Solar Heating Technologies

Buildings require heat for a variety of purposes, from space heating to hot water. While some of this heat can be provided through passive solar design, additional heat is usually needed in cold weather, and is needed year-round to provide hot water on demand.

Solar heating technologies can provide this more intense heat. Solar heating systems are based around a material that absorbs the energy carried by sunlight and releases it in the form of heat. This heat is then transferred to air or water which can be used immediately or stored in its heated state until needed.

Small-Scale Water Heating

Water heating in residential and commercial buildings is a common application for solar heating technologies. Solar hot water systems are installed directly on or next to a building and connected to its plumbing system to provide hot water on demand. Two types of solar heaters can be used in this way.

The first is called a flat plate collector, which pumps water through a series of pipes enclosed in an insulated box with a glass panel on one side. When sunlight passes through the glass, its energy is absorbed in the pipes, producing heat. Because the pipes are enclosed, most of their heat is retained and transferred to the water moving through them. This heated water then moves on to a separate storage tank where it retains its heat and is pumped into the building as needed.

A second type of solar water heater is called a batch collector, or more formally, an integral collector storage system, because it combines its collector and storage aspects in one device. In this system, the pipes used in a flat plate collector are replaced with the storage tank itself, still enclosed with a glass cover. One side of the tank is glazed to absorb higher levels of solar energy, which it transfers as heat to the water stored inside.

Each solar hot water system has its advantages and disadvantages. As they combine multiple components in one device, batch collectors are typically more efficient and cost-effective. But in colder climates, flat plate collectors can be preferable since most of their components can be stored inside the building, protecting against freezing temperatures in the winter.

Small-Scale Space Heating

A variation on the flat-plate collector is typically used for space heating. Instead of pipes, a heat-absorbing plate is installed in an insulated box. Solar energy entering the box is absorbed by the plate which releases heat back into the box. Air is then blown or pumped through the box to be heated as it passes over the plate. This heated air is then pumped directly into the building as needed.

A transpired air collector, another solar technology used for space heating, also depends on an absorbent metal plate to capture sunlight and heat air, but draws the air through holes in the plate itself instead of blowing air over the plate in an enclosed box. This technology allows far more heat to be transferred to the air and, as it requires fewer components, is more cost-effective than most flat-plate systems.

Solar Cooling and Refrigeration

Heat generated by solar panels can be used to power cooling systems. In fact, solar heaters match up well with a building’s cooling needs, because they produce more energy in the summer when air cooling needs are highest.

Standard cooling devices depend on heat to separate a mixture of an absorbent and refrigerant fluid. The refrigerant is then rapidly condensed and evaporated to create the cooling effect in an air conditioner or refrigerator. In a solar cooling application, solar heating technologies simply replace electricity as the source of heat.

The two technologies powerful enough for use in solar cooling applications are evacuated tube collectors and concentrating collectors. Both are also used in large-scale commercial and industrial heating applications, as seen below.

Large-Scale Commercial and Industrial Heating

Two other solar technologies can provide high levels of heat for use in commercial and industrial applications. The first is an evacuated tube collector, which uses a series of glass tubes, each attached to a strip of absorbent material. When the tubes are manufactured, the air is evacuated from them, allowing them to transfer heat more efficiently. During use, the absorbent strips transform solar energy into heat, which is captured and transferred by the evacuated tubes with minimal loss of heat. While these systems are very efficient and powerful, their manufacturing process significantly increases their costs.

Another solar heating technology that can produce more intense heat is a concentrating collector, or parabolic trough collector, which relies on a trough-shaped mirror that reflects sunlight onto a tube in the center of the trough. This tube receives intense energy and produces a large amount of heat.

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