A popular educational program for renewable energy is the Junior Solar Sprint. I spent some time analyzing the dynamics of these cars, and considering ways to improve their performance. Here is some analysis that you might find helpful.
Another way of building a solar-powered model car is to convert an inexpensive, radio-controlled car such as can be obtained at a discount store. Here is a description of how to do it.
It is sometimes interesting to know the strength of the sunlight that is striking a surface. Here is a description of how to build a simple pyranometer based on a PV cell.
I continue to contemplate the difficult task of building a solar kiln for firing ceramics.
I recently rebuilt my 17 year old solar water heater.
Many people are working toward a future "Hydrogen Economy", in which Hydrogen is an energy transport and the energy to produce it comes from renewable sources. Here are some calculations related to this, and some discussion.