Power from the Sun Photovoltaic energy
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rom the Sun • powe r f r e fro pow m
The Sun – a free source of energy The Sun produces a huge amount of energy – both light and heat – that sustains us and keeps our planet Earth alive. Amazingly, in less than one hour the Earth receives enough energy from the Sun to supply all our world’s power needs for a full year. Here we consider how sunlight can be easily converted to electricity to help power our homes, offices and factories. Indeed wherever we need electricity Power from the Sun can help us while protecting our environment.
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How do we make electricity from the sunlight? The process to convert sunlight into electricity is called photovoltaic and we can trace this word back to Greece and Italy. Photo comes from the Greek language meaning light and voltaic in honour of an Italian physicist Count Alessandro Volta whose name is used for a measure of electricity (electromotive force) - the volt. Often the word photovoltaic is shortened to simply PV for ease of use. The sun and the science The fundamental component of a photovoltaic system is the PV cell – often called solar cell. A solar cell is shown in the diagram. Solar cells are made of special materials called semiconductors. Silicon is currently the most common semiconductor used in solar cells. When sunlight shines onto the solar cell an amount is absorbed as energy into the semiconductor material.
This energy knocks electrons loose from the semiconductor’s atoms allowing them to flow freely inside the material. Contacts on either side of the cell capture these electrons converting them into an electrical current – power from the Sun. In a typical PV system many solar cells are grouped (in strings) together to make a PV module or panel. A photovoltaic system is made up of a number of PV modules where the more modules the greater the energy produced. The more sunlight the more power! However this does not need to be from a cloud free sky – even on cloudy and rainy days useful amounts of power are generated. PV works both from direct sunlight and also indirect (diffused) sunlight from cloudy skies. Indeed partially cloudy conditions can actually increase the output from a PV system!
Specially Treated Semi-conductor Material
Why Power from the Sun? Unlike most other forms of electricity production, PV is effectively limitless - only depending on the Sun! After less than 3 years (and this time is reducing as technology improves) a PV system is energy neutral (ie supplying back more energy than that used to manufacture) and the life for a PV installation is 25 years or more (estimated as at least 30 years) and can also be recycled.
While there are other “clean energy” solutions such as hydro, wind and tidal generation these are not ideal or indeed practical in many situations. They do not offer the local energy production that a PV system can deliver down to individual households. PV is completely silent, very reliable with low maintenance and can easily be fitted directly to a building with absolute minimal impact on the environment.
Coal, oil, gas and nuclear are all finite resources and will run out – the only question is when. Beyond this they have significant environmental concerns be this from carbon dioxide (CO2) emissions or radioactive waste. PV has none of these drawbacks.
PV is called a renewable energy source coming as it does from a natural resource, the Sun, which is naturally replenished (renewable). Other renewables include wind, tide, solar thermal and geothermal. A typical domestic PV system can save in excess of 1 tonne of CO2 emissions per year – over 25 tonnes in its lifetime!
How much CO2 do various electricity generation methods make in their life? Lifecycle greenhouse gas emission estimates for various electricity generators Technology Estimate (g CO2/kWh) Solar PV*.......................... 32 Nuclear ............................ 66 Natural gas....................... 443 Oil/diesel .......................... Coal with scrubbing.......... Coal without scrubbing..... *Polycrystaline silicon, thin film less than 20 gCO2/kWh
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Some common myths about PV PV modules are all made abroad and buying PV is not supporting our local economy The modules are only a part of a PV system. Though they are the most obvious part! Estimates are that for every 7 jobs in manufacturing modules 30 jobs are created for the other parts of a PV system including installation and routine maintenance.
More energy is needed to make a PV system than it ever gives back Not true! After 3 years or less a PV system is “carbon neutral” producing more energy than was used to manufacture. This 3 years is reducing as technology and manufacturing processes are improved and is expected to be under 2 years very soon and is already under 1 year for certain technologies (thin film).
