Which should I choose: Solar PV or Solar Thermal?
In general we favour solar electricity for several reasons, which we have listed below. There is a case for saying do both if you have the space and budget, particularly if you have already installed 4kWp of solar electricity on your roof, and would be into the lower tariff band if you installed more. Also if hot water generation is your main concern then it is worth installing solar hot water rather than electricity - it is inefficient to generate electricity and use it to heat water, it is much more efficient to generate heat energy in the first place.
Our reasons for choosing solar electricity over hot water are as follows:
- Firstly the financial returns are currently better. The Renewable Heat Incentive has yet to be finalised so this may change; however at the time of writing (January 2011), the FITs offer a better financial return.
- Secondly solar electricity is a real "no hassle" technology. There is no need to install a new tank, possibly resulting in a perfectly good tank being needlessly thrown away. Solar thermal systems also need more maintenance and do sometimes get air locks in them.
- Thirdly the energy generated by solar electricity is much easier to measure -
and must be measured using a 'Total Generation Meter' for the purposes of working
out the feed-in tariff.
In contrast it is much more difficult to know exactly how much energy has been generated by solar hot water panels. All you can do is look at the thermostat in your hot water tank and read the temperatures at the top and bottom of the tank at various points during the day. The problem is that as soon as you let more water in from the mains, the temperature at the bottom of the tank will fall by several degrees, regardless of whether the sun is shining or not. Keeping track of gains from the sun is very difficult. It is for this reason that the Renewable Heat Incentive will be based on the energy the system is "deemed to produce" rather than the energy it actually produces - Finally solar PV uses the light from the sun rather than the heat. A solar PV system will generate a high return on a sunny day, whether that day is in January or in July. It relies on light from the sun, not heat. In fact it will generate energy even on an overcast day.
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