glass laminate rooftop showing photovoltaic cells
Glass laminate photovoltaic cells at St Pancras Station, London © Historic England Archive
Glass laminate photovoltaic cells at St Pancras Station, London © Historic England Archive

Low and Zero Carbon Technologies

Low and zero carbon (LZC) technologies generate energy from renewable or low carbon sources and emit low or no carbon dioxide emissions.

In 2019 the UK Government announced a target of net zero for UK greenhouse gas (GHG) emissions by 2050. Reaching net zero requires reduction of emissions across the whole of the country including historic properties whether businesses or households. Low or zero carbon technologies that generate electricity or heat or both with low or no carbon dioxide (CO₂) emissions are vital to meeting this target:

In assessing the benefits of these low and zero carbon energy sources for historic buildings you will need to consider:

  • Does it suit the particular building and use?
  • What are the carbon reduction benefits?
  • Will the potential savings exceed the whole-life energy costs?
  • Can the system be fitted safely with no significant adverse impact on the building and its historic fabric
  • What will be the visual impact on the setting of the building or heritage asset?
  • Are there any planning controls that affect your choice and positioning of the installation?

These technologies, particularly those used for generating heat, are more effective within buildings with a highly energy efficient fabric, and where heat demand and loss have been reduced to a minimum.

The output of many of these energy supplies can fluctuate. They will often need to be balanced with electricity supplied from the National Grid, importing or exporting as required.

Apart from the initial set up costs, operation and maintenance costs, and de-commissioning of redundant systems need to be considered. These can be higher than for conventional supplies. Some systems can also have relatively short lifespans which can have implications for life-cycle value.

Photovoltaics (PV)

Photovoltaic cells convert radiant energy from the sun directly into electricity. PVs generate electricity whilst there is daylight, so the energy must either be consumed as it is being generated, stored in batteries, or exported to the National Grid. The amount of electricity generated will depend on the size and type of the array as well as the amount of sunlight.

PV units are normally roof-mounted but can also be used away from the building. For a PV array to be at its most efficient the array should face south and not be in shadow from buildings or trees, as even small shadows can seriously impact on the amount of electricity generated.

The key considerations for these systems are the orientation of the panel, avoiding shading, inclination and the visual impact.

Energy Efficiency and Historic Buildings: Solar Electric (Photovoltaics)

Published 15 October 2018

This guidance covers the issues associated with installing solar photovoltaic (PV) panels on a historic building or on the land of a historic site.

Learn more

Case studies

The National Trust has installed 172 high-efficiency HIT® photovoltaic modules on the new visitor centre roofs at Sutton Hoo, the Anglo-Saxon burial site. These panels will generate around 42,000 kilowatt hours of electricity per year, enough to supply more than 10 average homes.

At Grade I listed Kings Cross Station, the building-integrated PV in the glass roofs is expected to produce 175,000 kilowatt hours of electricity each year, saving over 100 tonnes of CO₂ emissions per annum. There are 1,392 custom-made glass laminate units over the 2,300 square metres of the glass roofing.

Solar water heating

Solar water heating systems use the sun’s energy to heat water, which can then be used for hot water. The collectors are normally roof mounted but can also be mounted away from the building they are serving. The sun heats the fluid held in the collector which is then pumped to a hot water cylinder to heat the water.

For a system to be at its most efficient the collectors should face south and not be in shadow from buildings or trees.

The key considerations for these systems are the orientation of the collector, avoiding shading, inclination, having the space to accommodate a larger hot water cylinder and the visual impact.

Further advice on solar water heating is available from the Energy Savings Trust

Heat pumps

Heat pumps take heat from the air, ground or a water source and use it to provide heating or cooling or both. The heat energy is upgraded from a lower temperature to higher temperatures by using a compressor. The higher temperature heat can then be used for space heating or cooling.

Ground source systems use vertical boreholes which may need to be drilled down to 200 meters deep, or horizontal collector loops which are buried underground up to two meters deep. For example the bore hole for the ground source heat pump at Wimpole was 150 metres deep. The extent of land and access to it will determine what system will work. Horizontal loops are a simpler installation, however large areas of land are required outside the building to accommodate the loops. The depth needed for vertical boreholes depends on the geology of the site and the amount of energy to be required.

An additional means of topping up the heating, such as gas boilers, may still need to be retained for peak heat loads. The radiators will need to be a larger size as the circulating water temperature is not as hot as with a conventional gas system. If there is an existing radiator system and larger radiator cannot be installed, it maybe that the water temperature will need to be boosted by a gas boiler. You will also need to think about plant room space to accommodate the heat pump.

The key considerations for these systems are the assessment of the site’s geology, hydrogeology, and archaeology.

Water source pumps work in a similar way to ground source but extract heat from a large body of water such as a lake or river. Systems can be either closed-loop or open-loop where the water is taken from the main body of water, pumped to the evaporator and returned to the water source. You will need to consider how the pipework gets from the water source to the building and how the low energy heat can be used within the building.

Air source pumps extract heat from the outdoor air using a fanned heat exchanger. The heat can be used directly air to air, or air to water for a conventional low temperature hot water system. The key considerations for air source heat pumps is the visual impact of the external unit and internal units, noise generated from the fan, and how the heat will be used within the building.

