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Solar Hot Water Heating

Solar hot water heating is the process of absorbing the energy from the sun and using it to raise the temperature of water. The principles are very basic and for this reason solar heating is quite inexpensive, especially with the grants that are available from the government. Even in Northern European countries, they can still provide up to 25% of the heating and hot water requirements of a building. Depending on natural gas prices in your area, they will pay for themselves in a short period of time and make you massive savings from then onwards.

How Much of my Hot Water or Heating Can a Solar System Provide?

Depending on where in the world you live, a solar heating system could provide more hot water than you need. In most countries, you could realistically expect to get 50%-75% of your hot water from typical a solar hot water system, given that you will probably not want to completely cover the sunny-side of your roof in solar panels. Even in Northern Europe, it is common for households and businesses to get 15%-25% of their hot water AND central heating energy this way.

Central heating is normally needed during winter, especially during dark mornings. As there is little sunlight during these times, it is usually much more efficient to use the energy for generating hot water. Passive solar heating and ground source heat pump systems are much more efficient techniques for warming your building.

Can Solar Panels be Used to Cool a Building?

Solar systems are being developed that use the evaporation of water as a means of cooling the air in a building. The hot water from a solar panel is used to compress a refrigeration gas to a liquid state. This liquid can then be passed through a heat exchange where it absorbs heat from the air, cooling it just like in a refrigerator. The liquid expands when it absorbs the heat, ready to be compressed again by the hot water for re-use.

So, your solar panel could help you to heat water when you need it to and cool your building during hot weather.

How much do Solar Hot Water Systems Cost?

Prices vary throughout the world, with super-efficient Evacuated Solar Panels in China costing as little as 190 US Dollars, 100 GB Pounds or 160 Euros. This is about 80% cheaper than solar panels sold in the West and over 30 million homes in China now have these panels. They are so effective that they even work during overcast weather and sub-zero temperatures.

What are Solar Panels, or Solar Collectors?

Solar panels, or collectors, are basically large areas of heat-absorbent material with water running through them. If you wear black clothes on a sunny day, you will become much warmer than if you wear white clothes. Solar panels work on the same principle, absorbing sunlight into the panels, where it then turns to heat. This heat is transferred to the water, or heating fluid, by conduction. They are mounted on rooftops (preferably South-facing in the Northern Hemisphere, or North-Facing in the Southern Hemisphere), or on a wall that receives a lot of sun. They work best when angled at about 45 degrees. They are sometimes mounted on stands and can be motorised to track the sun across the sky, so that they are always facing it.

How Does Hot Water from the Solar Panel Reach my Hot Water Tank?

There are several different types of solar hot water systems on the market. These are broadly categorised as Active and Passive. Active systems use pumps to circulate the fluid through the solar collector and the water tank. This requires some power input, often from a small solar electric (Solar PV) panel mounted next to the hot water panels to keep the entire system to zero emissions. Passive systems rely on convection to move the water. The hot water tank is positioned higher than the level of the solar panel. Warm water from the panel rises up through a pipe to the water tank, whilst cooler water sinks down a pipe from bottom of the tank, back into the panel for further heating.

What are the Different Types of Solar Panel?

A solar panel, or solar collector, can take many different forms. The most effective use evacuated (partial vacuum) glass tubes. These consist of two tubes, one inside the other, separated by a partial vacuum to reduce heat loss (rather like a Thermos Flask, or double glazing). The front side is transparent, so that the sunlight can shine directly onto the fluid inside the tubes. The inside surface of the back of the tube is mirrored to reflect sunlight back through the water, so it heats the water twice. These are the most expensive solar collectors available, but they provide more heat than any of the others, even on an overcast day with sub-zero temperatures. They are, however, more fragile than the other types.

Flat collectors are another type of solar panel. They usually use a sheet of metal, covered with a black plastic coating to help the panel absorb heat. Water pipes run along the underside of the metal sheet, collecting the heat and transporting it to the tank. These are less expensive to produce, but not as efficient at trapping heat as evacuated tubes.

Formed plastic collectors are the third type. These are the least expensive and least efficient. They are very basic, often being a series of black plastic pipes exposed to the sun, through which water flows. These are often used to heat the water in swimming pools.

For non-domestic use, large arrays of parabolic collectors can be used to focus sunlight onto a water pipe. Lines and lines of parabolic (almost flattened, U-shaped) mirrors are used to collect sunlight from a wide area and concentrate it onto a pipe running through the mirrors. These are very inexpensive and very effective, but they are not suitable for mounting on a typical roof or sun-facing wall.