Renewable heat is an application of renewable energy. It refers to the renewable generation of heat, rather than electrical power.
Many colder countries consume more energy for heating than electrical power. For example, on an annual basis the United Kingdom consumes 350 TWh of electric power, and 840 TWh of gas and other fuels for heating. The residential sector alone consumes a massive 550 TWh of energy for heating, mainly in the form of gas.
Renewable electric power is becoming cheap and convenient enough to place it, in many cases, within reach of the average consumer. By contrast, the market for renewable heat is mostly inaccessible to domestic consumers due to inconvenience of supply, and high capital costs. Heating accounts for a large proportion of energy consumption, however a universally accessible market for renewable heat is yet to emerge.
Modern techniques for generating renewable heat
- Renewable natural gas is defined as gas obtained from biomass which is upgraded to a quality similar to natural gas. By upgrading the quality to that of natural gas, it becomes possible to distribute the gas to customers via the existing gas grid. According to the Energy research Centre of the Netherlands, renewable natural gas is 'cheaper than alternatives where biomass is used in a combined heat and power plant or local combustion plant'. Energy unit costs are lowered through 'favourable scale and operating hours', and end-user capital costs eliminated through distribution via the existing gas grid.
- Heat pumps move heat from one place to another, and can be used for both heating and cooling. Heat pumps are capital intensive, but economical to run and can be powered by renewable electricity. Two common types of heat pump are air-source and ground-source heat pumps (GSHP), depending on whether heat is transferred from the air or from the ground. Air conditioning units are usually air-source heat pumps, and many models allow pump based heating and cooling, and continue to be effective with external temperatures as low as -15°C. The efficiency of a heat pump is measured by the coefficient of performance (CoP): For every unit of electricity used to pump the heat, an air source heat pump generates 2.5 to 3 units of heat (i.e. it has a CoP of 2.5 to 3), whereas a GSHP generates 3 to 4 units of heat. Based on current fuel prices for the United Kingdom, assuming a CoP of 3-4, a GSHP can be a cheaper form of space heating than oil, LPG and electric storage heaters. It is however more expensive than mains gas. Geothermal energy, which is used to a great degree in Iceland, is extracted using heat pumps.
- Wood-pellet heating and other types of wood heating systems have achieved their greatest success in heating premises that are off the gas grid, typically being previously heated using heating oil or coal. Solid wood fuel requires a large amount of dedicated storage space, and the specialised heating systems can be expensive (though grant schemes are available in many European countries to offset this capital cost.) Low fuel costs mean that wood fuelled heating in Europe is frequently able to achieve a payback period of under 3 to 5 years. Because of the large fuel storage requirement wood fuel can be less attractive in urban residential scenarios, or for premises connected to the gas grid (though rising gas prices and uncertainty of supply mean that wood fuel is becoming more competitive.)
- Solar heating is a style of building construction which uses the energy of sunshine to provide an economic supply of supplementary heat to a structure. One application, solar water heating, works in conjunction with an existing water heater, and is based on solar panels fitted to the roof. In contrast to photovoltaic panels which are used to generate electricity, solar water heating panels are cheaper to manufacture, and capture a much higher proportion of the sun's energy.
It will take time to build a supply infrastructure for renewable energy for heat. Therefore, if the world economy is to sustain the highest possible proportion of renewable heat, energy efficiency must be promoted.
Improvements to insulation can cut energy consumption greatly, making a space cheaper to heat and to cool. However existing housing can often be difficult or expensive to improve. Newer buildings can benefit from many of the techniques of superinsulation. Older buildings can benefit from several kinds of improvement:
- Solid wall insulation: A building with solid walls can benefit from internal or external insulation. External wall insulation involves adding a decorative weather-proof insulating panels or other treatment to the outside of the wall. Alternatively, internal wall insulation can be applied using ready-made insulation/plaster board laminates, or other methods. Thicknesses of internal or external insulation typically range between 50 and 100mm.
- Cavity wall insulation: A building with cavity walls can benefit from insulation pumped into the cavity. This form of insulation is very cost effective.
- Programmable thermostats allow heating and cooling of a room to be switched off depending the time, day of the week, and temperature. A bedroom, for example, does not need to be heated during the day, but a living room does not need to be heated during the night.
- Roof insulation
- Insulated windows and doors
- Draught proofing
Underfloor heating is significantly more energy efficient that traditional methods of heating:
- Water circulates within the system at low temperature (35°C - 50°C) making gas boilers, wood fired boilers, and heat pumps significantly more efficient.
- Rooms with underfloor heating are cooler near the ceiling, where heat is not required, but warmer underfoot, where comfort is most required.
- Traditional radiators are frequently positioned underneath a poorly insulated windows, heating them unnecessarily.
- ^ Department of Trade and Industry report UK Energy in Brief July 2005 (URL accessed Mar 18, 2006)
- ^ Department of Trade and Industry, 2005 study on Renewable Heat (URL accessed Mar 18, 2006)
- ^ Swedish Gas Centre 'Sustainable Gas Enters the European Gas Distribution System'
- ^ Energy research Centre of the Netherlands 'Heat from Biomass via Synthetic Natural Gas' (URL accessed Mar 22, 2006)
- ^ Energy Saving Trust 'Ground source heat pumps'