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Comparison of types of 'Solar powered' air conditioning.

view of solar powered air conditioning cells

Solar energy has always seemed the ideal power source for air conditioning. After all, the sun is generally shining when the air conditioning load is at a maximum! However as yet they are not available at an affordable price, and most can at best be considered to be solar assisted air conditioners or solar air coolers, not solar air conditioners. We look here at the different types and their strengths and weaknesses and compare them to other energy and greenhouse gas reduction options.

The main approaches which have been tried are:

Photovoltaic Solar Cooling (evaporative cooler based)

Because a well designed evaporative cooler has a very low energy use, it is feasible to power an evaporative cooler completely from the sun using a photovoltaic array (solar cells). A number of different approaches can be taken, but to get most or all of the power from the sun, separate solar cells are located on the roof of the building. Electric power from the cells is then fed to the cooler. Night time operation can be covered either by batteries or by interconnection with mains power.

Advantages of this approach are:

The disadvantages of this approach are:

Currently the best way to implement this approach would be to use a very low energy use evaporative cooler, like the COOLMAX and then purchase a conventional solar power system.

Photovoltaic Solar Cooling (conventional air conditioner based)

In this approach a solar photovoltaic array (solar cells) are connected to what is substantially a conventional air conditioner, (although typically a particularly efficient design is chosen). Because of the enormous power requirement of a conventional air conditioner, all the ones I have seen are actually only solar assist air conditioners. Based on published data, I estimate that generally solar power only contributes about 10-20% of the power used. (Although if an efficient approach is used the energy use might be 30% less than the energy used for a conventional air conditioner.

Advantages of this approach are:

The disadvantages of this approach are:

Solar absorption (or adsorption) Cooling

This uses solar thermal collection to provide the heat for an adsorption or absorption chiller. These chillers work in a similar manner to the old style kerosene fridge or a propane camping fridge, except that you provide the heat with high temperature water from solar collectors, rather than burning kerosene or propane.

Advantages of this approach are:

The disadvantages of this approach are:

Solar A/C using desiccants

Air is dehumidified using a desiccant (think silica gel, although a range of materials, mainly liquids have been tried) The air can then be cooled by evaporating water. Practical systems typically incorporate heat exchangers and other components.

Advantages of this approach are:

The disadvantages of this approach are:

Solar thermal induced ventilation

A "heat chimney" can be used to induce a draft to give ventilation without requiring a fan. The chimney is generally painted black, so it absorbs heat. This heat transfers to the air inside the chimney, which rises due to natural convection. The air is replaced by air drawn from outside, thus ventilating the building. Often this would be used in conjunction with geothermal cooling. In geothermal cooling air is drawn through tubes set in the ground. As the ground is cooler than the outside air in summer, it cools the air in the tubes.

Because wind forces are generally stronger than buoyancy forces, even on what appears to be a still day, effective systems generally also use wind induced suction.

Advantages of this approach are:

The disadvantages of this approach are:

House Taming

'House Taming' is modifying your house and the way you use it, to reduce energy use and greenhouse gas production. Important parts of 'House Taming' are:

Advantages of this approach are:

The disadvantages of this approach are:

To find out more about reducing home energy use, and to do a quiz to help you decide what is the most cost effective thing for you to do, go to House Taming: How to reduce greenhouse gases in comfort.

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