A solar thermal collector that stores heat energy is called a "batch" type system. Other types of solar collector do not store energy but instead use fluid circulation (usually water or an antifreeze solution) to transfer the heat for direct use or storage in an insulated reservoir. Water/glycol has a high and is therefore convenient to handle. The direct is captured using a dark colored surface which absorbs the radiation as heat and conducts it to the transfer fluid. makes a good thermal conductor, especially and . In high performance collectors, a "" is used in which the collector surface is coated with a material having properties of high-absorption and . The selective surface reduces heat-loss caused by infrared radiant from the collector to ambient. Another method of reducing radiant heat-loss employs a transparent window such as clear plastic or plate. Again, materials are the most effective, particularly the type optimized for solar gain. glass or "" (tm) has low-emissivity properties, which may be useful, particularly for solar cooking applications.

As it heats up, thermal losses from the collector itself will reduce its , resulting in increased radiation, primarily infrared. This is countered in two ways. First, a glass plate is placed above the collector plate which will trap the radiated heat within the airspace below it. This exploits the so-called , which is in this case a property of the glass: it readily transmits solar radiation in the visible and ultraviolet spectrum, but does not transmit the lower frequency infrared re-radiation very well. The glass plate also traps air in the space, thus reducing heat losses by convection. The collector housing is also insulated below and laterally to reduce its heat loss. The second way efficiency is improved is by cooling the absorber plate. This is done by ensuring that the coldest available heat transfer fluid is circulated through the absorber, and with a sufficient flow rate. The fluid carries away the absorbed heat, thus cooling the absorber. The warmed fluid leaving the collector is either directly stored, or else passes through a to warm another tank of water, or is used to heat a building directly. The temperature differential across an efficient solar collector is usually only 10 or 20°C. While a large differential may seem impressive, it is in fact an indication of a less efficient design.