February 2010 Archives
Recently we were contacted by a visitor who is interested in Rankin Cycle Generators and Stirling Engines. He shared the following thoughts and we wanted to put them here to stimulate discussion and help him find an answer. Directly below is his question and below that is a response from an engineering consultant we've worked with on past articles and projects.
Question: Hello I have noticed an explosion in Stirling engine and rankin cycle generators recently, all of which are either powerd by gas, diesel, oil or the sun. Despite weeks of web searching I have been unable to locate any manufacturers of a Stirling generator which can be powerd by the heat from a log burning wood stove. I'm told by some manufacturers that's because the temperatures of a log stove are too low? 500c doesnt sound low to me! Plus the hot side of the Infinia solar dish system isn't much hotter than boiling water and it works.
I've seen YouTube videos of people running a Stirling engine from a cup of tea... So why isn't there a wood log burning stove for generating power, I just dont get it? My personal stove develops 4.5Kw of hot water every hour in addition to another 3Kw of convection heat. There has to be some way of tapping that and turning it into electricity surley. Anyone have any answers? (send Biomass Authority an email and we'll pass it on). P.S. I don't have the facilities to build my own set up but I could modify an existing one if they will sell just the Stirling engine and generator.
Response: I have been hearing about Stirling engines my entire life, and yet I've never seen one producing energy that I can recall. I know there are a few examples out there, some of which are connected to solar concentrators.
However, if a Stirling engine could compete with the internal combustion engine, it would have replaced it a long time ago. It is not being suppressed by our government, and the patents on it, if there ever were any, would have expired before the Civil War since Mr. Stirling first described it in the early 1800's. I think it's just one of those ideas that sounds attractive on paper until you try to implement it and then realize it's not competitive with the alternatives.
There's a lot of information already on the Wikipedia regarding Stirling engines, and so I wouldn't be able to add much in the way of insights as to why they haven't caught on. It seems that their disadvantages significantly outweigh the fact that they can, in theory, run on any heat source. But the cost of the fuel is only one factor in the equation. The other is the cost of capital and for a Stirling engine, that seems to be its downfall. It takes an enormous engine to produce a small amount of output and all of those materials are costly and must be amortized over the life expectancy of the engine. So until fuel becomes a bigger part of the equation, I don't expect we'll see many examples of Stirling engine generators. But if fuel prices increase several fold over what they are now, then maybe they'll make sense.
Below is an illustration sourced from Wikipedia of Robert Stirling's 1816 patent application of the air engine design which later came to be known as the Stirling Engine.
Ecovative's solutions use a combination of mushroom roots "mycelium" and local feedstock (which means in can be made on site anywhere in the world, further reducing the impact of transportation in use). This might include cotton gin trash, buckwheat hulls or hazelnut husks. The end result is a direct replacement for styrofoam that can be created without using any petroleum, electricity or heat but offers the same thermal and physical properties as styrofoam.
One unit of this biocomposit requires ten times less CO2 and eight times less energy than the same volume of styrofoam. In the world of products helping to make a material difference this is an outstanding step forward and worth considering for any business that ships products or home owner considering insulation options.
Biomass Resources
Biomass Companies
