Renewable energy heating systems

Fossil fuels, greenhouse gases, pollutants – these are the first things that spring to mind when the word “energy” is mentioned. So what springs to mind when we add the word “renewable”? And how can the average person use renewable energy sources in their build?

Renewable energy is – quite simply – energy that comes from sources that can be regenerated or cannot be depleted. There are five basic sources of renewable energy, wind, water, the sun, the earth and biomass. All of these can be used in differing ways to provide an optimum amount of renewable energy for each individual household and its different requirements. Before thinking about any system, it is wise to think about your heating requirements and look at energy efficient measures, such as wall and floor insulation, to keep your need for heat to a minimum.

Solar heating is probably the best-known form of green energy. After all, solar energy is the source of all life on earth! In just half an hour, enough of the sun’s energy reaches the earth’s surface to satisfy the world’s energy demands for a year. Given that this power is clean, free, silent and limitless, it seems a shame not to use it!

There are three main forms of solar energy:

Passive heat – this is the heat that we receive from the sun and can be taken into account when designing a building so that less additional heat is required.

Solar thermal – the most familiar use of solar power where the sun’s heat is harnessed to provide hot water for homes or pools.

Photovoltaic – the energy from the sun is used to create electricity to power appliances and lighting.

Photovoltaic installations use cells to convert solar radiation into electricity; as the light shines on the cell, it creates an electric field across the layers causing electricity to flow. Uses can range from calculators and torches right through to complete integrated systems for homes, public buildings and offices.

Solar panels can provide heating as well as domestic hot water and heat for larger installations such as swimming pools. The panels are fitted to the roof and retain heat from the sun’s rays, which is then transferred to a fluid. A hot water cylinder stores the water that has been heated, ready to be used later. To be suitable for solar water heating, a property will need 2-5 m2 of roof or wall that faces southeast to southwest. There should be no other buildings or trees overshadowing it, as this will decrease the output. The roof must also be strong enough to take the weight of the panels especially if they are going to be placed on top of existing tiles. Ideally, there will also be space to locate an additional water cylinder. The cost of installation will depend on a number of factors including the size of the collector, type of roof, existing hot water and heating system and the geographical location. Obviously a small property in the far south will incur lower installation costs than a large manoir in the north!

Solar systems are generally low maintenance and usually require only an annual check by the householder and a more detailed check by the installer every three to five years. It is important to check that the collectors carry the Solar Keymark or CSTBat certification. This means that the installation will be eligible for a 50% tax rebate.

Biomass comes from organic matter, either directly from plants or indirectly from industrial, agricultural, domestic or commercial products. It is often referred to as ‘bio energy’ or ‘bio fuel’. There are two main forms of biomass, woody and non-woody. Woody biomass includes all forestry products, energy crops and trees such as willow which are fast growing and grown especially as a ‘crop’. The second type encompasses animal waste, biodegradable products from food processing and high-energy crops, such as rape, sugar cane and maize. As far as the householder is concerned, the most usual use of biomass is in the form of wood pellets, chips or logs.

As any French resident or frequent visitor to France, will know, wood is an incredibly important part of rural life and for good reason. It is the most common form of heating by far in the countryside and an orderly woodpile is an essential accessory to French country life! For many people in rural France, wood is either free or cheaply available and as such it will continue to be an important source of energy. The only real downside is the amount of time and effort it takes to faire le bois!

The most usual way of heating a home in this way is by a stove. They can be fuelled by pellets or logs but only pellets are suitable for use on ‘automatic feed’ type stoves. Stoves are normally around 6 -12 kW in output and those with a back boiler provide hot water too. Alternatively a boiler can be connected to the central heating and hot water systems to provide a greater volume of heat – 15 kW and more. Such boilers will use all forms of biomass and are often found in commercial situations. For example, many of the fuel-powered boiler rooms within schools in the Landes area, have been replaced with wood powered boilers. This enables them to use the by-products of the logging industry. As the largest forest in Europe, the paper and sawmills of the Landes create a huge amount of “waste”. Combined with roadside prunings and “un-wanted” wood from the Atlantic beaches, this “waste” becomes a source of energy.

Tax rebates are also available for the installation of biomass systems. The system must function at least 65% efficiency and conform to the appropriate standards. A full list of these, along with the requirements for all other renewable installations and the amount of rebate available, can be found on

Ground source heat pumps are increasing in popularity within France. They use lengths of pipe buried underground, either in a borehole or trench, to absorb heat from the earth. This is then transferred to the house by means of a pump. A heat pump can provide 100% of the central heating requirements of a house but usually only pre-heats the hot water. This means that a top up (usually a chauffe eau) heater will be required. A heat pump is still using some electricity so this has to be factored into running costs. Depending on its efficiency, for every 1kW hour of electricity used to power the system, around 3-4 kW hours of heating will be produced.

