-Lab. 

source:http://www.solarserver.com

Airbus Defence and Space enters solar cell production contract with MicroLink Devices for next generation unmanned air vehicles

MicroLink Devices (Niles, Illinois, U.S.) on May 18^th, 2016 announced that Airbus Defence and Space has issued a production contract for MicroLink's epitaxial liftoff (ELO)-based multi-junction solar photovoltaic (PV) sheets for use on the new Zephyr S platform.

MicroLink has developed a lightweight, flexible, high-efficiency solar PV sheet that is an enabling technology for electrically powered, area and weight constrained applications such as unmanned air vehicles, which run on renewable energy.

Unmanned air vehicle runs exclusively on solar power

The Zephyr platform is a new class of unmanned air vehicle that operates as a high altitude pseudo-satellite (HAPS) enabling affordable, persistent, local satellite-like services.

The aircraft runs exclusively on solar power, and the Zephyr aircraft is at the forefront of the HAPS arena, holding world records with regards to absolute endurance (more than 14 days) and altitude (more than 70,000 feet). The British Ministry of Defence currently has ordered two Zephyr S from Airbus Defence and Space.

The Zephyr S is designed to fly continuously for over a month before having to land. The vehicle can then be refurbished and redeployed.

The combination of high-efficiency and low mass enabled by ELO-based solar cells provides superior performance compared to any other currently available solar cell technology platform, MicroLink emphasizes.

MicroLink's ELO solar cells are a perfect match for the HAPS platform. The resulting solar sheets have specific powers in excess of 1,000 W/kg and areal powers greater than 250 W/m².

MicroLink's ELO technology was sponsored by numerous U.S. agencies including NASA, DARPA, the Air Force Research Laboratory, the Office of Naval Research, NAVAIR, Army Research Office, Army REF, CERDEC, and the Department of Energy.

“We are extremely pleased to have developed a relationship with the Zephyr team four years ago and to transition our high-performance solar sheet development efforts into a production program,” comments Dr. Noren Pan, the President and CEO of MicroLink Devices.

“We are also thankful to Airbus for their purchase order and the confidence they have in MicroLink's solar sheet technology and manufacturing ability. We know of no other flexible solar sheet that offers a comparable performance in terms of power and weight and reliability under a wide temperature range.”

source:http://www.solarserver.com/

UNSW engineers reach a new world record: Solar PV cell efficiency pushed to 34.5%

A new solar photovoltaic (PV) cell configuration developed by engineers at the University of New South Wales has pushed conversion efficiency to 34.5% – establishing a new world record for unfocused sunlight and nudging closer to the theoretical limits for such a device.

The record was set by Dr. Mark Keevers and Professor Martin Green, Senior Research Fellow and Director, respectively, of UNSW’s Australian Centre for Advanced Photovoltaics, using a 28 cm² four-junction mini-module – embedded in a prism – that extracts the maximum energy from sunlight.

It does this by splitting the incoming rays into four bands, using a hybrid four-junction receiver to squeeze even more electricity from each beam of sunlight.

Result confirmed by NREL

The new UNSW result, confirmed by the U.S. National Renewable Energy Laboratory (NREL), is almost 44% better than the previous record – made by Alta Devices of the USA, which reached 24% efficiency, but over a larger surface area of 800 cm².

“This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient,” said Keevers.

“Extracting more energy from every beam of sunlight is critical to reducing the cost of electricity generated by solar cells as it lowers the investment needed, and delivering payback faster.”

The result was obtained by the same UNSW team that set a world record in 2014, achieving an electricity conversion rate of over 40% by using mirrors to concentrate the light – a technique known as CPV (concentrator photovoltaics) – and then similarly splitting out various wavelengths. The new result, however, was achieved using normal sunlight with no concentrators.

Study sets an aggressive target of 35% solar cell efficiency by 2050

“What’s remarkable is that this level of efficiency had not been expected for many years,” said Green, a pioneer who has led the field for much of his 40 years at UNSW.

“A recent study by Germany’s Agora Energiewende think tank set an aggressive target of 35% efficiency by 2050 for a module that uses unconcentrated sunlight, such as the standard ones on family homes.”