In addition to heritage consents for heat source installations, you may need to get consent, a permit and a licence from the Environment Agency for an open-loop ground source or surface water source heating and cooling system.

Heat Pumps

Published 4 December 2017

This guidance note covers the issues associated with installing a heat pump in a historic building.

Learn more

Wind turbines

Wind turbines convert the kinetic energy of wind into electricity. They can range from small domestic turbines to large wind farms. Small turbines are normally mounted on poles well above buildings to benefit from greater wind speed. Turbines can be mounted on buildings but are visually intrusive and could create noise issues.

Installations are likely to require planning permission as well as heritage consents.

Further advice is available on our Wind Energy web page. 

Hydroelectric power

In hydroelectric schemes kinetic and potential energy of running or tidal water is converted into electrical energy. The energy output depends on the product of volume flow rate and height through which the water falls (the ‘head’). High head systems are much more cost-effective.

Hydro systems require a high degree of maintenance, particularly for those parts exposed to the water. Filter screens require regular checking to clear any debris.

Systems usually require Environment Agency approval and conditions can be onerous. An environmental impact assessment will usually be a condition of any planning consent.

It is possible to bring back historic watermills and their original mill wheels back into use to generate hydroelectric power. Other former mill sites and remaining structures may also qualify for hydroelectric schemes. An example is the National Trust’s Gibson Mill, a 17th century cotton mill.

The key considerations are sufficient hydraulic head from the body of water to the turbine, rainfall catchment area, visual impact of the dam or weir and turbine building if they don’t exist, the environmental impact of diverting a water flow, impact of the pipeline to transport the water to the turbine and then the outflow where the water returns to the water course.

Micro-Hydroelectric Power and the Historic Environment provides further advice on micro-hydroelectricity schemes and historic sites.

Case study:

The National Trust’s video Power from the past lights up Cragside describes the trust’s green energy project at Grade I listed Northumberland home. In 1883-7 Lord Armstong built a hydroelectric turbine system to generate electricity for his house. The power house is listed Grade II* and includes a Thompson double vortex turbine and a R.E. Crompton double magnet "Trade"-type Gramme ring compound dynamo which is the earliest known surviving example. The new Archimedes screw produces enough energy to light all 350 light bulbs in the house.

Combined heat and power (CHP)

Combined heat and power is the name given to energy systems that produce both heat and electricity in a single process. Electrical energy is generated using an engine that runs on a single fuel, typically gas, though this could also be biomass fuel. The thermal heat energy produced as part of this process is captured and used for heating buildings.

CHP works well when it is in constant use. Ideally you need to have a constant heat demand all year round to use the waste heat so the machines are not switched off. They work well in district heating systems or networks for the varying heat demand profiles from different users all through the day.

The technology was largely devised from power station developments but packaged units are available for retrofit in homes and smaller buildings all the way to large multi-building installations.

The heat generated from CHP systems will largely replace boiler plant, but boilers will still be required to meet peak heating and hot water demand.

The key considerations are the need for a consistent heat load all year round, space for the engine and flue, and access for maintenance.

The Department for Business, Energy and Industrial Strategy’s Combined Heat and Power guidance provides more detailed guidance including site assessment.

Biomass boilers

Biomass boilers are like conventional boilers but use wood chips or pellets to generate heat. Biomass boilers tend to be larger and fully automated systems have an auger to feed the boiler, a hopper and a fuel and ash storage area. The fuel store needs to be dry and big enough to keep sufficient stock of chips or pellets to minimise the number of deliveries.

Biomass fuel can be brought commercially or harvested and processed locally but supplies need to be from Forest Stewardship Council (FSC) certified sustainable sources. The carbon foot print of deliveries needs to be factored in too.

Biomass installations require more frequent and complex servicing than conventional oil or gas boilers. Boilers also need to be cleaned regularly in order to keep them free of ash, and the feed systems need to be checked weekly.

Biomass boilers are covered by a number of regulations including the Clean Air Act. Local authorities have the powers under this Act to request the measurement of dust emissions from biomass boiler exhaust stacks and require arrestment plant to be installed to control dust emissions. Where the local authority has designated a ‘Smoke Control Area’ biomass boilers must be approved as an 'exempt appliance'. Biomass energy generation is unlikely to be acceptable in urban areas due to the emissions.

Further advice on solar water heating is available from the Energy Savings Trust.

Case study:

The National Trust has installed a biomass boiler at Dyrham Park as part of a new conservation heating system to help preserve the English tapestries and Dutch paintings. The wood chip is sourced from woodlands just north of Dyrham Park. The chips are a woodland management by-product.

The National Trust has also installed biomass boilers at other historic properties: Croft Castle, Barrington, Dunham Massey and Killerton.

Fit for the Future network

Fit for the Future led by the National Trust, is a cross-sector network supporting hundreds of practitioners to make their organisations more climate-friendly, adaptive and resilient and achieve carbon net zero targets. Historic England and other heritage organisations are members.

The network helps people share ideas and practical experience through events, workshops, showcases, newsletters and online resources.

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