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Frequently asked questions

Technical consultant, Jim Milner, answers your queries about the projects featured on It's Not Easy Being Green.


What is biodiesel?

Biodiesel is a biofuel equivalent to petroleum diesel. It's usually produced from vegetable oils, but vegetable oil is not biodiesel.

Biodiesel is less toxic than table salt and more biodegradable than sugar. It's not classed as a flammable liquid.

The technical name for the production of biodiesel from natural oils and fats is transesterification. It's a complicated process, but the main principles are as follows:

  • Vegetable oil is dried to remove any water. The quantity of free fatty acids in the oil is obtained by chemical analysis, so the correct amount of catalyst can be calculated.
  • Next, the oil is heated and mixed with the catalyst (strong base) dissolved in an alcohol. The oil is stirred for approximately two hours, by which time the chemical reaction should be complete.
  • The oil is left to separate. The waste products sink to the bottom and the raw biodiesel floats to the top. The waste products are drained off.
  • Finally, the biodiesel is washed to remove impurities and dried ready for use.

The production of biodiesel is potentially hazardous, but if you're careful, methodical and you thoroughly research the subject before starting, you could make it yourself.

Do I need to modify my vehicle to run on biodiesel?

In theory, no - biodiesel is a direct replacement for petroleum diesel and can even be mixed with it. However, it doesn't perform well in cold conditions and can cause other problems too.

Most vehicles aren't designed to run on biodiesel. For example, some rubber fuel seals used on engines may fail if high concentrations of biodiesel are used. Biodiesel-tolerant ones are available, but these can be expensive to fit.

Some engines aren't suitable at all, so it's best to check with the vehicle manufacturer before using biodiesel.

Is biodiesel easy to store?

Yes, it can be stored in regular fuel containers. To find out how much you're allowed to keep, contact your local environment agency.

For more information on biodiesel, take a look at our Green contacts.

Water wheels

Can you send me the designs for the New House Farm water wheel?

Each wheel must be designed for its particular site. However, the basic design of a water wheel is simple. All you need are good DIY skills and lots of time. Just make sure the angle of the buckets to the radius of the wheel is 114°. There's more information available on the web - just search for 'water wheels'.

The wheel at New House Farm turns too slowly to generate electricity easily, so it's connected to a 44:1 ratio gearbox and then to a permanent magnet alternator. The electricity from the alternator is rectified and stored in a 24v lead-acid battery bank. From here, it's fed to a pure sine inverter, which converts it to mains 240v electricity and feeds it into the house lighting (which isn't connected to the mains from the meter).


Can I build my own wormery?

Yes, you can. A wormery consists of a worm-tight box divided into two sections by gauze - you can use anti-weed barrier available from garden centres. The worms and waste are kept in the top section, and any liquid runs into the lower section.

The top section can be made up of several boxes stacked on top of each other, with holes in the bottom of each one to allow the worms through. The worms start in bottom box and migrate up the stack. When all the worms are in the top section, the lower sections can be emptied. The top box then becomes the bottom, and the process starts again.

For more information on wormeries, take a look at our Green contacts.

Grey water

Is it safe to use the grey water from sinks and baths?

It depends on what the water was used for. Depending on the source, grey water can contain the following:

  • chemicals, from washing detergents, bleach, etc
  • food, from washing up
  • skin cells and other biological waste, from bathing and washing.

Some detergents are biodegradable but may be alkaline, so check carefully. Grey water can also 'go off' quickly, so may not store well.

The technology to solve these problems is available, but it's often expensive or uses lots of energy. Storing and using rainwater is usually easier.

Greenhouse heating

How does the greenhouse heating system work?

During the day, hot air from the top of the greenhouse is sucked by a fan down a pipe and into a hole in the ground. The hole should be filled with something that absorbs heat - rocks and stones are most common. There must be enough gaps to let the air through easily.

At night, when the temperature in the greenhouse drops, cool air is sucked down the pipe and blown on to the warm rocks. These warm the air, which then passes back into the greenhouse to heat it. This simple system has also been used to heat conservatories.

The fan can be powered by solar panel, and a battery so the fan continues to work at night.

Solar water heating

Can you get a solar water heating system for under £1,000?

Basically, yes. For less than £1,000 you can buy:

1 x 20 evacuated tube roof panel
1 x 150 litre domestic solar hot water tank
1 x water pump
1 x solar hot water controller

This isn't a home-made system and can be bought by anyone. Evacuated tubes are the most efficient method of water heating compared with other systems, such as flat panels made from copper or plastic.

What you don't get for your money is fitting, a plumber and any associated pipe work or electrics. But if you're good at DIY, there's no reason you shouldn't be able to fit the system yourself.

This system should be enough for two adults and two children, but remember no two households are the same.

For more information on green living, visit Green contacts.

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