Renewable energy suggestions for a new build house in Spain...

SanPedro

Am a total noob to all things renewable... so please bare with me.

Just purchased a plot of land in Southern Spain. It's a slot between 2 existing terraced type properties and we will have a garden area at the back.

Rear of the house faces south west and get's plenty of sun all afternoon. Still getting 9.5 hours of daylight at the moment.

Thermal solar water is de rigeur out here and all new properties have to include one. I've rented a house with a solar water heater and am impressed with how much hot water it generates, when the sun is shining. On cloudy days, not so great. So some kind of back-up would be required.

So the main issues are, that despite near 40C temps in summer in can drop down to freezing in winter.

House design: would like to incorporate as much passive solar effect as possible for winter, yet negate the oppressive heat that is present in summer.

Electricity generation: what sized system solar PV for a 250 sq m property (comprising main house and holiday flat/granny flat) i.e. how much square footage of roof space is needed to generate a useable amount of electricity?

And there's no feed in tarif in Spain, so is there a means of storing generated electricity for later?

Heating: no piped gas here. Been considering either a biomass boiler. ground source heat pump, either via radiators or underfloor heating.

Biomass seems hugely expensive for what seems to be a fancy woodburner. Apart from quicker/cleaner/more convenient operation what other benefits are there over a traditional wood burner with a back boiler? And whilst I say it can get cold, the temp will be up to 18C on Monday ., so 20K on a biomass system seems overkill.

A friend in the UK has a central heating system powere by his wood burner and uses small gas water heater for his hot water. Would these work with underfloor heating? Or just traditional radiators?

The ground source option seems more appealing but I'm not sure we have enough space out back... and the house sits atop a solid rock, literally. Garden space is around 20m x 10m.

We work from home so ideally need a system that can run all day (economically), which I believe these systems are ideal for, especially running an underfloor heating system.

I know it's a long shot... but would appreciate any and all answers, and any ideas on budgeting even more welcome.

neilball

Have you thought about an air source heat pump to feed your underfloor heating, which can be reversed in summer for underfloor cooling. As long as you are not aiming for very high or very low water temperatures it can be quite economical. Add in some solar PV and that helps offset some of the running costs when the sun shines.

You will still probably need conventional VRV/VRF fan coils for summer, and you could add in a wood burning stove for backup heat should there be a power cut. Add an immersion heater in your hot water tank and you're running almost entirely on electricity with a bit of biomass for the stove.

SanPedro

Do these work similar/same to the reverse air-con units that are popular here? Or are they indeed the same?
There's a bunch of them in the house I'm renting at the moment... they are less than a year old. They are branded 'fagor' and seem to be re-branded Frididaire units.

Are they cost effective to run? There's a pellet burner in house which TBH doesn't seem all that effective.

I didn't know they could be used to run underfloor heating cooling, presumably a wet system?

That would be neat as the system would be less intrusive than big boxes on the walls. The indoor temp in most houses is much colder than the outside on many days. I had the heating on this morning, yet you could be walking outside in the sun without a jacket.

What sort of running costs? ie p/kwh.

neilball

An air source heat pump has a refrigerant to water heat exchanger in a unit around the size of a regular boiler, with the same type of outdoor unit you see for regular air conditioning. You can also get units with integral hot water tank heated from the heat pump, often with an immersion heater as backup.

The size of the unit depends on the size of the house and the thermal output needed. I live in Scotland and have a ground source heat pump feeding my whole house underfloor heating, and it has a 2.5kW compressor giving around 11kW of thermal energy to the UFH or hot water system. I average around 12,000 kWh per year in electricity for my 4 bed home with 2 adults and 2 kids. I work from home so the house is heated most of the winter. My annual consumption covers heating, hot water, lighting, and power - I have no other energy use apart from a wood burning stove in the Lounge which gets used in very cold weather (think minus 15 at night, minus 5 in the day, for a week to 10 days) but even then the heat pump could scope if I simply used it constantly. My current electricity tariff will see me pay around £1300 per year based on my current level of consumption.

I have friends with a similar sized house built at the same time as my house, and they spend £2500-£3000 a year on oil for their oil-fired central heating, and still complain that there house feels cold. They also have their power and lights electrical costs on top of this!

So in your case if you plan to have wet underfloor heating/cooling via an air source heat pump I would expect it to work well and be cost effective to run.

Solarphil

Would have thought one option for the solar thermal would be to install a larger well insulated thermal store (a larger tank) thus on sunny days you'll be able to store more of the potential heat and use this on the less sunny days.

Solar PV would make a lot of sense as you'll get around 1700kWh per kW of panels installed, so the payback assuming grid cost of €0.15/kWh with a 4kW system and assuming 100% use of that power (which if you've got your larger thermal store you could use by dumping that power as heat into the store with an immersion) then assuming a system cost of £6k you'll get a payback of about 6 yrs.

As @neilball says that would also work well with a VRV system

As long as your building from scratch then the building shell first route is always the best route put in plenty of insulation it keeps the heat out in summer and the heat in in winter which lowers the amount of work you'll have to do outside the hours of free heat and power from the sun.

Have fun!

johntheexpat

Insulation, insulation, insulation.  protect yourself from the cold and protect yourself from the direct heating of the Sun, then balance out the rest with heat exchangers.
When the temperature drops the COP of air source heat pumps drops, so you use more electricity to get each KWh of heat into the house.  It can drop to a COP of 1 if the temp. is low enough (ie might as well use a fan-heater).  Hence the need for proper insulation.  You may as well do as much as you can to keep the hard won warmth.
As the temperature rises, the cooling efficiency of ASHPs also drops.  Hence the need for insulation, you may as well do as much as you can to keep the hard won cooling.

But a lot of this is pointless unless you have the most efficient kit around the house.  Pointless having a really inefficient freezer belting heat out of the back of it which you then have to negate by turning the air-conditioning up.  And its pointless having really efficient heating if actually a lot of your heat is being supplied by inefficient freezers and other white goods.  (Although the EU have done away (supposedly) with inefficient vacuum cleaners with other goods to follow).  So careful planning along those lines will probably save you a decent % of your on-going electricity costs.

So, I would advise you first and foremost to concentrate on insulation, followed by efficient white goods and then start looking at heating/cooling.