Let us assume that you are looking to cook instant noodles (ramen). So you've calculated that to bring the one-eighth of a gallon of water in the pot to boiling point and cook the ramen, you will need to apply 120 kJ of energy. However, your electric stove and microwave are both out of commission (Bummer).

You turn on the hot water faucet and allow it to get as hot as possible - 125 degrees Fahrenheit. You then calculate that in order to get 120 kJ of energy from the faucet, you will need about a third of a gallon of water.

So, you have the same amount of energy as you would using the stove. Will the hot tap water cook the ramen as well as if it were heated to boiling point on the stove? NO!

Therein lies the difficulty with renewable energy.

Fossil fuels are like the hot stove burner - ready at a moments notice to provide copious quantities of high-grade energy - boiling, baking, frying, grilling, or just simmering whatever you desire.

Renewables are like cooking your food with the hot water from the sink. Yes, your landlord may provide you with free hot water, but the temperature just isn't there. All the joules in the universe can flow from that sink and it will never boil. And when your neighbor decides to stand in the shower for two hours, all hope is lost.

What we must learn to do as a society, is to do our defrosting, simmering, and reheating using renewable energy while saving fossil fuels for the frying and broiling. In other words, use renewables to meet the need for low-grade energy (e.g. heating water and buildings) while saving fossil fuels to meet the need for high-grade energy (e.g. generating electricity).