Useful information about solar energy

Amorphous silicon cells are dark browny red, easy and cheap to make, and are used in solar calculators and watches. However they have one disadvantage – they lose power after 8 or 10 years.

Triple cells are made from three layers of silicon, each layer absorbing a different light frequency. This means that they are better than other types of cells at producing power when it’s cloudy, or when they are partly in shadow. In addition they are cheap. They were an interesting development but you rarely find them. This is because they are also made from amorphous silicon and lose power too quickly, so that they might not even last the promised ten year guarantee period.

Mono and Polycrystalline cells have proved effective over many, many years. Polycrystalline cells have nice shining blue crystal patterns. Monocrystalline cells are plain dark blue and give slightly more power per cm² than polycrystalline cells. However because polycrystalline cells require less energy to produce, they take less time to recoup the energy that goes into their production. Most of the cells here are polycrystalline cells which are the most useful.

Early solar panels were made with plastics containing Fluoride, which is toxic. However today they are made with PVC instead which is recyclable and non toxic. 

It is said that solar cells are ecologically unviable because they require such a large amount of energy to produce.  Information is available that, depending on the methods of production, solar cells will recoup the energy used within 3 to 7 years.

Poly and mono crystalline cells have now been in use for around 40 years. The very early solar panels had some problems with broken back covers, so water or humidity could damage the silicon cells. Plus some old series of AEG solar panels were made with aluminium connectors between the single cells inside the panel which also caused problems after 10 years or so. All modern solar panels use silver connectors and do not have these problems.

Every single silicon plate in the panel increases the voltage of the panel by 0.55V. Every solar cell has more or less this same voltage regardless of its size because the size of the solar cell affects the power in amperes but not in volts. Therefore to create enough tension (volts) to charge batteries it is necessary to connect a series of many solar cells together, with the bottom (+) of each cell connected to the top (-) of the next one. In this way all the volts are added together. For example 36 solar cells will produce 19.8V when the sun is shining on them. This is the voltage required in order for the electricity to flow into the battery, and therefore most solar panels sold are comprised of 36 cells. The solar plates are combined to make large modules behind special glass coated in PVC to protect it from the weather. The frame is made from aluminium or stainless steel. On the back are the plus and minus connections for the wires. In many solar panels there are also one or more diodes which ensure that energy continues to flow into all the solar cells even when some are in shadow. If you connect two or more solar panels together it’s important to separate them with diodes . This is useful if you connect solar panels of different output voltages, like different amount (36 and 40) of cells or anytime when there is more than a 2V difference.

Fix your panels securely and make sure that they are somewhere where shadows (from trees, pylons, etc.) won’t fall on them because the shadow of even a few leaves or bird droppings will cause a considerable loss of power. It’s good to clean your solar panels from time to time to ensure the greatest possible energy from them. In summer you may get more energy than you need so it’s good to fix your panels at the correct angle for the winter sun rather than the summer sun. The panel should be at a right angle to the winter sun. You can find this angle by putting the corner of a book at right angles (90 degrees) to the panel and tilting the panel until the shadow of the book disappears.

For caravans and mobile homes it is easier to keep the panels flat on the roof, otherwise you have to adjust the position of the panel every time you move. When the sun is not shining the panel gives out the most in the flat position. However a good compromise generally seems to be 45 degrees.

In summer the sun makes the panels very hot, and cell temperatures of over 65 degrees C may actually reduce the power by up to 75%! So it’s good to have a gap of at least 3cm beneath the panel and the roof, so that the breeze will be able to take away the heat and keep the panels cool. It can be clever to position mirrors either side of the panels to reflect the light in from different angles. 

Extract taken from “Do it yourself 12 volt solar power” by Michel Daniek.

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