Generating electricity from the sun, solar PV (photovoltaic) panels are a great eco-friendly addition to any home, but there are several considerations to be made before you commit.
This comprehensive guide covers everything you need to know, from how solar PV panels work, how much they cost and the grants available, through to what's involved in the installation process.
(MORE: Solar Panels)
How Does a Solar PV System Work?
Solar PV panels have silicon cells in them that are doped in chemicals. Silicon is the main component of sand and is the second most abundant product in the world, but converting the ‘sand’ into usable PV cells uses a lot of energy.
When the sunlight hits the cells they create an electric current. By stringing lots of cells together the electric current is increased. A typical solar PV panel will have around 60 cells and modern panels will be able to generate around 320 Watts in strong sunlight.
Types of Solar PV Panel
Typical solar PV panels have a glass front surrounded by an aluminium frame. Silicon cells are stuck to the underside of the glass and connected together with thin metal strips.
There are three main types of silicon cells:
- Thin film
Monocrystalline cells tend to be black in colour and are slightly more efficient (around 21%) than polycrystalline cells but are also more sensitive to heat.
Polycrystalline cells tend to be blue-ish in colour and are slightly less efficient (around 19%). They can often be less expensive as the manufacturing process is less intensive.
Thin film technologies are quite a bit less efficient (around 11%) than the mono or polycrystalline cells, but the cells are a lot less sensitive to heat and can also be used on curved surfaces and lighter weight structures.
The cells are often supplied as ‘mats’ that can be glued to a roof or as coloured glass that can then be used as Building Integrated (BIPV) such as wall cladding or glass fencing and balustrades.
How Much Does a Solar PV System Cost to Install?
A typical 4kWp solar PV system will cost between £5,500 and £9,000 for an on-roof system.
Any additional framework will carry additional cost. Integrated panels such as those that look like slates or tiles, or those that are bedded into the roof to replace the roof cladding, will also have additional costs and range in price between £9,000 and £15,000.
How much money will I save on my electricity bill?
The amount of money that you will save on your electricity bill by installing solar PV panels will depend on how much of the generation you actually use.
If you are not at home most days then the solar PV generation will only power the fridge and any other electrical appliances that happen to be running during the daylight hours.
Editor's Note: Homebuilding.co.uk partners with the UK's best solar panel suppliers to match your requirements with their products. Simply answer a few questions on what you need from your solar panels and we’ll put you in touch with a suitable partner.
Are There Any Grants Available for Solar PV Panels?
Solar PV panels are specifically not covered by the Green Homes Grant. There are no specific national grants or incentives available for the installation of solar PV panels since the end of the Feed In Tariff (FiT) but energy companies will now enter into an agreement to buy your surplus generation from you, albeit at a fairly low rate.
The price offered does change from supplier to supplier so it may be worth shopping around.
Is Solar PV Still Worth the Investment Now the Feed-in Tariff has Ended?
The Feed in Tariff (FiT) paid a generous incentive for the generation of renewable electricity and at its peak the figure was around 46p/kWh with the price guaranteed for 25 years. The tariffs decreased over a number of years until the scheme ended completely.
The cost of installing solar PV systems also decreased and as the cost of electricity also rose the return on investment is still potentially very good if you can use your own generation.
It is not difficult to use all the generation in the winter months so it is really the summer generation that will define the return on investment.
Doing the maths on an average 4kWp system if you know you can use around 65% -75% of your annual generation then the investment is still good as it will represent around an 11 year payback depending on what you paid to get it installed.
(MORE: Renewable Heat Incentive)
Where Should I Install Solar PV Panels?
Solar PV panels are typically installed on a pitched roof in a southern direction in the UK. Panels can also be installed on outbuildings or on purpose built frames in a paddock.
There are some frames that can also move to track the sun and optimise the generation.
What is an Integrated Solar PV Panel?
Integrated Solar PV panels, often referred to as Building Integrated Photovoltaic (BIPV), are panels that replace the cladding and become part of the roof (or wall) rather than on the roof.
The integrated solar PV panels can look like slates or roof tiles or can be complete panels that have a tray system to go under the panels or special trims to join the panels together as well as edging details to complete the roof.
There are now products available that replace wall cladding as well as glass balcony systems and ‘clear’ glass solutions for atriums, light-wells and glazed roof lights.
