This guide to solar power is taken from How to Live Off-Grid: Journeys Outside the System by Nick Rosen. You can buy the book here.
The age of solar power is fast approaching, but its not quite here yet. Cost and efficiency are improving all the time, but not fast enough for our liking. The wearable solar panel pictured is expensive as a phone charger, but still cheap as a fashion item.
There are three kinds of solar panel, based on the way the silicon is cut. The first is monocrystalline. That is the most expensive and the most efficient (at 15 per cent) at converting the sun�s rays into energy. The second is polycrystalline, which, as its name suggests, is the combination of more than one slice of crystal; it�s 13 per cent efficient. And the least expensive and efficient (at 9 per cent) is called amorphous. There is an exception to this rule: in conditions of low sunlight, such as prevail in the UK for most of the year, amorphous is as efficient as monocrystalline. I would still recommend the more expensive panel, though, as it will charge your battery faster when it is sunny.
The active ingredient in solar panels, the cell that converts sunlight into electricity, is made from silicon, the second most common element after oxygen. Ironically, there will be a world shortage of solar cells (and, consequently, high prices) until at least 2009 due to production bottlenecks. Manufacturers like Nanosolar are developing new technologies that require less silicon by cutting silicon wafers more thinly, but that will not increase supply in the short term. Shell Solar has a different solution. It is banking on a variant based on copper indium di-selinide (CIS). In 2008, expect to see a new generation of solar panels which have mirrors to concentrate the sun�s rays and are up to 25 per cent efficient.
For a basic 12V kit like the one on my bus, with one 50W panel, but two heavy-duty batteries so that you can always have one of them fully charged, the cost would be as follows:
PRICE LIST IN STERLING (ADD 25% TO GET THE PRICE IN DOLLARS)
50 Watt panel �243.44
two batteries �199.00
very basic regulator �18.09
4mm copper cable �50
two cigarette lighter sockets from Maplins �3.98
cheap inverter (for occasional 240V use) �30
(figures from Raisystems at Townhead)
So you can get started with a basic system that will power your phone charger, computer and car stereo most of the year for around �550. As you add more or bigger panels, and more batteries, the price, naturally, rises accordingly. Piet Defoe at Townhead reckons that a typical small domestic set-up for solar panels might be 4 � 85W panels costing �1,544.80 (including VAT) plus a regulator (�25 to �80) and an 800W pure sinewave inverter at �621.25. The installation, assuming a straightforward job, would cost about �400 and the batteries would be extra, perhaps �350 for four mid-range batteries. So, a total cost of about �3,000. This would provide power for lights, computers, TV and the like for nine months of the year, though it won�t do washing machines with heaters, storage heaters, electric kettles or immersion heaters. (For the coldest, darkest three months of the year, from early November to late January, a small wind turbine, or a micro hydro if you have flowing water, would be needed to supplement the solar.)
Once you have decided to go for a solar panel (or panels) you must decide exactly where to site it. You need to place it at the correct angle so as to maximise the solar power input, which will mean finding True South � not to be confused with Magnetic South (in Australia, replace �South� with �North�). The first thing you need is your latitude and longitude. I have a GPS reader on my Suunto watch but not a clue how to make it work, and the Suunto office were of little help when I asked them. But there is another way, if you have Internet access (I am grateful to Steve Spence of the Green Trust for the following instructions). Go to http://www.astro.com/cgi-bin/atlw3/aq.cgi?lang=e, enter your country and town, or even district, and the calculator will give you your latitude and longitude. Now click over to http://www.geocities.com/senol_gulgonul/sun/, type in your longitude and latitude in the space provided, and this web tool will give you your solar noon time (which was 11.44 in the morning on the day I happened to try it). Go outside and hold a stick at a ninety-degree angle to the ground. The shadow cast by the stick at your solar noon is a direct line from True South to True North. This is the direction in which your panel should be pointing for maximum solar power.
Now you need to find out the angle of tilt. This makes a huge difference through the year as the sun�s angle to the earth changes wildly with the seasons. Click over to the Wattsun website, http://www.wattsun.com/resources/calculators/photovoltaic_tilt.html, and enter just your latitude number. You will get a table showing each month, the sun�s angle to the earth, and the degree of tilt you need to maximise your solar absorption. You will have to adjust the tilt through the year, and you can also manually change the direction in which the panel is pointing through the day if you have time. The technology exists to change the tilt and track the sun automatically, but you end up dealing with fiddly machinery that itself needs electric power to run. Clive Menhenett from Magrec showed me a �sun-tracker� at Big Green, and it worked fine, but in the end it may be simpler and easier just to move the panel yourself from time to time. It depends how busy or lazy you are and how crucial it is to maximise the efficiency of your panel.
For sun charts, declination maps and an inclinometer (complete kit), visit http://www.jshow.com/sunkit/listings/6.html.
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