Renewable Energy on Ecotopia '93, France

This year, on Ecotopia, there are two systems at display, and they are both used for supplying the camp of energy.

First of all, there is the hot water system, which is used to pre-heat the water for the kitchen, for dish-washing and for showering. Then there is the photo-voltaic system. This system consists of a number of small units, each containing one or more solar panels, a rechargable battery, and a regulator. A description of both systems will follow.

About this booklet

This booklet is written to introduce you to different techniques of less- or non-pollutive, renewable energy. It's aim is to let you realise the possibilities of renewable energy in your own house, village, town, city or area.

If you want, you can attend the workshops that are given on this theme. They will be announced on the publication board.

The question if renewable energy is preferable to other energy sources, is not discussed in this booklet. Neither are related topics like climate change, deforestation, ozone-layer problems, and so on. This booklets gives no information about a strategy to realise renewable energy in your area, nor about legislation or EC-politics. Workshops on this topics will (hopefully) be given during Ecotopia by other people.

This booklet will costs you, due to
printing costs and low-budget,
3 (magic) eco's

Hopefully you will achieve something form reading this booklet, and attend the workshops, so we can stimulate the alternatives...

Ace, Arno, Ruud.
Support Network on Renewable Energy

Solar energy for production of hot water
the basics.

A solar heating system for production of domestic hot water consists of a solar collector connected by a piping system to a water tank (see picture). In the solar collector, the sun's energy is absorbed and transformed to heat by a liquid (usually water) in the solar collector's channels. This liquid transports the heat through a piping system - the solar collector - to the tank, where heat is transferred by a heat exchanger to the domestic water system.

The solar collector

The solar collector is often placed on the roof, but can just as well be situated on a framework placed on the ground. The total area of solar collectors needed for a single family system varies from four to six square meters, depending on consumption, orientation and efficiency of the collectors and the place on the globe. In principle, the collector consists of a black plate containing channels or pipes (the absorber), mounted in a protected, well insulated casing. Normally, the top is covered with single or double glazing, sometimes with transparant plastic. The solar collector liquid circulates in the absorber, which absorbs the heat from plate and pipes, and transfers the heat to the water (storage) tank. The storage tank has to be very well insulated too.

The storage tank

The storage tank contains about 50 liter of water for every square meter of solar collector area. Solar energy (heat) is transferred to the tank by a heat exchanger, which is placed on the bottom of the tank. Cold water enters the tank at the bottom, and heated by the heat exchanger. Since hot water is lighter than cold water, it will rise to the top of the tank. From the top of the tank there are pipes to the shower and water taps. It is possible to put a second heat exchanger in the tank, which takes its heat from a conventional wood, oil, or gas stove. This heat exchanger will only work if the solar collectors can not provide enough hot water, mostly on very cloudy days. This second heat exchanger can also be an electrical heating element.

Circulation of liquid in the system

There are two systems: natural circulation and mechanical circulation.

In a system of natural circulation the tank has to be placed above the collectors. Because hot water rises to the top, there will be a natural circulation to the tank, since the collectors are heating the water. In a mechanical system, a pump is used to circulate the water. The tank may be placed below the collectors.

Temperature control


When mechanical circulation is used, an electronic device is needed to switch the pump on or off. If the water in the solar collector is hotter than that in the tank, the pump will start. If the temperature in the tank is higher, it will stop.

Build it yourself or buy them !

The most simple solar collectors are easy to make. You will find an example at Ecotopia.

More complex systems, consisting of electronic temperature controls, a pump, a well insulated tank, and efficient collectors, are available at special companies, and also in shops that normally install the piping in your house. In some countries, the state gives money to promote the installing of solar colecctor systems.

A pond collector for the shower system at Ecotopia

To produce warm water for showering, there is a so called 'pond' collector. It consists of a hole in the ground, with black plastic in it. The hole is filled with water, and is covered by transparant plastic.

The black plastic functions as the absorber. It catches the heat of the sun and transfers it to the water.

The transparant plastic works as insulation to avoid evaporation. (Evaporation cools the water, just like sweating cools your body.)

The size of the collector is about 1500 liters, but can be varied easily depending on the size of the hole and the amount of plastic available. However, the bigger the amount of water, the slower the water will heat. If you take a very large amount of water (like a lake) the temperature will rise only one or two degrees during the day.

The pond should not be to deep, because the less water you have per square meter of absorber area, the more the temperature of the water will rise.

At Ecotopia, we will fill the pond in the evening. During the day, the water will become hotter. You can't have a hot shower in the morning ! Then, at a certain point, we will open the tap and people can shower with warm water untill the pond is empty.

The dish-washing and kitchen hot water system

The first system ('the dish-washing system') consists of four solar collectors like the ones described earlier, and a 1000 liter storage tank. The system of natural circulation is used.

Water is circulating through the solar collectors, where it is heated, and the tank. The water can rise to 30 or 40 degrees on a sunny day. Since there are no heat exchangers in this system, the water is not drinkable.

The second system uses mechanical circulation. It consists of one big solar collector, a 120 liter storage tank, a pump and a temperature control device.