“So things are moving faster in solar cell efficiency than many experts expected, and that’s good news for solar energy,” he added. “But we must maintain the pace of photovoltaic research in Australia to ensure that we not only build on such tremendous results, but continue to bring benefits back to Australia.”

source:http://www.solarserver.com

NREL helps DOE assess progress made by the U.S. solar industry

Analysts and researchers at the Energy Department's (DOE) National Renewable Energy Laboratory (NREL) played a significant role in a suite of studies released on May 18^th, 2016 by DOE's SunShot Initiative.

The studies identify the progress made by the U.S. solar energy industry toward SunShot's goal of achieving cost parity with traditional energy sources by 2020.

"We're close to 70 percent of the way toward achieving the SunShot Initiative's 2020 goals,” said Robert Margolis, NREL senior analyst and project manager.

“These reports provide a perspective on how far we've come and how much more can be done to advance solar technologies.”

Focused on the lessons learned in the first five years of the 10-year Initiative, the reports identify key research, development, and market opportunities that must be addressed in the coming years and beyond 2020 to help the United States achieve cost-competitive solar energy.

Among the conclusions from the study series, a recurring theme emerges that sustained innovation across all levels of the industry –from component and system-level improvements, to streamlining access to solar and developing new business models across sectors –will help achieve DOE's SunShot goals.

Further solar price-reduction, new deployment strategies

In conjunction with key stakeholders, the “On the Path to SunShot” series findings will be used to focus researchers on key innovations and further develop solar price-reduction and deployment strategies over the next five years of the Initiative and in the decades beyond.

Cost of electricity from solar has dropped by as much as 65 percent

Since the SunShot Initiative was launched, solar technologies, solar markets, and the solar industry itself have changed dramatically. Cumulative U.S. solar energy deployment has increased more than tenfold, while the cost of electricity from solar has dropped by as much as 65 percent. 

source:http://www.solarserver.com

New report: Over 4 million off-grid solar-powered devices sold in the second half of 2015

In response to demand from investors, manufacturers, distributors and other players in the off-grid solar industry, The Global Off-Grid Lighting Association (GOGLA) and the World Bank’s Lighting Global program have joined forces to produce the “Global Solar Off-Grid Semi-Annual Market Report” covering July to December 2015.

According to the report, during the second half of 2015, over 4 million off-grid branded and quality verified solar-powered devices were sold, with Sub-Saharan Africa and Asia accounting for nearly 95% of sales.

The new report gathers semi-annual product sales data, allowing for a systematic identification of key trends, analytical insights and other valuable market intelligence for the sector.

In addition, and for the first time, data on revenues is included, providing for a more complete picture of pico-PV products and solar home systems during this period.

Over the last 3 years, 27 million people have benefited from solar-powered off-grid products

There are 1.2 billion people worldwide without access to the power grid, and they spend about USD 27 billion every year on both phone charging and lighting with kerosene, candles, battery torches or other fossil fuel-powered technologies.

Solar-powered portable lights and home kits offer a better, cleaner service at lower cost. The key to understanding the development of this fast-growing market is quality, nuanced data.

A full analysis of the social impact results of these sales will follow soon, but over the last 3 years, 27 million people have benefited from such products.

Moving forward, this new and ongoing market intelligence not only helps industry members and financiers to make informed decisions, but it also strengthens the case for the developmental impact made by the sector – critically important for governments, investors and donor agencies.

source:http://www.solarserver.com

MNRE: India reaches 7.45 GW of solar PV generation capacity

India's Ministry of New and Renewable Energy (MNRE) has published new figures on power generated from various renewable energy sources.

According to Central Electricity Authority, Ministry of Power, India’s solar PV capacity now totals 7.45 gigawatts (GW), wind totals 33 GW, and total renewable generation capacity reached 66 GW.

Government up-scales target for renewable energy capacity to 175 GW by 2022

The Minister further stated that the Government has up-scaled the target of renewable energy capacity to 175 GW by the year 2022 which includes 100 GW from solar, 60 GW from wind, 10 GW from bio-power and 5 GW from small hydro power.

While framing the scale-up Plan for 100 GW of grid-connected solar PV by the year 2022, it was envisaged that the public sector undertakings (PSUs) will contribute around 10 GW, Shri Piyush Goyal, Minister of State (IC) for Power, Coal & New and Renewable Energy stated.

Further, 36 central PSUs have given their commitments to develop 18.9 GW of renewable energy projects, as part of the Green Energy Commitment.

source:http://www.solarserver.com

New IRENA data: 2015 sets record for renewable energy; Generation capacity grew 8.3%

 

Renewable energy generation capacity increased by 152 gigawatts (GW) or 8.3% during 2015, the highest annual growth rate on record, according to new data released by the International Renewable Energy Agency (IRENA).

