Photovoltaic Electricity

In a typical UK house a system with a PV array tilted towards the south would generate approximately 750kWh/year per 1kWp installed. So a typical 2 kWp system (around 20 m2 of multicrystalline modules) would generate around 1500 kWh per year.

This is rather less than half the estimated electricity demand of a typical UK house. Output will be reduced by shade or non-optimal orientations or tilt angles.

Cost is affected by a number of variables depending on whether the installation is new or retrofit, the size of the system and access etc.

They say that best ventures to be in are those that make money while you sleep - this adage might be applied to PV except that it has the potential to make money while you are out earning. During daylight hours the PV system could be quietly pumping energy into the grid.

The Science

It's all physics and some of it complicated! - involving the movement of electron shifting when light energy strikes certain specific materials. The purists can look it up but essentially - a photovoltaic cell consists of two or more thin layers of semi-conducting material, most commonly silicon.

When the silicon is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC). The electrical output from a single cell is small, so multiple cells are connected together and encapsulated (usually behind glass) to form a module (sometimes referred to as a "panel").

The PV module is the principle building block of a PV system and any number of modules can be connected together to give the desired electrical output. There are different ways of configuring cells.

Monocrystaline silicon cell cut from a single cylindrical crystal of silicon. Complex to make and most expensive but highest conversion efficiency (sun's energy to electricity) about 15% Multicrystalline Silicon Cells: Commonest form, made from cells cut from an ingot of melted and recrystallised silicon. Simpler to make but cheaper than monocrystaline - conversion efficiency about 12%.

PV technology is more about tomorrow rather than today. PV is more flexible than wind energy - whereas wind produced power requires standby generation for low wind and high wind days PV electricity is produced even on dull days and really scores in desert countries.

Although PV gives nothing at night and still needs supplementary power for night requirements, continuity is easier to plan for via batteries and back up power needs are easier to predict.

Photovoltaic energy like wind has zero CO2 emissions - however it has been estimated that it needs 4-9 years to recover the energy invested in their manufacture before they truly become carbon neutral. A big plus for Solar rays are that they are silent and compared to wind turbines are relatively unobtrusive. They can even be designed into large structures to enhance their appearance.

PV is maintenance free and Japanese systems have been running for over 30 years.

If you have any queries on Photovoltaics contact:

George Jardine
Renewables Energy Manager
CMS UK