Posted in response to someone advocating solar energy as a replacement for hydrocarbons, in response to this post:
"Obviously, if you don't immediately use the energy you generate with your solar panels, you need to store the electricity. Let us now look at a few batteries and see how they compare on the energy density (energy per weight) with gasoline.
Type MJ/Kg Application
Li - Ion 0.6 iPhone
NiMH 0.4 Prius
Alkaline 0.6 Duracell Rabbit
NiCd 0.14 RC cars
Lead Acid 0.14 Cars' lights, engine start
As we can see in this table, battery technology is clearly far behind liquid fuels in terms of energy density and compactness: to store the same amount of energy as in gasoline, the batteries would weigh a little less than 100 times more. This is one side of solar energy and transportation that not everyone fully understands. The incredible energy density of liquid fuel and the amount of energy that is required to operate a car is often overlooked due to the low price and high availability of gasoline. Think about it: if we want to drive a typical electric car 20 miles, we will have to charge batteries with our 1 square meter panel for 50 days (or 50 square meters for 1 day). If we were to drive the gasoline version of this car, we would only need ~1 gallon of gasoline!