I was a bit surprised that the roof used on your constructions looks like corrugated iron. Do you think you can add a kind of vegetable roof, which may have a better isolation ? If the weight is not too important, it may also be a possibility to have "personnal garden" for small food.
This idea is really interesting and there are many solutions for generating electricity from sludge management. http://www.motherjones.com/blue-marble/2009/05/top-6-ways-convert-poop-electricity
I am thinking about a mechanism based on dry toilets collected every day/week and centralised in one place that produce electricity. The innovation can be to include within the toilets a battery that can be used by the families. These battery can then be used for day to day usage.
OpenIdeo has already created a business model for sanitation management in ghana. Take a look at http://fr.slideshare.net/jocelynwyatt/ghana-sanitation-opportunities