“Renewable Capacity Statistics” 2016 finds that as of the end of 2015, 1,985 GW of renewable generation capacity existed globally.

USD 286 billion invested in renewables in 2015

“Renewable energy deployment continues to surge in markets around the globe, even in an era of low oil and gas prices. Falling costs for renewable energy technologies, and a host of economic, social and environmental drivers are favoring renewables over conventional power sources,” said IRENA Director-General Adnan Z. Amin.

“This impressive growth, coupled with a record USD 286 billion invested in renewables in 2015, sends a strong signal to investors and policymakers that renewable energy is now the preferred option for new power generation capacity around the world.”

Solar capacity increased by 37%

2015 was a record year for both wind and solar due in large part to a continued decline in technology costs. Wind power grew 63 GW (17%) driven by declines in onshore turbine prices of up to 45% since 2010. Solar capacity increased 47 GW (37%) thanks to price drops of up to 80% for solar photovoltaic (PV) modules in the same time period.

Overall, capacity has increased by roughly one-third over the last five years, with most of this growth coming from new installations of wind and solar energy. 

In terms of regional distribution, the fastest growth in renewable generation capacity came in developing countries.

Central America and the Caribbean expanded at a rate of 14.5%. In Asia, where additions accounted for 58% of new global renewable power generation capacity in 2015, capacity expanded at a rate of 12.4%. Capacity increased by 24 GW (5.2%) in Europe and 20 GW (6.3%) in North America.

“The significant growth rates for renewable generation capacity in developing economies are a testament to the strong business case for renewable energy,” said Mr. Amin.

“Renewables are not just a solution for industrialized countries, they are also powering economic growth in the fastest growing economies in the developing world.”

At year end, hydropower accounted for the largest share of the global total renewable power generation capacity with an installed capacity of 1,209 GW, the majority of which are large-scale plants.

Wind and solar energy accounted for most of the remainder, with an installed capacity of 432 GW and 227 GW respectively. Other renewables included 104 GW of bioenergy, 13 GW of geothermal energy and about 500 MW of marine energy (tide, wave and ocean). 

source: http://www.solarserver.com

JinkoSolar repays outstanding convertible senior notes due on May 15th, 2016

 

JinkoSolar Holding Co., Ltd. (Shanghai, China) on May 18^th, 2016 announced that it has repaid the entire remaining balance of its 4.00% Convertible Senior Notes due on May 15^th, 2016.

The total cash redemption, including the Principal, accrued interest up to and including May 15^th, 2016, totaled USD 47,940,000.

“With this final payment, we have further strengthened our balance sheet and increased our operational flexibility,” commented Charlie Cao, JinkoSolar's Chief Financial Officer.

“We will continue to focus on deploying our healthy cash flows towards areas that will generate long-term shareholder value.” 

source: http://www.solarserver.com

Solar Heating Systems

A roof does not necessarily have to be orientated exactly to the south in order to serve as a mounting surface for solar collectors. Variations from southern orientation of up to 30° lead to only low losses. Even absolute east or west orientation can be offset through the use of a corresponding larger collector surface. A roof's slope can even be between 20° and 60°, whereby a solar heating system with less slope has a higher energy yield in summer, and one with more slope has a higher energy yield in winter. Special stands are recommended for flat roofs.

Smart Dimensions a must

Properly dimensioned solar heating systems offer the best guarantee for satisfactory operation. Precisely knowing a household's hot water consumption is required when finding the proper dimensions but one should also take into consideration the possibilities of lower consumption. For these questions, the advice of a specialist is recommended. A tip for deciding the dimensions for a small solar heating system: daily hot water consumption of 50 liters per person (at 45° C) yields a collector surface of 1.2 m² by 1.5 m² per person.

Choose a Suitable System

Two circuit, indirect system with controlled circulation

Two circuit indirect systems with controlled circulation are most predominant in Germany. These use heat-transfer fluid that is transported by pumps to the hot water storage tank. Once there, the solar heat is transmitted from the heat transfer fluid to the potable water through a heat exchanger. In order to protect solar heating systems from freezing damage, there is a water-antifreeze mixture in the circulation pipes, and, due to separate circuits, the heat-transfer fluid and the domestic water do not mix. The heated potable water can then flow to the hot-water faucets. In comparison, one circuit systems heat water directly in the collector (usually in countries without danger of freezing).

