PV Solar cells are made from layers of semi conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced. Groups of cells are mounted together in panels or modules that can be mounted on your roof. The solar panels generate direct current (DC) electricity. For off grid systems this can be used to charge batteries. For grid connect systems the solar panels are connected to a Grid Inverter, which converts the electricity to alternating current (AC) that can then be used in your property, or exported to the grid.
It is the amount of light that falls on the solar panel that determines how much electricity it will produce. It doesn’t have to be a clear, blue sky and bright sun for the solar panels to work. They will work in all weathers, throughout the year, typically from when the street lights go off in the morning until they come on again at night. However, on a dull, cloudy and wet day the solar panels will produce a lot less electricity than on a bright sunny day.
There are 2 main types of solar panel, silicon based (the most popular) and thin film (the relative newcomer) Silicon solar panels are split into two types, monocrystalline and polycrystalline (also called multicrystalline) This distinction refers to the process by which the silicon cells are manufactured, however there is very little difference between their performance in the UK. They comprise of a number of solar cells (often 72) within single solar panel. These solar modules generate the most electricity for their size, which is measured as their efficiency.
Thin film solar modules use a different semi conducting material, there are several types on the market. Rather than having many solar cells in one solar panel, thin film modules have a single, uniform covering of the semi-conducting material. Thin film solar modules work with a broader spectrum of light, so that they produce more electricity per annum , per Wp, than silicon solar panels. In particular they can be less effected by orientations away from south, and by shading. However, thin film solar modules need a larger surface area for the same power rating, and weigh slightly more, as the solar material is sandwiched between two glass sheets.
Probably more important than the type of solar panel is the make. Just as with other products there are different prices and qualities of solar module. Run by the Sun Ltd isn’t tied to one manufacturer, and will advise which is the best value product for your system.
All solar panels that qualify for the Feed in Tariff (FIT) must have a manufacturers output warranty for 25 years. This states that they will still perform at 80% of their original rating after this period of time. In our experience, solar panels from a good quality manufacturer will perform for 30 years or more, and the failure rates are very low, less than 0.0001%. However there are many examples of cheaper solar panels failing much earlier, well within warranty period, and also of warranties not being honoured when the solar panels were just imported from overseas, with no UK distribution network.
Good Quality off-grid solar systems are built to the same standards, and usually come with a 10 year, 90% performance warranty, although in most instances will last as long as the grid connected systems.
Solar Panels are rated in 2 ways. They are both industry standards, and are often highlighted by manufacturers, but can be misleading…
Firstly, all panels have a Watt Peak (Wp) rating. This is the electrical power of the solar panel, measured in watts, by an industry standard test. It is roughly equivalent to the power that the solar panel will generate when the sun is directly shining on it. It is also close to the maximum power power it will generate, and is certainly much more than the solar panel will generate on a dull day. When many solar panels are linked together the Wp figure becomes kWp (kilowatt peak) is 4000Wp is more commonly written as 4.0kWp.
It is important to remember that this Wp rating is only indicative of the solar panels performance in very bright light, and thus not always indicative of how the solar module will perform throughout the varying light conditions of a typical year.
Secondly panels are also given an efficiency rating. This shows what percentage of the light power shone onto the solar module in the industry test was converted into electrical power, divided by the area of the solar module. A solar panel with an efficiency of 16.7% is converting 16.7% of the energy shone onto it, per square meter. Typically the higher the Wp rating, the higher the efficiency rating.
However, this is again, only equivalent to bright sunlight, and also a less efficient panel might actually give a higher annual energy yield, but will just need a larger surface area.
For example the LG Solar NeoN 300Wp module has an efficiency rating of 18.3%, and a surface area of 1.6m2 whereas the Solar Frontier thin film SF150Wp solar module has an efficiency of 12.2%, and an area of 1.23m2. You need 2 x SF150Wp modules to achieve the same Wp rating as the LG Solar 300Wp module, using more surface area, 2.46m2. In a typical UK year the 2x Solar Frontier modules will produce more power (yield) than the 1x LG Solar module although they have the same total Wp rating, and a lower efficiency rating. Sorry that this is complicated – remember Run by the Sun Ltd will help guide you, and recommend the best solution for your solar system.
Solar PV needs little maintenance. You need to keep the solar panels relatively clean, and also ensure that trees and other vegetation doesn’t grow and overshadow them. In the UK solar panels that are tilted at 15° or more will be cleaned by rainfall. Bird droppings and other debris can be removed with water and a little washing up liquid. Specialist window cleaners are available who can reach roof mounted solar panels if needed.
