Renewable Energy in France
Heating systems can make use of renewable energy by transferring heat from the ground or air for domestic home and water heating. Find out more...
Residential properties account for 28 percent of France's energy consumption. Of this, 75 percent is used for heating and another 15 percent is for the production of domestic hot water. With the current focus on consuming less energy in daily activities, renewable energy solutions provide ecological, efficient and economical options.
There are several distinct approaches to reducing energy consumption. These include the use of heat pumps, solar water-heating, biomass and condensation.
This group can be sub-divided into three elements:
- Air source
- Ground source
- Water source
They all share the same fundamental principle of operation: the exchange of heat through the medium of a refrigerant. In the simplest and most common form, the domestic refrigerator is a heat pump. The warm air inside the refrigerator compartment is absorbed by the refrigerant passing through the evaporator pipe work in the walls and this heat is given off by the condenser pipe work at the rear of the unit.
Air-source heat pumps
The air-source heat pump captures the heat (calories) contained in the exterior air and then transfers that heat to the inside of a building. The efficiency of this system is measured by its Coefficient of Performance (COP), which should be between 3 and 5, that is, 1 kW of electrical energy consumed returns between 3 and 5 kW of heat energy.
This group can be sub-divided into the ways in which the heat is emitted. This is either via air (air/air) or via water (air/water).
Air/air: The air/air heat pump is also known as a reversible air-conditioner. Warmed air is circulated either by individual wall-mounted units or a centralised system situated in the loft and then ducts carry the air to each room.
Air/water: An air/water heat pump works by circulating heated water around a dwelling; the heat is emitted via underfloor pipes, fan-coil units or radiators. The underfloor heating is relatively more economical, as the water is circulated at a lower temperature (no hotter than 30°C), but the large surface area acts as a very effective emitter. The fan-coil units, which are similar in appearance to a car radiator with a fan mounted below it (but housed in an aesthetically acceptable enclosure), are typically supplied with water at 45°C. The radiators are similar to those used in conventional central heating systems, but the water circulated through them is at 55°C.
Air-source heat pumps can also be used to produce domestic hot water through the use of a cylinder linked to the system and with, an additional module, they can be used for heating a swimming pool. For principle residences, air/water heat pumps with a COP greater than 3.3 are eligible for a tax credit of 15 percent (as of April 2013).
The air-source heat pump can operate even with outside air temperatures as cold as -15°C. The outside unit must be mounted in an open space. The advantages are that it is ideal for use in small systems; it is easy to install in either new-build developments, during renovation or as a one-off retro-fit system; it takes up very little space both outside and inside and the installation costs are low.
Ground-source heat pumps
A ground-source heat pump captures the heat contained in the earth. This type of system is also known as geothermal. The heat stored in the ground is more stable than that in the air and in winter remains at a higher temperature. As a result, compared to an air-source heat pump, more heat is available for transfer by exchange to the inside of a building. The COP of a ground-source heat pump is typically around 4.5 times that of electric heating systems, so 1 kW of energy consumed by the operation of the heat pump returns 4.5 kW of heat to the house. The heat is circulated in the same manner as that of the air/water heat pump.
Geothermal heat pumps capture the heat from the ground in two ways. The heat pump is supplied by a water/glycol mixture circulating in plastic tubes. These tubes can be laid in a horizontal network adjacent to the property to be heated. The network is buried between 60cm and 1.2m below the surface of soil and takes up an area 1.5 to 4 times the area to be heated indoors. The heat in the soil at this depth is regenerated by effects of the sun, rain and wind. Therefore, the ground above the pipes must be left free from development as the construction of garages, parking areas or swimming pools would block the ability of the ground to become recharged and the roots of trees could damage the pipes.
Alternatively, the tubes can be installed vertically in drill shafts adjacent to the property. The number of shafts and their depth varies depending on the size of the property and the quality of the ground, but normally a minimum of two shafts drilled to a depth of 80m is required. It is obligatory in France to notify the Regional Directorate of Industry, Research and the Environment (Directions Régionales de l'Industrie de la Recherche et de l'Environnement - DRIRE) and the appropriate prefecture before any drilling operation takes place. Vertical geothermal installations are not particularly suitable in soils that have a high rock or clay content.
Ground-source heat pumps can be used to produce domestic hot water through the use of cylinder linked to the system and with, an additional module, they can be used for heating a swimming pool. For principle residences, ground-source heat pumps and the exterior pipes are eligible for a tax credit of 26 percent (as of April 2013).
The advantages of ground-source heat pumps are that there are no units mounted outside the property, they provide heat regardless of the outside temperature, they emit a minimal amount of noise and there is very little maintenance required.
Water-source heat pumps
The water-source heat pump is similar to the ground-source heat pump except in this case the exterior tubes are used to extract heat from ground water, wells or lakes. The COP of 4.5 is similar and again the heat is emitted via underfloor heating, fan-coil units or radiators. The water is an excellent source of heat as the temperature is usually greater than 10°C and the calories are regularly recharged by the effects of sun, wind and rain. The main requirement is to have a sufficiently large body of water to absorb the extraction of heat, as too small a volume would very quickly become frozen if the extraction rate was greater than the capacity to regenerate.
