Type of Solar Panel

Solar panels designed to absorb and retain the heat from the sun’s rays can be made up of either flat plates or evacuated tube collectors.

• Flat plates are most common and tend to be cheaper but need more surface area than evacuated tube collectors. They use dark absorber plates, protected by clear covers, to retain the heat most effectively. Flat plate systems have an efficiency of around 30% and are cheaper to install.
• Evacuated tube collectors have glass tubes which have air evacuated around the pipes containing the fluid to be heated. This makes evacuated tube collectors more efficient as heat loss by convection is almost totally eliminated. Evacuated tube collectors tend to need less area and have an efficiency of approximately 40%, but can be more expensive.

Active or Passive System

The fluid in the solar thermal system can either be moved by a pump or be allowed to flow naturally. In a passive system the water moves by natural convective flows. In an active system the heated fluid is transferred to the hot water cylinder by a pump. Active systems are usually easier to fit but are often more expensive due to the need to install a pump.

Open or Closed Loop

The collector panels can either directly heat the water that is used in the hot water system (i.e. comes out of the hot tap) or they can heat an intermediary fluid, which then transfers heat to the water.

Open systems heat the hot water directly whilst closed systems use an intermediary fluid and a heat exchange system. Closed systems are most suitable for areas that have periods of freezing weather, as the liquid in the external part of the system can contain anti-freeze.