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Frequently asked questions
With any new technology, there will inevitably be lots of questions about how it works. We hope that the following sections will answer any questions that you might have but, if you have any other questions, please contact us.- Is it sunny enough in the UK to make money from solar panels?
Yes - Feed In Tariff rates are calculated so that UK installations will produce a 5-8% return, based on average UK weather patterns. Although solar panels in the UK won't produce as much energy as, for example, panels in Spain, the Feed In Tariff in the UK is a lot higher than in Spain to compensate for this.
Solar PV panels only need light in order to produce electricity. They work best in bright sunlight on a cold day, but still produce some electricity on a cloudy day and even work when it's raining ! All of our calculations use average annual solar data for your area to predict what you will generate in an average year. Although you may only produce a couple of units on a cloudy winter's day, you could produce more than 20 units on a sunny day in May. A south facing property in Derby should produce around an average of 750 units per kilowatt of installed solar power each year. - How much electricity will I produce?
The total output of a solar system is dependent upon :
- available roof space - approximately 7.5 m² of roof space is needed per kilowatt of installed solar power.
- orientation - ideal location is South West to South East
- the roof pitch - ideally located on a pitched roof at 30o to 45o
- the amount of shading from nearby trees, buildings, etc
- the interaction between the panels and inverter chosen
Generally an ideally located system in Derby will produce around 750 units of electricity each year per kW installed. Optimising the design of your system is critical, so we offer a free, no obligation survey and quotation. This will also include a detailed financial assessment, based on your location and electricity usage.
For an estimate, based on data you provide please get an estimate.
To arrange a survey, please contact us.
- Will the solar panels produce all the electricity I need?
No - a solar PV system has a maximum power at any one time and, whenever you exceed that maximum power, you will automatically get the extra electricity from the National Grid. So, on very cloudy days or at night, you will be using electricity as normal from your electricity supplier. Also, even on a very sunny day, if you run several appliances at once, these may exceed the maximum power of the PV system, so you will get some of the electricity free from the solar panels, but the rest from the grid.
However, it is possible to install a PV system that over a year will generate at least as much electricity as you consume. On sunny days you will be exporting extra electricity to the grid and at night you will be buying electricity, but overall you sell as much as you buy so are effectively "electricity neutral".
To achieve this, you will need to install quite a large system AND adopt plenty of energy saving measures to keep your overall electricity usage down. A 4kW system (which is about the largest domestic system that might be fitted, requiring about 30m2 of roof space) would generate around 3000 units of electricity, which is slightly less than the national average electricity usage. By reading some of our energy saving tips, it is easily possible to reduce your electricity usage to well below 3000 units per year.
- Why do quotations from different solar panel installers give different output figures?
All installers should be using the Government SAP (Standard Assessment Procedure) to estimate the amount that you will produce from a solar PV system.
SAP uses a national average amount of sun and some basic assumptions to estimate how many units of electricity will be produced by each kilowatt of solar power. Some example SAP figures for unshaded roofs are:
Roof Average Output per kW installed (in kWh) S facing - 30o pitch 833 S facing - 45o pitch 818 SE/SW - 30o pitch 798 E/W - 30o pitch 708 Because the SAP figures do not take location into account, you would be given the same output prediction in the South of England as you would in the North of Scotland. Being based in Derby, we prefer to give our customers a more accurate, realistic prediction of what they will generate, so we use some solar software, called PVSOL to calculate this. This software takes everything into account including the type of panels and inverter used, shading from trees, location in the country, etc. Generally for a south facing property in Derby it predicts around 700-750 units per kW, ie much lower than the SAP estimate.
We include both the SAP figure and the PVSOL figure in our quotations, but base all financial payback estimates on the lower of the two, so that you have a more realistic expectation. Since everyone should quote the SAP figure, you should be able to compare one quotation with another.
Be very wary of any company that predicts outputs that are higher than the SAP figure, unless you are in the very south of England. Higher figures have nothing to do with them supplying better panels, they are just making over-exaggerated claims to try to get a higher price for the same system. It is very unlikely that these over-exaggerated claims will be backed up by a performance guarantee.
We prefer to give more realistic estimates, which we also back up with a performance guarantee, so that our systems are more likely to perform better than we quote, rather than leave customers disappointed.
- What is your system performance guarantee?
All our installations are covered by our standard installation guarantee against any defect or problem arising from poor workmanship or design errors for a period of 2 years.
All estimates of system performance are primarily dependent on the level of solar radiation in a particular year, but we understand that the financial analysis depends on these estimates being reasonably accurate.
