I want to talk about overunity. Anyone that has looked around this blog knows that I have a special place in my heart for refrigeration, “heat pumps” more generally speaking. Vapor compression systems have fascinated me for years. It has been shown that by taking advantage of the phase change properties of certain fluids, it is possible move heat from one place to another, which in a well designed system requires less energy in the form of work than the heat energy moved. This is overunity. Put simply, you get more out than you put in. Now mind you, this does not suggest an efficiency greater than 100%; far from it. Actually , a heat pump operating at higher than 50% percent would be impressive. The same heat pump in certain conditions may move five units of heat for every unit of input energy required for the operation. Energy is conserved and entropy rises from a total systems perspective.
Heat pumps are a fascinating subject for which I have written extensively about. Up until recently, I planned on incorporating a heat pump (mostly built from scratch) into about every step in my energy management system of living. Refrigerator, water heater, dehumidifier, clothes drier, and home heating, were all suitable applications in my mind. Since moving into the Squatch, so many projects have crossed my mind, I often get frustrated and lost in all the mess. I need to simplify. The last few weeks of heating the coach with the propane heater has given me an idea of what it takes to keep the place warm. It’s not much compared to an average home, but even for the small heating load, the heat pump required to do the same job would be of considerable size, complexity, and the electrical demand would be tough to supply with photovoltaics in the gloomy Portland winters. Even the addition of wind power generation, it seems like a tall order without a damned large battery bank.
Additionally, I’m not a huge fan of photovoltaics. They may make sense financially, especially when a grid connection is not possible or expensive to acquire. They make practical sense to anyone who wishes to have reliable power when blackouts and brownouts may become a more common occurrence with an aging and strained electrical utility grid. I have a solar panel, purchased used from a coworker. I will likely have more panels in the future, but I’m not convinced they are a sensible way to go. Although a long lasting photovoltaic panel will produce more electricity in its lifetime than was required to manufacture it, I’d imagine most of these panels are made with a great deal of fossil fuel energy. So, in terms of carbon footprint, or whatever you want to call it, they are not the sustainable alternative some make them out to be. Perhaps worse, is the finite and environmentally hazardous supply of materials which go into their manufacture.
“Net Energy Gain” is a concept that describes the amount of energy available from a source minus the energy required to obtain it. If an energy source has a NEG of less than one, it’s not really worth doing. I think some of the first oil to be extracted in Pennsylvania came gushing out of the ground so forcefully that the NEG was something like 150. Today, the lack of easy to get oil has led to the disaster that is Tar Sands extraction which has an NEG in the single digits. Coal is another source of energy with a high NEG, but it is too falling as much of the easy to extract coal has long since been burnt. Natural gas is yet another, however with hydraulic fracturing, the NEG is much diminished. All sources of energy whether they are fossil fuel or “sustainable” must meet this NEG requirement. I feel this simple calculation fails to consider the long term results of externalized costs such as air, land, and water pollution, as well as biodiversity loss.
I wanted to bring up Net Energy Gain because I think it is nearly the same as the Coefficient of Performance found in heat pumps. In most energy sources we may use NEG to describe the energy required to convert a source from one form to a useful form. With fossil fuels, this manifests as the conversion of chemical energy stored in the hydrocarbon chains into heat and dynamic energy, driving a turbine which runs a generator producing electricity. Wind converts pressure differentials to mechanical to electrical. Photovoltaics convert visible light directly into electrical potentials.
It should not be surprising that the energy sources we have made the greatest use of are the ones with very high NEG or COP. Our gluttonous demand for this cheap energy has left us weak, frail, and shocked to deal with the reality of low NEG energy sources. The economic obsessive of growth demands ever greater extraction; damn the consequences.
I rattled through all of that to say I’m making a change of course. I seek an alternative to the alternatives. My interest of late lies in pyrolysis of biomass. When dried, high carbon biomass heated in a low oxygen environment will off gas carbon monoxide and hydrogen gas. These highly flammable substances together know as “Wood Gas” can be combusted in the presence of oxygen in order to provide the heat to continue the pyrolysis, with enough left over for home heating, domestic water heating, and maybe electrical production. Once the biomass is completely pyrolized, the process stops, and what is left is commonly know as “char” or “biochar“. This inorganic form of carbon is largely inert and can be buried in the ground where it could remain for thousands of years. The net result is carbon negative in that the carbon dioxide sequestered from the atmosphere by the original plants, is only partly released in the combustion process. The porous nature of the biochar at a microscopic level makes its surface a suitable home for soil microbes, helps maintain soil fertility and water retention.
My plan, which I will elaborate more on later, is to build another small rocket stove and explore ways to pyrolize woody material and introduce the resulting gas into the combustion flue. Later, I would like to enclose and insulate the furnace to improve performance. Next, I’d like to add a water jacket or heat exchanger to harvest heat for household purposes. Later, I would like to use some of the wood gas to run a small generator that could recharge my battery bank in place of solar panels or a wind turbine.
This will be a lot of work, but I like it because the materials are simple and common, it has many different uses, and it’s carbon negative. Well, that’s enough for now. It took me about a thousand words to get to the point. I think that’s a record.