Combined heat and power generation (CHP)

​Coal power plants burn coal and convert the heat into electrical energy. Not all of that heat becomes electrical energy, though. The coal burns releasing heat. The heat boils water in the pipes above turning it into steam. The steam powers a turbine, which then powers a generator, and you get electrical energy. ​Notice how the heat moves in all directions.

Most of the heat leaks out of the power plant. Only one-third of the thermal energy powers the generator. The other two-thirds are lost as waste heat. So, why not use the waste heat to heat more water pipes? The heat is not hot enough to boil water, but it is warm enough to heat homes or offices.

Another set of water pipes is built absorbing excess heat from the boiler. The pipes carry that heat to nearby buildings. Now one-third of the thermal energy from the burning powers the turbine. Another third goes to the heating system and only one-third is lost as excess heat. This power plant combines electricity generation and heat distribution.

It's much more efficient than before. ​The process of burning fuels like coal, oil, and a natural gas loses lots of heat. In order to use these combustible fuels, we have to spend money and time to dig them up. It becomes costly after awhile. However, there is something else we could burn. Garbage or solid waste to be more precise. ​One way to get rid of waste is to burn it in a large burning chamber like this.

It's called an incinerator. Combine a power plant with an incinerator and that heat generates electricity in the same way a coal power plant does. Pipe the heat to a district heating system and you have a waste to energy power plant that combines heat and power generation. It does three things: generates electricity, provides heating, and gets rid of waste. In Sweden, waste to energy power plants are common.

Half of their waste is sent to waste to energy plants every year. That's about 2.2 million tons. Sounds heavy, right? Well, Sweden also imports 700,000 tons of waste from other European countries every year. Now that's a lot of garbage. ​So how productive is waste?

One ton of waste produces enough electricity to power a small household for an entire year. One ton of waste produces only a third of the energy that comes from a ton of coal or oil, but waste doesn't cost us any money to dig up. Even if we add a cleaning system burning waste releases lots of carbon dioxide, which adds to global warming. But if waste is left in landfills, it just takes up space and releases a potent global warmer methane when it decomposes. So, even though waste to energy plants release carbon dioxide at least we get useful energy from waste. ​Today there are more environmentally friendly energy sources like solar or wind power, but combined heat and power plants allow us to harvest both electricity and heating from one fuel source like coal or even garbage.

Now that's pretty efficient.