Q 15.2 1. Describe how a building might be designed to passively collect solar energy. 15.3 1. In theory, biofuel combustion releases CO2 but does not contribute to global warming. Why is this so? 15.5 3. What factors are likely to limit the growth in the number of hydroelectric facilities in the future? 15.7 2. What factors limit the widespread use of geothermal energy? 15.8 2. What is vampire power? Give examples of this kind of energy use in your home and classroom.