How Photovoltaic Works
A typical PV system uses panels of solar cells, made from semi-conducting materials that react with sunlight to produce electricity. This electricity is then transferred into the home to power appliances and provide lighting, or if surplus to requirements, is sold to the local electricity network.
The PV panel
As an individual solar cell only generates a low voltage, approx 0.5V, a number of cells are wired together to form a solar panel or 'module' that can generate anything between 80-165kWp. Modules are then connected together to form a PV array that will be typically fitted onto a northerly facing roof at an angle of between 30º and 50º in order to receive maximum sunlight.
North-easterly and North-westerly facing systems can be installed with only a 5% reduction in panel efficiency but panels placed on a sourtherly orientation do not receive adequate sunlight to generate sufficient electricity.
It is extremely important that all the solar panels in a system are free from shading during the daylight hours. Even the partial shading of one cell in a panel will lower its power output. As the cells of a panel are connected in series the weakest cell will bring the others down to its lowered power level, which can reduce the efficiency of the whole panel by as much as fifty percent.
The PV System
PV systems are quoted in kWp (kilo Watts peak), which is the rating of DC power produced by the system at any one time during optimum lighting and temp erature conditions. The DC power needs to be converted into AC before it can be used with household appliances or is transferred onto the national energy grid.
This is done via an inverter, and, through the exchange process some power is lost. A well installed PV system should produce between 750kWh and 850kWh of AC electricity annually for every 1kWp of PV installed.
The panels and the inverter account for a major portion of the cost of a PV system but there are additional components required to ensure that the system operates safely, reliably and to current regulatory electrical. Below are some images of what inverters look like:
How big should my photovoltaic system be?
There is no one right size for photovoltaic systems. Every site is unique and the needs of system owners vary, too. System size depends on several factors, including how much electricity (in kilowatt-hours or kW-h) you consume, the orientation of the system, the tilt of the system, available space.
After first looking for ways to reduce your energy consumption since saving energy is typically cheaper than generating it. Furthermore, the smaller your overall consumption, the smaller and cheaper the system you'll need.
An easy rule of thumb is to take your annual consumption (in kWh) and divide that by 1300 kWh/yr. (1kW of PV will generate about 1300 kWh per year). This will give you an estimated system size.
For example, the Smiths consume 6000 kWh per year. If we divide 6000 by 1300 we get 4.6. This means the Smiths need about 4.6 kilowatts (kW) of photovoltaics to completely offset their annual consumption. Contact Realsolar and see how we can help you come up with more exact numbers based on your specific needs.