As there are no moving parts a professionally installed PV solar system is usually very reliable. However it is to be expected that the grid inverter will need changing at some point in the 20 year lifespan of the FIT scheme. Therefore it is important to regularly monitor your PV system, so that you familiarise yourself with how much energy it produces, and are able to spot when something goes wrong. The latest systems have the option to be connected to internet monitoring systems, allowing you to check on the performance whilst sitting at a desk.
For maximum energy yield in the UK the ideal position for grid connected solar panels is to face south, at an angle of 30 to 45 degrees. However advances in solar panel and grid inverter technology, and the big fall in price of solar panels means that the majority of UK housing is now suitable for a PV solar system. So roofs facing anywhere towards the south, from due east to due west can be considered.
Similarly there are now approved mounting systems for most types of roof covering, and roof angles, from flat roof to 90° facades. Thatched roofs are still a problem thought!
To generate the maximum output through the winter months off grid solar systems usually require that the solar panels are mounted at a steeper angle – between 60° to 75° ,to better catch the low winter sun. For this reason of grid solar systems are often installed on ground mounted structures, which can be designed to optimise the angle for the latitude of the installation.
Solar panels that are shaded don’t perform as well as those without any shading, which is quite obvious. However, because the individual solar cells and linked together in series, and then the solar panels are also linked together in series, a relatively small area of shade can have a larger detrimental effect on the total output. This is because the flow of electricity is reduced in the shaded area, and a little like squeezing a hose pipe, a small restricted area has a knock on effect on the whole system.
All solar arrays will have some shading at some point, even if it’s just at dawn and dusk as the sun comes over the horizon. The important thing is to ensure that shading is minimised when the potential for electricity generation is highest, ie in between April and October, and between 8am and 5pm.
By choosing the correct solar modules, designing the layout, and also specifying the correct grid inverter steps can be taken to greatly reduce the effect of shading. For example, correctly aligned thin film solar panels are less susceptible to shading than silicon solar modules. But turned through 90° they may be no better. Special grid inverters can work with solar array split into 2 sections, or even each solar panel can work independently of the others in the array, allowing installations on many small roof areas, facing in different orientations.
Before installing a PV solar system Run by the Sun Ltd will assess the structural strength of the roof. This forms part of our site survey. The solar panels themselves are not very heavy, typically between 15 to 20kg each, but added together a complete system might weigh 300kg.
If your roof is in good condition, and has been built in the last 100 years, then it is most likely suitable. For older properties, or for roofs that are obviously in a poor condition a structural engineer might be required, or remedial works might need to be carried out before the installation. For example it would be a good idea to re-felt a flat roof before installing a solar system on top, and then having to remove it 5 years later to then make good repairs.
For commercial properties it is usually necessary to get a structural survey to ensure that the roof is able to safely take the weight of a solar system that is often much larger, and therefore heavier than a domestic system.
On 1st April 2012 the government made a change to its policy for Feed in Tariff (FIT) solar systems. From that date only properties with an Energy Performance Certificate(EPC) rating of ‘D’ or better are able to claim the full FIT.
Approximately half the properties in the UK meet this specification. Older properties might need a little help, with double glazing, energy efficient boilers and wall insulation to achieve the rating.
Before installing a solar array Run by the Sun Ltd will arrange for an EPC assessment to be carried out on your property. The proposed array can also count towards the rating, so for example an ‘E’ rated property should score a ‘D’ with the solar array, so will qualify.
Commercial properties also require an EPC, which Run by the Sun Ltd can also arrange to be carried out.
In England, Wales and Scotland, you don’t need planning permission for most home solar electricity systems. As long as the solar panels don’t protrude more than 200mm from the plane of the roof when installed, and are not higher than the existing roof ridge then you are covered by ‘permitted development rights’
Exceptions are for those who have listed buildings, or live in conservation areas, national parks or world heritage sites. With many years of experience Run by the Sun Ltd can help give you guidance, and if there is any doubt you should always consult your local planning officer.
For commercial properties the planning requirements have also been greatly simplified. It is however still always best practice to enquire before starting any installation.
For grid connect solar systems we have an insurance backed, all inclusive warranty that covers all workmanship, mounting components, wiring, photovoltaic panels and the grid inverter for the first 10 years of the installation. This also covers the labour and access costs to sort anything out should it go wrong, giving you great peace of mind.
In addition the solar panels will have a 25 year performance warranty, and the grid inverter may have an optional extended warranty.
For off-grid systems we offer a 5 year warranty on all our workmanship, and will also pay for any labour and access equipment required to make good during this time. Off grid components such as solar panels, batteries, charge controllers and inverters have different warranties dependent upon the manufacturer, which will be clearly stated in our quotations.