Solar PV FAQs
You may also need room – usually in your loft space – for your inverter, depending on the product you choose. The inverter converts the power produced by your solar panels into power you can use in your home. It needs cool air to circulate around it, and usually requires just over a cubic meter of space.
Finally, your roof needs to be structurally sound because solar modules are heavy. The great majority of roofs are strong, but this is certainly a factor your installer should check.
Your costs will vary depending on the components you choose; if you want high efficiency panels they will be more expensive, for instance. If you want solar modules integrated into roofing slates these may be more expensive still, but they are very attractive and can make good economic sense if you need to replace your existing roof slates.
• Monocrystalline solar is made from a single crystal of silicon. These are the most efficient, but also the most expensive cells to produce.
• Polycrystalline solar is made from blocks of silicon made up of many crystals. Both forms of crystalline solar are brittle and must be mounted in rigid frames.
• Thin-film solar requires only a thin film of silicon on a surface that can be flexible – for example on plastic. It is cheaper, but less efficient, so it needs a larger area. Some thin-film solar panels look lovely on historic properties with dark slate roofs in conservation areas.
• Bi-facial modules produce power from both sides of the panel. This is particularly useful for panels on/near highly reflective surfaces, such as light coloured roofs or stones. Bifacials can increase annual energy production by a considerable amount.
There is a widespread perception that solar suits only sunny countries. Actually a study by Oxford University’s Environmental Change Institute showed that there is a surprisingly small difference between the output of solar panels in summer in the UK and solar panels in Mediterranean countries. This is because heat can reduce performance and the longer daylight hours in northerly latitudes compensates for lower output.
Firstly, solar improves a building’s energy efficiency rating, which has a direct impact on valuation. Also, research by mortgage provider ING Direct shows that solar panels are the number one ‘non-essential’ item in clinching house sales, so having panels on your roof is likely to be an asset when it comes to securing a sale. However, installing panels badly is unlikely to help the value of your home. See our solar expert Ray Noble’s gallery of shame for examples of how NOT to install solar pv.
Solar Thermal FAQs
We would never recommend a solar collector facing north. However, many people are surprised to learn that there is not a great deal of difference on the total energy collected over a given year for all other directions. This is especially true for panels on a roof tilted at around 35 degrees, where the difference in performance between facing east or west, and facing due south, is only around 12%. It is important to be aware that if the output of the collector is reduced on an east or west orientation the collector area should be increased accordingly to ensure hot water needs can be met.
Your installer should also be a member of the RECC or HIES.
• Flat plate collectors. These are based on a thin heat absorber sheet, usually copper, backed by a tubing system to carry fluids. They are relatively thin, highly insulated and encased in glass. They are cost effective, with a range of mounting options and can reach efficiencies of 75-80%. They can be fitted on top of existing roof tiles, or in new-build or roof replacements where they can be integrated into roof tiles themselves.
• Evacuated tube collectors. A vacuum between glass tubing provides extremely efficient insulation and evactuated tubes can reach very high temperatures. There are two different categories of evacuated tube (direct flow and heat pipe). Both are similar in appearance but work in different ways. Heat pipe evacuated tubes can only be installed vertically but direct flow tubes can be installed vertically or horizontally.
You will not need to meter your solar thermal system, however, in order to be eligible for these incentives, the installer and product must be MCS registered.
Please note that average system cost is only indicative. Costs can vary significantly depending on your hot water delivery system.
Solar Trade Association manufacturer members have developed novel and unique solutions to this UK specific challenge that will allow a wider adoption of solar thermal with combi-boilers already installed throughout the UK. Major manufacturers like Worcester Bosch and Veissmann offer combi boilers that can accept preheated water from solar thermal systems.
The UK receives 60% of the solar energy received at the equator. Each square meter of the UK receives ample energy to operate an efficient solar panel system as long as the collectors are sized according to the required output. The prevalence of solar thermal in Scandinavia proves it can work effectively in colder climates than the UK.