In thermosiphon systems the regulator and the solar circulation pumps are not necessary because of convection: The solar radiation heats the heat-transfer fluid, its density then decreases as its temperature increases. The fluid becomes lighter and rises inside the circulation pipes. Therefore, a pump is not necessary. In order for such a system to function, however, the water tank must be installed above the collector.

Hot Water Storage Tank and Heat Exchanger

The purpose of the hot water storage tank is to stockpile energy for days with poor solar radiation. Its volume capacity should be 1.5 to 2 times more than the daily hot water consumption - that means 80 to 100 liters per person.

Enameled steel tanks are normally used, such as those known from conventional heating technology. They need a magnesium-or an external current-anode for corrosion protection. Stainless steel storage tanks have a longer life expectancy, but are more expensive.

Good solar storage tanks have a slim, cylindrical form in order to develop a layering of temperature in the tank. This allows for optimal usage of the heated potable water in the upper storage region, thus the entire contents of the tank don't need to be heated to the desired temperature. Undesired mixing of the tank contents through incoming cold water is prevented through a special pipe construction or a baffle plate. The arrangement of the solar circuit heat exchanger in the lower, colder tank area causes the solar panel to work at a more economical level of efficiency due to the low incoming water temperature.

Warm Water Storage Tanks with two Heat Exchangers

In order that the conventional heater does not have to reheat an unnecessarily large volume, its heat exchanger is located in the upper part of the tank.

The entire surface of the tank should be tightly fit with a layer of insulation at least 10 centimeters thick without any gaps. To further lower heat loss, the connections in the cold lower level are led out only from one area.

The Solar Heat Circulation

Within the solar heat circulation, heat is transported from the collector to the hot water storage tank. In order to minimize heat loss, the distance from the collector to the tank should be as short as possible. For systems in one or two family homes, copper pipes with a circumference of 15 mm to 18 mm are enough to guarantee an optimal transportation of heat. The pipes are sufficiently insulated with 30 mm of insulation. For pipes with a circumference of 30 mm, the insulation should have at least the same thickness as the pipe. The insulation must be able to withstand high temperatures, and the outdoor section has to be UV- and weather-resistant. The following materials are used as insulation: mineral wool, polyurethane pipe wrappers, and foam rubber.

Mountings and safety equipment in the solar circuit

The prevalent flow rate in small solar heating systems amounts to 30 to 50 liters per hour per square meter of collector surface. The solar circulation pump has to be able to guarantee this rate of flow. As a general rule, conventional pumps with an electric input between 40 W and 80 W suffice. Also, the pump should always be installed in the colder reflux of the solar circulation system. In this way the pump will not be exposed to high temperatures during operation. Finally, stop valves are mounted in front of and behind the pump, so that the entire system does not have to be emptied when replacing a defective pump.

The typical operating pressure of solar heating systems, which can be controlled by a manometer, lies at approximately 4 bar. The safety valve should open at an approximately 0.3 bar triggering pressure. With a recuperation tank, the heat-transfer fluid can be captured and then fed back into the solar circuit through one of the refilling taps. Thermometers fitted in forerun and reflux are used to check the system's operation. To prevent heat loss out of the tank because of insufficient solar radiation or at night due to convection (the heat-transfer fluid cools in the cold collector, and through the force of gravity, then circulates towards the storage tank) a rebound valve is mounted in the outward flow. The expansion tank keeps the pressure in the system stable and takes up the volume difference of the heat-transfer fluid that is caused by the temperature difference. For safety reasons, the volume of the expansion tank has to be sufficiently large. It should be able to take up the entire volume of heat-transfer fluid. The vent valve serves to ventilate the solar circuit after it has been filled with heat-transfer fluid. It is to be mounted on the highest part of the solar circuit.

The Regulation

Often a simple controller for temperature differences is enough to regulate a small solar heating system for water heating. Through the use of two temperature sensors, the regulator ascertains when the temperature in the collector discharge is higher than the temperature of the solar circuit heat exchanger in the tank, and then it activates the circulation pump. To start the pump, the solar regulator is usually calibrated so that the necessary temperature difference between the collector and tank is between 5° C and 8° C. If this temperature difference sinks to 2° C to 3° C, then the solar regulator will shut off the solar circuit circulation pump.

