There is a lot of information and misinformation around solar photovoltaic (PV) and solar thermal energy.
EvoEnergy hopes to have foreseen your questions and answered them below. If not, our expert staff are willing to answer any further questions on the phone or via email.
FUNDAMENTAL QUESTIONS
Q: What is the difference between a kilowatt (kW) and a kilowatt hour ( kWh)?
A: A kW is a thousand watts and a unit of power. It measures the rate of energy conversion. A kWh is the amount of work done, or energy used, when a kW of power works for one hour.
Q: What is a kWp, and how does it relate to kW and kWh
A: A kWp is the kilowatt 'peak' of a system. This is a standardised test for panels across all manufacturers to ensure that the values listed are capable of comparison. The test conditions for module performance are generally rated under Standard Test Conditions (STC) : irradiance of 1,000 W/m2, amodule temperature at 250C and a solar spectrum of AM 1.5. This spectrum can be found here, but is unlikely to be of any interest to anyone outside the industry. Suffice to say that it is a standardised test
Q: Do Solar Panels create energy?
A: A basic tenet of thermodynamics is that energy is never actually created only converted; solar panels convert solar energy into electricity rather than just creating it.
Q: What is photovoltaics (solar electricity), or 'PV'?
A: What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as light-electricity. And that is just what photovoltaic materials and devices do; they convert light energy to electricity, as Alexandre-Edmond Becquerel and others discovered in the 19th Century.
Q: What are the components of a photovoltaic (PV) system?
A: A PV system is made up of different components. These include PV modules (groups of PV cells), which are commonly called PV panels; a charge regulator or controller for a stand-alone system; an inverter for converting alternating current (ac) rather than direct current (dc) is required; wiring; and mounting hardware or a framework.
Q: How does the system work?
A: Daylight hits the photovoltaic cells and is converted to clean electricity. The inverter converts the electricity from direct to alternating current, for use in the home. When the solar energy system is producing more power than is needed it is exported to the grid. At night, power is imported from the grid in the normal way.
Q: What's the difference between PV and other solar energy technologies?
A: There are four main types of solar energy technologies:
1. Photovoltaic (PV) systems, which convert sunlight directly to electricity by means of PV cells made of semiconductor materials.
2. Concentrating solar power (CSP) systems, which concentrate the sun's energy using reflective devices such as troughs or mirror panels to produce heat that is then used to generate electricity.
3. Solar water heating systems, which contain a solar collector that faces the sun and either heats water directly or heats a working fluid that, in turn, is used to heat water.
4. Transpired solar collectors, or solar walls, which use solar energy to preheat ventilation air for a building.
Q: Will they work in the UK and during the winter?
A: Yes. Solar panel suppliers have enhanced the efficiency of solar power systems to the extent that it is now a very viable option even in cloudier climates. The important thing to bear in mind is that solar power depends on intensity of light, not necessarily direct sunlight. So even when it's overcast, your solar panels will be producing clean electricity to help power your home.
Q: What happens if there is a power cut?
A: Our photovoltaic systems for homes are entirely grid connected. If there is a power cut your system is automatically switched off. This is a safety measure designed to stop electricity leaking on to the national grid and to protect individuals who may be working to restore the power supply.
Q: Does the system need batteries?
A: No, the system is connected to the national grid. In the night, when the cells are not generating energy, electricity is bought from the utility company in the normal way. Any excess electricity generated during the day, for example when you are at work, is sold back to the utility company.
Batteries are only required if you want a truly off-grid solution and independence from any power cuts that might occur. They are also required if you own a property which is not attached to the grid in order that power produced during the day can be stored for use in the evening. Batteries add significant costs to a solar system so are normally only offered on specific request.
Q: How much energy do I need?
A: According to the Energy Saving Trust, the average 3 bedroom house consumes 3,300 units of electricity (kWh) a year (cooking and heating using non electric supply). However, we always recommend that you look at your last few bills or call your electricity supplier to find out how many units you consume, you can then compare this to the output of the system we recommend.
