Coll The Coll Magazine

Article by J.L. D. (2000)

Alternative Technology - is there a place for it on Coll?

You might well guess from the question posed by the title that I would answer yes, otherwise there would be no point in writing this piece. So what do we mean by Alternative Technology?

Well in essence it has come to mean taking a step back from the way mainstream civilisation performs certain tasks & adopting practices deemed to be a bit more rudimentary. I should think most people have heard the words & might even guess that wind & solar energy come into the equation but alternative technology also embraces other things too. Whilst the wind can be harnessed for the production of electricity or for pumping water & the sun too can produce electricity & heat water, there are other technologies, such as biomass production for fuel, reed beds for sewage treatment & even alternatives to the modern water closet (WC).

This magazine is not the forum for a deeply technical discussion on these topics but it's not a bad place for an article pitched at a more general level, particularly when it is pertinent to what some of us who live here get up to. Fear not, I shall spare you my complex analysis & equations regarding the aerodynamics surrounding the design of a wind turbine blade but I shall general nature where appropriate. Make of it what you will.

Solar Power

Coll, it is said, is one of the sunniest places in Britain. For those of us living here it may not always seem like it as the sun's heat may frequently be tempered by a strong wind blowing at the same time. Nevertheless, the sun's energy can be harnessed in a variety of ways - to generate electricity & to heat water. The sun radiates a massive amount of energy to space & the earth intercepts about 80,000 million watts. Around one fifth of this falls on land & is itself about 1500 times the total world energy demand. On a clear bright day Britain receives about 1 kW per square metre (for reference, 1 kW = 1000 watts = the rating of my toaster). To generate electricity, solar modules can be used. These are modern semiconductor devices (also known as photovoltaics) built up into larger units & then connected to give the required current or voltage to meet the system design. They do not in themselves generate electricity in the same form as the household mains supply, but lend themselves to charging & storing electrical energy in batteries. A converter (known as an inverter) can then be used to change the voltage to match that of the normal domestic supply so that conventional household appliances can be used. Solar modules combine very well with wind turbines to make a combined wind/solar small scale system. Such is the set-up I have built here on my patch & I'll give more details when I mention wind power.

The biggest gremlin with solar electricity is the cost, about 6 per watt. Solar modules (sometimes called panels) are expensive & at present their efficiency is low, typically only 15% at best. Even so, if you are keen then Coll seems a good place to be for sunlight.

Heating water is another way of utilising the received solar energy & is done with one or more solar panels. Here now is a real chance of achieving cost effective results if you DIY. Commercial solar panels are expensive & it may take many years to recover your costs, but it is comparatively easy to make your own. The panel itself is just a hollow receptacle through which water is passed. The water is heated by the sun & the heated water flows to the household hot water cylinder. The panel can be made from a central heating radiator (of a certain type such as those made by ' Stelrad'). As the radiators are now working in reverse & not radiating at all, we should really call them absorbers or collectors. Each collector is painted matt black & is housed in a simple wooden box only slightly larger than the collector itself. Underneath the collector is insulation to prevent heat loss & the top of the box is covered with a sheet of glass. The collector is essentially housed in its own mini greenhouse. By arranging for the solar panels to face sky-wards & to be at a lower elevation than the main hot water cylinder, the water heated by the panels will naturally circulate up to the hot water cylinder where it will transfer its heat gained from the sun to the household hot water. This is a process known as thermo-siphoning & requires no pumps or valves thereby simplifying the installation. Such a set-up is normally used in conjunction with other methods of heating water & might save 40% to 60% of the fuel usually used. A rough guide for a 'typical' family house might be to provide about 5 square metres of collector area, less for a small household. Modest woodworking & plumbing skills are all that is needed & if you can source some second hand radiators for the panels then the cost can be minimal too.

