RDES provides independent, impartial advice on the entire range of Renewable Energy technologies. Our team has experience and knowledge of each technology, providing up-to-date information on the feasibility, performance and cost of each type. The links below provide an overview of the following Renewable Energy technologies:
- Solar Photovoltaic
- Anaerobic Digestion
- Large Scale Wind
- Micro Wind
- Combined Heat and Power
- Solar Thermal
- Heat Pumps
Hydropower involves the extraction of energy from a flow of water. Potential energy from a flow of water down a slope is converted into kinetic energy. Micro hydro systems (< 100kW) consist of small scale ‘run of river’ schemes which divert a flow of water from the watercourse (river or stream) and pass it down a pipe (the penstock), developing pressure due to the drop or ‘head’. The water is then passed through a turbine causing it to turn a generator and produce electricity. Large scale hydro systems (>100kW) use a dam and therefore require a more detailed assessment of the environmental impact in terms of natural habitats, fish spawning and visual impact.
Factors to be considered for hydro systems include:
- Available head (low or high)
- Mean flow (variation throughout year)
- Proximity to a load or grid connection
- Environmental impact
- Land ownership issues
- Planning and environmental licensing requirements (e.g. Controlled Activities Regulations 2005)
Small scale hydropower is an extremely efficient technology which draws on a reliable and predictable resource. It also has a low environmental impact and a long lifetime. Although initially expensive, the costs per kWh of the energy over the lifetime of the project are very low compared to other forms of generation. Installation costs for a hydro system can vary between £6,000- £15,000 depending on the site and civil works required. The FiT scheme pays for any electricity generated by hydro systems thereby reducing the pay back periods and generating an extra income for the owner.
Photovoltaics (PV) is the science of converting energy from the sun into electricity. When sunlight strikes a PV cell, a flow of electrons is created which can be extracted as direct current (DC) electricity. This DC electricity must be converted into alternating current (AC) using an inverter which can then either be fed into the grid or used to power a battery for remote systems.
A wide variety of PV products are available on the market today from traditional crystalline silicon panels (typical efficiency 11-16%) to thin-film, flexible technologies (8-10% efficiency).
PV systems can be roof mounted, building integrated or installed as stand alone systems on the ground. In the UK, a roof tilt of 30 degrees is ideal but it is possible to mount systems on flat roofs using mounting frames. Building integration can be an attractive alternative replacing conventional building materials such as roof tiles, facades or glazing units.
It is a common misconception that the UK climate is unsuitable for PV systems, PV cells generate electricity under daylight radiation as well as direct sunlight. This means they still produce electricity on cloudy days albeit at a lower efficiency compared to sunny days.
Solar PV panels are suitable in locations where:
- The roof/wall is south-facing or at least within 90 degrees of south
- The roof is strong enough to withhold the weight of the solar panels
- There are no trees or buildings shading the proposed area
Solar thermal technologies utilise the heat from the sun to offset the water heating demand of a building. In general, the solar collector absorbs heat from the sun and transfers it to a working fluid (water or refrigerant), which is transferred to the water in a hot water tank either directly or via a heat exchanger.
Solar thermal is a pre-heat system, due to the intermittency and seasonal dependency of the solar resource, additional heating requirements are supplied by a conventional heating source via a secondary heat exchanger.
Generally there are two types of available solar thermal collectors available:
Flat plate collectors consist of a flat “radiator” absorber, covered by glass and insulated. These systems are cheaper but have a lower efficiency with low ambient temperatures and on cloudy days.
Evacuated tube collectors water is passed through an evacuated tube which contains a black absorber plate. Evacuated tubes are more efficient (up to 90%) and the system allows the water to be heated to high temperatures and remain effective even on cloudy days.
Solar thermal panels are suitable in locations where:
- The roof/wall is south-facing or at least within 90o of south
- There is sufficient space for a storage tank
- The roof is strong enough to withhold the weight of the panels (10kg/m2)
- There are no trees or buildings shading the proposed area
A wind turbine converts kinetic energy from wind power into mechanical energy and, ultimately, electrical energy. The kinetic energy is extracted from the wind by means of an aerodynamic rotor, which is connected to a generator to produce electricity. This generator is then connected to the grid to provide electricity for homes, offices and industry.
Wind farm developers must choose sites carefully in order to ensure that whilst there is enough wind to make the project commercially viable, there will also be the least possible adverse impact on the local environment.
A suitable wind farm site will:
- Have a good wind power resource of at least 7m/s (15mph) at the hub height of the wind turbines
- Not be too close to residential buildings (400m – 800m clearance is typical);
- Not be sited on or near areas of outstanding natural beauty, special protected areas, special areas of conservation, and sites of special scientific interest etc.
- Not be too near military or civil flight paths, tactical training areas, radars or airports (15km is a typical minimum radius).
If a site has been carefully chosen and planning consent is granted for the wind farm, it can then be constructed and will operate for up to 20 years. Wind farms offer a sustainable source of energy which will last for as long as the wind blows.
Biomass systems burn naturally grown fuel to generate heat for space, water or process heating systems. Biomass fuel is any solid, liquid or gaseous substance produced from organic materials. The most commonly used products are logs, pellets or chips from sustainable sources. The energy yield from the fuel depends on the energy and moisture content of the fuel. Fresh cut wood has a moisture content of 55-65% therefore it is typically dried to between 25-50% moisture content before it is supplied.
A biomass boiler can be used in almost any situation where a normal fossil fuel boiler is used and can supply heat with the same reliability as conventional boilers.
