By the way Susan -- solar and windmills don't make it because they are far to expensive.
Just the cost of battery replacements far exceeds the fuel cost of fuel for a small, properly designed -- highly efficient -- diesel power plant.
Never mind the availability of dual fuels that are nearly cost free -- except for village labor -- alcohol and plant oils.
Further -- the life span of solar and wind devices is much shorter than the small diesel -- plus orders more expensive in capital costs.
The target price for a 1000 watt -- continuous operation -- high efficiency -- long lasting reliability (minimum ten years before 'maintenance' -- but aiming for 50 years total life span) -- "power-plant" was established as being less than $350 US.
This was considered next to impossible when we started. But I have already put a package together that should cost less than $300 -- meeting all the above goals -- except making some people from industrialized nations rich selling it to 3rd world.