Glossary:

The use of wind as a renewable energy resource involves harnessing the power contained in moving air. Wind represents a vast source of energy that has already been harnessed for hundreds of years. The UK has the largest potential wind energy resource in Europe and wind power is currently one of the most developed and cost-effective renewable energy technologies. Wind turbines can be situated either onshore or offshore. Small wind turbines designed to be integrated into buildings are also becoming commercially available.

Dundee has Europe's largest urban wind turbines sited at the Michelin Tyre factory in the city.

Solar water heating uses collectors, usually on the roof of a building, to capture and store the sun’s heat via water storage systems. The collectors provide heat to a fluid that circulates to a water tank. The heat is primarily used for heating water in domestic dwellings, industrial facilities and commercial buildings. This includes the growing market for solar swimming pool heaters.

An example of the largest (equal) solar water heating system in Scotland can be seen at St Johns High School in Dundee where it heats the swimming pool.

Ground-source heat pumps are not strictly a renewable source of energy, because they require electricity to extract and make use of low-grade heat. However, there is no reason why this electricity could not be generated by another form of renewable energy. Heat pumps can be very energy efficient, producing four or five times the amount of heat energy for every unit of electrical energy needed. A heat pump takes the heat from a refrigerant fluid (or water) that is in contact with the ground, extracts the heat from this source and transfers it to a heat sink where it can then be circulated through a heating system. Although the refrigerant fluid is cooled by this process, it can be re-circulated back through the ground where it will absorb more heat before being passed through the heat pump again.

Dundee's Morgan Academy uses ground and air source heat pumps to provide space heating and cooling in the assembly hall area of the school.

Wood pellets (small compressed sawdust pellets) can be used to fuel stoves (with or without back boilers) and pellet burning boilers especially designed for the purpose. Pellet stoves require less attention compared to log appliances and are the most convenient wood fuel to use in a domestic setting. Integral fuel hoppers store enough pellets for 1 to 3 days operation and the ash pan only needs emptying between once a month and once a year. Wood pellet boilers are fully automatic and almost as convenient as using gas or oil. They are well suited to meet variable load demands and can be operated on a timer. Pellet stoves and boilers operate at high efficiencies of around 90%. Being a very dense fuel pellets require less storage space than logs or chips.

At present only pellet stoves and boilers exempted for use in Smoke Control Areas can be installed in Dundee. Contact us for more information.

As with wood pellets modern wood chip boilers can provide a high level of automation and convenience for wood fuelled space heating. Wood chip systems generally have an output of greater than 20 kW (suitable for a large farmhouse or larger) and are not cost effective or appropriate for typical domestic scale applications. Extensive fuel handling systems and fuel storage facilities are required for automated operation. It is important to be able to source a steady supply of woodchip with a consistent size and moisture content suitable for burning in a boiler, as not all chips are suitable for burning.

At present only wood chip boilers exempted for use in Smoke Control Areas can be installed in Dundee. Contact us for more information.

Solar photovoltaics (PVs) convert energy from daylight into electricity using a semiconductor material such as silicon. When light hits the semiconductor, the energy in the light is absorbed, ‘exciting’ the electrons in the semiconductor so that they break free from their atoms. This allows the electrons to flow through the semiconductor material (in a similar manner to a normal electrical circuit) producing electricity.

There are a number of PV technologies, including polycrystalline, monocrystalline and thin-film. Solar PV cells can be arranged in panels on a building’s roof or walls, and can often directly feed electricity into the building. With the latest PV technology, cells can also be integrated into the roof tiles themselves. Solar PV cells can be used in both stand-alone and grid-connected systems.

Dundee's Morgan Academy has a 10.5kWp PV array on its roof which generates electricity to power the schools ground source heat pumps.

Hydroelectric power is the energy derived from flowing water in rivers, or from man-made installations where water flows from a high-level reservoir down through a tunnel and away from the dam. Water power was used for centuries to power machinery, for example for grinding corn or in mills and factories, but was largely replaced by steam power in the Industrial Revolution. Water power is now mainly used to generate electrical energy.

Turbines placed within the flow of water extract its kinetic energy and convert it to mechanical energy. This causes the turbines to rotate at high speed. The turbines drive a generator that converts the mechanical energy into electrical energy. The amount of hydroelectric power that can be generated is related to the water flow and the vertical distance (known as ‘head’) through which the water has fallen.

In the smallest hydroelectric schemes, the head of water can be a few metres; in larger schemes, the power station that houses the turbines is often hundreds of metres below the reservoir. Hydroelectric systems can be connected to the main electricity grid, or can be part of a stand-alone power system. In a grid-connected system, any electricity generated in excess of consumption on site can be ‘sold’ to electricity companies. In an off-grid hydroelectric system, electricity can be supplied directly to the user or via a battery bank.

Wood is a very versatile fuel and can be burned in many different forms to provide central heating. Until recently wood fuelled heating has had the drawback of a lack of controllability. Automatic wood fuelled boilers, and many stoves, overcome this problem by utilising thermostats which automatically control fuel and air intake with very responsive and programmable temperature settings.

See wood chip boiler and wood pellet boiler and stove entries for more detail.

Heat pumps are electrically powered systems that tap the stored energy of the ground, water or air. The systems use the external environment’s relatively constant temperature to provide heating and hot water (and sometimes cooling) for buildings and industrial processes. Heat pumps operate on the same principle as a domestic fridge but instead of extracting heat from the food in a fridge and expelling it into the room, heat pumps extract heat from outside and, in effect, concentrate it, delivering useful heat to the building.

Marine energy usually refers to wave and tidal power. Both wave energy and tidal power involve harnessing the movement and energy contained in the ocean and converting it into electrical power.

Wave Energy - as ocean waves are created by the interaction of wind with the surface of the sea, waves have the potential to provide an unlimited source of renewable energy. Wave energy can be extracted and converted into electricity by wave power machines. They can be deployed either on the shoreline or in deeper waters offshore.

Tidal Power - this exploits the natural ebb and flow of coastal tidal waters caused principally by the interaction of the gravitational fields of the earth, moon and sun. The coastal water level fluctuates twice daily, alternatively filling and emptying natural basins along the shoreline. The currents flowing in and out of these basins can be exploited to turn mechanical devices to produce electricity. A variant of tidal energy is tidal stream (or marine current) technology. Tidal streams are fast sea currents created by the tides, often magnified by topographical features, such as headlands, inlets and straits, or by the shape of the seabed when water is forced through narrow channels.