The potential of solar energy is incredible. The sun is classified as an alternative energy resource. That means it will never end. Using the sun as energy resource is booth smart, economical and environmental friendly. Solar heaters does not pollute the environment in any aspects, even the manufacturing process in itself is friendly against the environment.

There are many different kinds of solar heaters on the market. For example the flatplate collector, evacuated heater and the concentrating heater. The heaters vary in booth size efficiency and of course price. To install a solar system in your house can be profitable, at least if you look in a long perspective. Especially since the first of June, when the Swedish government reintroduced the funds for solar panels. In countries with very high and even sun intensity during the year, is it almost foolish to not install a solar system. One of the few disadvantages with solar heaters are that they produces the most energy when we as least need it. In the summer the sun intensity is highest, but the need for energy is very low. But there are actually ways of storing the energy in big tanks from the summer to the need in the winter. The disadvantage is that it is quite expansive.

About 30 years ago the world experienced a major oil crisis. The major oil crisis was the beginning of a new way of energy thinking. People started discussing about alternative energy resources, which would be renewable and environment-friendly. Even though it began 30 years ago, however the fossil fuels are the biggest group of energy resources for producing electricity. But the alternative energy resources are advancing but not as fast as they should do. The incredible low electricity price makes it impossible for alternative energy resources to compete. However in the long run it is the nature that will have to pay the biggest price, if we do not do anything radical

The intensity of the sun's rays that penetrate to the bottom of the atmosphere depends on the clarity of the atmosphere and on the length of their path through it. The energy that is concentrated on a unit area of a particular surface depends upon the intensity of the sun's rays and the angle at which they strike the surface. The maximum intensity for a horizontalsurface occurs at noon at the time of the summer solstice for all latitudes outside of the tropics. For example, the maximum insulation on one square foot of horizontal surface is 93 watts at Ottawa (latitude 45°N) and 88 watts at Winnipeg (latitude 50°N). At the winter solstice the corresponding figures for noon on a clear day are 39 watts and 29 watts respectively. The radiation that falls on vertical surfaces is often of more importance in building design (because of windows) than the radiation on a horizontal surface. The orientation of a wall is an additional variable. A wall facing south at Ottawa receives a daily maximum of 45 Watts/ft² at noon on June 22nd or thereabouts; but at the equinox the daily maximum has increased to 65 watts/ft²; and the yearly maximum may be as high as 100 watts/ft² in winter if there is snow on the ground which reflects some sunshine onto the wall. East and west facing walls, on the other hand, receive their maximum irradiation in the morning and afternoon, respectively, when the sun's rays are almost perpendicular to the wall surface. The annual maximum for east and west facing surfaces at Ottawa is about 75 watts/ft². It occurs at midsummer approximately 4 hours before and after noon respectively (as indicated by a sun-dial). The magnitude of the daily maximum changes very little between midsummer and the equinox, so that the value of 75 Watts/ft² is representative of the daily maximum insolation on east and west facades during the period from April to October.

Different forms of solar thermal technology could be used from small scale to large-scale applications. A small system could be installed, usually on top of a roof, to heat water for each household. A moderate size system could use hot water and steam to warm water which could be used for public facilities, such as, schools and hospitals. Most of the sun’s heat is trapped in solar collectors. Most are a type of boxes which contain a cover to let in the sun’s rays. Then a dark surface is used to absorb most of the rays and collect the heat. A type of insulation is used to keep the heat from escaping while an insulated pipe or vent is used to pipe the heat or water away where it can be used. Most cover materials used are glass. This is a specially designed glass for solar collectors that do not scratch or break easily. This glass is usually well insulated to let the sunlight pass through. The sunlight passes through and is turned into heat. The glass helps to trap this heat. A dark colored material absorbs the heat. This material is usually a metal sheet or a container holding water, rocks, or bricks which are dark in color. Darker colors soak up most of the sunlight while lighter colors reflect the sunlight. After a solar collector traps the heat, vents and pipes move the heat to any location in the house.

There is an active solar heater and a passive solar heater. An active solar heater uses a type of fan or pump to move the heated air or water. A passive solar heater moves the heat without a fan or pump.

