Evaluating Solar Photovoltaic Panels & Modules
In this article we offer a broad overview of the types of panel that are available, the materials they are made of, explain what some of the data on the manufacturer specification sheets means and ask some questions, the answers to which will hopefully make your choice a bit easier.
What are Solar PV Panels Made of?
The primary material needed to make a Solar PV panel is silicon, how the silicon is engineered and treated gives rise to three different types of Solar Photovoltaic Panel, with different prices, uses and levels of performance.
- Monocrystalline PV Panels:
A Monocrystalline panel consists of a number of solar cells connected together to form a grid. Monocrystalline Solar cells are made using thin wafers of silicon cut from a single crystal. Silicon wafers are expensive to produce but are very efficient conductors. When comparing panels a Monocrystalline panel is likely to be the most expensive and the most efficient panel in terms of energy generation per sqm or per panel.
- Polycrystalline PV Panels:
A Polycrystalline panel is made in much the same way as the Monocrystalline panels mentioned above except the wafer is cut from a block of silicon crystal made up of many crystals. A Polycrystalline Panel will be slightly less efficient and slightly cheaper to buy then Monocrystalline.
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How to tell the differenceThe blue coloured cell on the left hand-side is a Polycrystalline PV Cell. The darker coloured cell is a Monocrystalline PV cell. |
- Amorphous Cells:
A Solar PV panel made from Amorphous cells need not neccessarily be built into a panel at all. We sometimes use Amorphous Cells in roofing materials, you can see some of the solutions where we use Amorphous silicon here. They are less expensive to produce but their efficiency is lower then their crystalline counterparts. Amorphous cells are made by spreading a thin film of silicon onto a material, amorphous cells have the added benifit of being flexible.
Peak Power (kWp):
With Solar Panels the maximum output power is measured in watts, generally speaking the larger the panel the more solar cells you can fit into it. An important point that needs to be understood is that UK installations very rarely if ever perform at peak performance.
A very useful tool provided free by the European Commission Joint Research Centre can be used to calculate likely solar yields on PV systems in the UK and around Europe, calculating the real kWh from quoted kWp figures:
Mounting Area:
If you got the chance to use the Solar PV Calculator above you will see that factors such as height above sea level, the tilt inclination of the panels and the location of the installation relative to the equator all have an impact on a panels performance.
You now need to specify what panels are most suitable based on the mounting area you need to work with. You could be limited by factors such as chimneys, shading, skylights or dormer windows. This factor along with your power requirements may well determine the size number, type and style of the panels you need to get.
Framed Solar PV Panels
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Framed Solar PV Panels are best employed when mounting panels on top of an existing roof or when being mounted on a stand alone system. PV Panels are usually fixed onto either a flat aluminium frame or rails. The frame or rails are then secured to the roof via holes drilled into the roof. When mounting PV Panels onto existing properties Framed Solar PV Panels are usually cheaper and quicker to install as no major structural roof work needs to be carried out. |
Frameless Solar Panels
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Frameless Solar Panels are best employed when integrating the Solar Panels into the roof, mounting directly onto roof battens replacing normal roof tiles or slates. We would then frame the panels using matching materials such as tiles or roof slates. Frameless Solar PV Panels offer a flush finish and form part of the roof. An attractive, cost effective option for new builds and when re-roofing. |
Planning Permission:
Installations above a certain size and in certain locations such as in national parks and world heritage sites will need planning permission. Planning permission is not usually required for residential properties unless then installation is over 4m high (unless on a roof, then no bigger than the roof and no higher than 200mm above the roof line). There is more about planning permission for solar PV systems here: Planning Permission for Solar Photovoltaic Systems.
It may also be worth looking at Solar PV Roof Slates and Solar PV Canopies to see what can be done when traditional panels are not the best option.
Guarantees and Warranties:
A Solar PV system is likely to be a big investment, if an individual panel doesn't pay for itself within the guarantee period and fails soon after the warranty expires, then financially the investment just wont make sense. In our exprience the guarantees supplied by the manufacturers can be relied upon as a good indication as to the quality and likely lifetime of the panel. It's often worth paying a little extra for a longer warranty.