We love our solar thermal panels and have been blown away by their performance. They were commissioned in late winter this year, so we have been able to monitor their output through the dull, cool spring and sunny, warm summer.
(Technical details: Worcester Solar Lifestyle 2 Panel Retro-fit Solar System. Bosch Thermotechnology Ltd. Total capacity 2.2 kW. System filled with glycol.)
An air-to-water heat pump acts as the secondary heat source and also provides on-demand heating when necessary.
- Cold water feeds into the bottom of the cylinder
- During daylight hours heat is generated by the solar thermal panels and is used to warm the water via a coil in the lower part of the tank.
- The heated water rises within the tank.
- By the end of the day the thermal panels have heated the water throughout the tank.
- On cold, grey winter days the water is generally heated to between 20-40°C (depending on the starting temperature and the number of hours of sunlight that day).
- On clear sunny, summer days, the water is heated to 70°C, which is the maximum allowed by the system.
- The heat pump is controlled by a timer, and comes on after sunset, if supplementary heating is required. The fluid in the heat pump circuit flows through a coil in the upper part of the cylinder, to raise the temperature to 55°C. This is a comfortable temperature for baths, showers, etc. Once a week a 65°C pasteurisation cycle is run to prevent legionella infection.
Since late winter we have barely needed the heat pump. The solar thermal panels have harvested energy from the sun to provide almost all of the heat for our hot water. Even on overcast days, the solar thermal panels have contributed some heat, so the pump has never had to heat the water from “cold”. Those two little panels have heated 250 litres of water to over 60°C almost every day for the last 3 months – amazing!!