An active solar heater would be the flat-plate collector. These are the panels on a roof that collect sunlight. Air or water is passed through the collector and is warmed by the heat that is trapped. It can then be moved to a storage place. Hot water that passes through a collector can then be stored in an well-insulated hot water tank in the home. One example used for storing hot air was to create a space under a house that contains a bin of rocks to store the hot air. The most popular way of using solar energy is to heat water. A collector, storage tank, and sometimes an electric pump make up a solar water heater. There are three types of solar water heater collectors: the flatplate collector, an evacuated-tube collector, and a concentrating collector. The evacuated tube collector is a tube within a tube. The inner tube is covered with a coating to absorb the sunlight but prevents the heat from escaping. Between the outer and inner tube is a vacuum, which also prevents heat from escaping. The concentrating collectors use mirrored surfaces to focus the sun’s energy to an absorber tube. There is an open loop or a direct solar water heater and there is a closed loop, or an indirect solar water heater. Household or portable water is circulated through an open-loop system. A closed-loop system involves using a heat-transfer liquid. An open-loop system circulates household water through collectors. This is an efficient design but has a holdback if using hard or acidic water. This water corrodes the system. These systems are ideal in warmer climates that do not experience much freezing. In mild freezing climates you would have to consider freeze protection. One way to protect from the freezing is to use a recirculation system. This is recommended in areas that go through one or two freezes a year.

A closed-loop system transfers the heated fluids from the collectors to household water stored in tanks. Since a closed-loop system uses a type of antifreeze mixture, a doubled-walled heat exchanger keeps the household water from being contaminated.

A passive design for solar heating is called a batch system. This is a large container that is on the ground or mounted on the roof. It has a glazed side that is directed towards the sun. Besides using solar energy to warm your home or water, another ideal would be to keep once’s home cool from the sun. The sun can cause temperatures to rise indoors. Therefore air conditioning is needed to provide some relief. However the cost of running an air conditioning in the summer can be expensive and it can have a direct and indirect effect on the environment. There are some alternatives to using air conditioning.

A passive cooling design can reduce the running time of an air conditioner. One way to keep the house cool is to keep the heat from building up. Most of this is sunlight that is absorbed by your house. The roof, sidewalls, and windows contribute to this. That is a major source of heat build-up. Another source, which is often overlooked, is running certain appliances, cooking, and air leakage from windows and doors. The color of a house can contribute to the heat build-up. A dark colored home can take in 70% to 90% of radiation. Most of this radiation is turned into heat, which results in the build-up. It is important to remember that a light colored wall reflects more sunlight than a darker colored wall. Most of the unwanted heat comes by the way of your roof. This is hard to control even with today’s roofing materials. Even the lighter colored shingles can take in 70% of the sun’s rays. One solution is to apply a coating that has a reflective property. White latex is a typical coating. Alternatively some coatings may contain glass and aluminum particles. A radiant barrier can be used under your roof to keep out the heat. This is basically an aluminum foil sheet that when it is installed, can reduce the heat intake by about 25%. They can come in a single layer or a vented multilayer which can serve as an insulating barrier. The heat that comes through your windows can account for up to 40% of the build-up. One way to reduce the heat coming through your windows is to use a reflective property on the window. You can put a plastic coating on the window that contain dyes or thin layers of metal. Most coatings are applied to the inside of the window. By having these reflective coatings on your window to cut down on heat it also keeps the interior from fading. The sun-control and combination films are two of the most common types of coatings. Sun-control films block out as much as 80% of the sunlight. This coating is recommended for the warmer climates. This coating while blocking out the sunlight may also reduce the brightness. Combination films let in some heat and light but also prevent the escape of this heat and light. This film is recommended for both hot and cold regions. One thing to keep in mind is not to apply the coatings to windows facing south if you want to use the sunlight in the winter to warm your home.

There are several different kinds of solar heaters, they vary in size, price and efficiency. We will just describe the most common and the most interesting on the market.

The most common one, with a dark absorber kept inside an insulated box. The solar heater looks like a flat box, which contains a dark absorber plate under one or more transparent covers. This is the cheapest and easiest solar heater system. It is a perfect system for house, pools and water heating. How it works: Sunbeams passes easily glass and hits the black absorber, and heat it up. The absorber becomes a temperature about ten degrees above the environment. And according to the thermodynamics second law, heat can only go from a warmer body to a colder body. So the absorber will emit energy to the water in the canals.

