Why choose solar electricity rather than solar hot water (solar thermal)?
First, what's the difference?
- Solar electricity generates electricity using the photovoltaic effect. This electricity is used to power the lights, TV and other appliances. Any surplus can be fed into the National Grid.
- Solar thermal uses the heat from the sun to heat water. This heat is then transferred to the hot water tank and used for baths and showers. It may also be used for underfloor heating.
Choose solar electricity because the financial returns are better!
Now that the government has introduced feed-in tariffs for solar electricity, the life time return on investment on photovoltaic (electricity generating) panels is between 6% and 9%.
This is much higher than the investment return on solar hot water systems.
The government is considering bringing in a 'tariff' incentive for solar hot water in 2011. However the details have not been worked out. In particular it is not clear whether the incentive will be 'backdated' to apply to systems installed before 2011.
It therefore makes sense to install panels for electricity generation, where the feed-in tariffs have already been announced, effective from 1st April 2010. Solar hot water is a completely different system and can easily be installed at a later date.
Some other differences to note:
- • Solar PV is a no hassle solution – no need to change your hot water tank
- Installing solar hot water often requires a complete change of tank, resulting in a perfectly good tank being thrown away needlessly. This is a hassle which doesn't apply to solar electricity.
- • The energy generated by solar pv is much easier to measure
- The energy generated from solar photovoltaic panels is easily measured – 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. - • 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.
Solar hot water panels will warm up in winter. However because the surrounding air is so much cooler, the heat will quickly dissipate into the air. Relatively little of it will be transferred to your hot water tank.