These solar PV systems can’t work in the UK – it’s too rainy and we don’t have enough sunshine Actually the amount of sunshine we have in the UK is not so different from that experienced in the country having the largest number of PV installations in the world – Germany! Even on cloudy days PV generates significant amounts of elctricity. Also it is often said that PV only works in the South. While power is slightly reduced installations in, for example, Edinburgh still are very productive and viable.
I don’t need that much electricity during the day when PV works so it’s not going to work for me The vast majority of PV installations are directly connected to your electricity provider (via the national grid) and the power produced during the day is used by others such as industry, hospitals etc. In fact the electricity that the PV system exports to the grid is paid for by your provider making even more money from the system. Typically over a full year around 30% of the electricity produced by a domestic PV installation is used by the home owner.
What is the FIT and how does it work? A Feed In Tariff or FIT is a mechanism used in many countries to help support renewable energy technologies. This is necessary because the cost of installing systems such as PV is relatively high and without this support widespread adoption of these renewables would not happen. Why do we need renewable energy? As is now widely recognised traditional energy sources such as coal and oil are not going to last forever and also are now linked directly to climate change because of their CO2 emissions. Thus most countries now are looking for alternative electricity sources and to encourage this support
Year System size
schemes now operate in many countries world-wide. In the UK the Government has a Renewable Energy Strategy (RES) target of 15% of electricity coming from renewables (such as PV) by 2020. To help achieve this goal the British Government’s Department of Energy and Climate Change (DECC) introduced the UK FIT “clean energy cashback” scheme in April 2010. This was specifically to encourage investment in small scale low carbon (renewable) electricity production in return for a guaranteed payment (tax free) for the electricity produced.
Lifetime: 25 years
< 4 kWp (new build)
Funding of projects up to 5 MWp
< 4 kWp (retrofit)
> 4 - 10 kWp
> 10 - 100 kWp
> 100 kW - 5MWp
Stand alone system (open space)
Payment in pence per kWh subject to RPI
Source: Department of Energy and Climate Change 2010 Notes: • To be eligible for the FIT projects up to 50 kWp must use Micro-generation Certification Scheme (MCS) approved products installed by an MCS accredited installer. Projects greater than 50 kWp apply for accreditation through the ROO-FIT process. • The rates paid are adjusted annually according to the Retail Price Index (RPI) and are guaranteed for 25 years • Electricity exported to the grid is paid additionally at a minimum of 3p per kWh where 50% export is assumed
It is not planned that this support will be needed forever. Firstly the cost of manufacturing renewable technology such as PV is reducing quite rapidly as the volumes increase and the technology is refined. Also the cost of existing electricity production (eg oil and coal) continues to increase as these resources become scarcer (they are finite unlike the Sun!) and the very real cost of pollution is taken into account.
or energy prices are higher, this is close or even achieved. It is likely the UK will achieve a grid parity cost from PV by 2020 at the latest. What is clear is the more PV is installed in the UK the sooner grid parity will happen and the less the UK will pollute! A win win scenario for all.
At some point the cost of PV electricity will be the same as existing polluting energy sources and that is called “grid parity”. It is not certain when PV grid parity will happen in the UK but some countries, where larger investments in PV have already been made Czech residential installation (Suntech modules)
You can use the electricity you generate - you don’t have to import from the grid.
You export electricity back
Electricity is created by solar
to the grid when you don’t
modules. Your electricity supplier
use it. You are paid an
pays you for each unit of electricity
You import electricity from the grid when you need additional power.
What are the main parts of a PV system? Solar powered radios
There are two main types of PV system and this relates to how the power is used. These are grid connected and off grid (not grid connected). In most cases grid connection is used but for some remote locations away from a grid or consumer goods (say a solar powered radio) then these are off grid.
1. Photovoltaic modules 2. Inverter
A typical domestic grid connected PV installation can be broken down into 3 main parts. PV modules, an inverter and meter.
2 3 4
3. Solar power meter National Grid
4. House consumption meter
PV modules (Suntech)
The PV modules produce electricity in a DC (Direct Current) form like a battery. This is connected to an inverter which converts this DC into AC (Alternating Current) which is the form of electricity used to power lighting, Inverter (SMA) appliances, heaters etc in the home. The inverter is connected to the grid (the normal way electricity is supplied to the home) via a meter that records how much power is Generation meter being supplied by the PV system. The other meter in the diagram is the normal meter used to record how much electricity is being used.