Anticipatory Planning for Building Construction

If you are building or renovating a house, but still cannot decide on a solar heating system, just remember that preparations for future installation of a solar heating system can be made during construction (ducts for two copper pipes 18' and a quintuple-core cable from the boiler room to the roof). This will save you a lot of work and money later. 

source: http://www.solarserver.com

Photovoltaics: Solar Electricity and Solar Cells in Theory and Practice

The word Photovoltaic is a combination of the Greek word for Light and the name of the physicist Allesandro Volta. It identifies the direct conversion of sunlight into energy by means of solar cells. The conversion process is based on the photoelectric effect discovered by Alexander Bequerel in 1839. The photoelectric effect describes the release of positive and negative charge carriers in a solid state when light strikes its surface.

How Does a Solar Cell Work?

Solar cells are composed of various semiconducting materials. Semiconductors are materials, which become electrically conductive when supplied with light or heat, but which operate as insulators at low temperatures.

Over 95% of all the solar cells produced worldwide are composed of the semiconductor material Silicon (Si). As the second most abundant element in earth`s crust, silicon has the advantage, of being available in sufficient quantities, and additionally processing the material does not burden the environment. To produce a solar cell, the semiconductor is contaminated or "doped". "Doping" is the intentional introduction of chemical elements, with which one can obtain a surplus of either positive charge carriers (p-conducting semiconductor layer) or negative charge carriers (n-conducting semiconductor layer) from the semiconductor material. If two differently contaminated semiconductor layers are combined, then a so-called p-n-junction results on the boundary of the layers.

model of a crystalline solar cell

At this junction, an interior electric field is built up which leads to the separation of the charge carriers that are released by light. Through metal contacts, an electric charge can be tapped. If the outer circuit is closed, meaning a consumer is connected, then direct current flows.

Silicon cells are approximately 10 cm by 10 cm large (recently also 15 cm by 15 cm). A transparent anti-reflection film protects the cell and decreases reflective loss on the cell surface.

Characteristics of a Solar Cell

current-voltage line of a si-solar cell

The usable voltage from solar cells depends on the semiconductor material. In silicon it amounts to approximately 0.5 V. Terminal voltage is only weakly dependent on light radiation, while the current intensity increases with higher luminosity. A 100 cm² silicon cell, for example, reaches a maximum current intensity of approximately 2 A when radiated by 1000 W/m².

The output (product of electricity and voltage) of a solar cell is temperature dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. The level of efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy.

Different Cell Types

One can distinguish three cell types according to the type of crystal: monocrystalline, polycrystalline and amorphous. To produce a monocrystalline silicon cell, absolutely pure semiconducting material is necessary. Monocrystalline rods are extracted from melted silicon and then sawed into thin plates. This production process guarantees a relatively high level of efficiency.
The production of polycrystalline cells is more cost-efficient. In this process, liquid silicon is poured into blocks that are subsequently sawed into plates. During solidification of the material, crystal structures of varying sizes are formed, at whose borders defects emerge. As a result of this crystal defect, the solar cell is less efficient.
If a silicon film is deposited on glass or another substrate material, this is a so-called amorphous or thin layer cell. The layer thickness amounts to less than 1µm (thickness of a human hair: 50-100 µm), so the production costs are lower due to the low material costs. However, the efficiency of amorphous cells is much lower than that of the other two cell types. Because of this, they are primarily used in low power equipment (watches, pocket calculators) or as facade elements.

Material	Level of efficiency in % Lab	Level of efficiency in % Production
Monocrystalline Silicon	approx. 24	14 to17
Polycrystalline Silicon	approx. 18	13 to15
Amorphous Silicon	approx. 13	5 to7

From the Cell to the Module

In order to make the appropriate voltages and outputs available for different applications, single solar cells are interconnected to form larger units. Cells connected in series have a higher voltage, while those connected in parallel produce more electric current. The interconnected solar cells are usually embedded in transparent Ethyl-Vinyl-Acetate, fitted with an aluminum or stainless steel frame and covered with transparent glass on the front side.

The typical power ratings of such solar modules are between 10 Wpeak and 100 Wpeak. The characteristic data refer to the standard test conditions of 1000 W/m² solar radiation at a cell temperature of 25° Celsius. The manufacturer's standard warranty of ten or more years is quite long and shows the high quality standards and life expectancy of today's products.

