Cooking with Solar

Solar Facts

  • During one day, the sun sends 10.000 to 15.000 times more energy onto the earth than we use.
  • Each year, some 2 billion tons of wood are "energetically utilised", which means burned, mainly for cooking purposes
  • Fuel wood accounts for 15-18% of global primary energy consumption, more than nuclear energy and hydropower combined
  • Today, over 2 billion people in the world suffer from a firewood shortage
  • Based on a one-year long field test, an average family in Southern Africa can save 30 litres of kerosene, 30 kg of LPG (Liquid Paraffin Gas) and almost a ton of firewood per year by using a solar cooker.
  • This means an estimated CO2 reduction of 1 ton/year per solar stove (average, 40% solar stove use p.a.)

Reprinted with permission from Sunfire.

Solar Cooking Bread

Analisa baked some bread with 3 different solar cookers and the gas oven.

Both the solar oven and the parabolic dish produced a better result than the gas oven. The solar oven was probably slowed down by opening the lid and letting the heat out to check the bread on a number of occasions.

Whereas the camp oven used in conjunction with the parabolic dish stayed extremely hot whilst checking the bread and would have returned to its original cooking temperature very quickly once the dish was refocused.

Following are the results.

Baking Wholemeal Bread starting at 10:15 amGas Oven on a high shelf set at 200C1 hour slightly burnt crustSolar Oven5 hours retained more moistureParabolic Dish3 hours slightly drier bread than from solar oven

In order to check on the cooking the parabolic dish was swung out of focus to make it safer to work with because any cloth used to lift the lid or any items of clothing, such as shirt sleeves could quickly go up in flame. There is also a risk of burning yourself (as with any stove) if you do not exercise care. Children should not be left unattended near it

Sunny Days

The last time that Analisa baked bread on the parabolic solar cooker, it was ready in an hour. She has also successfully used both the box cooker and the parabolic cooker as food driers. She placed sliced banana on S/S mesh inside the box cooker with the glass lifted a bit to let the moisture out and did the same inside a pot on the parabolic cooker.

Solar Cooker Comparison

Peter Pedals purchased a slim thermometer that can be inserted into a small hole which he drilled in the lid of a camp oven. He then put both the Parabolic cooker and a solar box (oven) cooker out in the sun at about the same time and measured their subsequent temperature rise.

Temperature Comparisons between Dish and Box Cookers10am:startParabolic DishTulsi Oven10:15Dish 120 º CBox 70 º C10:25Dish 130 º CBox 90 º C10:30Dish 133 º CBox 91 º C10:35Dish 135 º CBox 92 º C10:45Dish 160 º CBox 110 º C11:00Dish 185 º CBox 115 º C12:00Dish 200 º CBox 120 º C

Cooking the Evening Meal by Solar Power

You may have heard the joke about the Irish inventing a solar powered torch. The trouble with this joke is that it's not funny, solar powered torches exist just as solar powered houses exist. Instead of making the Irish look foolish as was the intention of the joke, it must rebound on the person who tells the joke as he or she has obviously not thought of storing the solar energy in rechargeable batteries.

In the same fashion as you can store the electrical output of photovoltaic solar panels you can also store the heat energy of a solar hot water system or the heat energy of a solar cooker with a well insulated container. This is where Thermos has come to the rescue with several models of Thermal cookware comprising of one or two stainless steel/carbon steel pots that fit very snugly inside of the large thermos flask for which it was designed (check the Thermal Cookware website).

The idea then is to commence cooking your meal with the solar cooker and then to complete the cooking process in the Thermos flask where the meal continues cooking very slowly like in a crock-pot for the rest of the day. This means that you can have your hot evening meal without burning any fuel and without spending a lot of time at the solar cooker.

The Thermos will keep it hot till the evening, making it possible to prepare dinner at a time best suited for solar cooking. Depending upon the ingredients, in many cases you only need to bring the food to the boil and then let the Thermal Cookware do the rest. On a sunny day you can get a pot to boil in probably around 15 minutes and certainly in less than 1/2 hour.

Slow cooking is the preferred method of cooking Chinese meals where the veggies retain their shape and texture and the protein is soft and tender because protein cooks at a lower temperature than carbohydrates. Slow cooking also enables you to have a hot meal where most of the nutrients stay intact and aren't destroyed by the heat of faster cooking. You will need to be aware of the different times required to cook different ingredients. Brown rice takes longer to cook than white rice and vegetables and so you will need to keep the brown rice cooking on the solar cooker for a little while whilst preparing your veggies. Because of its higher protein content, beans, lentils and wild rice will cook better at the lower Thermos temperature than brown rice and you won't need to cook wild rice on the solar cooker for as long.

One downside of the Thermal cooking process is that you will need to fill the entire Thermos flask with hot material. Thus, if you only want to prepare a small meal you should do so in a smaller sealed pot inside the larger pot filled with boiling water. Any quantity of air inside the Thermos flask will rapidly reduce the temperature and thus cease cooking the meal. The Thermal cooker if used correctly, will only drop 3-4øC per hour because of the superior insulating properties of the vacuum flask over any other material, allowing you to have a hot meal 8 hours after you placed the cooking meal in the pot. Don't be tempted to open the Thermos flask before you are ready to eat it because each opening represents a rapid heat loss.

As with Solar Powered Households, with the combination of a Solar Cooker and a Thermos pot, you can cook your meals without contributing to Global Warming by burning fossil fuels or by reducing tree cover for firewood.