Going off-grid for electric... crazy idea?

SanPedro

First off I should state this is not a UK installation, but for Spain.

I'm wondering about the merits (or otherwise) of going off-grid. The reason being that here in Spain there is no feed-in tariff and any surplus energy is lost to the grid. We are building a main house plus a rental property attached within the same plot. The standing charge for electricity, per house, would be around 30 Euros a month.

Both house will have solar water heaters and cooking would be via bottled gas. There would be the usual appliances like a fridge and washing machine, computers, TV, AV system (main house only). Probably and AC unit in each house as well.

We work from home so will be using electricity most of the day.

Any ideas what sized system would be needed to run both houses? We have a 3.5Kw 'Potencia' (supply) in the house we are renting, which is ok till you try and use a tumble dryer. Would a 7-8Kw supply be adequate?

And then there's the additional items like battery back-up and maybe even a generator in case of zero sun days during the winter months. And the big question... is it actually viable/reliable?

Lots of conflicting information out there on the web, so wondered if anyone here has some experience.

I would have stayed on the grid if there was similar set-up to the UK, or even if you could 'buy-back' surplus electric at a much lower rate... like a storage cost or something. Spain seems to be very anti solar PV at the moment, but given that I could save 800 euos a year on standing charges I thought it worth a look.

If I can get away with only having one mains supply to feed both houses it might be worth staying on the grid for peace of mind.

johntheexpat

What does the standing charge cover?  In the sense that here in France, the Standing Charge is a flexible feast, the less the maximum current you can pull before it trips out, the lower the standing charge.  So for a three KW max, the standing charge is 91 € per year, we are on 9KW max, for 122€/yr, which is fine once you get used to it.  1KW is about 200€/yr.  That's for economy 7.
Flat rate electricity starts at 52 euros per year for 3KW and the leccy is a priced half way between cheap and normal

johntheexpat

By going off grid, in all fairness, you will save a lot more than 800 euros per year, because you will learn to live without buying in electricity. If you have a connection, then it is easy to "just have a quick zap", which becomes a regular low level of usage, which then becomes more.

SanPedro

Thanks John

I realised I made an error in my last message in terms of the cost of the standing charge. We're on 3.3Kw 'Potencia', which is 23.19 per 2 months (0.115 euro p/day) plus a 2.46 euro tax and then VAT, coming out at 31 euros every 2 months. And this is the lowest tariff they do here in Spain. The actual electric rate is 0.13 euro p/kwh. The standing charge was pretty much half the usage on the last bill.

So the standing charge is more like 180 euros per house per year. No where near as bad as I thought (doh!!!)

I've worked out that we will be using around 59 euros of electricity for Jan/Feb, based on the current meter reading. So that's around 360 euros a year. But the house is very cold at the moment and I'm loath to have the heaters on all day as it will bump the bills up massively. Cost would probably be more over the year as we'll be needing the a/c on in summer... I can wrap up well in the house, but can't cope with the heat when it's pushing 40C.

Been trying to work out energy consumption for a typical A/C unit... so if it's rated at, say 2.5Kw then useage would be (on 8 hrs a day) 2.5 x 8 x 30 = 600 KWh, or 97 euros a month. I guess that would assume that the unit is on constantly keeping the air temp down.

If a decent solar PV sustem can power A/C units that would be perfect. They may not been be needed too much if we can design the house right.

Basquelle

Consider a reversible AC unit (called an air source heat pump) which will provide 3kW of heat for 1kW of electricity in winter and perform as a normal AC in summer.  Note that all AC/air pump units have high switch-on surge currents, not good if you are near your supply current limits.  

I think your biggest problem going off-grid will be the rental property: you may get used to working around the characteristics of your renewables system, but rental guests will not, they neither have time nor interest to learn it.

If you're still at design stage, the basics are:

keep the high south sun from inside the house, with window siting and window shading, catch all the low east and west sun you can;
keep as many interior built surfaces (walls, floors, ceilings) massive (ie heavy) and non-insulant (tile, concrete, stone), keep windows open at night in summer, closed and shuttered in the day so the surfaces can cool in the night air and absorb heat from inside the house by day;
insulate floor, walls and ceilings to the outside as much as you can, including draughproofing.

johntheexpat

My one problem with heat pumps is that they get less efficient as the temperature drops.  Normally at about -15C they only give out as much heat as you put in.  So a fan heater is just as good.
Admittedly for day to day stuff, where is just chilly rather than cold, they are very good indeed.  But don't decommission the wood burning stove on the day you plug in the heat pump.

Having said that, they are of course super efficient at heating swimming pools in summer.  So if you can get a multifunctional one,to heat the house, heat the pool and cool the house, then its a very good idea.