Other examples of PV installations include power plants (both grid connected and off grid) and consumer goods. PV modules cost around £2.10 per Wp and inverters £500 per 1kWp. The table below shows a rough indication of the costs for a typical 2kWp system. Cost breakdown for typical 2kWp system PV modules . . . . . . . . . . . . . . . . . .£4,200 Inverter . . . . . . . . . . . . . . . . . . . . . .£1,000 Wiring, meter etc. and installation . .£3,300 Total Cost . . . . . . . . . . . . . . . . . . .£8,500
Residential installation Spain (Suntech modules)
Commercial roof-top Germany (Suntech modules)
How PV can be part of your life In most domestic PV installations the PV modules are roof mounted. These can be either fixed on top of the existing roof or mounted into the roof itself. For existing houses it is simplest to mount the modules onto the roof and there are a number of fixing methods available to
achieve this without causing leaks! For new builds or where reroofing is planned Building Integrated PV (BIPV) is often used. The BIPV has a significant advantage in that it is more aesthetically pleasing and generally more sympathetic to the look of a building.
Agricultural building (Suntech modules)
Integrated PV - (Suntech BIPV)
Some points to have in mind • The modules work best when pointed at the Sun so South facing is best • Shading from trees or other buildings can reduce the system performance considerably • Though there is no smallest system in practice you will need an area around 8m2 or larger
• The life of the panels is in excess of 25 years. Make sure your roof is in good condition and will be able to last at least this long • PV modules can be quite heavy (as much as 15Kg/m2)! Some roofs may not be able to take the weight without additional strengthening – if the modules and support frame increase the roof load by 15% or more then a structural survey is usually required
How does the economics of a PV system work out? As a general rule a PV system will pay for itself in approximately 8 to 10 years. The FIT, which guarantees a price for the electricity you produce, lasts for 25 years (and is RPI – Retail Price Index – linked). So taking this 8 to 10 years to pay for the system then leaves effectively 15 years of profit. And remember all payments from the FIT are tax free! Some maintenance is needed for any technology of this type, but for PV as there are no moving parts this is typically very little. Cleaning of the modules can be
necessary from time to time (depending on location but typically once per year) but remember as the modules are on the roof this will most likely have to be done by a professional. The only part that is likely to need replacing during the life of the PV system is the inverter. In some cases these are guaranteed for 25 years but if not (often only guaranteed for 10 years) then you should factor in replacing this part which fortunately accounts typically for only some 10% to 15% of the total installation cost.
An example of a domestic grid connected PV system Size of system 2kWp (roughly 16m2 of roof space), retro fit, South facing no shading and located in the Midlands (based on irradiation of 850 kWh/KWp per annum)
Cost of system including all system components and installation................. £8,500 Electricity generated per year ...................................................................... 1,700kWh FIT income from generated electricity .......................................................... £700 per year Export tariff payment (supplying electricity to the grid).................................. £25 per year Electricity bill saving (assuming 50% home use, 14p/kWh) .......................... £119 per year Income ........................................................................................................ £844 per year Lifetime (25 years) income ........................................................................... £21,100 The payment for the FIT is RPI linked and the income from the exported electricity along with the savings will in effect increase this lifetime income. The detail of what the true return is on the initial investment needs to take into account other issues such as the cost of the money used to buy the system. However, it can be seen from this example that the system pays for itself in just over 10 years. The return on investment in the first year is just over 9.9%. Note there are some maintenance costs and possible replacement of the inverter that are excluded from this example.
What types of PV are there and how are they made? The two main technology types in common use are crystalline and thin film. One other type, concentrated photovoltaic or CPV, is noted for having one of the highest efficiencies (up to 50%) but requires mirrors or such like to focus the light onto a small PV element. This makes such technology really only suitable for land based generating systems. Suntech development center, China
Crystalline PV Crystalline silicon cells are in the main manufactured by thinly slicing a large block of silicon. Two types of silicon block are used â€“
one having a single crystalline structure called monocrystalline (c-Si); the other having multicrystal structure called polycrystalline (mc-Si). Monocrystalline are slightly more efficient than polycrystalline. A third type, Ribbon silicon, is polycrystalline and is made by drawing flat thin films from molten silicon avoiding the need to slice a silicon block. Typical module efficiencies range from 12% to 16% (where efficiency is compared to the energy output from the Sun being 100%).
