Domestic PV systems are usually roof mounted in an array of panels and are placed at angles best suited to receive the energy coming from the sun. The orientation of these panels would ideally be south facing, although PV systems will perform at almost any orientation (though output may be lower and the system should be sized accordingly). Panels should be installed in areas that are clear of tall buildings or trees in order to minimise shading, which can adversely affect the performance of the system.

• Photovoltaic cells are made from layers of semi-conducting material, usually silicon;
• Groups of these cells are mounted together in panels that can be fitted onto your roof;
• When light shines on the PV cells it creates an electric field across the layers;
• Sunlight is made of a stream of photons which are then absorbed and interact with the electrons found in the cells;
• The cells “upgrade” the electrons to a higher energy level which can then be utilised as an electric current;
• The stronger the sunshine, the more electricity is produced;
• The current is conducted by wires to the electrical system of the building and is then either used on-site, exported to the grid or stored in batteries for later consumption

The power of a PV cell is measured in kilowatts peak (kWp); the rate at which it generates energy at peak performance in full direct sunlight during the summer.

Inverters and meters

The current produced by the PV cells is in DC (direct current) format and needs to be converted to AC (alternating current) format to be used as conventional electricity throughout your home. This is done using an inverter, which simply transforms the DC power from the PV modules into AC power at a voltage and frequency that can be accepted by the grid. Once the inverter converts the power to AC, it can be used to power typical appliances, gadgets and lights.

In addition to the inverter, your system will need to have a meter. There are two different types of meter available:

• Generation meter: this records the total amount of electricity you have generated;
• Export meter: this records the amount of electricity that you are exporting back to the grid.

You don’t have to have an export meter to sell electricity back to the grid – instead you have an agreement with your electricity company where you are “deemed” to be exporting a percentage of the electricity you generate back to the grid and you are paid accordingly for this “deemed” amount.

Note: Some electricity companies will only offer the “deemed” option to their customers preferring not to install an export meter, other companies will install an export meter but at considerable cost to the customer.

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