Thermal energy storage solves the problem of cooking and washing.
I have a half-liter thermos bottle that leaks about 0.3 watts at ΔT ≈ 50° (635g of water dropped from 71.9° to 69.8° over five hours and 8 minutes), so any power supply averaging over about a watt would be sufficient to boil water in it—eventually. If you needed to do it in the 4 hours the sun was near peak on a single day, you'd need at least 15 watts. (I don't live in Africa, but I do live in a third-world country. Blown-glass thermoses are pretty widely available because, although they're fragile, they're light and never wear out, just shatter.)
Sand batteries are potentially extremely cheap and can easily deliver cooking temperatures. A super-low-tech version of this approach is "salt frying", where you preheat a few kg of table salt (melting point 800.7°) to frying temperature, then stir dry food into it. Most of the salt won't stick to the food, but the few grains that do won't cause the edibility problems that sand would.
TCES potentially offers much greater storage density and much greater controllability than these sensible-heat energy-storage technologies, since you can store the "heat" indefinitely.
Phase-change thermal energy storage is another potentially appealing possibility, potentially offering a stable cooking temperature for many hours, although I don't know of any suitable materials. The MgCl₂-KCl–NaCl eutectic, for example, doesn't melt until 401°. Maybe something like calcium stearate (m.p. 150°–180°) would work, but its heat of fusion isn't great, I'd be worried about long-term stability, and although it's easy to get anywhere in the world, it's probably a lot more expensive than salt. (Table salt is US$100/tonne, but the eutectic mentioned above would be closer to US$400/tonne.)
I have a half-liter thermos bottle that leaks about 0.3 watts at ΔT ≈ 50° (635g of water dropped from 71.9° to 69.8° over five hours and 8 minutes), so any power supply averaging over about a watt would be sufficient to boil water in it—eventually. If you needed to do it in the 4 hours the sun was near peak on a single day, you'd need at least 15 watts. (I don't live in Africa, but I do live in a third-world country. Blown-glass thermoses are pretty widely available because, although they're fragile, they're light and never wear out, just shatter.)
Sand batteries are potentially extremely cheap and can easily deliver cooking temperatures. A super-low-tech version of this approach is "salt frying", where you preheat a few kg of table salt (melting point 800.7°) to frying temperature, then stir dry food into it. Most of the salt won't stick to the food, but the few grains that do won't cause the edibility problems that sand would.
TCES potentially offers much greater storage density and much greater controllability than these sensible-heat energy-storage technologies, since you can store the "heat" indefinitely.
Phase-change thermal energy storage is another potentially appealing possibility, potentially offering a stable cooking temperature for many hours, although I don't know of any suitable materials. The MgCl₂-KCl–NaCl eutectic, for example, doesn't melt until 401°. Maybe something like calcium stearate (m.p. 150°–180°) would work, but its heat of fusion isn't great, I'd be worried about long-term stability, and although it's easy to get anywhere in the world, it's probably a lot more expensive than salt. (Table salt is US$100/tonne, but the eutectic mentioned above would be closer to US$400/tonne.)