One watt generates 3.41 BTUs, so each 250-watt device generates 852.50 watts per hour, or 7, 467, 900 BTUs annually.

FORBES: For IT Managers, Going Green Can Save You Some Long Green

The Spark's 39 Watt hour battery has both a high-powered USB port for tablets and a standard USB port for phones and other handheld electronics.

ENGADGET: Voltaic Spark Tablet Case powers your pad with the Sun's rays

The mariner uses a 250 watt free-spinning motor mounted in the front wheel for propulsion and high capacity 36 volt 9 amp hour advanced lithium battery (LiFEPO4) which provide a smooth, powered ride on flat and hilly terrain.

FORBES: Green Gear Test - Folding Electric Bikes