Biomass applications include:
- District Heating Systems – a number of heat users are supplied from a centralized boiler plant via a heat distribution network. End users can include domestic dwellings, schools, businesses, hospitals
- Industrial Processes – heat or steam requirements can be met through the use of biomass energy. Where a suitable heat load exists it may be possible to generate electricity for use on site or for export. Paper mills, distilleries and breweries offer excellent opportunities for biomass technologies
- Domestic Boilers – logs or wood pellets can be used as an alternative to gas or fuel oil in a small domestic boiler. Modern automated systems have advanced feeding and control systems and require minimal attention during operation
Important factors when considering biomass systems include:
- Proximity of fuel source (to minimise transport costs)
- Security of supply
- Space availability for fuel storage and delivery
Typical costs of biomass systems are between £400 and £1,000 per kW installed with payback periods of 8-12 years. Annual CO2 emission savings are between 0.19-0.43 tonnes per MWh of heat delivered depending on the type of fuel being offset.
Micro wind turbines convert the kinetic energy from wind power to electrical or heat energy. The rated capacity of micro wind designs varies from 0.1 to 15 kW. They are available in two basic configurations: rooftop-mounted and pole-mounted.
Rooftop-mounted wind turbines require a solid section of building at the roof line to directly attach the turbine; generally they installed on an exposed side of a building, mounted on a tower or wooden pole. Pole-mounted wind turbines require a small area of land.
Micro wind power turbines are applicable in locations where:
- The mean wind speed is greater than 4m/s at hub height
- There is good exposure to the prevailing wind directions
The current capital cost of a micro wind turbine is roughly £3,000 per rated kW installed. The annual energy yield is typically 1,000 kWh per rated kW installed at a location with a good 5m/s resource and exposure to the prevailing wind directions. Annual saving in CO2 emissions are 0.4 tonnes per rated kW in a grid connection application.
Heat pumps utilise solar heat stored in the natural surroundings, such as the earth, water and air, to provide space and/or water heating for a building.
In the UK it is common for ground conditions to have a high thermal mass from which heat energy can be extracted and utilised for heating buildings. A Ground-source heat pump (GSHP) uses the earth or ground water or both as sources of heat by using plastic pipes filled with an antifreeze solution laid in trenches 1.5 – 2m deep or boreholes to extract heat. GSHPs typically raise water to a temperature of 40°C which is most suitable for integrating with underfloor heating which requires temperatures of 30-35°C as opposed to conventional boiler systems which require temperatures of 60-65°C.
Air source heat pumps (ASHPs) contain a refrigerant liquid with a boiling point as low as -40°C which circulates within the system and evaporates when heat is absorbed from the outside air. The resulting refrigerant gas is then compressed adding further energy and raising the temperature to approximately 75°C. This heat is transferred into the water via a heat exchanger and used to provide space heating through wet heating and underfloor heating systems. Some air source heat pumps operate effectively at temperatures as low as -20°C.
The advantage of ASHP over GSHP is the reduced installation civil costs although they suffer reduced efficiency as the outdoor temperature decreases. Heat pumps can be used in any energy efficient building with a low temperature heat requirement and a building utilisation greater than 80% and can provide up to 100% of space and water heating requirements.
Anaerobic digestion (AD) is the microbiological conversion of organic matter to methane in the absence of oxygen. The biogas can then be used to produce heat and/or electricity while also producing by-products which can be used or sold as soil fertiliser and conditioner.
Fuel for AD digesters includes agricultural, household and industrials residues and sewage sludge. More specifically, residues from livestock farming such as dairy, beef and pig slurry and poultry litter and food processing waste such as those of vegetable processing and dairy farming industry.
Advantages of AD include:
- Reduce the emission of methane (an extremely strong greenhouse gas)
- Reduce odour and nitrate pollution of watercourses
- Financial benefits such as income generation from FiTs, sale/use of fertiliser
- Effective waste management
The most suitable AD technology is dependent on the composition and volume of the waste to be treated and space restriction on site. The volume and methane content of the gas produced is dependent on the digestibility of the waste and the reactor used to digest the waste. The digestibility and levels of methane produced can be determined through laboratory testing with various suitable technologies and typically takes a few weeks. A feasibility survey will determine the most suitable technology and the gas production rates for a particular application.
Combined Heat and Power (CHP) integrates the production of electricity and heat into one highly efficient process. CHP generates electricity by burning natural gas, biofuels or fossil fuels while also capturing the heat that is produced in the process, unlike conventional fossil fuel burning methods that waste vast amounts of heat. The captured heat can be used for heating, cooling, dehumidification or other processes that can be applied to site specific needs or can power extra income generating processes.
CHP applications include:
- Industrial CHP – the largest scale of CHP plant can range in size from a few MW up to the size of conventional power stations. Industrial CHPs produce high value heat which can be used on site while surplus heat can be used by local communities, excess electricity can also be sold to the grid.
- CHP with district heating – when connected to a district heating network, CHP systems can provide the heat and power requirements of local communities, towns or built environments with high heat loads.
- Small and Micro-CHP - small and Micro CHP systems deliver heat and power to individual buildings. Small scale systems provide small businesses such as hotels, care homes etc. and are up to 25kW maximum electrical output while micro systems power individual homes and are up to 1 kW in scale.
Micro CHP is covered by the FiT scheme while the renewable component of a mixed fuel load will be covered under the RHI scheme. CHP systems are up to 80% efficient and can provide cost savings of 15% over electricity from the grid and 40% over heat generated by on site boilers.