Silicon cell (Suntech)
The cells (number depends on the module size) are connected together in â€œstringsâ€? and then encapsulated against a thin glass sheet (with special anti reflective properties) to protect them from rain, dirt etc. The encapsulation prevents water ingress and holds everything together. A final framework supports the cell and glass structure.
Crystalline PV module during manufacture (Suntech)
Thin film PV Thin film PV (TFPV) is made by depositing very thin layers of materials onto a sheet or backing/substrate. Materials used for this backing include glass, steel and plastic. The advantage with thin film is the manufacturing cost is lower than crystalline. However at present thin film offers lower efficiencies than crystalline ranging typically from 7% to 10%.
There are 4 main types of thin film material used to make the PV effect: • Amorphous silicon (a-Si) and other thin-film silicon (TF-Si)
• Cadmium Telluride (CdTe) • Copper indium gallium (di)selenide (CIS or CIGS)
• Dye-sensitized solar cell (DSC) and other organic solar cells
Thin film (with backing) may be directly bonded to a glass cover sheet with a metal frame again producing a final module similar to crystalline. Alternatively the thin film can have a flexible backing sheet such as steel or plastic and a clear plastic cover layer that can then be mounted over curved surfaces.
Flexible thin film (Flexcell)
How do I estimate the likely output from a PV system? The PV modules and systems (many modules) are rated in units of Wp meaning Watt (power) and peak. Typically this is discussed in units of 1,000 so kWp. Generally all modules are tested under Standard Test Conditions (STC) so that all modules and systems can easily be compared. (STC: irradiance of 1,000 W/m², solar spectrum of AM 1.5 and module temperature of 25°C). Converting the module or system into meaningful power in terms of units of electricity (kWh) is quite straightforward.
At its simplest, one can take a location (say Manchester) and let’s say this is 800 kWh/kWp. So a 2 kWp PV system will produce 2 x 800 or 1,600 kWh of electricity per annum. The performance ratio of 75% is an estimation of efficiency for a typical fixed installation (the modules are not tracking the Sun). There are also many other influences that can affect the final output you can expect. In most cases a roof will not be at the optimum angle or perfectly South facing. There may be some shading and losses because of say a hill or such like obstructing the Sun close to sunrise and sunset.
The starting point is the level of irradiation in your location. This is typically easiest to see in the form of a map. In the example shown, this map is based on annual irradiation for optimum angled PV panels (30 degrees). Two scales are included: the top shows the irradiation over the country (kWh/m2) and the lower one a factor which can be used to convert the module/system power to actual units of electricity (kWh/kWp) based on a performance ratio of 0.75 (75%).
Genk Town Hall installation Belgium (Suntech modules)
To get the best estimation of what you can expect from a PV system at your location consult with a MCS approved installer who will be able to advise you. (see BPVA website). Utility Greece (Suntech modules)
I like PV, what do I need to do next? In order to benefit from the FIT (Feed In Tariff) the Governmental department DECC (Department of Energy and Climate Change) has stipulated that for all domestic installations (below 50kWp) the installation has to be carried out by an MCS accredited installer using MCS approved system components. MCS – Microgeneration Certification Scheme - is a standard of compliance to meet the Government criteria for eligibility to access financial incentives such as the FIT.
So the first step towards installing a PV system is choosing an MCS approved system installer. One advantage is that under existing Inland Revenue rulings the VAT charged for the system (parts and installation) is only rated at 5% VAT when installed by a VAT registered installer. The installer will assess your property and provide a quotation for installing a system along with a projection for the amount of electricity this will produce.