Natural Limits of Efficiency

Theoretical maximum levels of efficiency of various solar cells at standard conditions

In addition to optimizing the production processes, work is also being done to increase the level of efficiency, in order to lower the costs of solar cells. However, different loss mechanisms are setting limits on these plans. Basically, the different semiconductor materials or combinations are suited only for specific spectral ranges. Therefore a specific portion of the radiant energy cannot be used, because the light quanta (photons) do not have enough energy to "activate" the charge carriers. On the other hand, a certain amount of surplus photon energy is transformed into heat rather than into electrical energy. In addition to that, there are optical losses, such as the shadowing of the cell surface through contact with the glass surface or reflection of incoming rays on the cell surface. Other loss mechanisms are electrical resistance losses in the semiconductor and the connecting cable. The disrupting influence of material contamination, surface effects and crystal defects, however, are also significant.
Single loss mechanisms (photons with too little energy are not absorbed, surplus photon energy is transformed into heat) cannot be further improved because of inherent physical limits imposed by the materials themselves. This leads to a theoretical maximum level of efficiency, i.e. approximately 28% for crystal silicon.

New Directions

Surface structuring to reduce reflection loss: for example, construction of the cell surface in a pyramid structure, so that incoming light hits the surface several times. New material: for example, gallium arsenide (GaAs), cadmium telluride (CdTe) or copper indium selenide (CuInSe²).

Tandem or stacked cells: in order to be able to use a wide spectrum of radiation, different semiconductor materials, which are suited for different spectral ranges, will be arranged one on top of the other.

Concentrator cells: A higher light intensity will be focussed on the solar cells by the use of mirror and lens systems. This system tracks the sun, always using direct radiation.

MIS Inversion Layer cells: the inner electrical field are not produced by a p-n junction, but by the junction of a thin oxide layer to a semiconductor.

Grätzel cells: Electrochemical liquid cells with titanium dioxide as electrolytes and dye to improve light absorption. 

source: http://www.solarserver.com

Solar electricity: Grid-connected photovoltaic systems

Photovoltaic power plants convert sunlight to electric energy. The energy output of such PV plants will therefore reach it's peak at midday, meeting the daily energy consumption peak, when the spot prices on energy are highest.

A PV system with a nominal capacity of 8,96 kilowatt peak, as pictured, covers the electricity needs of two four person households. Picture: Sharp Electronics (Europe) GmbH

Despite this economic benefit photovoltaic power has not yet reached grid parity, the point at which the costs are equal to grid power (except some sunny islands like Hawaii that use diesel fuel to produce electricity).

Net metering (US and Canada) and feed-in tariff systems

Since no local energy storage facilities are needed, the limiting factors sizing grid-connected photovoltaic systems are the available space - often a roof - the investment costs and the regulatory frameworks including subsidy and promotion programs. Such programs can include investment subsidies, net metering or feed-in tariffs. With net metering the inflow of electrical energy is charged up against the electrical consumption at the same estate, using mostly a bi-directional working electricity meter. This system is widely in use in the US and Canada. Since there is in most cases no compensation for an inflow exceeding the yearly consumption, photovoltaic facilities will be mostly sized to provide no more energy than consumed at the same estate during the year; the grid is used only as a storage facility. Within a feed-in tariff system on the other side, providing (like in Germany) fixed and guaranteed payments per kWh, more output means more profit; so facilities will be bigger sized.

Schematic diagram of a photovoltaic system. Illustration: LGABW

Solar Power: Sunlight becomes the source of electricity.

A grid coupled PV system essentially consists of the PV panels (modules), one or several solar inverters, a protections device for automatic shutdown in case of a grid breakdown and a counter for the fed in solar electricity

The components of a grid-connected PV system include the PV modules, a power inverter, a safety device to power down at failures in the grid and an electricity meter. The "mains-commutated" inverter converts the direct current (DC) provided by the modules to alternating current (AC), simultaneously synchronizing the AC output to the AC in the grid.
The power-generating capacity of a photovoltaic system is denoted in kilowatt peak (measured at standard test conditions and a solar irradiation of 1000 W per m²). Today's PV modules will cover an area between 7 and 10 m² per kWp. Assumed that the modules are oriented to south and inclined at an angle between 30° and 35° such a PV system will generate in Middle and West Europe - depending on the exact latitude and other factors - between 800 and 1.000 kWh electrical energy per year and per kWp of nominal capacity. To exemplify: On a roof in Cambridge or Oxford (UK), a 4-kWp-plant with optimized module orientation and module inclination angle will provide about 3.380 kWh per year, at Sevilla (Spain) 5.640 kWh per year. The plant at Sevilla will therefore need an inverter with an higher input voltage than the one at Oxford.

