Solar Thermal Panels

Solar thermal panels simply collect the heat energy from the sun and convert this directly into heat for hot water and heating. Therefore when the intensity of the sun us greater more free energy is produced. Panels tend to be installed on the roof of buildings but in some case on the ground mounted on frames at an angle.

How does it work and are they efficient?

Radiant emittance is the power per unit radiated by a surface. This is measured in watts per metre squared (W/m2).  The intensity of the sun’s rays to earth varies in different weather conditions (see table below).

Sun’s radiance

Weather conditions Radiant  emittance (approx)
Clear summers day 1000 W/m2
Partly cloudy day 600 W/m2
Overcast day 300 W/m2
Heavily overcast 100 W/m2

The solar panel will use a percentage of the heat available on a particular day. The percentage used is dependent of 4 key factors to achieve maximum efficiency (applicable to the UK):

  • The gradient of the solar panel (30⁰-50⁰ horizontal)
  • The direction the panel is facing (south in the UK)
  • Shading (away from trees , surrounding buildings and chimneys)
  • The solar panel efficiency

Solar panels efficiency varies from one manufacturer to another. A solar panel that produces 3 kw would heat up 250 litres of water from 5-55⁰ in approximately 5 hours.

A central thermostat linked in with a controller continuously reads and compares the temperature of the panel and the water at the base of the cylinder. If the panel is hotter that the water at the base of the cylinder the controller sends a signal to the circulating pump to turn on. Solar grade anti-freeze is then circulated through the collector and the cylinder heat exchanger (coil), resulting in the water in the cylinder being heated.

Requires little maintenance
No fuel costs
Clean energy
Low running cost in comparison to fossil fuels
Potential to make money via RHI
Potential to save money on energy bills
Dependent of sunlight conditions
Must have a back up heat source incase solar panels do not cover demand due to poor sunlight.
Unattractive to some people