These are a few guidelines in selecting your MCS approved installer • How many systems have they installed in your area and can you see one? If you can speak to the customer and find out how happy they were with the installation and especially how happy they are with the power the system provides and does this match well with what they were told they could expect? • Are they fully insured to undertake this work? What happens if one of their workers has an accident? Fitting the modules onto a roof requires special training and compliance with H&S (Health and Safety) regulations.
• What guarantee do they offer? Typically there are two types: a product warranty for 5 or more years and a performance guarantee (typically 80% output after 25 years). The inverter may only be guaranteed for 10 years or so though some can now be guaranteed for up to 25 years. If less then make sure to factor in replacement costs! • What maintenance services do they offer? Roof mounted PV modules can get dirty (bird droppings, general dust etc.) and these can often be very difficult if not impossible for a home owner to safely clean. Make sure this is included as an aftercare service and factor in the cost.
Planning permission is typically not needed though in some cases (Listed Building, restricted area such as an Area of Outstanding Natural Beauty) planning permission may be required. Your installer should be able to help here but if in any doubt consult with your local planning authority.
Residential installation Germany (Suntech modules)
As far as financing goes to buy your PV system there are a number of options. You can simply buy this outright or at the other end of the spectrum packages are available where you in effect â€œrentâ€? your roof space and you get the savings of the electricity you use from the PV system and the person supplying the system gets the money from the FIT. In some cases in the latter scenario, the system can also transfer to your ownership after a defined payment has been made from the FIT.
San Francisco Airport installation (Suntech modules)
Solar Farm, Alamosa USA (Suntech modules)
Now you have read Power from the Sun the BPVA are sure you will want to know even more. From locating an MCS approved installer close to you, through to the latest news on the FIT and much more visit www.bpva.org.uk/powerfromthesun The BPVA thanks Suntech for their vision in supporting the production and distribution of this informative and educational booklet. Without their support this project would not have been possible.
Jargon busting AC Alternating Current. The standard form of electricity supplied through the grid to homes/factories etc.
Isolation switch A device (switch) to disconnect the modules from the inverter during maintenance etc. A fuse box is often part of this assembly.
BIPV Building Integrated PV. Typically this is where the PV is an integral part of the roof system. Removing the BIPV would allow the weather in (rain etc)!
k kilo meaning 1,000.
Blocking diodes Devices to prevent cell damage and reduce power loss when a module is in shade. BPVA The British Photovoltaic Association. A non profit making association dedicated to PV in the UK. CO2 Carbon Dioxide gas. What is now recognised by most experts as the main cause of climate change.
kWh A unit of electricity – typically what you are charged in. kWh/kWp/annum The irradiation value used to calculate how much you can expect from a PV system. kWp The unit used to specify the output from a PV module or system (Kilo Watt peak).
DC Direct Current (like a battery). The raw output from a PV module.
MCS Microgeneration Certification Scheme. Installer and system components have to be MCS certified to allow payment of the FIT for domestic (<50kWp) systems.
DECC Government department. The Department of Energy and Climate Change.
Module A PV system comprising typically a number of solar cells in strings (also called a solar panel).
DNO Distribution Network Operator (or can be DSO – Distribution System Operator or even TSO – Transmission System Operator). The company that delivers the electricity to the home.
EPC Engineering Procurement Contractor – a company who undertakes a full service installation (usually this term is used for larger commercial contracts). FIT Feed In Tariff (clean energy cashback). A method to encourage the uptake of renewable energy such as PV where payments are made for small scale electricity production. Grid The distribution network that delivers electricity throughout the country. Grid parity The point at which an electricity source such as PV matches the price from regular electricity supplies. Inverter The device that takes the DC power from the PV system and converts this to AC. Irradiation The amount of energy coming from the Sun. This varies depending on where you are (the further South in the UK the higher the value) and typically assumes a 30% angle (from flat) for a PV module. The units are usually shown for PV systems as kWh per kWp per annum.