Q: What if I produce more energy than I need?
A: Whenever your panels are producing more electricity than your home is using, it will flow back into the grid for other homes to use. As long as you have an arrangement with your energy company, you'll be paid for this power so you can be sure your energy bills will be even less and none of your clean, green electricity will be wasted. This setup eliminates the need for batteries. You can speak to your electricity provider for details or check at www.uswitch.com to check which energy companies offer arrangements like this. This is also something that EvoEnergy is willing to help with once a final system has been decided and your needs prescribed.
Q: Do you sell hot water systems as well as solar electric (PV) systems?
A: Yes, we sell both types of solar systems: Solar photovoltaic (PV) systems which generate electricity from daylight and solar thermal systems to heat water.
Q: What does energy conversion efficiency mean?
A: Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy consumed, or available to a device. The sun produces a lot of energy in a wide light spectrum, but we have so far learned to capture only small portions of that spectrum and convert them to electricity using photovoltaics. So, today's commercial PV systems are about 7% to 17% efficient, which might seem low. And many PV systems degrade a little bit (lose efficiency) each year upon prolonged exposure to sunlight. For comparison, a typical fossil fuel generator has an efficiency of about 28%.
Researchers are working on ways to convert more of the energy in sunlight to usable energy and increase the efficiency of PV systems, however. Some experimental PV cells now convert nearly 40% of the energy in light to electricity. In solar thermal systems (like solar water-heating roof panels), efficiency goes down as the solar heat is converted to a transfer medium such as water. Also, some of the heat radiates away from the system before it can be used.
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Q: Why should I use photovoltaics (PV)?
A: For a growing number of users, PV is the clear choice. You should definitely consider using a PV system if it operates better and costs less than the alternatives. The cost of energy produced by PV systems continues to drop. However, kilowatt-hour for kilowatt-hour, and depending on where you live, PV energy still usually costs more than energy from your local utility. Also, the initial cost of PV equipment is higher than that of an engine generator. But there are many applications for which a PV system is the most cost-effective long-term option, such as for power in remote areas.
The number of installed PV systems increases each year because their many advantages make them the best option overall. Consider the following issues:
Site Access - A well-designed PV system will operate unattended and requires minimum periodic maintenance. The savings in labor costs and travel expenses can be significant.
Modularity - A PV system can be designed for easy expansion. If your power demand could increase in future years, the ease and cost of increasing the PV power supply should be considered.
Fuel Supply - Supplying conventional fuel to the site and storing it can be much more expensive than the fuel itself. Solar energy is delivered free of charge!
Environment - PV systems create no pollution and generate no waste products when operating.
Maintenance - Any energy system requires maintenance, but experience shows that PV systems require less maintenance than other alternatives.
Durability - Most of today's PV modules are based on a proven technology that has experienced little degradation in more than 15 years of operation.
Cost - For many applications, the advantages of PV systems offset their relatively high initial cost.
System designers know that every decision made during the design of a PV system affects the cost. If the system is oversized because the design was based on unrealistic requirements, the initial cost is unnecessarily high. If less durable parts are specified, maintenance and replacement costs will increase. The overall system life-cycle cost (LCC) estimates can easily double if inappropriate choices are made during system design. Don't let unrealistic specifications or poor assumptions create unreasonable cost estimates and keep you from using this clean power source. As you size your PV system, be realistic and flexible, and select an experienced designer such as EvoEnergy to assist you.
Q: Are there disadvantages to using solar energy?
A: Solar energy technologies often have a higher first cost. This means that a person is likely to pay more money up front to purchase and install a solar system. Still, in nearly all cases, the high initial cost is recovered through substantial fuel savings within the life of the product (25-50 years). This time is significantly reduced by any government incentives in place such as Renewable Obligation Credits or feed-in tariffs.