It is also possible to run the system as a cooling system in the warmer months. By reversing the pump, heat can be extracted from the building thereby cooling it. For those who wish to be totally green, it is possible to install solar PV or another form of electricity generating system to power the elements of the system that need an electrical supply. This could be hydroelectricity or wind energy!

Most people think of wind turbines solely as huge structures grouped on wind farms supplying electricity to the national grid. However, individual turbines with a power output of only a few hundred watts are becoming much more common. Wind is another clean renewable source of energy that is being increasingly harnessed, especially by those in remote locations where a conventional supply would prove expensive. There are two types of turbine; mast mounted i.e. free standing and roof mounted. These can be sited directly on the home or an adjacent building. The ideal site would be a hill-top with clear exposure and away from other obstructions such as buildings and trees. Full details and prices of both on and off grid systems, can be found on or the English version .

Hydropower is one of the oldest and most proven methods of harnessing renewable energy. Improvements in technology mean that a micro hydro (under 100kW) scheme is now a useful means of producing electricity. Electricity is produced using the energy stored in the moving water. However, hydropower does require the source to be close to the site or a suitable grid connection and the costs of installation can be quite high. A feasibility study and site survey must be carried out by a professional who can advise on the viability of the project.



Good choice of stoves / boilers / cookers to suit all tastes and budgets.

Also helps with waste by using energy from products that are often disposed of in landfill.

The ash is excellent for the garden!

Requires storage space. Labour intensive to prepare.

May need to be purchased.


Photovoltaic cells release no greenhouse gases.

Proven, safe technology.

The panels are heavy and the roof must be strong enough.

May require space for another water cylinder.


Large potential resource.

Can be a practical solution for remote locations.

Turbines can last up to 20 years and require service checks.

Blades and batteries may need replacing depending on the system.


Old and proven method.

Useful power can be produced from even a small stream.

Installation costs high but can be less than grid connection in remote areas.

Need to allow for seasonal variations in water flow.

Requires specialist assessment.


Can provide a cooling element too.

Utilise “free’ ground heat.

Payback period is relatively short – usually three to five years.

Lifespan is longer than conventional heating and cooling systems.

Require space for the trench or borehole.

Require electricity to power the compressor and pump.

thats great Ed, please can you add a photo of yourself and you can add your website or business details on your profile page if you haven't already.

Hi All, I've been registered with SFN for quite a while but only just started using it, What a great place!

Anyway, I've just noticed this post, (after just asking on another post if there was a relevant place to introduce my business.) I think this may hopefully be helpful to some of you.

I supply and (can sometimes also install, depending where you are) wood pellet and log gasifying boilers.

If anyone has any questions I'm more than happy to try to help.



Interesting post James, thanks!

There's one 'but'. Anything electrical and definitely all of these so-called modern or hi-tech solutions rely upon the archaic and totally unreliable EDF which is an accident waiting to happen (those are not my words but coming from a former CEO of the EDF).

Victoria, sorry just re-read your post - so yours is Ground Source - who installed yours/what brand? We have an air source which is great normally but struggles in minus temps which is where the woodburner is a great secondary heat, though agree about wood, here in Herault it is about 55-60 euro a stere. We go through about 8 stere in a typical winter.

We have a heat pump and while when it works it works very well, it tends to break down every time the temperature goes below -5°. When the temperatures are low it also uses raw electricity to top up the heat which gets expensive.

I'd question wood being cheap - it is if you have access to free or practically free wood but at 50 euros plus for good wood it isn't. Our neighbour used to heat his house (approx 150 sq m) with two woodburners, OK he was French and liked it really warm, but he went through 40 steres of wood every winter and he had to split and cut all the logs to size.

I've also been very dubious about the efficacy of wind turbines since my daughter did a project on them for her Bac S- basically she worked out that to provide even a reasonable fraction of France's electicity needs via wind turbines you'd need to cover 50% of the total land mass with turbines. Given that she went to engineering school to study protection of the enviorenment she doesn't fall naturally into the 'rubbish renewable energy sources' camp.

sounds like a good idea Kerry, I'll treat the banks with caution though and check with my accountant first. cheers

we'll also be hoping to get the zero interest rate 30k loan from the bank to help fund the installation, insulation and pv. we're really hoping that by putting the investment into the upfront work we can keep the running costs down. we are looking at buying some kit direct or even from uk. Darren is considering doing a course in building management systems to help regulate the house himself, so that lghts left on, shutterrs open when should be closed problem is minimised. We know he could install that and programme it himself loads cheaper.

Ask at the mairie. My OH has the form stowed away in her files and if I ask her she might injure parts of my anatomy, being a bit busy and all. All remember was that it asked every question imaginable, including great-grandfather's shoe size, as usual and I groaned. However, I do not think I remember it being that fantastic. Something is better than nothing.

