We are members of the Solar Trade Association who have issued the advice below.

How to get the most from your solar water heating system

The purpose of a solar water heating system (Solar Thermal – ST) is to heat your hot water via the sun. The collectors on your roof or in your garden are designed to absorb the heat from the sun and transfer that heat to your hot water cylinder (or thermal store), so it can be stored for use when the householder uses their hot water taps, showers and baths.

The objective for a householder is allow their ST system to do as much work as possible to heat your hot water, rather than using the back-up heating system (e.g. boiler; immersion heater).  Used effectively, 60% of your annual hot water usage can be met (note 1) – but you need to allow your cylinder to be heated throughout the day from your ST system, and not use your back-up system until the end of the day.  This is how we suggest you achieve that objective:

  1. Set your back-up system to run at the end of the day e.g.  4 or 5pm
  2. Alternatively use the “boost” or “advance” on your heating controls
  3. If you have high water use in the morning, you may need to set your back-up system to run prior to that usage e.g. if 2 house hold members shower from 7am, set the back-up to run at 6am for 1 hour

By following these guidelines, it allows the maximum part of the day to raise the temperature of your cylinder from its lowest point to its highest.

DO NOT heat your cylinder with the backup system during the day.  If your cylinder is heated to 60°C with the backup, your ST system will only heat half your water at best.  Let your ST system do the work!

Heat will be generated during the day when there is light, and is most effective when there is full sunshine.  Most systems are designed so you have enough hot water generated throughout the day to meet your hot water requirements (note 2).  To get the most value from your ST system, you will probably need to change the way you use your existing heating system.  This data sheet is designed to help you to do this.  Firstly here are some water facts:

  Water in your house   Solar Water Heating System
10°C Cold water feed 10c°C to 70°C Possible upgrade in cylinder temp.  on a sunny day
37°C Bath a baby 20-50°C Avg cylinder heat range on a poor, overcast day
39°C Typical adult shower 50-80°C Heat transfer range from the collectors
60°c Maximum 160-240°C Maximum heat in collectors on a sunny day

In summary, even on an overcast day in winter, your ST system will be providing heat, saving you money on running your boiler.

Note 1 – Evidence provided by Energy Saving Trust field trials

Note 2 – In peak winter months, a ST system alone will not be sufficient.  Back up heating will be required

Who are the STA?

Solar Trade Association Logo
Solar Trade Association Logo

For over 30 years, the Solar Trade Association has been the leading voice for solar in the UK.  Established in 1978 as a not-for-profit trade association we represent a diverse membership across the solar power and solar heating industry.  The STA works with its members to achieve the right regulatory framework and incentives for solar to deliver an increasing contribution to the UK’s electricity and heating needs.