Wind power

First a few facts. The wind is a naturally occurring flow of energy, powered by the heat of the sun. The total power represented by the movement of air around the planet at any one time is enormous - far in excess of the total power demands of all mankind. If we harnessed 0.05% of that energy then we would have more than the human race currently uses. Food for thought........

Something little known by the layperson is the relationship between the power available in the wind & the change in windspeed. You could be forgiven for thinking that by doubling the windspeed you would get twice the power from it. Not so. The power available from the wind varies as the 'cube' of the change in windspeed, i.e., doubling the windspeed gives 8 times the power. A 100 mph wind has 1000 times the available power of a 10 mph wind. Now you know why it is such a destructive force. Historically wind was often used for grinding corn & pumping water. Today, pumping water is still an option & a wind pump is something I have planned in order to extract water from my well. More commonplace nowadays are wind turbines for generating electricity. It is not beyond the scope of the keen amateur mechanic to build a wind turbine from scratch & I have two of my own design built many years ago ready to erect here on Coll. Blade design for the rotor, & the electrical characteristics of the generator can all be encompassed in a set of equations which with simple workshop facilities & modest DIY skills can yield a good machine. Off the shelf commercial wind turbines can be bought & a system put together as an alternative to home construction. I have a mixture of my own & commercial machines. Four are mounted on the roof of one of my outbuildings along with two solar modules. Three of the turbines give a peak power output of 500 watts each (i.e. 1.5kW total) & the fourth just 100 watts. The solar modules have a peak output of 100 watts too. This set-up first charges a small bank of 12 volt batteries to store energy for when the wind is not blowing. When the batteries are fully charged the surplus power is then fed into the house where it is dumped into heaters such as oil filled radiators thereby warming parts of the house. This is achieved by converting the 12 volts from the turbines & batteries up to 240 volts first. It also means that in the event of a power cut on the island, I can run other household loads from my wind/solar set-up. Priority is given to the freezer but lighting & the TV etc can also be used as normal. Given the nature of the sometimes relentless winter winds here it seems a shame not to put it to good use. The key to success with wind turbines on Coll is to over-engineer them. Solidly built with plenty of guylines on the masts, plus the ability of the turbine to turn out of the wind as the speed rises should ensure success & make them storm-proof. Small scale systems such as mine are not prohibitively large either, with rotor diameters of around 1.5 to 2.5 metres. When the winter wind is howling outside, there is something rewarding about the fact that the electric blanket on the bed is being warmed by it. If I were renovating a remote dwelling I would give serious consideration to a small scale wind/solar system for all my electrical needs as an alternative to paying for connection to the island mains supply.


Energy stored in the tissues of living plants & animals is collectively known as biomass. Biomass materials used as fuel are known as biofuels. As Coll is largely treeless, a regular supply of logs for the fire is hard to come by. I am trialling 4 or 5 varieties of willow which if I am successful in establishing under the rather harsh conditions here can be coppiced on a 3 to 5 year cycle in the future. Willow is a good candidate for biomass as certain varieties can show exceptional growth in good conditions, sometimes as much as 8 feet a year. It's early days yet but two of the varieties have got off to a good start. If successful, then the logs can be burnt in combination with peat & cut out the cost of buying in fuel. Planted around the house, the plantation will provide the additional benefits of enhancing the habitat available to wildlife plus acting as a windbreak for the garden. For those interested, the two varieties that have shown the greatest promise so far are:

1) Salix Viminalis ' Bowles hybrid' (a hybrid of the common osier)

2) Salix x dasyclados

The above topics are those that I am already involved in or that I am planning. I mentioned in the introduction two others, namely, reed beds for sewage treatment & dry composting toilets. Whilst I have a variety of text books on these subjects I have no specific plans for their implementation & therefore do not feel qualified to comment - yet.

Watch this space

Images associated with this article:-

Three out of four turbines & two solar panels on the shed roof

Wind turbine on test

The key to success with wind turbines on Coll is to over-engineer them!
Coll Magazine - Article by J.L. D.

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