Some tips for planning a grid-connected PV system

- Size of the PV generator

The economically optimal size of a grid-connected PV system depends mostly on different financial incentives and legal parameters, since grid parity - meaning the costs of photovoltaic generated electricity are equal to or cheaper than the price of grid power - is achieved only in a very few regions today.Net metering concepts, as they are widely in use in the US and Canada, provide - like with stand-alone systems - no incentive to build systems that generate more electrical energy than consumed at the same estate during the year; the grid replaces only a local battery storage. Feed-in tariff systems on the other side render big systems with net excess profitable.

A PV system may cover the whole roof; the pictured solar roof (233 square meters) has a nominal power output of 24,2 kilowatt (kWp). Picture: Hieronimi regenerative Energien GmbH

- Required module space:

Within bigger systems mostly crystalline silicon modules are used today. To install a nominal capacity of 1 kWp (Kilowatt Peak) with such modules an area between about 7 m² (using monocrystalline cells) and 10 m² (using polycrystalline cells) is required.Otherwise unused pitched roofs are in many cases the most cost-efficient places to install a PV system, especially if they are oriented to south and inclined to a degree of about 30° to 37°.

- PV Orientation and Output

The efficiency of the photovoltaic process is at its highest if the sun rays hit the panel vertically. Therefore PV modules should be oriented to south (speaking of the northern hemisphere) and somewhat inclined; the optimal inclination angle depends on the location (including latitude, altitude and other factors). As a rule of thumb the inclination angle would be best between 3/4 and 4/5 of the latitude – resulting in angles of 32° to 38° in Middle and Western Europe or 30° to 36° in most of the US. However: Small divergences from the optimal orientation and inclination result only in even smaller reductions of energy output per year.

In order to most effectively use Solar Radiation, a PV Module or Collector of a photovoltaic system and Solar Heating System, respectively, is aligned to absorb or collect as much of the radiation as possible. The radiation's angle of incidence, the tilt angle of the module or collector, and the azimuth angle all play roles in achieving the greatest possible power production.

The azimuth angle (β) in the picture at right) specifies how many degrees the surface of the module or collector diverges from the exact south-facing direction. The tilt angle (α) specifies the divergence from the horizontal.

Experiments show that photovoltaic systems operate most effectively with an azimuth angle of about 0° and a tilt angle of about 30°. Of course small variances in these values are not at all problematic: with the system oriented towards the south-east or south-west, about 95 % of the highest possible amount of light can still be absorbed. Large systems with arrays are fitted with electric motors which track the sun in order to optimise output.

Installation of power inverters of a 123 kWp PV system in Germany.

- Power inverter:

PV systems provide direct current (DC) voltage. To feed to the grid, this DC voltage has to be inverted to the grid alternating current (AC) voltage by a »mains-commutated« or grid-tied inverter, synchronizing automatically its AC output to the exact AC voltage and frequency of the grid.

This MPP fluctuates during operation in an interval depending on the radiation, the cell temperature and the cell type und has so to be tracked by the inverter controlling unit.

The second important job of the solar power inverter is to control the PV system to run near its Maximum Power Point (MPP), the operating point where the combined values of the current and voltage of the solar modules result in a maximum power output. This MPP fluctuates during operation in an interval depending on the radiation, the cell temperature and the cell type und has so to be tracked by the inverter controlling unit.

source: http://www.solarserver.com

Solar Collectors: Different Types and Fields of Application

solar collectors transform solar radiation into heat and transfer that heat to a medium (water, solar fluid, or air). Then solar heat can be used for heating water, to back up heating systems or for heating swimming pools.

The use of solar heat

The heart of a solar collector is the absorber, which is usually composed of several narrow metal strips. The carrier fluid for heat transfer flows through a heat-carrying pipe, which is connected to the absorber strip. In plate-type absorbers, two sheets are sandwiched together allowing the medium to flow between the two sheets. Absorbers are typically made of copper or aluminum.

Swimming pool absorbers, on the other hand, are usually made of plastic (mostly EPDM, but also of polypropylene and polyethylene), as the lower temperatures involved do not require greater heat capacity.

