ROCKY RIDGE RESEARCH
ONE HORSEPOWER550 foot-pounds per second
.7098 BTU per second
.1781 calories per second.
This equivalence of mechanical to heat to electrical energy allows us to convert and compare different systems. We regularly convert one kind of energy to another without thinking about it. We turn the thermostat up and some stored potential becomes actual heat. We cook some breakfast and another exchange takes place We go to work so we can pay for the car, the gasoline, the place to live, the food to eat, and hopefully at least a little more than that. We regularly audit the economics of a system. We balance our check book, or let someone else do it for us. But an audit of the energy we use is not a common concern but should be a decisive step in judging anything, gasoline, for instance. I remember gas for 20 cents a gallon. I was making what was considered a good wage at the time, one dollar an hour. I exchanged an hour of my time for 5 gallons of gas. Inflation has moved the decimal point but it's still about the same exchange of time. We really should include the cost of the military to keep the supply coming, but any number would only be my opinion. Gasoline contains about 134,875 BTU per gallon. The human body is about a one quarter HP system, so you traded about 700 BTUs of work for a potential 674,375 BTUs. That's way over 99 percent energy efficiency, what a bargain! But wait a minute, you can't only count the work for that hour. It took a lot of energy to get you there. You had to have the place to live, the food to eat, the car, and everything else needed to provide you as a worker at that time and place. All that is called embedded energy. Like how much coal did it take to provide the electricity to run your home? And how much energy did it take to mine and transport the coal? The embedded energy is factual and must be considered if any system is to be sustainable.
If you put only 5 gallons of gas in your SUV and head down the road for an hour you might be 60 miles away, and probably out of gas, but to find your True speed you have to count the hour of your time it took to buy the gas. You really traveled at 30 miles an hour. You also have to count the time it took to earn the money to buy the vehicle and the insurance and the upkeep. Things haven't changed very much since Henry David Thoreau challenged one of his friends to a race from Walden Pond to the city. His friend said it wouldn't be much of a race since he would get on the train and be there in a little while. Henry said, no, to be fair you start earning the money to buy the ticket and I'll start walking and I'll be there before you will.
The internal combustion engine has been developed, improved, and refined over the last hundred years but still exhibits poor thermal efficiency. The average automobile engine converts only ten to twenty percent of the potential heat energy in the fuel to mechanical energy, most is lost as unburned fuel and heat in the exhaust and excess heat lost in cooling. If the modern automobile were only a system of transportation and our uses logical, most of the problems have obvious solutions.. If transporting people and goods were the primary goal the design for an efficient and logical system is quite simple, but the problems are entrenched in the whole fabric of our society. This system of hardware and infrastructure is ripe for radical improvement.
Our second most used energy is electrical. One popular portable electrical generator uses a 9 horsepower gasoline engine to produce 4500 watts of electrical power. With the advertised fuel consumption there is 34.4 horsepower available as heat energy in the fuel to produce 6.04 horsepower of electrical energy for a thermal efficiency of 5.6 percent. Most of our electrical power comes from conventional steam power plants using external combustion to heat water and power a turbine. They are quite a bit more efficient than internal combustion but still exhibit low thermal efficiency. The latent heat required as the water changes state from liquid to gas, the high tempuratures required for power, and exhausting the expanded gas to atmosphere are the main reasons. The railroad steam locomotives had a thermal efficiency of around 4 percent. Modern electrical generating systems burn coal cleanly and can be over 30 percent efficient.
Assuming it will continue to be desireable to change heat to electrical energy, external combustion seems to be the most efficient way to go. Any source of heat may be used from geothermal to nuclear, but burning hydrocarbons is the most common. The nuclear option, in my opinion, is a net energy loss. All they do is boil water for a net thermal efficiency of available to produced energy of a small fraction of one percent.