Solar photo-voltaic (PV) systems to generate electricity are more popular (but see sections on grants and economics) and becoming more affordable. They consist of large panels mounted on frames, either on a roof or near the ground and, for residential properties, generally do not require planning permission. The output from panels can be connected to the mains, via an inverter and control equipment, or can be stored in battery arrays for off grid properties or to even out supply and demand. South facing locations are preferred and shading from trees or other buildings can dramatically reduce output, even if only a small part of the array is shaded. Current regulations permit a maximum of 3.6kW of micro-generated electricity to be connected to a single phase of the grid and installation must be certified by a registered professional installer.
Wind
Wind power is a good energy source in the right location and wind turbines range from small direct drive turbines, typically 5kW maximum output, to large geared
turbines generating 15kW upwards. Installation costs are high and a proposed installation needs thorough assessment of ground conditions, average wind speed and any obstructions such as trees and buildings, as well as planning permission. A big advantage of a wind turbine over solar PV is that energy is generated 24 hours a day and, unlike sunshine, we get most wind during winter months, when the energy requirement of a house is greatest. As with solar PV, the ending of feet-in tariff makes the economics of a domestic turbine doubtful. Britwind is a UK manufacturer and installer of small turbines.
Hydro
Water power from a constantly flowing stream is potentially a great energy source for electricity generation but is complex and expensive to engineer. It has potential for a community energy scheme.
Biomass
Biomass energy systems range from large scale industrial schemes (e.g. wood or straw burning in power stations; digesters producing methane gas) to domestic wood burning stoves and boilers. Although widely regarded as renewable energy systems, this is only the case if the fuel is replaced – pruning actively growing trees or re-planting to replace felled trees. Wood pellet domestic boilers may use wood from non-sustainable sources and involve high carbon transport of bulky loads, often imported. Suppliers of kiln dried logs may be using fossil fuels or electricity to hasten the drying process, whereas naturally seasoned wood has a much lower carbon footprint.
Domestic wood burning stoves are very efficient room heaters but need a constant supply of dry logs (1-2 years of seasoning under cover) or they will be inefficient, polluting and cause dangerous tar deposits in chimneys. New UK regulations limit the emissions of wood stoves and some manufacturers (e.g. Esse) have produced helpful information on new developments. In choosing a wood burner, it is important not to select a much bigger stove than needed – a small stove running at a high temperature is much more efficient and less polluting than a big stove that never really gets hot. Some stoves have a water jacket so they can provide domestic hot water or supplement a central heating system. Whilst attractive in principle, this can result in heat being removed too rapidly from the stove, leading to a low working temperature and inefficient burning.
Esse and other manufacturers supply wood fired cooking stoves, styled like original Aga/Rayburn cookers, that may be single purpose or include a water jacket for heating/hot water. These can be very efficient but, if you are considering the central heating option without an alternative heat source, think hard about the amount of firewood you will need, the regular stoking and what happens if you go away in winter. Whichever type and make of wood fired cooker you consider, it is crucial that it is designed specifically for wood burning – expecting a conventional solid fuel cooker to burn wood efficiently and controllably, even if “converted” is unrealistic.
Wood pellet boilers are possibly a direct replacement for gas or oil fired domestic boilers and eligible for Renewable Heat Incentive. They require a regular supply of processed wood and bulk storage, with a mechanised feed system. Yougen is a website with useful information on this technology.