Uses the same technique as a magnifying glass (lens), it gathers the sunbeams on one spot. This causes a very high temperature, which you can use fore either melting for example iron or heating up water. A concentrated solar heater looks like a satellite dish, and with help from mirrors you can concentrate the sunrays on one spot.

This model consists of glass-tubes evacuated from air, (vacuum). The absorber is placed inside the tubes, and is with that effective isolated. Which eliminates conductive and convective heat loss.

An evacuated collector produces energy even when the sun is not shining.

How? While the air is withdrawn in the tubes the vacuum prevents the collected heat from streaming out, and at the same time it blocks the cold air outside the tubes. These solar heaters are much more effective but they are also more expensive to buy. But a evacuated solar collector might be a good investment at least if you live in a country where the sunshine is limited.

Here you can see a chart over the sun intensity in Sweden:

You can also combine a flatplate collector with an evacuated to obtain an ultimate system. The big disadvantage is the price, but is very effective.

A project since the beginning of the 80`s in the middle east. You have a quite shallow pond with a black bottom. It is filled with water mixed with salt. The water can get very hot, 70 degrees or above the boiling point. This makes it possible to extract electricity with a turbine. The advantage is that it is a quite cost effective system, but a pond-system requires a very big space.

But it is not so efficient, only about 2 percent of the sunlight are transformed into electricity. But even though the price for the electricity from a pond-system can compete with nuclear power-system.

Clean power source, it does not pollute the environment! Even the manufacturing process

Of the solar heater is very gentle against the environment.

The sun is a great energy resource, and it will never end.

Some solar systems works even if the sun does not shine (evacuated heaters). Which Could be useful in countries like Sweden where the sunshine is limited depending on season. In countries with high and even sun intensity during the year, is it very cost effective to install a solar heater system.

The price! If only the companies could lower the prices…

A solar heater produces most energy when we do not need it, in the summer. But there are ways to store the energy from the summer to the winter.

Today with the incredible low electricity price, is it very hard to get a solar heater system profitable. When you buy a solar heater system you have a very high initial cost, after that you only have to pay very little for technical allowance. The energy you will get for free! And for a family with an average sized house it can be profitable, at least if you look in a long perspective. In countries like Cyprus, Spain and Turkey is it almost foolish to not install some kind of system in your houses.

Money is not the only aspect you have to consider, also the environment is at least as important. We can not keep on exhausting the environment, something have to change And why not start with our choice of energy resources. One day, and quite soon the fossil fuels will end, and then we have no other options then using the alternatives energy resources.

From the first of June the Swedish government reintroduced the allowance for solar system. A person that owns a house is entitled to the allowance. For more information about the allowance please visit boverkets homepge, www.boverket.se

A calculation for an average house with these conditions:

Sunpanel area: 10 m²

The system is written of after 20 Years

Energy production per year: 4200 kWh

Interest: 5 %

Total investment 45 000 SEK

Sun heater components 22 000 SEK

Accumulator tank and expansion container 16 000 SEK

Bought work 7 000 SEK

Yearly interest and repayment by installment 3 600 SEK

Capitalcost per kWh 86 öre

Energycost per kWh 2 öre

Total cost per kWh 88 öre

After that the fonds had been reintroduced:

Total investment 45 000 SEK

Sun heater components 22 000 SEK

Accumulator tank and expansion container 16 000 SEK

Bought work 7 000 SEK

Yearly interest and repayment by installment 3 600 SEK

Fonds -5 000 SEK

Capitalcost per kWh 77,5 öre

Energycost per kWh 1.8 öre

Total cost per kWh 79,3 öre

These numbers can be compared with Vattanfall`s 50,35 öre

Scientists say and have said that solar system will have its big breakthrough in the beginning of the 21:st century.
And why not? , there is very big potential in solar energy. You only have to pay an initial cost fore the equipment, the energy you will get for free. And perhaps that’s where the biggest disadvantage is, the price. But the solar systems are getting less expensive, and more efficiency. And the market for solar energy is growing.

We think that solar energy is really something for the future. And when we say solar energy we mean booth solar cells and panels. Absolutely best is a combination of them together.

Internet: http://www.torget.se/users/c/celander/index.htm

Books: Solvärme i vårt hus, Robert Larson

Larsons förlag 1998

ISBN 91-514-0321-8