Solar heating is a means of collecting and storing energy, in the form of heat, harnessed from the sun. A passive solar heating system passively collects and transfers that energy. Skylights and greenhouses are examples of passive solar heating systems because they passively accept solar heat in but do nothing to actively enhance that process. Active solar heating, on the other hand, actively enhances the collection, storage or transfer of that energy. Active solar heating systems use fans and pumps to distribute the collected heat.
The collectors in an active solar heating system are typically made of silicon-based solar cells, also known as photovoltaic cells, which absorb the sun’s light. Solar panels, made up of solar cells, are usually installed on the roof of a home or a building; the larger the number of cells, or size of the panels, the greater the solar radiation.
There are two general types of active solar heating systems. The difference between them is based on the substance that is used to collect and transfer the heat in the solar collector. This substance is usually either liquid or air. Liquid-based systems, also known as hydronics, typically use water or an antifreeze solution to collect and transfer heat. Steam and hot water radiators are one of the oldest forms of hydronic heating systems. Air-based systems typically come in one of two forms — air room heaters or transpired air collectors. Both heat rooms, but do so via different mechanisms.
Whether the solar heating system uses air or liquid, the collectors are usually installed on the roof of a building or home. The stored energy, however, in liquid-based systems is typically housed in the basement or some other lower level location.
Active solar heating systems may be connected to the general power grid and in some cases, if the system produce excess solar energy beyond what a household needs, it may be sold back to the public utility. The goal of an active solar heating system is to heat approximately 40–80 percent of an interior space. Ideally, an active solar system should combine functions—heating air and water—thus enabling the system to work year round.
In abundantly sunny areas, an active solar heating system can greatly supplement electric, propane, or oil derived heat and greatly reduce heating bills. Although installation costs can be high, more and more governmental bodies are offering tax exemptions, credits, and deductions to encourage individuals towards this environmentally-friendly option.