Solar panels
 
There are 2 main types of solar panels which use completely different technologies to make use of the energy from the sun:

* Solar Water Heating collectors: These panels absorbs the energy from the sun and transfer it to heat water.
* Photovoltaic or solar electric panels: These panels transform the solar radiation directly into electricity.

This article is focusing on (PV) Photovoltaic Panels.

Types of PV Panel

The are 3 basic types of construction of PV panels, though they all use silicon, the same material used for transistors and integrated circuits. The silicon is treated or "doped" so that when light strikes it electrons are released, so generating an electric current. I won't geek out too much on the science of pv panels, if you are interested check: http://en.wikipedia.org/wiki/Photovoltaic_module

Polycrystalline Photovoltaic Cell
Polycrystalline (or Multicrystalline) cells are cut from a block of silicon, consisting of a large number of crystals. They have a speckled reflective appearance and you will be able to see the thickness of the slice.

These cells are slightly less efficient and as a consequence, require larger space to provide a given amount of power. The exception is that these panels can be more efficient in extremely hot conditions, such as the desert.
Monocrystalline Photovoltaic Cell
Monocrystalline cells are also a slice, but cut from a single crystal of silicon. In appearance, they have a smooth texture and again you can you see the thickness of the slice.

These are the most efficient, especially in cloudy or low light conditions and so are recommended for UK installations. These panels have the smallest surface area per watt, so are also best where there is limited space.
Amorphous Photovoltaic Cell
Amorphous cells are manufactured by placing a thin film of amorphous (non crystalline) silicon onto a wide choice of surfaces. These are the least efficient and least expensive to produce of the three types. Due to the amorphous nature of the thin layer, it is flexible, and if manufactured on a flexible surface, the whole solar panel can be flexible.

One characteristic of amorphous solar cels is that their power output reduces over time, particularly during the first few months, after which time they are basically stable. The quoted output of an amorphous panel should be that produced after this stabalisation. The circuit is often etched onto the panel as required.

As a further confusion, you can buy flexible panels for traveling which may contain separate crystalline solar units within flaps that fold over each other, such as my first Brunton panel. Most flexible panels however are amorphous type, such as ones designed for yachts.



Buying Panels

I recommend only using crystalline panels. These are made in small units, which are wired in series to produce solar panels. As each cell produces a voltage of between 0.5 and 0.6 Volts, a certain number of these units will be required to produce a given voltage, often rated at 12volts.

It is worth bearing in mind that the standard open voltage of a 12volt panel will be about 21volts, which will be sufficient to charge a 12volt battery. Once within a closed circuit (ie when it's running), the voltage will probably then fluctuate between 13-16volts during the day, depending on the intensity of the sun hitting the panel.

Panels may have up to 80 or more of these small units wired together, making panels that range from 1w to about 350w output. 80watt is a pretty standard size and multiples of these are then chained for any given system.

Since solar panels are expensive, it is important to get them for a good price. If you pay over the odds, it could increase your payback period by years. As a rule of thumb, I have learned to look for panels that are within the £3 - £4 per watt range. If you are buying off ebay, which is a great source for panels, this price should include postage and packing as well.

Once you have paid for them and they are running, they will happily continue to yield electricity for many years (often quoted at 20-25 years). Who knows really how long they will continue to work.

Try and buy panels that come within sturdy frames and under toughened glass. This will minimise damage and help them to last longer.

Setting up your panels

For maximum efficiency, solar panels should be mounted on a south facing roof at a 30° - 40° angle from the horizon, depending on your latitude and the season. Always try and keep them away from any shadows from trees, surrounding buildings or chimneys which may arise at any time of the day.

Making sure that the panels point directly south will increase long term gain. Some solar farms have special mounts that move the panels during the day to always point directly at the sun.
I say this, but my system suffers from lots of shadowing, which does adversely affect performance, but I live in a flat, so it's tough tits.

The output of your panels should then be wired to a charge controller. If you have multiple panels, you must wire them to keep the correct voltage for your charge controller/ batteries. If you wire them in parallel, the voltage will remain the same (or average of their outputs) and the ampage output will increase. If you want to increase the voltage, you can wire them in series (ie + connected to -).

Most smaller systems, up to 500 watts are fine kept at 12volts, however as power output increases above that, the ampages can get very high, which make them more dangerous and require much thicker and more expensive wiring and connections. Most systems above 1000w will wire the panels in parallel to increase voltage. Larger charge controllers often have have switches between 12 and 24v and even 48volts in some. As an example, a 3kilowatt system, suitable for a household would measure 250amps at 12v, 125amps at 24v and 63amps at 48volts.

It is also worth mentioning that whilst you should rate your system for the maximum capacity of your panels, you will very rarely or never get this performance in the real world. I get on average little over half of the rated output of my panels. With better positioning, I guess they may achieve 75% performance on a good day. However if you set your system up to the rated spec, it will ensure that the system is safe.

Please continue for more information about charge controllers >>>


 
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