So, we also offer a performance guarantee that the electricity generated by the panels in the first full year should be more than 80% of what was predicted at the time of commissioning, providing there are no local environmental changes (eg new trees, new buildings, etc). In the unlikely event that the first year performance is significantly less than this, please contact us as soon as possible and we will at our discretion and, depending on what is reasonable, provide a full or partial refund, repair or replace the system.
- What is the difference between hybrid (HIT), monocrystalline and polycrystalline panels?
Until recently, monocrystalline panels have been are the most efficient, because the solar cells are made from pure drawn crystalline silicon wafers. Polycrystalline panels are made up from the offcuts from the silicon wafers, to create a cell made up of several bits of pure crystal. Because the individual crystals are not necessarily all perfectly aligned together and there are losses at the joints between them, they are not quite as efficient. However, this mis-alignment can help in some circumstances, because the cells work better from light at all angles, low light, etc.
The only real difference is that for a given area of roof, you could get more power output from monocrystalline panels than polycrystalline. However, when there is space for both, it is better to go for the cheaper system and for panels that are sized to fit your roof well. In fact, because of the method of manufacture of the two types, the power generated per square metre is virtually identical - as explained in the sketch below:
Mono-crystalline The Cells are 14% efficient, but pure cells are octagonal, so there is unused space in the corners. This lowers the amount generated per square metre from a panel.
Poly-crystalline Cells are 13% efficient, but are formed into rectangles, with very little unused space on the panel. Overall the amount generated per square metre is similar to moncrystalline
You can now get a hybrid panel (eg Sanyo HIT), which has a thin layer of amorphous solar film behind the monocrystalline cells. The extra amorphous layer extracts even more energy from the avialable sunlight, particularly in low light conditions. These are the most efficient panels available at around 19% efficiency. However, unless you have a very small roof and want to extract the maximum amount of energy from it, we would not recommend using the hybrid panels at the moment. Hybrid panels are a lot more expensive than mono or poly-crystalline panels, so that the increase in energy produced does not justify the extra cost of buying them.
- How much does a solar PV system cost?
Prices depend on the number of panels installed. For domestic properties, system sizes are usually between 1.5 and 4 kiloWatts (kW) and cost between £7000 and £16000.
We will design an optimum system to suit the available roof space and your budget. We offer a free, no obligation survey and quotation. This will also include a detailed financial assessment, based on your location and electricity usage.
To arrange a survey, please contact us.
For an online estimate, based on data you provide please get an estimate.
- How long does it take to payback?
The traditional payback calculation is to divide the initial outlay by the annual earnings. For a typical south facing system this gives a payback period of 10 to 12 years.
However, this method does not take into account the interest that would have been earned if the investment had been put into the bank. The graph below shows what the payback period would be if the interest rate was 2% above inflation throughout the life of the investment. It shows a payback period of 12-14 years.
On an East-West facing roof the traditional payback time is around 14 years, or 17 years taking bank interest into account.
- What if I sell my house?
The FIT contract with an electricity supplier will be fixed for 25 years. If you sell your house before that, then you are likely to sell the solar panels and hence the contract at the same time.
The remaining value of the contract is quantifiable, so you should be able to negotiate this additional value on top of the house price. Unlike buying a car, which loses value as soon as you buy it, a solar system will immediately add more value to your house than the cost of the panel. The longer you stay in your house, the less the remaining contract will be worth, but it will still add extra value to your house compared to a house without solar panels.
- Shouldn't I wait until the cost of solar panels comes down?
The Feed in Tariffs will be regularly reviewed so that they give an approximately 5-8% return at the time you sign up for them. As the cost of solar panels comes down, so will the level of feed in tariff payment. The cheaper the panels get, the less need there is to offer an incentive for buying them. So, although solar panels are likely to cost less to buy in a few years time, you will also earn less from them. The maximum incentives are given to the "early adopters" who are effectively helping to bring down the price for everyone else by pushing up demand.
- Why do quotations from different solar panel installers use different rates of return?
Many installers only provide a simple rate of return figure of "total income and savings / initial investment". This often indicates that you might earn more than 10% annual return on your money.
Although you may be earning 10% of your initial investment each year, unlike other investments, you first have to recover your initial capital before any additional income provides you with a return on your investment. So, over the 25 year period of the Feed In Tariff contract, the actual interest rate that you have earned on your initial investment is much lower than 10%.
That is why we prefer to use the Net Yield, which is a much fairer, more realistic figure and enables you to compare an investment in solar panels to keeping your money in the bank.
- What is the Net Yield?