Q: What is wrong with wind power?
Wind power is an excellent technology and vital in the renewable energy mix required to wean Britain off its unsustainable fossil fuel addiction. However, it requires a lot of space and is only practical when there is an average wind-speed of around 6m/s. This means that it is rarely suitable within an urban landscape. Even when placed rurally it is still constrained by planning permission and the whim of individual planners.
EvoEnergy dreams of a country covered by PV and wind and are happy to recommend accredited and reputable installers to work with. The two technologies complement each other quite well, especially in an off-grid situation as it is windiest when least sunny and vice versa.
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Q. Isn't solar power expensive?
A: Solar installation adds as little as 4% to the build cost of an average three bedroom home, but can add this to its final value when sold. It also helps 'future proof' a home against rising fuel prices making properties doubly attractive to price conscious house buyers; as fuel prices continue to rise, energy efficient renewably powered homes will continue to sell at a premium. Retrofits to existing properties tend to cost from around £9k for a 1.44kW PV system. It can't be denied that this is a significant initial outlay, but the systems are guaranteed for 20+ years (depending on the panels chosen) and are expected to degrade at well under 1% per year. With fuel costs expected to rise over this period it can still be seen as an economic investment rather than just an environmental one.
Q: How can I connect my system to the grid?
A: Connecting a PV system to the distribution network will require permission from the Distribution Network Operator (DNO). The DNOs in the UK have different policies when it comes to connecting PV systems to their networks, and so different rates will be paid for exported electricity. We will make the necessary arrangements for grid connection. Currently the trend amongst suppliers is not to install export meters but to pay a fixed amount per kilowatt peak installed. This means that you will be rewarded for the electricity generated from your system even when you use it in your home - potentially doubling its value. Most of the big utilities will buy back the energy you generate for the same price as they sell it to you although this is something that EvoEnergy will help you find out.
Q: What is net metering? Is net metering available where I live and work?
A: Net metering is a policy that allows homeowners to receive the full retail value for the electricity that their solar energy system produces. The term net metering refers to the method of accounting for the photovoltaic (PV) system's electricity production. Net metering allows homeowners with PV systems to use any excess electricity they produce to offset their electric bill. As the homeowner's PV system produces electricity, the kilowatts are first used for any electric appliances in the home. If the PV system produces more electricity than the homeowner needs, the extra kilowatts are fed into the utility grid.
Q: Which electricity supplier should I use?
A: We have a good knowledge of the various tariffs available and are happy to advise the tariff that best fits with your lifestyle and energy usage. If you need to switch supplier it is not a complicated process and is something that we're happy to help with.
Q: How long will the Payback period be on these panels?
A: Please see the section of our website dedicated to payback
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SUITABILITY
Q: Does EvoEnergy service the whole of the UK?
A: For domestic jobs under 1.5kW we generally operate in the M1 corridor; from the south of London to Manchester/Liverpool, between Bristol and Norwich. For jobs 2.5 - 4kW we will service the majority of England and Wales. For jobs over 4kW then we can even ship equipment overseas as required. In all cases, please call us for an obligation free quote and we can direct you towards trusted installers wherever you might be.
Q: How long will it take to install my system?
A: PV systems can be installed and ready to produce electricty in 2-8 weeks from the time the design has been agreed.
Q: Can I use photovoltaics (PV) to power my business?
A: PV systems can be blended into virtually every conceivable structure for commercial buildings. You will find PV being used outdoors for security lighting as well as in structures that serve as covers for parking lots and bus shelters, generating power at the same time. Indoors, PV systems are used to offset and operate all kinds of electrical systems, including lights, cooling systems, and appliances.
Today's modules can be built into glass skylights and walls. Some resemble traditional roof shingles. Architects can use building-integrated PV to design buildings that are environmentally responsive, aesthetically pleasing, and produce their own power. Building-integrated PV provides a dual-use building material, reduces PV system costs by using the building as the mounting or support structure, and reduces utility bills through on-site power production.
