This is an idea I've had wandering around my brain for a while. Given any energy "source" (such as wind, or a river) where there may be surplus energy over the long term but not sufficient energy to cope with peak loads, you face the issue of storing that surplus energy. This is generally done by converting it into electrical energy, then using that to create a chemical change in a battery, which, later, you reverse and reclaim the electrical energy which you re-convert to kinetic energy in some cases. At each stage, you have inefficiency: kinetic > electric > chemical > electric > kinetic so you have 4 state-changes each of which is inefficient. Granted the original source is free (more or less), it's still not all that good. If you have the ability to create a reservoir and store the surplus water at stage 1, then you can overcome this. However, reservoirs are not something you can always do. There are, indeed, hydro schemes that use this method: a relatively small water supply is stored and used to generate electricity at peak demand times - although it is, by nature, something of a one-shot system: once you use the water you have to wait for the reservoir to refill. Pumped-storage can work well if you have surplus electricity (from, for example, coal or nuclear which is hard to shut down and re-start) but you still need a reservoir, and, to be effective, that needs to be pretty big.
This gets me to my thought. The key is to store gravitational potential energy - and this could be done using a large mass. Since the mass can be much denser than water, it doesn't need to be so big. You could use surplus energy to lift a mass up a tower, then when the demand was high, allow the mass to descend and generate electricity. This could be installed, for example, in tower blocks, in mines, more or less anywhere there's vertical space. The equipment and techniques are common-place (much the same as for an elevator) so there's no research requirement. There isn't even a need for a really tall space, since to some extent a larger mass could be used in a shorter space. It could also (given suitable systems) allow low-density constant energy (a stream or wind) to lift the mass. Have to admit I haven't quite got my head around a mechanical way for that to work but I'm sure it could be done or you could do it electrically at the cost of another state change.
There are some systems that use a massive flywheel to store energy. This has some drawbacks, most notable being the frictional losses of spinning a wheel (the vertical mas would, when not being used, be stationary) and the potential for damage if it does go wrong (the vertical mass could fall but would, hopefully, only affect the space immediately under it).
Elevated mass gravitational energy storage doesn't work out as well as you might think. The return on energy investment is very low. Here is a page that puts some numbers to it compared to flywheel and other technologies.
What about compresed air tanks. How cheep to build means more to me than how efficient. What about compressed air.
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Jeffrey Hodgins wrote:What about compresed air tanks. How cheep to build means more to me than how efficient. What about compressed air.
The physicist in the link above (pretty much everything he's written is fabulous) also addresses compressed air in that same article.
posted 5 years ago
Yeah that is a really good article. The only thing I'd take issue with is that his gravity solution misses the most obvious point that, especially if you build it in from the start, you don't need to restrict it to 1 room vertically. Granted, in a typical house, you can't make it really tall, but you can still scale it up by a factor of 3, say, bungalows excepted, and if I recall right, gravitational potential energy is given by mgh where m is mass, g is acceleration due to gravity, and h is height - so 3x the height the same mass stores 3x the energy, etc. It's still less scary than a flywheel, and more efficient - the mass at rest has zero losses. Ideally, you'd also want to use mechanical energy directly for mechanical things, so removing some of the inefficiency. (Like a windmill or watermill, in fact) Old-time factories used mechanical power distribution - they had shafts running around the factory distributing power from a central source.
There are 2 good points out of this:
First, use less energy! The guy in the article uses much less than the average american household, chances are he's decided that washing the dishes by hand and drying the clothes on a clothesline are good options, which of course they are (I doubt readers here need telling that). Someone in the comments also made this point: use yourself as an energy source more.
The other point is thinking small: you're not trying to cope with a 90-day power loss scenario for a whole city block - a reserve of say as week for one house is fine. This same argument goes to the generation, too: renewable can work, and there are many state funded schemes on a grand scale, but what would really work is spreading the power generation in small bits all over the place: to be fair, there is a big increase in the UK in photovoltaics, thanks to a government-backed scheme to get them installed. Naturally, the government have now backtracked on that and the scheme is worth less, but it looks as though there's now enough momentum to keep it rolling. The same kind of scheme would be pretty useful (especially with the typical UK climate and the fact that we're 50+ degrees north and so don't get really good sun anyway) for micro hydro and micro wind and maybe bio-digesters, sadly they don't seem keen to do such things.
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