Photovoltaics

Photo = light & voltaic = electricity

Photovoltaics is a technology that utilises light to generate electricity. As such it is an essential tool in the development of more sustainable methods of electricity generation. Simplistically, electricity is generated by the photons from sunlight colliding with electrons within the solar cell.

Solar cells are solid state devices that produce direct current electricity from light. They are arranged into interconnected groups to form a module. In turn photovoltaic (PV) modules are connected together into photovoltaic arrays. A module is big enough to power a single device with larger applications such as a family home requiring an array. PV arrays can be built into the fabric of a building, in its roof or walls, or developed as a stand-alone system as we see connected to street lights or on caravans.

PV cells use both direct light and indirect or diffuse light and so are effective even in temperate climates and operate under grey overcast skies, not just on bright sunny days.

As in most cases they constructed largely from silicon, the manufacture of PV modules has relatively green credentials, although the need for batteries for storage in off grid situations can somewhat sour this.

Most UK implementations of PV will be grid connected PV systems. In these systems there is no need for battery storage. The PV system is connected to the local electricity network (grid) and any electricity not consumed locally can be sold to the electricity supply company. Where the local PV system is unable to provide all electricity demanded, for example at night, then electricity is bought from the grid. The ‘grid’ acts as the storage system.

An inverter will be required to convert the low voltage (12 volt) DC electricity generated by PV to high voltage (230 volt) alternating current (AC) consumed by most UK appliances.

How much?
A typical domestic system will need between 1500 and 2000 Watts peak (Wp)
Typical modules have power output of 75 to 120 Wp.
Therefore, 10 to 20+ modules will be required.

I have ‘tirelessly’ searched the internet for illustrative costs from various sites and articles of various ages I’ve come up with the following prices each from an individual source:

£4,000 to £9,000 per kWp installed.

£8,000 and £15,000 on a typical domestic installation of 1.5 kW.

…this works out at £12 000 – £14 000 for a 2 kWp system for a house.

To provide a PV power supply capable of meeting the demand from a typical domestic energy efficient house costs in the region of £20,000.

…costs can be around £5,000- £8,000 per kWp installed with most domestic systems usually between 1.5 and 3 kWp.

Which gives an average of somewhere around £6,000 per kW so £10,000 for a typical domestic installation of 1.5 kW. As this will save you several hundred pounds a year on electricity costs the financial payback is long. The overall cost-benefit will only tip into the positive if you personally value the ecological benefits highly.