Cheap fossil fuel has allowed us to waste the majority of our energy, filling the planet with pollution and waste heat. Our car engines are only 25% efficient and coal power plants are not much better. Corn ethanol is one of the worst wastes of biomass: An acre of corn produces about 330 gallons/year if you cook it using fossil fuel.
Use the ethanol as a heat source and the net yield drops to 214 gallons/year. Car gas mileage is 30% lower with ethanol. At 25 miles/gallon we can only drive 25 X 214 = 5350 miles per year on an acre of corn.
If we take that same acre of corn and burn it to make electricity to charge an electric car, we will be able to drive the car 22 times as far! About 117,096 miles per year!
- The energy content of dry corn biomass is about 7000 Btu/lb or 4100 kWh/ton
- With an 85% efficient CHP plant the net power out is .85 X 4100 = 3485 kWh/ton
- An acre of corn yields about 8.4 dry tons/yr or 8.4 X 3485 = 29,274 kWh per year
- The Tesla electric car goes 4 mi/kWh (EPA) 4 X 29,274 = 117,096 miles!
We don’t have very many 85% efficient Combined Heat and Power (CHP) biomass power plants in the U.S. In fact, only 8% of our power plants are CHP plants. But Denmark has 53%, Holland 39% and Finland 38%. CHP plants are extremely efficient with many exceeding 90% efficiency! The secret of CHP is to locate the plant near where heat is needed. The waste heat from electricity generation is then sold along with the electricity so the only real waste is the heat that escapes into the air or past the heat exchangers in the stack.
CHP requires a different way of thinking. You must look first for places you can sell heat. Electricity is easy to distribute but heat is harder so location and sizing of plants must follow the heat demand. Mammoth gigawatt-scale power plants cannot do CHP unless they are built adjacent to a mammoth cement plant, kiln or steel plant. Most mammoth plants today dump about 2/3rds of their power into a stream or ocean just to get rid of it. A horrible waste!
High-rise buildings, hospitals, industrial parks, shopping centers, apartments, housing tracts and hotels are all excellent candidates for CHP power. Hot water, heat and cooling needs are generally comparable to electric power needs so 50% efficient electrical generators are a perfect fit: The wasted heat from the generator is simply used as heat. Fortunately, the needed technology is appearing just on schedule. Fuel cells can generate electricity with 50-60% efficiency from natural gas or syngas from biomass. One of the reasons mammoth power plants were built in the past was that only very large turbines were efficient. The other reason was pollution control. Neither reason applies today, as gas and biomass burn clean, particularly in a fuel cell.
Fortunately, we have a glut of natural gas from new shale bed discoveries. Gas is very convenient in cities, while biomass can generate carbon free power in more rural areas. Switching from coal power to CHP gas power has a massive impact on greenhouse gas emissions. Natural gas produces only 55% as much carbon as coal. CHP plants are three times as efficient (85% vs. 28%) so the resulting emissions are only .33X.55= 18% of a coal plant producing equivalent power! That’s a better improvement than the planned 40% CO2 output of Futuregen and we don’t have to wait decades for it to happen. With 3X better fuel economy, natural gas is way cheaper than coal and we won’t run out of natural gas for a long time.
Giant power plants are custom designed and take 10 years to build. Smaller, modular CHP plants can be based on standard pre-approved designs with components built on mass-production lines like cars. The capital cost can be much lower than large plants. There are several mass-produced home-sized CHP units coming on the market now based on fuel cells. Honda already shipped 50,000 of their Ecowill units in Japan. These units are 85.5% efficient by using generator-wasted heat to make hot water.
What we need now are standard CHP generator designs in the 1-MW to 5-MW size that can run on natural gas or biomass. A biomass unit could be used on a farm to heat greenhouses, cold storage, fish ponds or brick production. Burning 2 MW of biomass would produce 1 MW of heat and 1 MW of electricity. 1 MW of electricity is 8,760,000 kilowatt-hours per year, worth about $876,000 per year. The heat is worth about 1/3 as much. Carbon credits and Renewable Energy Credits add to the income.
To feed a 2-MW gasifier with corn, the farmer would need only about 68 acres of land. Other, more prolific feedstocks like elephant grass could probably get by with only 23 acres. In Germany they have straw bale gasifiers that simply require the farmer to throw in a new bale periodically. The control microcomputer rings the farmer’s cell phone with a text message whenever a new bale is needed.
This decentralized free enterprise approach could revolutionize our power structure in short order. Denmark changed their utility laws in 1990 and within 10 years 45% of ownership of power generation had shifted to consumer owned and municipality-owned CHP plants (25%) and wind turbines (20%). Ironically, ten years is about the time it takes to build one giant nuclear or “clean coal” plant. Distributed power eliminates the need for massive expansion of our power grid to connect old-style monster power plants. Distributed power also reduces power transmission losses since power is consumed near where it is generated.
The U.S. is way behind in efficient power generation because our utilities laws encourage massive inefficient power plants. If we can change that legal environment we can unleash a revolution that will dramatically reduce pollution and global warming, create good jobs and reduce our heat and power costs. The problems are political, not technical!