The Ultimate Post Peak Oil Sustainable Home
After thousands of years of constructed dwellings, it is about time that humans create a home that could be the "home of choice" for a low energy future... for life after the oil crash... or life after the Eosawki (End of Society as We Know It
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A key feature in the design of My Sustainable Home is that it can continue to function indefinitely. By that, I mean that my children and grandchildren will be able to live in the house to ripe old ages, and all features of the house will continue to function. That is what makes this house unique from a typical sustainable and/or renewable energy home and/or year-round geothermal home.
If possible, the home would be designed to function even longer than that... perhaps hundreds or thousands of years. The trick is thinking of that when designing it in the first place.
I'll point out two things in your design that I suspect would fail within a decade or two.
a. Car lead-acid batteries - I don't know the life of these, but it isn't a lifetime long... this means you have no more energy storage method
b. Wood stove - As has happened in the past, wood becomes in short supply after some number of years as many people begin to use it as a source of fuel... which means you freeze during winter, as do your pipes, and your food
I thought a lot about energy storage. I believe the simplest way to store energy is mechanically, using the energy generation system to lift some mass... and then reverse the process to restore the energy when it is needed later.
If you have ever seen a chair-life used at a downhill ski area, you might have noticed the huge block of cement used to hold the ski cable tight. This mass is held up by three centimeter thick steel cables, which attach to the mechanism by way of some pulleys. This would be a perfect energy storage system. With the proper gearing, almost any mechanical source of energy could be stored simply by cranking up the huge block. I haven't done the math on this though, so using this as a battery might require a fairly high lift, or a mass that is larger than possible.
A better choice, but only suited for certain locations, is to use two ponds of water... one higher up, perhaps on a hill, and the other down low, in a valley. The water in the top pond has the stored energy. When needed, it is drained into the lower pond, which returns the energy. In this case, I would purchase a dozen pumps/generators, but only use one at a time. The remainder would provide for replacements when this one failed... and eventually spare parts. I would be concerned about rubber parts and lubrication though, so there might need to be a solution for doing these, as I doubt custom rubber products, or high quality lubricants, will be around forever.
After thinking about all the storage solutions, including batteries, the mass-lift ideas that I just mentioned, and others, I settled on the heat-storage system as one that is fairly simple and mechanical. Heat is stored in the summer, and retrieved in the winter, and used for all the energy needs of the home. It certainly is possible to design and build a home that can simply hold its internal temperature, and such a project has already yeilded success. But to have hot water, cold water, freezer space, refridgeration, and electricity is a taller order. With the Sterling Engine, heat energy can be converted into mechanical energy, and from there, into electrical energy.
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Of course, there are still problems with this design. First of all, what would be the cost of a Sterling Engine, or number of them, that could convert a 150 to 200 degree F heat difference into enough energy to run an very electricity efficient home? And, what sort of parts would need replacing in said Sterling Engines? Would they last longer than a PhotoVoltaic and chemical battery system? Can it even be calculated?
Would there be any substitute for converting the heat energy to electricity? Could a thermocouple system be devised? Would the thermocouple corrode or decay? Could it be replaced without advanced manufacturing?
Even without the electrical system, my design would still allow for heating and cooling of water, air, and food... but again there are issues with the use of pipes to move the hot and cold water from one area to another. How long to pipes last? If they are laid down first, and concreted into the storage tanks, then how can they be repaired if they clog up from mineral deposits? Is there a way to soften water without a constant supply of salt? What mechanism would be needed to do this?
So, yes, at this point, the design needs a lot of scrutiny. It wouldn't do much good to build a house that would not function properly, would fail after less years then a conventional system, or that would cost prohibitively less.
With the coming of peak oil, and the very likely collapse of the global economic system, this is the time to be figuring things out.
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Say your house needs an average power of 200W over a period of, say 10 hours when no other energy source is present. (I'm assuming a couple of compact fluorescents and just essential services such as pumps, no electric cooking or TV watching of course.)
1. How much energy is that? 200 Joules/sec * 60 sec/min * 60 min/hour * 10 hours = 7.2 million Joules. - This is what we have to store by mechanical means.
2. Let's be kind and assume 50% efficiency, taking into account that the generator may be 80% efficient and another 30% is lost in the friction of the mechanical device. This means we need to store around 14 million Joules of energy.
3. Let's raise up a car through a height of 10 meters. That means we have a potential energy of mgh = 1000kg * 10m/s/s * 10 m = 100,000 Joules or 0.1 million Joules. This means you have to scale up your car raising device up by a factor of 100. You need 100 of these devices, or if you raise each car up by 100 m (300 ft), 10 such devices.
4. The scale of such mechanical storage frightens me.
5. Let's perform the same calculation for water storage. Suppose we have a difference in height of 10 m. The problem now is that efficiency is dropping to 20% (I think I'm still being kind). Thus we need to store 5 times our actual requirements in potential energy, roughly 35 million Joules.
6. The mass of water required: 35 million Joules = mgh = m*10*10. This means mass = 350,000kg.
7. 1 kg of water is roughly 1 litre of water and there are roughly 4 litres in a gallon. so 350,000/4 = roughly 100,000 gallons. That's, like 10 big rainwater tanks, actually it's rougly about the volume of an olympic swimming pool, maybe half an olympic swimming pool is more accurate.
8. Constraints against water energy storage are 1. What if it gets cold and stuff freezes? 2. You need a height diff. of 10 m, where do you get it? 3. You need a lot of storage if you don't want to lose your working fluid to evaporation.
My conclusions are 1. mechanical storage is a nightmare. 2. Water storage might be feasible, but requires a fairly impressive scale. 3. I'm coming around to the stirling engine idea more and more. (see next comment). 4. I'm still a fan of a large stack of lead-acid batteries. Yes, they may fail, but, if properly maintained, they should last 20 years apiece and they'll be in plentiful supply for the forseeable future.
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As I said above, I'm sort of coming around to the idea of having one monster tank buried deep underneath the house that gathers hot water all summer and would serve as both house heating in winter, hot water for bathing, and as a heat source for electricity generation when needed. Multitaskers are always good (IMO).
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