Before the installation of a water-source heat pump system is planned, it is obligatory to seek permission from the authorities (this would be the Préfecture for the département or the local office of the DDE, Direction Départementale de l'Equipement). The system requires maintenance to ensure it remains free from algae build up and to keep the filters clear and free flowing. The noise emissions are similar to ground-source heat pumps.
Solar Water Heating
The most widespread application of solar heating is for the production of domestic hot water. The system comprises one or more panels that absorb and concentrate the solar radiation and heat a fluid contained within. The panels may be either glass fronted boxes containing copper pipes under a black sheet that absorbs the radiation or glass tubes with copper tubes inside. Either way the fluid is circulated by a pump and thus transports the heat from the sun back to a cylinder containing the water for domestic use.
The system is regulated to stop the circulation if there is insufficient solar radiation to heat the domestic water. If this occurs, the water is heated by a back-up system of either an electric element in the cylinder or an additional coil in the cylinder, which is connected to a heat pump or a conventional boiler. As a safety measure, the system must incorporate a mixing valve to prevent water at the tap being hotter than 60°C.
An individual solar water-heating system can produce between 60 and 80 percent of the hot water needs of a family of four over a year. If the system is expanded, it can also produce enough hot water to preheat a central heating system, supplementing around 25 percent of the annual heating requirements.
In central France, a properly installed solar panel would save a quantity of energy equal to approximately 500 kW per m² per year. The greatest advantage of solar water-heating is that the hot water is virtually free once it is installed. The only cost is the electricity required to power the circulating pump. Moreover, there is no generation of CO² or any other greenhouse gases.
The panels may be mounted on the roof of a house or on a ground-based framework adjacent to it. The critical requirement is that the solar panels are pointing to the south and they are inclined at between 30° and 45° to the horizontal.
Solar water-heating systems installed in principle residences are eligible for a tax credit of 32 percent on the cost of the equipment, including TVA (as of April 2013).
The burning of wood and its derivatives for the production of heat has varying levels of return depending on the efficiency of the burner. The modern advanced wood burning systems can have an efficiency rate of at least 50 percent and in some cases as much as 80 percent. The burning of four cubic metres of wood can save up to a tonne of oil and avoid releasing as much as 2.5 tonnes of CO² into the atmosphere.
The types of biomass-burning appliances can be subdivided into three groups:
- Stoves that are used to burn logs or granules
- Inserts or closed hearth fires (generally log burning appliances)
- Solid fuel boilers that can be used as part of a central heating system (these are designed either for logs or granules)
A drawback in the use of wood as fuel is the high level of maintenance required. Regular cleaning of the appliance and sweeping of the chimney is essential for efficient performance and for safety. The advantage is the neutral impact on the atmosphere and the ready supply of fuel in forested regions of the country. Boilers and other biomass burning appliances used for heating or the production of hot water may be eligible for a tax credit of 15 percent for new installations and 26 percent for the replacement of an existing less efficient boiler or stove (as of April 2013).
Technically, this is not a renewable energy as it is still burning fossil fuels directly in the production of heat; however it does introduce a degree of energy efficiency because a traditional boiler loses a large proportion of its energy via the flue. By contrast, in a condensing boiler the water vapour contained in the flue gases is extracted and the energy is passed into the central heating system by heating the water in the return path to the boiler, thus the burner consumes less fuel in raising the water temperature.
The difference between a conventional and a condensing boiler can be measured in the temperature of flue gases. These are 120 to 180°C from a conventional boiler, but only 50 to 60°C from a condensing boiler. In comparison to an older classic boiler, around 25 percent of the energy formerly lost to the atmosphere can be recovered. Even a modern classic boiler is 15 percent less efficient than a condensing boiler.
A plume of vapour is emitted from the flue of a condensing boiler so it's important to select the site with care so that the steam does not cause a nuisance. In addition, the acidic liquid produced by the combustion in a condensing boiler needs to be plumbed into a suitable drain.
The condensing boiler may be eligible for a tax credit of 10 percent when installed in a principle residence (as of April 2013).
Installation and Commissioning
Regardless of the form of renewable energy solution chosen, it is essential to ensure the work is carried out by a professional who is trained and experienced in this activity. For certain aspects, such as handling refrigerant fluids, electricity and chimney sweeping, the regulations require certain levels of competence. For example, it is illegal for anyone to buy, sell or work with refrigerant fluids unless they have been trained and certified to do so. Heat pumps should always be commissioned by an accredited engineer.
Retaining the heat brought in to a house with effective and appropriate insulation is an essential part of bringing about energy savings. The purchase and fitting costs of insulation are eligible for a tax credit of 15 percent and for double glazing 10 percent as long as the double glazing is fitted in conjunction with another form of energy saving for example loft insulation or a heat pump (as of April 2013).