The Ultimate Post Peak Oil Sustainable Home

[valuesystem]

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

Comments

Mechanical energy storage

[dtbrookes]

I've devoted some thought to this and I think that mechanical energy storage is not particularly feasible. I'll do some sample calculations for you so you can see the scale of the problem:
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.