Wasted Heat to Usable Electricity

When one energy form is turned into another, like when we convert electricity into light, the process is very rarely truly efficient. Instead, there is always some waste in the form of heat energy. For example, power plants are only around 33% efficient: only one third of the chemical energy in the coal or oil burned is turned into useable electricity.

Take an incandescent light bulb. If you've ever touched one after being on for any period of time at all, you're bound to get burnt. Just look at the IR image of an incandescent light bulb below: at the top, this particular bulb was reaching temperatures upward of 300 degrees fahrenheit!

Image Courtesy of Zaereth

Bruce E. Logan, professor of environmental engineering has devised a solution to harness low-grade heat (heat that is low to mid temperature that is not very energy dense, like exhaust from a car or power plant heat waste) and turn it into electricity. His solution involves an ammonia battery that can be regenerated using the waste heat we talked about earlier. 

Without heat, the battery could go through one cycle, similar to the way that your average AAA single-use battery operates. Typical rechargeable batteries can be regenerated by running electricity the opposite way it usually goes, forcing the reaction that is occurring in the battery to go in reverse. 

What is unique about the ammonia based battery however is that it can be regenerated back to full capacity using waste heat instead of electricity, allowing the cycle to continue once more without electrical input.

Image of the Ammonia based battery
Image Courtesy of Wulin Yang/Penn State

Right now the system isn't incredibly optimized (as you can probably tell from the photo above); right now about 29% of the chemical energy that gets stored into the battery is converted to electricity. This can be compared to around an 85% efficiency for lead-acid batteries (the type that you'd find in your car). However this efficiency will be able to be brought up significantly as they sure up all parts of the battery.

This battery could have some exciting impacts on the efficiency of energy production. Look at nuclear power plants for instance. These plants need very high temperatures in order to produce electricity, and after the heat is utilized, it is moved to those humungous cooling towers that you associate with nuclear power plants. Those aren't the things that are producing the electricity - it's for cooling the fluid! By adding these ammonia batteries to systems like these, the amount of heat that is wasted and put to the atmosphere can be reduced significantly while simultaneously increasing the amount of electricity that is produced. Seems like a win-win to me!

Image courtesy of Own Cliffe

Unfortunately I was not able to go in detail on the workings of the battery and the cool complexation reactions that allow this thing to work, but if you're interested in learning more about what exactly is happening here, a paper on the subject (that explains the process surprisingly well) can be found here.