Assessment of the energy needs for cooking local food in Uganda: A strategy for sizing thermal energy storage with cooker system

Abstract

Energy for cooking accounts for a significant part of the daily energy needs in developing countries. Cooking energy is mainly based on biomass (firewood and charcoal), both in urban and rural areas. Several studies have demonstrated the potential benefits of changing to other fuels for cooking, in terms of health, environment, sustainability and cost. Another strategy is to develop cooking solutions based on renewable energy technologies, to facilitate the use of intermittent solar and wind energy sources for cooking. The design of the new technologies, like the oil based heat storage and the associated cooker solution then requires knowledge of the energy required for cooking for the particular storage and cooker concept.Energy needs for cooking local food items in Uganda have been determined from laboratory cooking tests and from a survey on institutional cooking practices at selected schools in Uganda. The food items cooked include dry beans, rice, cassava, plantains (matooke), maize flour, fresh beans and sweet potatoes. The total energy used for cooking, boiling, and simmering was measured and time taken recorded. The moisture content and specific heat capacity of the food items were documented and used to estimate theoretical energy requirement for cooking. The effect of soaking dry beans on the energy required to cook was investigated. Results showed that for high moisture content food items like matooke more energy is required to boil than to simmer. On the other hand, for dry food items (beans), more energy is required after boiling to fully cook the food items.For an oil based thermal energy storage solution, supplying hot oil to a dedicated cooker, the results indicate that 14 L hot oil at temperatures of about 200 °C can be sufficient for the daily cooking energy needs for a household of 5 persons. The quantity of oil required can be reduced significantly if there is a pump to enable oil recirculation as cooking progresses. Furthermore, to enable up scaling to institutional use, the school survey done revealed that about 2.6 kg of firewood is used to cook 1 kg of dry beans and about 1 kg of firewood used for 1 kg of maize flour.