Economies of scale

[5928]

I had a 3.99kW System installed for £12700. I may get to £30 a week average over 52 weeks if we have a good August/September.

Someone I know has had a quote of £7700 for a 1.9kW system on their second home which they don't let. They were asking me if it is economical. They are barely in the house most of the time and were asking if it would generate enough in winter to deal with a 500W heater being on for a few hours in the day. I said I doubted it would on most days in the deepest of winter. He doesn't even have a fridge running and often turns the electricity totally off when he isn't there so he will get nothing out of the free electricity part of the scheme.

What are peoples' thoughts on the overall economics given the chap would get no utilisation of free electricty? I don't think the Feed-in-Tariff alone will be beneficial enough but I'm open to other views hence posing the question here.

[adam2]

As a very rough guide, a PV system in UK winter conditions should produce an average of one hours peak output a day.
That is a 1.9KWp system should produce about 1.9KWH a day.
That would clearly run a a 500 watt heater for some hours, but not continually 24/7.

For unattended premises, an electric dehumidifier might be better, all the energy used ends up as heat, but it also removes moisture which is often a probem in unattended premises.
The loading is usually a couple of hundred watts, the PV system should therefore supply most but not all of the energy used.
Outside midwinter it might supply all the energy used.

[biffvernon]

As a very rough guide, a PV system in UK winter conditions should produce an average of one hours peak output a day.

That's an interesting rule of thumb. I just checked my figures. I have a 3.94kWp system. In the 120 days of November, December, January and February last, which the Met Office say was the cloudiest on record, I got a mean of 3.2kWhr per day. So yes, a reasonable rule of thumb for estimating in your head.