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North East Renewable Energy Directory
Technology Variations
The most important part of a PV system is the cell, the part that turns the sunlight into electricity. There are four main different types of solar PV cell that can be used to make up the solar panel:
- Thin Film Silicon
- Polycrystalline
- Monocrystalline
- Hybrid - combines both monocrystalline and thin-film silicon to produce cells with the best features of both technologies
Solar PV products and arrays are rated by the power they generate at Standard Test Conditions (STC - 25 °C, light intensity of 1000W/m2, air mass = 1.5), defined as kilowatt 'peak' (kWp) power. The following table compares the features and UK performance of these four technologies for stand-alone modules and for building integrated systems:
Thin Film | Polycrystalline | Monocrystalline | Hybrid | |
Cell Efficiency at STC | 8 - 12% | 14 - 15% | 16 - 17% | 18 - 19% |
Module Efficiency | 5 - 7% | 12 - 14% | 13 - 15% | 16 - 17% |
Area needed per kWp - for modules | ~16m2 | 8m2 | 7m2 | ~6m2 |
Area needed per kWp - for BIPV (variation due to tile spacing) | Solar metal roofing - 24m2 Glass-glass laminate - 25m2 | Glass-glass laminates - 10 - 30m2 | Sunslate - 10m2 Glass-glass laminates - 8 - 30m2 | n/a |
Annual energy generated per kWp (south-facing , 30° tilt) | 800 kWh/kWp | 750 kWh/kWp | 750 kWh/kWp | 900 kWh/kWp |
Annual energy generated per m2 (south-facing, 30° tilt) | ~51 kWh/m2 | 100 kWh/m2 | 107 kWh/m2 | ~146 kWh/m2 |
Annual CO2 savings per kWp | 344 kg/kWp | 323 kg/kWp | 323 kg/kWp | 387 kg/kWp |
Annual CO2 savings per m2 | 22 kg/m2 | 40 kg/m2 | 46 kg/m2 | 60 - 65 kg/m2 |
In general, thin film cells perform better in low light conditions but require more surface area than crystalline modules for the same output. Crystalline cells require a smaller surface area and make up 85% of the market. The costs for modules made from these different technologies are comparable.
There are two main types of photovoltaic systems – stand-alone or grid connected:
- Stand-alone systems (Off-Grid) - Most homes get their electricity from the National Grid, the national network for electricity distribution. Stand-alone or off-grid systems are suitable for those homes that are not connected to the grid. These systems typically have a battery to store unused electricity and, if necessary, an inverter to generate AC electricity. These can work out to be highly cost effective if compared against the cost of becoming grid connected.
- Grid connected - Grid-connected systems provide electricity for the building and for selling back to the grid. These systems do not use a battery as the storage mechanism is the grid itself with surplus electricity being fed back into the grid when it is not needed. All grid connected systems require an inverter for converting the DC power to AC power. Over the past few years it has become common for electricity supplier to ‘buy back’ surplus power. . Grid connection needs an agreement with the local electricity supplier to ensure that the system will not produce power if there is a fault with the grid or if maintenance work is being undertaken down stream of the system.
