Solar PV

Electricity from the Sun Solid state (transistor) technology uses energy in the sun’s rays to trigger electron flow through specially treated silicon ‘wafer’.
With enough active cells linked together the resulting photovoltaic (PV) panel can produce enough power to do useful work. There are no moving parts and nothing to ‘wear out’ – free electricity forever then?
Well not quite; the panels are complex fabrications using composite materials and unfortunately the integrity of the structure is ultimately attacked by nature’s elements and a gradual but inevitable drop in performance can be expected.
The better manufacturers will offer performance guarantees up to 20 years or so (typically 80% or rated output) - payback times and project life needs to be realistic in this regard.

Applications
Small scale (under 1kw or 8m2) can be worthwhile where mains electricity is not available or cannot be supplied economically and the electrical load is modest.
The panels will charge a battery bank to provide constant power, day and night.
Connecting the battery bank to an inverter can provide 240volt a.c. mains power – although again output will be limited. Suitable installations include boats, caravans and outbuildings, etc. and can power laptops, Hi-Fi, TV, general lighting, small refrigerators, etc.

Larger scale arrays, to justify the increased cost, need to be ‘grid tied’ i.e. they will convert the power directly to mains voltage which is then ‘exported’ back to the electricity supplier when supply exceeds the domestic demand.
As long as the panels are producing power there will be a reduction in electricity purchased from the grid supplier and consequent savings arising.

To be completely self sufficient (i.e. electricity exported is the same as electricity consumed from the grid) will require a large investment.
Average UK domestic use is 4,700kwh a year and, with a realistic output of 0.300kwh/day/m2, you would need a 40m2 array at a cost of £20-25k to be self sufficient.
Paying presently 10p/kwh for grid supply means a very unattractive 50 year pay back, not helped by little better net price on the exported electricity.

Why bother?
For small scale PV the case is primarily for convenience and practicality and the smaller capital expense is easier to justify.

Larger scale PV, however, is becoming increasingly viable, firstly unit costs are falling steadily as the uptake increase and, secondly, the government’s statutory obligation to meet CO2 targets means that grants and subsidies are widely available. Capital grants of 50% can greatly assist with installation cost whilst, from 2010, a new structure of feed in tariffs mean that exported electricity might yield as much as 40p/kwh for the domestic producer.
These changes will mean a much quicker commercial payback and an attractive investment.

Aside from the investment value, there is an important environmental benefit too; in the UK electricity (primarily produced from inefficient coal and gas power stations) is the ‘dirtiest’ form of power available – 422 grammes of CO2 emissions per kwh of electricity consumed. That is 4 tonnes a year for an average household. Solar PV installations can make a massive dent in huge CO2 emissions which is why there is a global push for this technology and it worth considering PV alongside other renewable energy.

If you would like more information on small or large scale PV or a site survey for PV potential Ecolyf will be pleased to help and provide impartial advice.