Q: Can I use photovoltaics (PV) to power my home?
A: PV can be used to power your entire home's electrical systems, including lights, cooling systems, and appliances. PV systems today can be blended easily into both traditional and nontraditional homes. The most common practice is to mount modules onto a south-facing roof or wall. For an additional aesthetic appeal, some modules resemble traditional roof shingles or can be built right into glass skylights and walls. This building-integrated PV provides a dual-use building material, reduces PV system costs by using the building as the mounting or support structure, and reduces utility bills with on-site power production.
Q: What sort of projects are suitable for solar installations?
A: A project with a brief incorporating social and technical innovation is an ideal candidate for building-integrated PV (BIPV). The most important aspect to consider is the location of the site. The solar installation must receive as much light as possible. Shadows cast by tall trees and neighbouring buildings must be kept in mind during the design process. The best location for solar PV is on the south-facing roof or side of a building.
Q: How big a solar energy system do I need?
A: The size of solar system you need depends on several factors such as how much electricity or hot water or space heat you use, how much sunshine is available where you are, the size of your roof, and how much you're willing to invest. After talking through your exact needs we will be well placed to recommend the size of system you use.
Q: How do I know if I have enough sunlight for PV?
A: A photovoltaic (PV) system needs unobstructed access to the sun's rays for most or all of the day. Climate is not really a concern, because PV systems are relatively unaffected by severe weather. In fact, some PV modules actually work better in colder weather. Most PV modules are angled to catch the sun's rays, so any snow that collects on them usually melts quickly. There is thus enough sunlight to make solar energy systems useful and effective nearly everywhere in the United Kingdom.
Even hail won't damage most PV systems. Most homes have adequate roof space for a PV system, but you will have to size your system first to discover how much space is required. If you don''t have adequate roof space, look at other options such as integrating the system into a wall or putting the system in the backyard. You could also use the system to cover a porch or patio in the backyard or mount the system on the roof or wall of a garage. Remember: an energy-efficient building requires a smaller PV system.
Q: What are the effects of shade?
A: Shading is critical. Minor shading can result in significant loss of energy. This is because the cell with the lowest illumination determines the operating current of the series string in which it is connected. This is one of the areas covered in the survey carried out before any installation. We use modern arrays that can bypass the affected diodes to minimise shade effects; but these effects must still be considered.
If shading is unavoidable, or poor light is expected on a regular basis, then we will modify our designs and possibly even the type of cell we use. This can obviously only be taken on a case by case scenario.
Q: How can the energy outputs of the different products be estimated?
A: The following energy outputs can be used as a rough rule of thumb for the UK (assuming a reasonable tilt, orientation and system efficiency). The panels shown in the products section all give the size dimensions and the maximum expected power for each panel. For every 1kW of maximum production, it can be estimated that, in Britain, 800kWh of energy will be produced over an average year.
Q: How is the angle of optimum panel inclination found for different latitudes within the UK?
A: The maximum total annual solar radiation is usually at an orientation due south and at a tilt from the horizontal equal to the latitude of the site minus approximately 10-15 degrees. For example 30 degrees is an optimal tilt in Southern England, increasing to almost 40 degrees in Northern Scotland.
Q: How do the panels perform at different angles and orientations?
A: If the optimum angle is not achievable, over 90% of the maximum annual energy can still be achieved at 10 degree and 50 degree tilts. South-facing vertical facades generate around 70% of the maximum.
Q: Can I design and install a photovoltaic (PV) system myself?
A: Maybe! However, unless you are very handy or experienced in home wiring, we suggest using experienced professionals to design and install anything more than the simplest application, for the following reasons:
- You have to pay 15% VAT on the PV cells rather than the 5% accredited dealers.
- You might void the manufacturer's warranties.
- You might not have a functional system after spending your hard-earned money on the system.
