A diagram of the Steward Wood micro hydro system setup
Building your own renewable energy systems from recycled materials
Merlin Howse of Steward Community Woodland describes how a low impact, sustainable community in a Devon woodland generates its own power
Steward Community Woodland was born five years ago, when a group of us looking to set up a sustainable living and working woodland project bought and moved into Steward Wood on the edge of Dartmoor in Devon. With a need for electrical power but no thoughts of having a connection to the grid, we looked into renewable ways of producing this. Using reclaimed parts from skips and recycling centres has meant that a lot of the systems we have used to produce power, especially in the early years, cost little or nothing to build. It makes so much sense, both financially and in terms of our environment, to Reduce, Reuse, Repair and Recycle.
Bike generators: starting out with human power
Humans provided our first source of power through cycle generators. A person cycles to turn a generator that produces electricity that is either used immediately (the most efficient way) or stored in batteries (which is less efficient but can be more convenient). Our cycle generators were used to power laptop computers on which we created and updated our website and at public events to provide educational entertainment.
We have had three different designs of cycle generator all using reclaimed exercise bikes and permanent magnet (PM) motors. The exercise bikes are easy to get hold of from the local tip but the motors can be a bit trickier to find (one model of Whirlpool washing machine has a good PM motor). The principle of the design is to turn a generator (an old PM motor) with the flywheel of the exercise bike. It is therefore important to get an exercise bike with a good sized flywheel. In our first design, we used friction drive – we mounted a small wheel on the generator and held it tight against the flywheel on the cycle. But this didn't work very well due to slippage. For our later designs, we used a belt drive which worked much better. All you need to do then is take the current from the generator and use it! We produced up to seven amps when charging a 12 volt battery, but four or five amps (50-60 watts) is a far more maintainable average output. It was enough to power a laptop computer and a lot of our website was developed whilst cycling like this! See our website for more details: www.stewardwood.org.
Micro Hydro Power
It didn't take much cycling before I became interested in alternative methods of power production. Fortunately, there are some streams in our woods which flow during the wetter parts of the year. This got us thinking about small scale hydropower.
Hydropower is clean and renewable, and a cheap and reliable source of energy compared to solar and wind power. All that is required is a suitable amount of flowing water.
Our first hydro system was built at no cost using only reclaimed parts. We used an old Stuart Turner brass rotary pump (found at the local recycling centre) to provide the turbine. By forcing water under pressure through the pump it spins the impeller which can in turn rotate the motor. The pump is working in reverse, thereby generating electricity. With some old polypropylene piping, we delivered water to the turbine from 20m (66ft) height.
The generator is one of the PM motors that we had previously used on some of our cycle generators. It took a fair amount of work to modify the shaft of the motor to fix to the pump and to ensure there were no leaks, but the results were worth the effort, drawing less than one litre (2 pints) per second from the stream. This system produced a mere 12 watts of power at an efficiency of less than 10%. But having spent no money on the project this was a good return and kept us in lighting and some computing over the winter of 2000 without having to pedal.
The pump worked fine, but we became frustrated with frequent blockages within the casing. We eventually switched to a 10cm (4in) diameter plastic paddle wheel, previously the cooling fan on the back of a large induction motor. This was turned with a jet of water from the penstock (pipe). It proved to be slightly more efficient than the pump impeller and blockages were less frequent due to the size of the jet.
A Pelton Wheel generator
Having established that it is perfectly possible to use reused pumps or even a simple paddle wheel, we decided to buy a professionally fabricated Pelton Wheel to be able to compare the performance differences. A Pelton Wheel is an impulse turbine in which pairs of cup-shaped buckets are mounted around a wheel. A high-pressure jet of water hits these, causing the rotor to turn.
With grant funding, we were able to purchase a 10cm (4in) diameter bronze cast Pelton Wheel. Having looked unsuccessfully for three years to find secondhand larger diameter pipe, we decided to buy new 150m long x 6cm diameter (500ft x 2in) plastic pipe with some of the remaining grant money. But continuing in the spirit of previous designs, we used a reclaimed valve and mounting for the jet at the bottom, and an onion bag over an old fan housing in a salvaged plastic bath for the filter at the top. The generator we are currently using is also a reclaimed Whirlpool washing machine PM motor.
This new system meant we could double our head (height the water comes down) and minimise friction losses giving us 35-40m (115-130ft) of head and a possible flow much greater than previous systems due to the increased diameter of pipe used. As a result, we can now produce 100 watts without using much more water than in our previous system.
