Passive solar water heating systems

experiential explanation of passive solar water heating

A simple way to passively heat water with the sun:

paint a container or bucket black,
pour water into it,
put it out in the sunlight,
wait a few hours..

..presto! Free hot water, compliments of Ra, the ancient Egyptian Sun God. The bucket system is a "passive" system because it does not use any moving parts or electricity.

scientific explanation

Photons radiating from the sun reach the bucket's surface and are absorbed by molecules at the surface. As molecules absorb light, the energy is converted to angular momentum --making the molecules move and rotate faster. We observe the faster motion as an increase in heat. Heat travels as the energy in the motion is transfered to other nearby molecules as molecules bounce into each other --faster molecules tend to transfer some of their energy to their slower (cooler) neighbors. In this way, some of the heat from the bucket travels to the water. The transfer of heat is called thermal conduction and obeys the laws of thermodynamics[1] including the law of conservation of energy[2], not to be confused with human-legislated conservation laws[3]. For more on this, follow these links:

hot water from the sun

We enjoy hot water for washing hot showers and loosening grit and grime from our skin, clothes, dishes, floors and pets, and increasing ambient temperature in a home, shelter, pool or spa. Heat from the sun is heat from nature. There is an emotional warming component of solar heat not found with heat generated from alternate sources and ultimately indirect solar.

batch collectors

Passive "Batch" collectors are a more sophisticated form of the bucket example. The collectors are coated with a dark, absorbent surface. Each collector consists of an insulated metal box, covered with a solar glass or glazing material, and containing a tank of sorts that is larger than a bucket and holds water. Usually batch collectors are filled with pressurized water.

strengths

Batch collectors operate without the need of "active" pumps or controls, so they don't need much maintenance. Also, because they don't have any automatically moving parts, they can be the least expensive system to purchase, build, and maintain.

weaknesses

Batch collectors are not as efficient as "active" collector systems. Also, batch collectors should be installed only where freezing is not a problem, because the water pipes that feed the batch collectors (and the storage tanks) are prone to freeze damage. Owner participation is usually required to prevent freeze damage, by manually draining the batch collector during near freezing weather conditions. Draining the water can be awkward, because water weighs about 8 pounds a gallon, and collectors usually have a capacity over 50 gallons each. A 50 gallon collector's water would weigh over 400 pounds.

Passive water heating systems in the catalog

DekkaSupply.com > Solar and Radiant Hydronic Heating > Passive systems and modules

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