- Electricity can be dangerous; you might get hurt.
- You might damage your home or appliances during installation.
The goal of a stand-alone system designer is to assure customer satisfaction by providing a well-designed, durable system with a 20-year life expectancy (or more). This depends on sound design, specification and procurement of quality components, good engineering and installation practices, and a consistent preventive maintenance program.
A thorough knowledge of the availability, performance, and cost of components is the key to good system design. Price/performance trade-offs should be made and re-evaluated throughout the design process. When you start your design, obtain as much information as you can about the components you might use. After studying all the issues, you can do an initial sizing of the PV system and get some ideas about specifying system components.
Extra points to remember are:
- Method of fixing/ integration into the fabric must be detailed.
- Ensure that the fixing does not cover or shade any part of the PV cells.
- PV laminates are often constructed with only a narrow border.
- The fixing must allow for thermal expansion without breaking the glass.
- Weather sealing involves standard construction practices but all materials must be suitable for the temperatures likely to be met (i.e. temperatures at the back of the modules can rise to 80ºC if they are poorly ventilated or higher if they are directly insulated).
- The mounting option must allow for safe maintenance and possible replacement of individual modules.
- The life of the support structure must be at least that of the PV array. The preferred materials are aluminium, stainless steel or glass-fibre. Protection from corrosion is important especially as residual currents may be present.
- Wind loading
- Any extra weight
- How and where to run electrical wiring ( this may penetrate the waterproof skin)
- Where to place junction boxes.
Q: How can the energy benefits of the PV cells be maximised?
A: Orientation, shading and the temperature of the PV elements all impact on their output and must be considered at the design stage. Of course, the more energy efficient the building, the greater the overall benefit of the PV cells. Some PV products have now been designed to provide thermal insulation as well as electricity - eg flat roof systems and solar metal roofing systems that include insulation and solar glass laminates with low emissivity glass.
Q: What are the relevant codes of practice and articles of legislation?
A: British Standards
BS EN 61215
BS EN 61646
The Electric Supply Regulations 1988
The Building Regulations 1991 (and amendments)
The Construction (Design and Management) Regulations 1994
A 'Power purchase agreement' will need to be negotiated if electricity is to be sold. This is not as tricky as it sounds as electricity networks and supply companies are legally obliged to cooperate with solar installations. This is also something that EvoEnergy will help with.
Q: Why would I buy my solar system from EvoEnergy?
A: Please see our section dedicated to exactly this question.
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LIFETIME & PROBLEMS
Q: How long do photovoltaic (PV) systems last?
A: A PV system that is designed, installed, and maintained well will operate for more than 20 years. The basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than 30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly. It is estimated that performance will decrease by under 1% per year, which would mean that in 50 years they'd still be 60% efficient, but nobody really knows past the guarantees given.
Experience has shown that most problems occur because of poor or sloppy system installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of the electronic parts in the balance of systems (BOS): the controller, inverter, and protection components. Batteries fail quickly if they're used outside their operating specification. For most applications (uses), batteries should be fully recharged shortly after use. In many PV systems, batteries are discharged AND recharged slowly, perhaps over a period of days or weeks. Some batteries quickly fail under these conditions. Be sure the batteries specified for your system are appropriate for the application.
Q: What happens if something goes wrong?
A: All panels come with a 20+ year performance warranty so in the unlikely event that you experience problems, the supplier should be on hand to diagnose your problem and if necessary, arrange a home visit to ensure that everything is working as it should be. The installation comes with a 5 year warranty so you can be sure your service will be of the highest standard.
Q: What maintenance and cleaning do the systems need?