Photovoltaic PV for short. The process of making electricity from the Sun. Derived from photo meaning light and volt being a unit of electromotive force. PV Short for photovoltaic. Renewable When used in the context of renewable energy means an energy that comes from a natural source such as the Sun, wind and tide – they are naturally replenished. RPI Retail Price Index. A measure of the change in cost of living expressed as a % compared to the previous year. SAP Standard Assessment Procedure. In various forms used to determine the energy efficiency of homes (eg SAP 2005). Solar cell A building block of a PV module – a semiconductor PV generator (typically silicon). STC Standard Test Conditions. Allows PV modules and systems to be compared. Irradiance of 1,000 W/m², solar spectrum of AM 1.5 and module temperature of 25°C. String A linking of multiple solar cells inside a module. W Watt – unit of power.
Suntech – The world’s largest manufacturer of photovoltaic modules
The British Photovoltaic Association - BPVA
Solar modules are the “heart and soul” of any PV installation. If
trade association dedicated to photovoltaic energy. The
you want to be certain that the modules you choose are
BPVA provides a credible and representative platform for
amongst the best available, there is only one logical choice:
the entire PV industry.
The British Photovoltaic Association is the UK’s industry
Our mission is to ensure that photovoltaic energy
One out of every 10 PV modules installed world-wide is
establishes itself as the leading renewable energy source in
produced by Suntech. With 3 gigawatt of installed capacity in
the UK, providing significant environmental and monetary
80 countries, Suntech modules have produced enough energy
to replace three nuclear power plants. Whether domestic residence, agricultural building, industrial facility, or solar power plant, Suntech Power offers the highest possible quality solar modules: durable, reliable – and costeffective. In short: Suntech offers the best price/performance ratio and long-term yields for all types of solar installation. Suntech offers performance, reliability and warranty terms above the basic industry standard. As well as world-class
The primary objectives of the BPVA are: Education Bring about increased awareness of the potential for PV throughout the UK from the consumer to Government (regional and national). Inward investment and growth Assist both UK based and overseas members in their business development in the UK, resulting in job creation in the UK PV industry.
research and development capabilities, state-of-the-art
Policy To take part and influence policy and regulatory
production processes and subsidiaries on every continent, the
forums, working to create frameworks for PV power
company offers its customers the following benefits:
development and adoption. To engage with DECC and
• Reliability: Suntech solar modules are produced according to the highest technical standards using top quality components. These products are guaranteed for better performance over time, backed up by an industry-leading, 25-year transferable warranty.
other UK Government departments to ensure the PV
• Quality: Suntech solar modules are tested more rigorously than is required by international standards, providing the reassurance of higher product reliability and substantially better safety levels.
• A fully independent non profit making association 100% dedicated to photovoltaic in the UK - Focusing on the technology and application of PV - An ambassador for PV both in the UK and representing home interests internationally - No favour: all members treated equally
• Innovation: With a world class team of 400 researchers and developers, Suntech is continuously improving its products for better performance. • Support: A global network of local staff and partners means on-the-spot support at any time. • Peace of Mind: Suntech’s solid financial foundation, which has led to international success and market leadership, offers long-term security. All Suntech products are independently tested so they all carry the trusted certification marks of TUV, UL, CE, IEC and, of course, are MCS-certified for the UK market.
industry receives appropriate attention. To represent the interests of the UK PV market on the international stage. Key facts behind the BPVA:
• Dedicated to make the most of the UK market for PV - Educate and inform the consumer and other user groups - Stimulate interest in PV in a broad range of applications - A catalyst to investment – both indigenous and from abroad • Dynamic management - Streamlined structure to react fast to market demands - Close contact to members through Board level representation - Proactive; driving force behind PV in the UK
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For more information about the BPVA please visit
the Sun • po w ro m f er r e fro ow mt p • he n Sun u S • powe e r fro m the Sun • powe h t BPVA Members Showroom The Building Centre 26 Store Street London WC1E 7BT Monday to Friday 9.30 am - 6.00 pm Saturday 10.00 am - 5.00 pm
Published by the British Photovoltaic Association (BPVA). Kindly supported by Suntech Europe. 1st edition © 2011 BPVA Though every effort has been taken to ensure accuracy in this document the BPVA cannot take any responsibility for errors. Incentives such as FITs can change with time. Please consult www.bpva.org.uk/powerfromthesun for any updates.