Like described earlier, water runs through the collector and the tank and is heated by the sun. Inside the tank is a heat exchanger. Cold drinking water runs through the heat exchanger and is heated by the hot water in the tank.

Using the sun to produce electricity

(the photovoltaic system.)

A photovoltaic system consists of three parts: solar panels, rechargable batteries and a regulator. Photovoltaic systems produce electricity directly from light.

The solar panels

Solar panels are made from pure silicium. Almost one-third of the earth is covered with silicium (sand). The proces to purificate the silicium is rather complicated, and uses a lot of energy. If managed badly, it can hurt the environment.

To the pure silicium some impurities are added, to make the electrical process happen. This impurity is mostly a pretty unharmfull chemical element, like borium, and added in super small amounts (a couple of atoms per cubic centimeter). Sometimes however, arsenicum is used, which is poisonous and dangerous as waste.

Light falls on the solar panels, and since light is energy, gives energy to free electrons in the impurified silicium. Those electrons can travel freely then, to transport and loose their (extra) energy at another place, for instance the battery or some electrical tool like a radio or lamp. The electrons return to the impurified silicium, ready to get some new energy from the light that falls on them.

Most solar panels produce 12 Volt, a very safe amount of electricity to work with. However, if you put more panels together, the voltage can get a lot higher (10 panels can produce 120 Volt, which can be dangerous to work with).

The batteries

Storage of electricity is always a problem. For small systems, batteries are used. Most batteries use heavy metals like lead or sink and some acid solution to transfer electricity to chemical energy and the other way around. Nowadays, batteries can be recycled but they are still the most pollutive component of solar electricity.

The regulator

The regulator is an electronic device that protects the batteries from overloading. The regulator also protects the battery from deep-decharching, which is bad for most types of batteries.

The photovoltaic systems at Ecotopia

For most systems, we used panels which produce 55 peak-Watt at 12 Volt.

A peak Watt means, that at maximum solar input, one solar panel can produce that amont of energy. Most time of the day, and on cloudy days, the solar panels produce less than 55 Watt.

Also, we have a convertor, that converts 12 Volt to (normal ?) 220 Volt, so the video and fax and slide projector can work. When you convert electricity, you loose some of it. Inside the video and fax, are converters which convert 220 Volt to 12 or 14 or sometimes 9 Volt. You might see that this is rather a waste of energy, but most shops don't sell electrical appliances that work on 12 Volt. (or they sell it more expensive...) Some Calculations

To imagine how much (or less) energy there is available, you may estimate the average input of the sun during Ecotopia at 4 hours a day maximum input. For one panel of 55 peak-Watt, you can gain 4 x 55 Watt maximum per day.

Maximum input:

number of solar panels x 55 x 4 = ..... Watt per day.

What do we use it for ?

It might be clear that electrical appliances must be build in a way that they use as less energy as possible. A normal refrigerator may use 10 times as much as one with a clever design...

An electrical appliance (like a lamp, radio, drill, computer...) of 5 Watt, working for 4 hours a day, consumes 4 x 5 = 20 Watt a day.

Now make the following calculations:

Amount of power the appliance uses x hours per day = ..... Watt per day.

You can use the following list to calculate:

Lights, used at the camp:5, 10 or 20 Watt each.

Radio: 10 Watt

Cassette deck: 40 Watt

TV (small, no colour): 60 Watt

Big computer: 200 Watt

Laptop computer: 20 Watt

Slide projector: 180 Watt

Pump for solar collectors:100 Watt

Fax: 20 Watt.

(these numbers are not very accurate... all you can get from it is an estimation)


Toilet light: 2 bulbs of 10 Watt, 1 of 5, from 22.00 at night till 8.00 in the morning, total 10 hours:

25 Watt x 10 hours = 250 Watt per night.

Try to make this calculations for the things you see around you. For instance, try to calculate how much energy is used in the ecobar.

Right now, the systems in use are divided as follows:

Ecobar: 4 panels

Office + 220 Volt converter: 5 panels

Bakery, Dish-washing, Path to Ecobar: 3 panels

Path Lighting, Doktor's Lighting, Workshop tent: 2 panels

Path lighting from last camp to small toilets: 2 panels

Toilet lighting and hand wash pump: 3 panels

Yurt (big round green tent) and kitchen: 2 panels

(All panels 55 Watt each, except: Yurt (40 Watt); Toilets (20 Watt)

Other Sources of Renewable Energy

There are many different other sources of renewable energy. Think of the power of water, wind, the waves, the hot springs that come from the inside of the earth in some places. Also, biomass (the combustion of plants instead of coal and gas) and biogas (digestion of organic material) can contribute greatly to renewable energy.

Energy Efficiency

Although renewable energy is an alternative to fossil fuel and nuclear power, it can not be effective if we keep on consuming too big amounts of energy. Energy savings can be reached easily in many fields, ranging from switching of the light when you don't need it to complete energy waste reuse systems in factories.

Overproduction and social structure also contribute to the waste of energy, as well as using certain materials (one-way plastics for instance) do.

Support Network On Renewable Energy (SNORE)
Rijksstraatweg 37-46
The Netherlands
Phone: +31-80-603917