A: Solar photovoltaic systems are silent in operation, have no moving parts and require no maintenance. Solar thermal systems have a few moving parts (inside the pump) but these are virtually maintenance free, you may need to replace the anti-freeze in a solar thermal system after about five years. Most of the time the rain will keep the modules clean. However, a build up of dirt can affect system performance. The degree of soiling will depend on the location but usually dust accumulation and self-cleaning reach a steady state after a few weeks if the array tilt is at least 15 degrees. In extreme cases dust may cause a power reduction of about 10%. At low tilts horizontal glazing bars can trap debris which could lead to shading of part of the array. The design of the system should aim to minimise uneven soiling.
The modules can be cleaned with either a hose or, if possible, soapy water and a non abrasive brush.
Q: Doesn't the glazed front reflect light away from solar photovoltaic (PV) modules?
A: Not really, no. Solar PV modules constructed with a glass front have two characteristics that reduce light reflection. In order to optimise electrical yield the glass is treated with an anti-reflective coating which greatly increases the transmittance through the glass so to maximise the amount of light reaching the solar cells. Secondly the outer face of the glass has a slight granular texture. The result is a matt like finish rather than a mirrored, again this is actually intended to maximise yield. These two characteristics greatly reduce reflection from the glazed front face of solar PV modules when compared with conventional glazing.
Q: Will I ever have to go without power?
A: Your home will still be connected to the National grid. If at any time your solar panels are producing less electricity than your home is using, or at night time, you will just receive electricity in the normal way. Only if there is a power cut will you not be able to generate electricity.
Q: How long do PV systems last?
A: A well-designed and maintained PV system will operate for more than 20 years. The PV module, with no moving parts, has an expected lifetime exceeding 30 years. Experience shows most system problems occur because of poor or sloppy installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of electronic parts included in the Balance of Systems (BOS) - the controller, inverter, and protection components.
Q: When will solar electric systems replace coal and nuclear power plants?
A: Right now, our nuclear and fossil-fuel-based energy is quite inexpensive compared with the cost of solar energy. Oil and coal prices are low in most places, so solar energy still can't compete on a first-cost basis in many regions of the world, such as the United States. As this situation changes, we'll begin to see many more solar energy systems being built in areas that now use fossil fuels and nuclear energy for electricity generation. In the UK the govenment has committed to 10% renewable energy production by 2012, and 20% by 2020.
Another driver in the deployment of solar systems is public demand for clean energy. Fossil-based energy pollutes the environment, and nuclear energy creates hazardous waste. If we stop to consider the environmental and health costs of fossil-fuel and nuclear energy, then solar energy already makes sense today.
However, in developing countries where there is little or no supply system for conventional energy, solar energy is being used more and more. It can be much less expensive than many other options, and the environmental benefits associated with this cleaner form of energy are significant. In developing countries, the key barriers to wider use are the need for financing and for electric distribution networks.
Q: When will I be able to buy a solar electric or PV-powered car?
A: Because most automobiles are very heavy and aren't very efficient, it would be very difficult to power one with solar cells. But if a car were built specifically for PV, it could provide suitable transportation. As we've seen in many student-built vehicles for competitions, solar cars are very light and efficient and have enough battery storage to travel for miles on a cloudy day or at night. Solar cars can travel the speed limit on normal highways, but only as long as the sun is shining or until their batteries run down.
A more realistic car would be another kind of electric vehicle, one that many companies are working on right now. These cars could be charged by solar panels during the day, for example, while people are at work. They could also be plugged in at home for charging when the sun is not shining.
The benefits of solar cars are obvious: they don't pollute, and free sunlight is their fuel. The drawbacks are that, using today's technology, a solar car has to be very lightweight for the panels to provide enough energy to power the car at road speeds, and it has to have enough battery storage to travel long distances without sunlight (e.g., at night and on overcast days).
As part of continued research and development, many organizations are improving the systems used in solar cars to make them more efficient and cost effective and thus more widely used (the systems, anyway). Wider use of solar electric cars (or other electrics) probably depends on the availability of inexpensive, lightweight, compact energy storage methods. Car companies are making great strides in this area with the new gas/electric hybrids, and future progress is likely to be rapid.
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