Renewable Technologies
Why Renewable Technologies Matter
Buildings account for a significant share of the UK's total energy use. Heating, hot water and electrical appliances all consume energy that has traditionally come from burning fossil fuels such as gas, oil and coal. Burning these fuels releases carbon dioxide, contributing to climate change, and because they are finite they will eventually run out. Renewable technologies offer an alternative: they generate or collect energy from sources that naturally replenish themselves — the sun, wind, ground heat and water — reducing both carbon emissions and long-term energy costs.
For construction professionals, understanding renewable technologies is increasingly important. Building regulations now expect new homes and commercial buildings to meet higher standards of energy performance, and many clients want to incorporate renewables from the outset. This lesson covers the main categories of technology used in buildings today: solar, wind, heat pumps and water technologies.
Solar Energy
The sun delivers an enormous amount of energy to the Earth's surface every day. Two distinct technologies capture this energy for use in buildings, and it is important not to confuse them.
Solar Photovoltaic (PV)
Solar photovoltaic (PV) panels convert sunlight directly into electricity. Inside each panel are photovoltaic cells made from semiconductor materials, usually silicon. When light strikes the cells, it knocks electrons loose, creating a flow of direct current (DC) electricity. An inverter converts this to the alternating current (AC) used by household appliances.
The main benefits of solar PV are that sunlight is free, running costs are very low once the panels are installed, and the system reduces a household's electricity bills. Any surplus electricity generated can be exported to the national grid, earning the owner a payment. On the limitations side, solar PV depends on sunlight intensity — output falls on cloudy days and drops significantly in winter when days are shorter. Installation costs are high, and the panels occupy a significant area of roof space, which may not always be available or structurally suitable.
Solar PV converts sunlight into electricity. Solar thermal converts sunlight into heat. They are different systems with different purposes.
Solar Thermal
Solar thermal collectors are roof-mounted panels containing a fluid that absorbs heat from the sun. The heated fluid passes through a heat exchanger inside a hot water cylinder, warming the stored water for use in showers, baths and taps. Unlike solar PV, solar thermal does not generate electricity — it only heats water.
The benefits include reduced hot water bills, lower carbon emissions compared with a gas boiler, and low running costs. The limitations are that the system only provides hot water (not electricity), output depends on sunshine, and in cold or cloudy periods a conventional boiler or immersion heater must top up the water temperature. This means solar thermal rarely completely replaces a backup heating system.
Wind Turbines
Wind turbines use the kinetic energy of moving air to spin blades attached to a generator, producing electricity. In domestic and small commercial settings, two main types are used: pole-mounted turbines, which stand on a freestanding mast in an open space, and building-mounted turbines, which are fixed directly to the roof or walls of a structure.
The key benefit of wind power is that it is a free, renewable resource with low running costs once installed. Unlike solar, wind turbines can generate electricity even in poor weather or at night, provided the wind speed is adequate. However, wind turbines come with notable limitations. They produce noise and have a visual impact on the landscape, which can lead to planning objections. They require consistent wind speeds to be effective and are poorly suited to urban areas where buildings disrupt airflow. Building-mounted turbines in particular can transmit vibration and noise into the structure, which can be disruptive for occupants.
Pole-mounted turbines stand independently on a mast in an open area away from the building, typically in a garden, field or open site where wind speeds are higher and less disrupted. Building-mounted turbines are attached directly to the roof or wall of a structure. Building-mounted models are more compact but tend to be less efficient because the building itself creates turbulence in the airflow, and they can cause vibration and noise problems within the building.
Heat Pumps
Heat pumps work by moving heat from one place to another rather than generating heat by burning fuel. They operate on the same principle as a refrigerator, but in reverse — extracting low-grade heat from a natural source (the ground, air or water) and upgrading it to a higher temperature for use in heating a building. Because they move heat rather than create it, heat pumps are highly efficient.
Ground Source Heat Pumps
A ground source heat pump (GSHP) uses a ground loop — a long length of pipe buried in trenches or boreholes — filled with a water-and-antifreeze mixture. The fluid absorbs heat from the ground and passes it through a heat exchanger to a refrigerant. The refrigerant is then compressed, raising its temperature further, before transferring the heat to the building's heating and hot water system.
Ground source heat pumps are very efficient, typically producing 3 to 4 units of heat for every 1 unit of electricity used to run the pump. They work reliably throughout the year. The main limitations are the high upfront installation cost, the significant area of land needed for horizontal ground loops (or depth for boreholes), and the disruption caused during installation when trenches or boreholes are excavated. The pump also requires electricity to operate, so the system is not entirely independent of the grid.
Air Source Heat Pumps
An air source heat pump (ASHP) extracts heat from the outside air, even when temperatures are as low as −15°C. A fan draws air over a refrigerant-filled heat exchanger; the refrigerant absorbs the heat, is compressed to raise its temperature, and then transfers it to the building's heating system. ASHPs are easier and cheaper to install than ground source models because no ground loop is needed — the unit simply sits outside the building, similar in size to an air conditioning unit.
The benefits include suitability for most types of home and relatively straightforward installation. The limitations are that efficiency decreases in very cold weather (when heat is needed most), the outdoor unit takes up external wall or ground space, and the fan produces some noise.
Water Source Heat Pumps
A water source heat pump extracts heat from a nearby body of water — a river, lake or borehole — using a submerged coil. Water maintains a fairly constant temperature throughout the year, making this type efficient and reliable. However, water source heat pumps are limited to locations with suitable water access, and installation costs are high.
Ground source heat pumps typically produce 3 to 4 units of heat for every 1 unit of electricity consumed, making them significantly more efficient than conventional electric heaters.
Water Technologies
Alongside energy generation, sustainable buildings aim to reduce mains water consumption. Several technologies collect, recycle or harness water to cut demand on public water supplies.
Rainwater Harvesting
Rainwater harvesting captures rainfall from a roof and channels it through gutters and downpipes into a storage tank. The collected water is filtered and used for non-potable (non-drinking) purposes such as toilet flushing, garden watering and car washing. It is not safe for drinking or cooking without extensive treatment.
The benefits are a reduction in mains water demand (lowering bills) and a reduction in surface water runoff, which helps to reduce the risk of local flooding. The limitations include the need for storage tanks (which take up space), separate pipework to carry the harvested water to its point of use, and filtration systems to remove debris.
Grey Water Re-use
Grey water is waste water from baths, showers, basins and washing machines — water that is slightly used but not contaminated with sewage. A grey water re-use system collects this water, treats and filters it, then recycles it for toilet flushing and garden irrigation.
The benefits are reduced mains water consumption and lower water bills. The limitations are that a separate pipe network is required to keep grey water apart from both fresh water supply and foul water drainage. The water must be treated or filtered before reuse and must never be used for drinking, cooking or food preparation.
Hydro-generation and Tidal Generation
Hydro-generation uses flowing river water to drive turbines and generate electricity. Tidal generation works similarly but is driven by the predictable ebb and flow of ocean tides. Both methods produce zero direct carbon emissions once the infrastructure is in place, and tidal generation is particularly reliable because tides follow fixed astronomical cycles. The limitations are that both systems are restricted to sites with suitable water flow or tidal conditions, capital costs are high, and installation can disrupt aquatic habitats.
Grey water has been in contact with soaps, skin cells and other contaminants from bathing and washing. Rainwater may contain pollutants washed from roof surfaces — bird droppings, moss, particulates and trace chemicals. Neither is safe to drink without the same level of treatment applied to mains water. Both can be filtered for toilet flushing or irrigation, but drinking water must meet strict quality standards that these systems do not provide.