solar water heaters

I have the 150lt version of this, for aesthetic reasons I didn't really want one with a coupled round tank like you see on many properties.

With it facing almost exactly due South I get totally free piping hot water for probably 300 days of the year. It has the optional 2kW heater for times when there is no sun at all.

Downside is that even in the height of Summer it can lose a fair amount of heat overnight but there is still usually enough for a couple of brief morning showers.

When I'd had it for a couple of years and got a reasonable handle on what it was costing me in electricity I decided to install a secondary conventional 100lt tank for winter use. It too has a 2kW heater element but being 100lt instead of 150 it therefore theoretically should consume about 2/3 of the electricity the heater in the solar unit would however because it retains heat for much longer in practice the cost is in fact closer to half.

Also I've plumbed it so that the cold water feed comes from the the solar unit hot outlet meaning that the temperature of the water which goes into it is not necessarily cold but whatever the temperature of the water in solar unit happens to be at the time which should rarely if ever be lower. I also have a bypass arrangement so that when the sunnier days arrive I can switch wholly to the solar.

Using just the the tank in the Winter then on average I'm consuming around 3kWh per day of use so taking the absolute case where I had to use electricity say every day for 4 months that's 3 x 120 or 360kWh which, costed at a nominal €0.24/kWh (the average unit cost for a typical Spanish household in 2018) works out to under €90/pa. Most should be able to get their electricity significantly cheaper than €0.24.

Capital costs have been around €1100 for the solar unit and €200 or so for the secondary tank plus incidental materials so let's say maybe €1400, I did the plumbing myself so no labour costs.

We live miles out in the campo and our neighbours have recently had a quote for exactly what you want. They have lived here for 40 years and used solar power on their finca where they previously lived. Having the experience of this they assumed that they would again install a similar system. The quote - from a professional specialist well respected company - was around 2.5K by the time all the bits and pieces had been factored in.. They decided that (as they had no wish to do any work themselves!) this capital cost simply could not be justified given that they already have an existing gas boiler, which they find extremely economical.

We ourselves have an all electric house, no gas, and use a heat pump for all hot water. We also have a separate heat exchanger for the underfloor heating which, admittedly , we don’t often use. All our cooking and the usual TV/computer/ appliances/dishwasher/washing machine and so on and the hot water and our total electric bill is rarely more than 70 or 80 Eu per month. I don’t have to buy gas, or mess about changing bottles, or order gas. I was rather suspicious when we moved in as I expected costs to be astronomical, it that strikes me as quite reasonable for everything. If we do use the heating in winter, then of course the bill escalates, but we really don’t need it often.

No air con? 

We have it and also our under floor heating can be turned to ‘cold’ for the summer if we need it. We very rarely use it - fans quite sufficient and using the system employed by most inhabitants of very hot countries, we find that lowering the blinds and effectively keeping the sun ;out’ in summer works very well.