How solar PV systems work
Solar photovoltaic (also known as solar PV) systems convert energy from the sun into electricity. You can save money by harvesting this free energy.
Solar PV systems can be relatively simple, with their main components being solar panels or modules. Read on to find out more about solar PV systems, including which type generates the most electricity, and how they're made.
Types of solar panels
Solar panels are made of a thin layer of semi-conducting material sandwiched between a sheet of glass and a polymer resin. When exposed to daylight, the semi-conducting material becomes 'energised' and this produces electricity.
There are four basic types of PV panel: monocrystalline, polycrystalline (or multicrystalline), hybrid and thin film (or amorphous silicon). All are made from silicon but differ in the way the material is cut and treated.
PV panels differ in efficiency – how much of the sun's energy is used by the system per unit area – and in price.
- Monocrystalline solar panels are made of silicon formed into bars and cut into wafers. They have the highest purity of silicon making them efficient, with a higher power output than polycrystalline panels. They look dark and uniform.
- Polycrystalline panels are made by melting raw silicon together to make wafers – a faster and cheaper process than monocrystalline panels. They look blue and speckled and contain many crystals in each cell. They’re cheaper but can be less efficient.
- Hybrid cells combine crystalline cells with thin film cells. They're also known as HIT solar cells. This makes the panels even more efficient, but they cost more.
- Thin film (or amorphous silicon) cells can be the cheapest but also the least efficient. They're flexible but rarely used for residential projects.
Solar tiles and slates are also available. These are installed in the same overlapping way as ordinary roof tiles and can be more aesthetically appealing than fitting solar panels on top of an existing roof. But solar tile systems are pricey. They can cost double the amount of an equivalent solar PV panel system – so they’re not as cost-effective.
You can also buy ground-mounted systems instead of fitting solar panels on your roof. Some state-of-the-art systems can rotate to follow the sun and maximise the amount of electricity they produce. But they may also need foundations and can be pricey.
When deciding which type of solar cells to go for, it's best to look at cost-per-watt (£/W) of power output. You can do this by dividing the total cost of the solar system you are being quoted for by the total power output of the system.
Solar panel efficiency
More-efficient panels will tend to cost more. Before taking the plunge and buying expensive panels, it's worth also taking the size of your roof into consideration. If you have enough space, cheaper, less-efficient panels could end up being more cost-effective over time.
However, if space is limited, you would probably want to maximise efficiency to get more power out of your few panels.
Solar panel modules and system
A solar PV system usually comprises solar panels, an inverter, isolator switches, a PV-generation meter and cables.
Some things to think about when considering installing a solar system:
- The more panels you can fit on your roof, the more expensive the system will be to purchase and install. But the more electricity you will produce.
- The electricity produced by the PV panels is direct current (DC). Before it can be used in the home, it has to be converted to safer alternating current (AC) using a box called an inverter. This is often placed in the loft.
- It's worth noting that the inverter doesn't have the same lifespan as the panels. If it fails, a replacement inverter could cost at least £1,000.
- For safety, isolator switches are also placed before and after the inverter.
- A PV-generation meter is connected inside your home, so you can see a real-time display of how much electricity the system is generating. This data is used to calculate your Feed-in Tariff payment, which provides cash in return for generating your own electricity if you are registered for it.
How are solar panels made?
A good-quality manufacturing process involves checks at every stage – from how individual cells are checked and connected, to how well panels are scrutinised for defects before they leave the factory.
We’ve outlined the process below, based on an audit of solar PV factories we carried out a couple of years ago.
1. Connecting solar cells
Individual solar cells are sorted by power. They’re soldered together into strings to form a solar panel (or module). Usually a panel is made up of 60 cells. They’re checked for tiny cracks or other defects using electroluminescent testing. Damaged cells should be rejected.
The cells are placed between layers that protect them. The layers are fed into a laminating machine, like an oven, and melted into one. This needs to done carefully so air bubbles don’t form and damage the panel’s electrical insulation. If humidity gets in, lifespan could be reduced.
A frame is then put round the panel to protect it. Tightness is key. A junction box is attached to connect the panel to the inverter using cables. The connection between the solar panel and the inverter must be waterproof and not too tight, so as not to apply too much pressure on the panel and damage the cells.
4. Quality control
A flash test, with a sunlight simulator, helps determine the panel’s capacity. The panels are then sorted by how much power they can produce, and priced accordingly. Further quality controls may be carried out, for example, to find breakages or so-called hotspots.