Solar Thermal

What are they?

Solar thermal (ST) panels utilise sunlight to heat water and are typically referred to as ‘solar hot water heaters’. ST panels are different to photovoltaic panels which produce electricity from sunlight. ST panels transfer the sun’s energy to a liquid which is heated and then circulates between the panel and the building, and are most often used to provide domestic hot water.

To maximise their efficiency, ST panels are usually mounted on a north facing pitched roof or on a flat roof using an A-frame (facing north) to support them. ST panels still produce significant heat on a cloudy day.

Advantages / Disadvantages

Provide a strong and visible environmental /  sustainability message.

Low maintenance as panels need periodic cleaning and  checking only.

The technology is usually only appropriate to use on buildings north facing orientation can be achieved and  which aren’t overshadowed.

Costly, to the point that it is often more effective to spend money earmarked for ST panels on PV panels instead.

Energy efficiency

ST panels generate hot water to contribute to the domestic hot water system, which means less gas or electricity is consumed for this function in the building.  Impacts of solar thermal applications are generally small.

Running costs

The hot water generated will reduce electricity or gas costs depending on the fuel being displaced.

Retrofit / improvement opportunities

ST panels should work effectively for 20 to 25 years after installation before needing replacement. Other parts of the system (such as storage cylinders and pumps) may need replacement in this period.

ST panels can be easily retrofitted to a roof providing the building has a demand for hot water and a hot water distribution system (i.e. not  point-of-use electric water heaters). Adequate, accessible roof space with exposure to the sun is important.

Consideration also needs to be given to roof loadings, the safety of roof access and the avoidance of any compromise of the watertightness of the roof.

Applicable buildings

All buildings with available roof space and where an unshaded north facing orientation can be achieved will benefit from the application of ST  panels. Careful design is required to ensure that the building can use or adequately store the hot water produced otherwise the panels can be damaged.

Floor plate implications


Occupant comfort

No issues.

Maintenance implications

ST panels have relatively low maintenance requirements. Periodic cleaning  is required and a leak inspection and check of pumps should take place every year.


ST panels are likely to be north facing or as close to south-facing as  possible to maximise their output. Panels either have a shiny reflective appearance or are a series of tubes mounted together into a panel formation. There will be insulated water pipework connected to them.

Questions to ask

  • Who owns the ST panels?
  • Who in the building receives the hot water that the ST panels generate?
  • What costs / savings do the panels create for the tenant?
  • More information

References required