Performance of solar thermal and photovoltaic panels in Guernsey

January 2nd, 2012 by Gavin Lanoe

The roof of my home with four 215 watt photovoltaic panels and one panel of evacuated tubes for solar hot water on the left (click image to expand - ©RLLord)

I installed four 215 watt photovoltaic panels and a solar thermal panel composed of 30 evacuated tubes on the roof of my home two years ago.

This brief article looks at the amount of energy capture by these systems and the return-on-investment.

Solar hot water

In 2011 my home’s solar thermal evacuated tubes collected 2132 units of heat. My home used 4490 units from the mains supply so the solar energy collected accounted for 32% of my home’s heating needs in 2011.

In 2010 the solar thermal panel of tubes provided 41% of my home’s heating needs.  The reduction from 2o1o to 2011 was due to the poor summer weather.

The collected solar energy saved £343 in 2010 and £351 in 2011. Although the number of units collected in 2011 decreased, the increase in the cost of energy more than made up for this.

The initial investment for the entire system including the dual coil hot water cylinder was £2500. The cost of the solar thermal evacuated tubes was £500 so adding a solar thermal collector to a compatible hot water system could pay for itself within two years.

With this system the total cost for all of my home’s hot water and heating for 2011 was £338.54.  Using a Guernsey gas (propane) supply would have cost approximately £1270.

Solar Photovoltaic panels

In 2011 the photovoltaic panels generated 729 kWh (units) of electricity.  This produced a saving of £120 against my home’s electricity bill.

Including electricity produced in 2010, the total payback on the PV panels so far is £165 against an initial investment of £2500.

Payback at this rate looks to be around thirty years. Interestingly, the payback when calculated last year was about 50 years.

This reduction is partly due to the increase in the cost of electricity but mainly due to an increase in the amount of electricity produced by the PV panels due to the clearing of some trees adjacent to my home that shaded the PV panels in the morning.

In conclusion solar water heating is economically justifiable with a very short payback period. The solar thermal kits are inexpensive and can be added to most existing hot water systems.

Solar PV is still expensive for the return-on-investment but the cost of the equipment (PV panels and inverter) is coming down, and the cost of electricity is increasing, so the return-on-investment is happening sooner.

If you need advice on getting started with your own solar hot water or PV system please get in touch by email to Gavin @  For more information please visit my website.


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