CCAT - Solar Heating

Solar Heating
Water heating and space heating require huge amounts of energy. This is usually obtained from natural gas, electricity, or wood, which are resource intensive and pollution causing. The sun's energy can be harnessed for heating on any day that you can see your shadow. There are four main ways to use solar energy for heating: passive water heating, active water heating, passive space heating, and active space heating.

The Golden State of Solar Power
by Nicholas "River" Hume (Fall 2005)

Passive Water Heating
The most effective method of passive water heating uses a plate collector, with a water tank 1 foot higher than the collector (usually on a roof). A plate collector is a shallow rectangular box with copper pipes running up and down inside of it. The top of the box is made of glass and the backing and pipes are painted black. As the sun heats the water in the collector, the water expands and moves up into the tank. This displaces cold water, which flows back into the plate collector. This system, known as a thermal siphon, heats the water in the tank without the use of a pump. As water from the tap or from a pressure tank is forced into the cold inlet of this water tank, hot water is forced out the top. A simpler form of passive water heating is to keep a black barrel of water or a black hose in the sun. The problem with the black tank method is that the water heats up very slowly. With the black hose method, your hot water supply is limited to the volume of water in the hose.

Solar Shower at CCAT
HSU Student Website (Spring 2000)

Active Water Heating
This is the most commonly used type of solar water heating. It is similar to the plate collector method described above, except that the water is pumped between the solar collectors and the storage tank. This allows the tank to be in the house or basement, instead of on the roof. On a long sunny day, a solar water system will probably heat the water as much as needed. On a short or cloudy day, however, a solar water system will only pre-heat the water. Pre-heating saves a lot of energy, but to attain the desired supply of hot water year-round, most solar water systems are backed up with an on-demand water heater. On-demand water heaters heat the water as it is being used, and are much more efficient (and longer lasting) than tank water heaters. In climates with near or below-freezing temperatures, a frost protection system must be incorporated.

Solar Hot Water Heating at CCAT [PDF 70.4KB]
HSU Student Handout by Lisa Murgatroyd

Solar Water Heating System
HSU Student Website by Andy Karnitz (Spring 2002)

Passive Space Heating
This type of space heating is usually accomplished by attaching a greenhouse or sunroom to the sunny side of your house. The air in the greenhouse heats up as the sun shines in, and that heated air rises into your home through windows at the top of the wall. Commonly, the back wall of the greenhouse is made out of rock or brick. This material acts as thermal mass; storing heat as it warms up in the daytime, and releasing this heat at night.

Active Space Heating
The most common type of active solar space heating is radiant floor heating. This is actually a solar water heating system, except that instead of storing the hot water in a tank, the water is pumped through copper pipes that wind back and forth just beneath the floor of your house. The heat from the water dissipates into the air from the copper pipes and rises through the floor. These systems only work well in places with a low proportion of cloudy days.