Do I Need Planning Permission to Install Solar PV Panels?
- You don't have a listed building
- You don't live in a conservation area or an Area of Outstanding Natural Beauty (AONB)
It is also important to remember that permitted development does not cover the elevation of the property that faces the road.
Any installation on the roof cannot protrude more than 150mm above the plane of the roof and cannot protrude at all above the highest part of the roof. The highest part of the roof is usually regarded as the ridge, not the chimney.
Do I Need Building Regulations’ Sign Off?
Solar PV panel installations will need Building Regulations approval. There is an electrical connection and there is a structural element to the installation as well.
Most of the time the installers will be members of a relevant competent persons scheme and should therefore be able to self certify the installation and sign off the building regulations notification.
If the installation is not fully notified it could affect your insurance.
How Much Space Do Solar PV Panels Take Up?
A typical solar PV panel measures around 1m x 1.6m and will generate between 250 and 350W depending on the panel.
A typical solar array (a few panels together) will have a peak output of around 4kWp so you would expect an array to typically have between 12 and 16 panels.
How Much Electricity Do Solar PV Panels Generate?
Depending on where you are in the UK the generation output from a PV array will be different.
As an example if we look at London we would expect an unshaded 4kWp system to generate around 4,000kWh (units of electricity) per year but in Edinburgh this figure would drop to around 3,400kWh per year.
Optimising Your ROI
The best way to optimise the return on investment from your solar panels is to use all the generation. It is also best to use the electric generation for energy that would normally have been electric.
If you redirect your electric generation to your hot water cylinder rather than your electric car charger then because that would normally have been heated by gas then you are only offsetting the cost of the gas which is around 6p/kWh and electricity is around 16p/kWh.
Try and run electric appliances, such as washing machine and tumble dryer, during the daylight hours if you can. The more energy you use the better the return on investment.
How Long Do Solar PV Panels Last?
There are solar PV panels that are operating today that are over 50 years old. The accepted useful life expectancy of a solar PV panel is around 25 years with an average generation decrease of around 0.5% per year.
That said, some manufacturers, such as SolarWatt will guarantee an 87% output after 30 years on their glass-on-glass panels and LG will guarantee 90% output after 25 years on some of their panels.
Does Solar PV Work Well With Solar Batteries?
Solar batteries, or home batteries, are devices that store electricity so that it can be used at another time. These systems work well with solar PV systems because you can charge up the batteries during the daylight hours and then use the power later when it is dark.
Batteries have specific storage capacity and also limited discharge capacity. You may install a battery that can hold 14kWh of charge but you may only be able to discharge at a maximum rate of around 2kWh.
Therefore if you happen to cook on an electric stove at night you may use 5kWh for cooking but you will only get 2kWh from the battery. The other 3kWh will come from the grid.
Are Solar Thermal Panels Better Than Solar PV Panels?
Solar thermal panels are effectively more efficient at absorbing energy than solar PV panels but they are not as versatile when it comes to using that energy.
Solar thermal panels only heat water and in 90% of installations they are only really supplying heat to the domestic hot water requirement.
Solar PV panels generate electricity so can supply energy to any electrical appliance or have it redirected to the hot water cylinder or electric car.
Do Solar PV Panels Require Much Maintenance?
The maintenance requirements for solar PV panels are minimal. Usually its simple visual checks to make sure that the panels are clean and that there are no signs of wear and tear such as the frames corroding or the wires coming loose and then degrading as they flap about in the wind.
If you have a generation app then it is also easy to track the generation so that you can be aware of any changes that may be caused by deterioration in the system. A periodic inspection of the wiring should also be carried out by a suitably qualified electrician to make sure that the wiring is still safe.
How Do I Find a Good Solar PV Installer?
The best way to find a good solar PV installer is through word of mouth. You could also check the Microgeneration Certification Scheme (MCS) website for local contractors and then ask them for references, preferably including references that are a number of years old.
What Else Do I Need to Consider?
Solar PV potential did not die when the Feed in Tariff ended. The technology is tried and tested and well understood.
New developments in the industry are potentially more efficient but improved efficiency at the expense of durability is not sustainable. The quality of the products is as important as the quality of the installer.
As the products are designed for the long term, this is not an area for compromise.
David is an expert in sustainable building and energy efficiency and is also director of Heat and Energy Ltd.
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