Solar Thermal

Solar thermal systems use heat from the sun to warm hot water, which can be supported by a conventional boiler or immersion heater to make the water hotter or to provide hot water when solar energy is unavailable. Hospitals may be able to make use of large roof surface areas to accommodate solar thermal technology, although it is also possible to deploy smaller scale systems.

Estimates for the costs and savings associated with this technology were derived from data given in the NHS Energy Efficiency Fund (Final Report February 2015) and also data from EEVS’ database of energy efficiency projects in the NHS. Two different sets of costs and savings were used across different organisation types to reflect the differences in procurement and economies of scale for larger organisations such as Acute Hospital Trusts versus smaller stand alone buildings such as General Practice Surgeries. In general, it would be expected that the smaller stand alone buildings have a higher technology cost per square foot compared to an NHS Trust, which is likely to have greater buying power.

The cost and carbon savings associated with expected reductions in kWh consumption were extrapolated over time using the cost and carbon intensity projections provided by the DECC/HM Treasury Green Book guidance on valuing energy use and greenhouse gas emissions.

The resulting figures were sense checked by stakeholders with experience of building energy efficiency interventions.

Case study sources

NHS Energy Efficiency Fund Report

Green Book supplementary guidance: valuation of energy use and greenhouse gas emissions for appraisal

Financial Calculations


Energy savings were normalised using the energy spend of the NHS trust from which the various data sources were taken. This gave an average saving of £11,000 annually per trust based on the gas costs in 2015 and expected value of Renewable Heat Incentive tariff payments. Smaller buildings such as General Practice Surgeries, an average saving of £130 was used, based on expected kWh savings and RHI for a building size of 400m2. This was then scaled according to floor size for other segments including Dental Practices and Adult Social Care. Values for both were extrapolated over time using costs from the Treasury Green Book guidance.


Average capital costs per NHS trust normalised by energy spend were taken as £200,000. Average costs for smaller stand-alone buildings (GPs, Dental Practices) were taken as £4,000.

Carbon Calculations

Average carbon savings per trust were calculated using carbon intensity projections from the DECC/HM Treasury Green Book guidance and hence change annually over the expected lifetime of the intervention. In 2015, the carbon savings derived from the expected kWh savings were 90 tCO2 per annum for NHS Trusts and 0.25 tCO2 per stand-alone building.


Building energy efficiency interventions will have a wide variation in their scope, likely costs and savings, depending on factors such as the existing technologies and the funding sources used for the project. The results are therefore indicative rather than definitive, and are intended to give a sense of scale for the potential savings.