For domestic solar hot water systems it has been found that installing 1m2 of flat plate collector, or 3/4m2 evacuated tubes per person will give satisfactory results. Heat loss through the system will be larger the smaller the collector is, therefore it is unusual to install a collector of less than 2.5m2 in the UK.
So it is important to beware of underestimating the size of the collector needed, as any cost savings may be outweighed by reduced performance if a system is too small.
Battery Storage FAQs
New guidance is coming soon from MCS, based on empirical data from Loughborough University and Advance Further Energy informed by real world data from our members. This guidance will help to ensure you receive accurate information on how your battery storage system will perform with a solar system from your MCS registered installer.
Some storage systems incorporate a range of technologies already in one case, such as an inverter, writing and smart controls. Other systems are built up for each customer out of separate units, typically; a battery, inverter and separate controls. So be sure to ask what you are getting.
We recommend comparing the benefits you could get with a battery and solar storage system to a solar only system to make your decision, bearing in mind the VAT benefits of installing both together.
Reputable installers will offer advice on the size of the battery for your system. If you are in all day, a 5kWh battery should be sufficient, although to get maximum savings you might wish to opt for a 10kWh battery or larger.
The capacity rating of batteries can be confusing, since there is a difference between ‘total’ capacity and ‘usable’ capacity because a battery will never fully discharge to avoid damage. Be sure to understand the usable capacity of any unit – this is what is used to save energy from solar power. Furthermore, you will also need to understand the battery’s power output. Consider if the battery will be powerful enough to meet the load of the electrical equipment that you want to run in your home simultaneously. Your kettle, for example, may need to be able to draw 2kW of power from your battery alongside your fridge and other electrical items.
So be sure to understand both the power output as well as the usable capacity of your storage unit.
As a rough guide, a fully-charged 6-7kWh system could usually store sufficient energy to power your lights, fridge-freezer, TV and computer over at least eight hours. Bear in mind appliances such as washing machines can use 2-3kWh in one go. And during the winter time your solar system will produce less power to store, though you should be able to top it up from the grid when power is cheap. Economy 7 and other Time of Use Tariffs (TOUTs) will enable you to do this. Data from Elexon on real world domestic consumer consumption patterns on weekdays in Spring suggests, roughly, a 2kWh battery would support average domestic consumption levels between 5.30pm and 8.00pm (or up to 7 hours overnight).
Incomplete charging can reduce the life of some batteries so some systems will from time to time be programmed to fully charge from the grid in order to complete the charging cycle and maintain your system.
At the technical level, solar PV generates direct current (DC) and battery storage units store and discharge DC, so both require power to be converted to alternating current (AC) to be used in the home or to export onto the grid. DC-Coupled systems put the solar PV modules and battery storage unit on the same side of the inverter. Alternatively, AC-Coupled systems put the battery storage unit on the grid side of the inverter and use a separate inverter to convert the power back to AC when the battery discharges. If you already have solar PV and now want to install battery storage you are likely to be offered an AC-Coupled system. However, if you are installing a new solar and storage system from scratch you are more likely to be offered a DC-Coupled system. It is not uncommon for households to want to operate in power cut conditions. However, this is not strictly necessary given power cuts are rare in the UK. Some battery systems can operate in a power cut and in some cases this would require changes to the wiring in your home – you will need to check with the battery manufacturer. Note that complex changes to your electrical wiring can be costly.
If you do not have solar already and are installing a new solar and storage system from scratch, the good news is that you will only pay 5% VAT on both the solar and storage. For new installations what you will be paid for your exported electricity remains as yet unclear as details have not been published on how the new Smart Export Guarantees will work or what the price per unit may be. As well as seeing our SEG pages, you can also see our League table where we list suppliers who are offering the best SEGs. The STA would like to see all exports from homes with solar and storage qualifying for the SEG.