Heating and storage are united in a reservoir collector. Arrays of reservoir collectors do not need circulating pumps or regulating mechanisms, as the drinking water is warmed and stored right in the collector.

Highly efficient absorber surfaces

Absorbers are usually black, as dark surfaces demonstrate a particularly high degree of light absorption. The level of absorption indicates the amount of short-wave solar radiation being absorbed that means not being reflected. As the absorber warms up to a temperature higher than the ambient temperature, it gives off a great part of the accumulated solar energy in form of long-wave heat rays. The ratio of absorbed energy to emitted heat is indicated by the degree of emission.

In order to reduce energy loss through heat emission, the most efficient absorbers have a selective surface coating. This coating enables the conversion of a high proportion of the solar radiation into heat, simultaneously reducing the emission of heat.

The usual coatings provide a degree of absorption of over 90%. Solar paints which can be mechanically applied to the absorbers (with either brushes or sprays), are less or not at all selective, as they have a high level of emission. Galvanically applied selective coatings include black chrome, black nickel, and aluminum oxide with nickel. Relatively new is a titanium-nitride-oxide layer, which is applied via steam in a vacuum process. This type of coating stands out not only because of its quite low emission rates, but also because its production is emission-free and energy-efficient.

Flat-plate Collectors

Sketch of a flat-plate collector

A flat-plate collector consists of an absorber, a transparent cover, a frame, and insulation. Usually an iron-poor solar safety glass is used as a transparent cover, as it transmits a great amount of the short-wave light spectrum.

Simultaneously, only very little of the heat emitted by the absorber escapes the cover (greenhouse effect).

In addition, the transparent cover prevents wind and breezes from carrying the collected heat away (convection). Together with the frame, the cover protects the absorber from adverse weather conditions. Typical frame materials include aluminum and galvanized steel; sometimes fiberglass-reinforced plastic is used.

The insulation on the back of the absorber and on the side walls lessens the heat loss through conduction. Insulation is usually of polyurethane foam or mineral wool, though sometimes mineral fiber insulating materials like glass wool, rock wool, glass fiber or fiberglass are used.

Flat collectors demonstrate a good price-performance ratio, as well as a broad range of mounting possibilities (on the roof, in the roof itself, or unattached).

In order to reduce heat loss within the frame by convection, the air can be pumped out of the collector tubes. Such collectors then can be called evacuated-tube collectors. They must be re-evacuated once every one to three years.

Evacuated-tube collectors

Sketch of a heat pipe collector

In this type of vacuum collector, the absorber strip is located in an evacuated and pressure proof glass tube. The heat transfer fluid flows through the absorber directly in a U-tube or in countercurrent in a tube-in-tube system. Several single tubes, serially interconnected, or tubes connected to each other via manifold, make up the solar collector. A heat pipe collector incorporates a special fluid which begins to vaporize even at low temperatures. The steam rises in the individual heat pipes and warms up the carrier fluid in the main pipe by means of a heat exchanger. The condensed liquid then flows back into the base of the heat pipe.

The pipes must be angled at a specific degree above horizontal so that the process of vaporizing and condensing functions. There are two types of collector connection to the solar circulation system. Either the heat exchanger extends directly into the manifold ("wet connection") or it is connected to the manifold by a heat-conducting material ("dry connection"). A "dry connection" allows to exchange individual tubes without emptying the entire system of its fluid. Evacuted tubes offer the advantage that they work efficiently with high absorber temperatures and with low radiation. Higher temperatures also may be obtained for applications such as hot water heating, steam production, and air conditioning.

How much energy does a solar collector provide?

Graph of efficiency and temperature ranges of various types of collectors (radiation: 1000 W/m²)

The efficiency of a solar collector is defined as the quotient of usable thermal energy versus received solar energy. Besides thermal loss there alwas is optical loss as well. The conversion factor or optical efficiency h0 indicates the percentage of the solar rays penetrating the transparent cover of the collector (transmission) and the percentage being absorbed. Basically, it is the product of the rate of transmission of the cover and the absorption rate of the absorber.

The specific costs of collectors are also important. Evacuated-tube collectors are substantially more expensive (at 511,29 - 1278,23 Euro /m² collector surface) than flat-plate collectors (153,34 to 613,55 Euro /m²) or even plastic absorbers (25,60 to 102,26 Euro /m²). However, a good collector does not guarantee a good solar system. Rather, all components should be of high quality and similar capacity and strength.

source:http://www.solarserver.com