The most we have produced is 300 watts but there have been two problems. Firstly, the generator started overheating, and secondly we weren't using that much power (we were not used to it, you see) and the batteries started over-charging! Also, this system requires quite a lot of water and is only possible at the wettest times of the year. We usually therefore leave it charging at 100 watts using a smaller jet, hence smaller flow.
Crystalline or Amorphous Solar Panels?
Photovoltaic solar panels are not something you can easily knock up in the home workshop! They involve a large industrial manufacturing process, often by a multinational oil company, and they are expensive. They are useful however if other sources of power are not available and they are marginally more sustainable than nuclear or fossil fuel power. We have purchased (again with grant funding) different types of panel in order to compare them in different conditions: Kyocera 80W and 120W polycrystalline panels, a BP 75W monocrystalline, and a 65W amorphous panel. Although they are not the most green of renewable sources of energy, they are very convenient, low maintenance and provide power in summer when the micro-hydro is not operational. Of course, we use much less power in the summer with longer days and less computing and forestry work.
It is early days for making comparisons but we have found that the amorphous panels are generally less efficient, being the biggest and lowest power, but better suited to ambient light (cloud cover). The crystalline panels are much more efficient in direct sunlight. The other advantage of the amorphous panels is that they are much less breakable.
Making a wind turbine
A wind turbine is something you can make yourself in the home workshop and we have experimented with this. The more work put into a generator the more efficient it will be. It is possible to make something very crude that will produce power but may only work in high wind speeds. However, you also have to be careful that it doesn't fall apart in high wind as this could be dangerous. If you are interested in building your own, see Hugh Piggott's home page listed below. Manufactured wind turbines do tend to be efficient. One reason for this is the shaped blades, which are difficult to perfect when made by hand. We do not have any working systems in operation. This is principally due to planning restrictions, but also because of the wind turbulence in a woodland site. We may apply for planning permission to put up a wind turbine in the near future.
Wood gasification is a process where wood is burned in such a way that a flammable gas can be extracted before combustion. This wood gas can then be used either directly for heating or it can be filtered, cooled and fed into a converted petrol engine. The engine can drive machinery, a vehicle (as was common during the fuel shortage of the Second World War) or a generator.
We are currently researching the possibility of using this technology to generate electricity and power forestry machinery such as a sawmill. This means we will be able to use our off cuts and 'waste' wood to power the machinery.
Batteries & Related Control Equipment
In order for these renewable energy systems to be effective, it is necessary to store the power for later use. This process involves using regulators and control equipment to safely put the charge into a battery. Because we feel that batteries are not an environmentally responsible solution and because new batteries are expensive we have chosen to purchase them second-hand. A lot of commercial enterprises replace batteries well before their life expectancy is up which provides the perfect opportunity for anyone to reuse them.
Reducing Energy Consumption
The energy we generate on site is used for domestic lighting and computing, and is now of sufficient quantity to power electric tools for forestry work. The battery voltage is 12 volt and we have a 2 kilowatt inverter that converts the battery voltage to standard 240 volt mains power. With funding from the Woodland Trust, we bought an electric chainsaw. This enables us to demonstrate completely sustainable forestry practice using a combination of hand tools and renewable energy. Unfortunately we are still at the mercy of the weather, and this last season has been so dry that we have found ourselves short of power.
Conservation is the key! Because our power is so limited, we have learned to conserve electrical power to a large degree. With seven adults and four children on site, we use no more than 100 watts of power (that's less than 10 watts each). 100 watts is the amount used by a standard light bulb. We have also managed the project and the woodland using this power. So by remembering to turn off the light in the spare room or exchanging a few bulbs for energy efficient ones, it is possible to conserve as much power as we have! Electric heaters are the biggest users of electricity domestically and we are fortunate enough to have plenty of wood to fuel our heating needs.
All the electricity used in writing this article on my computer and to charge the batteries for the camera to take the photos here was produced using the renewable methods described above. More information about our renewable energy systems is available on our website.
Steward Community Woodland: www.stewardwood.org
Hugh Piggott's wind power pages: www.scoraigwind.co.uk
Evans Engineering micro hydro (suppliers of our Pelton Wheel): www.microhydro.com
Wood gasification information: www.green-trust.org/woodgas.htm
Merlin Howse lives at Steward Community Woodland, an eco-community in a 32 acre mixed woodland on the edge of Dartmoor. If you would like to visit and get involved in this permaculture project there are regular visitor weekends. Call 01647 440 233 or see www.stewardwood.org. The community is hosting a two week residential Permaculture Design Course from 21st August to 4th September taught by Devin Ashwood in association with the WEA.