As for PV, well yes. I looked at SMA, and others, but think they have by far the best equipment available. If going for that, buy direct because it is cheaper than a French supplier, If you use an SMA registered installer, they get the bonus points on the SMA scheme and may cut the bill a bit.

Our total m2 is less than yours, but it will be interesting to know anyway.

ooh interested about the grants Brian. what was the reference please? We're going out to tender for ground source heat pump with underfloor heating later this year for our renovation in Herault. I'm expecting prices to be around 30,000 euro inclkuding excavation and underfloor heating with reversible cooling. we're looking at putting pv on the roof too which has a south facing aspect but my hubby is keen to keep the energy for our usage see the Sma sunnyboy inverter. we're going out to and 2 other gsh supplers later this year with our plans. i'll update you with the costs. ours is 330m2 total heating requirement although not all will be habitable initially.

Tony, our quotes were two years ago, just about the same (except the one where we need to have excavation prepared ourselves) things covered. The difference is that we did not have the boiler and radiators in the package, since neither are necessary having replaced those for the solar/wood stove system we have. The entire existing heating system in the house probably makes up the overlap between yours and ours, therefore the upper price of 30K sounds a bit expensive and the lower would probably come out cheaper than here had we gone ahead with the ground source (which we still may eventually). So, no not absurd at all. It was simply not clear that you were including the house end beyond underfloor... here are, as we found out in 2010 as well, grants to part fund ground source if other things like insulation are up to standard. Our mairie gave us the forms but apart from not having the money for the heating, our insulation was not up to standard, so we have it filed away somewhere.

Earlier I mentioned a heater that is economical and good. have a look at The sunnyheat panels produce infrared heat, cover areas up to 25 sq m, are very slim (can be disguised as posters or the like). they are German made, so that usually means quality. The initial outlay is expensive but the payback is fantastic, their life long and energy consumption (apart from payback) environmentally very interesting.

Carol, the payback could be far higher than the UK but neither actually achieves what is promised because the power companies are sharks - that's putting it nicely. Integrated, self-standing PV pays itself back in three to four years on average.

Tony. Firstly those quotes were absurd. Our worst quote was only €12000 and the lowest €8000, but we would have had to pay extra for the excavation ourselves. As you say, it is best for underfloor heating but then it is usually used with another energy source for ambient room heating when it is very cold.

Wow, thanks. That's like the A to Z of renewable energy sources. Got me thinking!

Is there a huge difference in the sell back in the UK compared to France? we have friends who whilst renovating their large house, put 18 photovoltaic panels on their roof, going back 6 months later and adding another 6...this was during the period when the government were offering top dollar for sell back. My friend tells me when bored she watches the electricity metre going backwards...they pay almost nothing in electricity bills and receive back hefty payments (this is a 3000 plus square foot house) 5 beds and 2 bathrooms but with only two adults and one near adult child living there. They considered ground source but live next to a stream and the garden floods on a regular basis.

Good post. Ground source will probably be our next project. Once our roof is replaced we are installing PV but for our own domestic use and not to sell back. We have the fortune in that amongst friends we have several with sell back who are not really seeing an enormous reduction on their bills so are disappointed, whereas one couple have their own integrated system which is drastically reducing their mains bill. It will take several years to pay off and it is highly likely they will need to upgrade at about the same time, but the system itself is installed and it will be the panels with the technological advances that will be replaced. Even now in the winter and on the cloudiest days, they get up to one-third of their daily supply from the system.

However, as I began, a ground source will be a project in the future as against the simpler PV installation. Because we have very shallow soil with bedrock very near the surface, excavation will have to be done for us with diggers. We know where, have dug sample trenches and know how to route the pipes, which will be into a cellar where the pump can very easily be installed and from there it will feed into our heating very easily. The hot water is either solar or our wood stove, this winter we have not used the electric backup once (as yet) and I think during the coldest weather last year it might have been twice for a couple of hours a time. Even on sunny days at present, the external temperature (the collectors) has gone up into the 60s, enough to heat the water for a couple of hours here and there. We did not need to light the stove until well into October and depending on a combination of weather and indoor temperatures, especially at night, may be able to put the stove off in late March. By then it will heat the hot water supply based on the last three winters.

Like our friends with their own PV, we would also wish to install a smaller collector on the old cowshed I use as a workshop with enough power for power tools, lighting and heating when necessary. An acquaintance sells what I would described as heating panels rather than radiators, that are plug in electricity but can be conceal as pictures or panels when wall mounted and heat by radiation. My wife has seen them, not I so at the first opportunity I might grab the catalogue and add it to this thread later. Anyway, they are low consumption, long life and if you move you can take them with you, needless to say they are pricey to begin with. If attached to regular mains they save on bills and are ecologically more sense anyway.