paper presented at the 'encuentro solar 2002' in benicarlo, spain in june 2002
the 'solar cr�perie' - promotion of solar cooking by selling pancakes
dr. michael g�tz
the 'solar cr�perie' (solar pancake shop) is a car trailer equipped with different solar cookers and many kitchen tools. it is used every summer in central europe for cooking demonstrations. pancakes are sold at music festivals or ecological fairs and food is cooked for parties and school camps. the kitchen is not as 'user friendly' as initially planned, but with a trained crew it is an impressive tool for the promotion of solar cooking. furthermore, thermal storage elements for evening cooking will be tested this summer.
solar cooking is promoted very often for applications in the developing countries. nevertheless, in europe and in the united states, some organisations and private companies try to convince members of the first world to use solar cookers as well. reasons to do so are the solidarity with poor countries, the general promotion of renewable energies, education in schools - or just the fun of solar cooking. the ulog group has been founded almost 20 years ago to work in two sectors : first, in poor countries to show people how to build and how to use solar cookers and second, to use and promote solar cooking also in europe in order to be credible for the first task ! it is our conviction to only promote technologies which we do use ourselves as well.
2. the idea of the solar pancake shop
how can we inform people about the wonderful possibilities of solar cooking? the most interested come on their own initiative and ask for information. to get in contact with the others, you have to go out and meet them. for years, members of the ulog group have been showing solar cookers at markets and fairs, but they have come to realise that the impact of a table with a few box cookers is not enough and that to truly impress visitors a shiny, big and completely furbished kitchen is needed. in 1997, this dream was finally realised thanks to the help of a german manufacturer of car trailers (koch), globosol, and a lot of voluntary work. a complete kitchen was integrated into such a trailer and since then, the resulting mobile unit is being pulled to any market, festival or fair and set up within an hour or two. in the beginning, the trailer was meant to be rented out without staff - an idea which proofed to be unrealistic as we will show later on. one year later, a second, slightly smaller kitchen was built for use in germany; whilst the first one stays in switzerland for most of the summer.
3. technical details
the main cooking equipment are two scheffler parabolic cookers of 2 m2 each (s140) which stand at the south side of the kitchen. each parabolic cooker has a cooking 'plate' which can be handled from inside the trailer, at a reasonable working height. each one of these cookers has an approximate power of 700 watts . the heat comes from below the pane only, so modern insulated double-wall panes can be used which reduce heat loss and speed up cooking. initially, one cooker had a mechanical clockwork and the other a photovoltaic tracking to compensate the movement of the sun. the mechanical clockwork was a constant source of trouble, as it had a tendency to stop moving... it has been replaced this spring by a photovoltaic tracking as well. nevertheless, we should not forget that this clockwork was of an early generation and today's mechanical clockworks can be as reliable as the solution using photovoltaics. for cooking, panes of up to 12 litres can be used. for baking pancakes, small pancake plates are placed on the parabolic cookers. with full sunshine, the two cookers together can prepare up to 30 pancakes per hour. for baking cakes, cooking stews or keeping food hot, there is a box cooker and an insulated basket as well. there is a small table, a kitchen sink (running water supplied by a footpump), there are kitchen tools, knives and forks, ... the location of the kitchen is very important : first, there should be no shade during as many hours of the day as possible, and second, the trailer must stay east-west, with the two parabolic cookers on its south side. even the position of the waiting clients has to be considered: late in the afternoon, their shadow can be disturbing. the question of where to set up the kitchen has to be discussed early with the organisers of any event.
the solar kitchen has been used for the last few years in switzerland, germany, france and croatia. it is either rented by an ecological organisation (wwf, greenpeace), by the organisers of festivals, or used by members of the ulog group on their own account. pancakes and other dishes have been prepared at ecological fairs, music festivals and school camps. in 2001, we have sold 1000 pancakes, of which 1/3 were prepared by the sun. besides the pancakes, we prepared couscous, chilli con carne, soft cheese with potatoes, curry with rice, coffee and tee, and many other dishes.
a few examples of events where the solar kitchen was in use :
4. impact and problems
of course, the solar kitchen is very much appreciated and truly astonishes people on a bright and sunny day. there is indeed no better way to be convinced by solar cooking than by eating a solar dish! on the other side, on a cloudy day or even more so when it rains, pancakes have to be cooked on a gas stove and the parabolic cookers are then only exposed. on such days, they are often perceived as 'funny toys' or people comment that at least 'in africa, they have sunshine every day'. the setting up of the kitchen takes from 1 to 2 hours even for a trained crew. taking it down is even worse, the two cookers have to be put back into the trailer where they fit by a few centimetres only. this work is done in the evening when everybody is already tired. the initial idea to let people rent the kitchen without staff was therefore abandoned. the actual formula is to rent the kitchen with 'technical staff', i.e. we set up the kitchen, check the function of the parabolas from time to time and help with the cooking. the actual cooking crew, however, is furnished by the organisation which rents the kitchen.
5. is it worth the driving ?
cooking at fairs and festivals is related to many hours of driving. this holds true for solar as well as for conventional attractions. we estimate a typical driving distance of 3 km per cooked pancake. one can ask the question if this doesn't cancel out the ecological gain of a pancake made by solar energy. nevertheless, we think that the promotional effect of our presence at festivals is worth the invested diesel (and we shouldn't forget that we normally replace a conventional food selling trailer which would also do a lot of driving ).
the solar cr�perie in its actual technical set-up is limited to daytime cooking. we often observe that there are rather few clients in the the afternoon, but that there are more and more hungry people after 5 o'clock when the sunshine is getting less intense. we therefore developed a plan to build heat storage elements in order to cook in the evening and to harvest the solar energy of the time when there are no clients. this project was accepted for funding by the energy department of the swiss government and the first storage elements are about ready. (many thanks to the solare br�cke for their help!). one of these elements is using the heat capacity of a metal block (aluminium) to store the heat, the second works with the latent energy of melting tin (at 230�c). the second element should reach its working temperature much more quickly than the first and should work most of the time at a constant temperature of 230�c. both elements are to be tested in july and august of this year.