It is important to understand that a PV project should be treated as a long-term investment. Your capital is invested in the solar panels, rather than remaining in the bank earning interest. Unlike other investments, you cannot easily retrieve your initial investment.
Once you have bought the panels, you first have to recover your initial investment and then any additional income provides you with a return on your investment.
The Net Yield is the interest rate that the bank would need to offer for the entire 25 year period, before it would be better to keep your money in the bank than invest in solar panels. If the bank interest is lower than the Net Yield then if you put all your solar income into the bank each year, you will have more money after 25 years than if you had just left your initial capital in the bank the whole time.
For a typical South facing installation, the Net Yield is around 6-8%; on an East-West facing installation it is 4-5%.
This is quite a conservative figure because we do not take into account the effect of above inflation rises in electricity prices which are expected. All earnings from the Feed In Tariff are also tax-free, whereas bank interest is subject to income tax. Finally, although the Feed In Tariff will end after 25 years, the solar panels will still continue to produce free electricity for much longer than that.
- Why are the electricity suppliers paying Feed In Tariffs?
All electricity suppliers are subject to the Renewables Obligation Order, which requires them to gradually increase the percentage of electricity from renewables over the coming years (9.7% in 2009/10 rising to 15.4% by 2015/16). This order currently extends to 2037 to enable long term planning of renewable installations.
From April 2010, this Order will force all large electricity suppliers to pay feed in tariffs (FITs) to owners of solar electric installations and they will be contracted to do so for 25 years. The electricity suppliers benefit because it reduces the amount that they would have to otherwise invest in renewable energy schemes in order to meet their renewable obligations. However, they are also likely to pass on the some of the costs of providing FITs to all their electricity customers.
- Do I need Planning Permission?
Installation of solar PV systems constitutes a "Permitted Development Right", according to a Planning Amendment Act in 2008, so planning permission is only required in conservation areas or on listed buildings. If either of these apply to you, please check with planning before placing an order. Otherwise, we will send a standard notification letter to your local planning department as soon as we have received your deposit, so that there will not be any issues prior to installation.
- Will my roof support the weight of the panels?
The PV Solar system will be installed to all current building regulations standards and the mounting system manufacturer's guidelines.
Most roofs are comfortably capable of withstanding the weight of solar PV panels. We carry out basic dead loading checks to confirm that the roof loading will not increase by more than 15%. Above this, Building Regulations require an additional structural analysis to be done. We also check that the mounting system used is capable of withstanding the likely wind uplift loads in your area. If any calculations give us cause for concern, we will recommend that an external structural engineer does additional calculations prior to installation. We can arrange this and will charge the additional fee, as quoted by the external structural engineer.
- Do I need Building Control approval?
The PV Solar system will be installed to all current building regulations standards and all electrical works will be completed to the current 17th edition IEE wiring regulations 2008.
For all installations, we apply for a Building Control Building Notice to cover Part A (Structure) and Part P (Electrical Safety - Dwellings). The necessary compliance certificates will be provided on commissioning of the system.
Please be aware that many PV installers do not fully consider the structural and workmanship requirements of the Building Regulations. All installers should make an application to the local Building Control authority for them to inspect the structural changes to your roof, but many do not do this, and only give you an Electrical Safety certificate.
- What paperwork do I need to complete to get my feed in tariff?
It is only possible to be paid a Feed-In Tariff if your system is installed by an accredited installer, listed on the Gemserv MCS website. We are Approved MCS Installers, accredited with NAPIT (Certification number is NAP/13078/10/1), so are allowed to use the MCS certification mark.
Once the system has been commissioned, we provide you with an MCS certificate, which you will need to provide to a FIT supplier (not necessarily your current electricity provider), together with their contract form. All the major electricity suppliers have their own FIT forms for you to fill in. We can assist with obtaining and completing the forms if you wish.
- What does a site survey involve?
As members of the Renewable Energy Assurance Listed (REAL) scheme, we do not employ any high pressure sales tactics / discounting, etc. The site survey enables us to discuss your overall requirements and to measure the roof, trees, etc. We can also plan wiring routes through the property, discuss potential inverter locations, etc. In addition we also gather information about your current electricity usage and costs from your bills.
All of this enables us to provide a more accurate estimate of system performance and financial payback and to design a system that suits your needs / budget correctly. Since we are one of the few PV installers to offer a performance guarantee, it is important that we assess the site accurately so that we can give a proper estimate of the anticipated annual generation.
The final price per kWp will still be roughly the same as if you get an online estimate but the survey enables us to produce a more detailed, tailored quotation with accurate predictions for your specific property.
