How Well Does Solar Heating Work? The Advantages and Disadvantages of Solar Heating Systems

Solar radiation warms our oceans, creates our climate and grows our food. The sun delivers more solar energy to the earth in one hour than the entire world uses in one year. Modern technology is making it easier and more efficient to harness this unlimited source of heat. But how well does solar heating work?

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Solar heating is not the same as solar power. Both harness the heat and light from the sun, but solar power is the electricity that is generated from:

Solar cells, made out of semiconductor material (photovoltaic cells); or
From heating water to produce steam to turn a turbine and generator.

Solar heating simply takes the heat energy of the sun and transfers it to somewhere more useful, like your living room or throughout an entire building.

Architecture

We all know that a room in full sunlight gets hot. For centuries, humans have taken advantage of this free heat by constructing buildings to gather (or shield) the sun's rays. A well-thought-out design of a building and its surroundings can maximize the benefits to our indoor environments. For instance, in northern latitudes, solar heating works well when windows are placed on south-facing walls. Radiant heat is absorbed by objects in the room which then warms the indoor air.

Building Materials

Building materials can also be used to heat an indoor environment. In hot climate zones, homes are built with concrete walls. During the day, the rock absorbs solar energy and keeps the inside dwelling cool. At night, the warmed surface radiates the stored heat and releases into the home. It's a simple and elegant heating cycle that's virtually maintenance free.

Solar Heating Systems

Solar heating can efficiently supplement other primary residential heating systems. Large, dark surfaces will warm the surrounding air which can then be distributed throughout a building. Proper ventilation, such as a simple fan, will draw cooler air over the solar collector thus, keeping the cycle going. As long as the sun is shining, free heat can be drawn from the solar collector.

Advantages of Solar Heating

Sunshine is plentiful and free.
Easy to maintain. Once proper planning and construction is complete, solar heating is virtually maintenance free.

Disadvantages of Solar Heating:

Sunshine is not always available (i.e. at night or with overcast skies). Because of this, solar heating systems may only be sufficient to supplement other primary heating sources.
Solar energy innovation is advancing quite rapidly, especially around materials and heat storage systems. However, they are currently quite expensive (this is one reason why there is often a lack of support for solar power, despite its environmentally-friendly reputation).
Buildings that take advantage of solar heat require large surface areas such as roofs to collect enough solar radiation. Esthetics must be properly integrated into the design.

How much energy is received from the sun^[1]?

Approximately 174 PW of solar radiation enters the earth's atmosphere every year (1 PW = 1012 kW) and here's where it goes.

6% is immediately reflected by the atmosphere.
16% is absorbed by the atmosphere.
20% is reflected by the clouds.
3% is absorbed by the clouds.
4% is reflected by the light colored surfaces on the earth (i.e. deserts, snow).
51% is temporarily absorbed by the land and ocean. About 3/4 of it is radiated back to space, especially during the night. The rest is absorbed by the air, ground and plants.

References:
^[1] http://education.gsfc.nasa.gov/experimental/all98invProject.Site/Pages/trl/inv2-1.abstract.html