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Microgeneration renewable energy technology

Information

Microscale renewable energy technologies are becoming more commonly installed or incorporated into buildings. These technologies include photovoltaics (PVs), solar thermal, micro wind turbines and heat pumps.

In general, these systems transform energy from the sun, wind or geothermal sources and convert it into a source of energy for the property in which they are installed, either as providing electricity, power or for heating the property. Some systems will have isolation switches installed.

There are some common hazards associated with these systems because they are generally installed on the external envelope of a building. They therefore pose a hazard for non-structural collapse, which may in turn cause structural collapse.

Solar panel (photovoltaic) systems

Refer to Solar panel (photovoltaic) systems

Solar thermal

Another type of renewable energy technology can have the appearance of PV panels but operate differently. Similar to PV systems, solar thermal systems are installed on the roofs of properties. These convert energy from the sun into thermal energy for the property through a 'collector', which can be a panel or tubular system. Unlike PV systems, solar thermal systems use the collected energy to heat a transfer fluid, which in turn is stored and then used to heat the property. This heat transfer fluid will contain antifreeze, can reach temperatures of about 200°C and have pressures of up to 6 bar.

 

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Figure 14: Solar thermal system - photograph courtesy of Peter Martin

Micro wind turbines

These are small-scale wind turbines used to generate electricity. Turbines operate by the wind rotating the turbine blades connected to a shaft that rotates in a generator.

Similar to PV systems, the electricity generated by wind turbines is DC, which is converted to AC by an inverter.

Wind turbines are installed with both a wind turbine controller, which can stop the blades turning in high winds, and an isolation switch, which allows for safe maintenance or repair.

This equipment is easily identifiable as it will be located at a certain height above the roof. If the blades are not rotating, no electricity is being generated.

Micro wind turbines can be used in off-grid applications, such as signposts or caravans.

 

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Figure 15: Micro wind turbine

Microturbines

Microturbines can operate on natural gas, propane, landfill gas, biogas, diesel, aviation or kerosene fuels. They can be installed individually or as multiple units functioning in parallel to produce electricity independently from the grid.

Heat pumps

Heat pump systems work by extracting heat from the surrounding air, water or ground. These systems are designed to heat a whole building and operate using the same principles as a refrigerator. They require electricity to power the pump; however, the electricity required might be generated by a small wind turbine or PV panel. There are three main types of heat pump; ground source, air source and water source. These systems do not have any known specific hazards.

Ground source heat pumps

Ground source heat pumps make use of the ground's constant temperature by converting and transferring this heat into a house or building, usually through radiators or underfloor heating. To extract heat, ground source heat pumps use pipes that are buried in the ground. A ground source heat pump circulates a working fluid (usually a mixture of water and antifreeze) through a loop of pipe (a ground loop) buried in the ground. Heat from the ground is absorbed into the fluid and then passes through a heat exchanger into a heat pump.

Air source heat pumps

Air source heat pumps extract heat from the outside air, in a similar way that warm air from a refrigerator is extracted to the outside. It can get heat from the air when the temperature is as low as -15°C. Heat from the air is absorbed at low temperature into a working fluid. This fluid then passes through a compressor, where its temperature is increased, and transfers its higher temperature heat to the heating and hot water circuits of the premises. The heated air can be circulated around a building through ducting. These systems are usually mounted on an external wall close to the ground.

Water source heat pumps

Water source heat pumps use the energy in water to provide heat suitable for homes and other buildings. The pump system takes heat from the water and transfers this heat to a gas. The gas is passed into a condenser that returns it to a liquid state, a process that releases heat. This heat is transferred to the heat distribution system in the home or building.

Hazards (for further information refer to National Operational Guidance: Utilities and fuel)

General

  • Installations (e.g. panels, glass from the panels, solar tubes, micro wind turbines or blades from turbines) may break and fall on personnel below
  • Installations may not be easily identifiable and may be hidden (flat roof)
  • It may not be evident whether a panel is PV or solar thermal; these are associated with different hazards
  • Arrays for PV or solar thermal that stand proud from the roof may cause a channelling effect, worsening a fire affecting the roof
  • Additional mechanical loading due to the weight of the installation, or additional wind loading caused by the installation, may cause early collapse of the roof if it is affected by fire
  • Poorly installed systems that may obstruct or restrict use of roof windows as means of escape, or may hinder firefighting operations
  • Restricted access to isolation switches
  • General electric shock risk from PV systems, wind turbines and heat pumps; PV systems and wind turbines generate direct current (DC) electricity

Solar thermal

  • Failure or breakage of the panel or tubes can result in hot fluid (more than 200°C) or steam being released, which can cause scalds or burns; this fluid can be present at pressures up to 6 bar

Wind turbine blades

  • Risk of electric shock if blades are spinning and wiring is damaged

Heat pumps

  • General electrical safety applies

References and further reading

BRE knowledge sheets