Suppose I had a property in the desert that was basicaly a solar farm. For some reason there were periods that I could not sell my power back to the electric company so I decided to continue to generate but store the excesss.
What would be the most efficient and practical way to store that energy. My first instinct tells me simply pumping a liquid to a higher level or possibly even lifting very heavy weights that could be slowly dropped to retrieve power. Winch a bunch of old cars up a steep hilll and let them go back down by gravity pulling a wheel.
Let’s say you have 10 acre solar farm. In the desert, it will generate around 7 megawatt-hours of electricity per day per acre using modern panels - so 70 MWh per day. That’s 2.52*10^11 joules.
(2) An average car weighs maybe 3,500 lb - that’s ~1600kg. To raise that one meter on Earth would cost you about 15.5KJ. Let’s say you have 1000 such cars. Lifting them all one meter is 1.55*10^7 joules.
So - divide (1) by (2) - to save the energy generated by your 10 acre solar farm in one day you will have to raise 1000 cars about 10 miles straight up (and of course to recover at least some of it, would have to lower them fairly carefully from there). That’s not accounting for reduced gravity up there (which would increase the distance).
Not exactly launching them into space, but still quite a distance.
For smaller scale, batteries are probably your best bet, though they are a bit pricey with current technology.
On a larger scale, pumping water to a higher elevation isn’t all that uncommon. This may be less practical in a desert setting where you’ll lose a lot of water to evaporation.
Another large scale option is to store the energy as heat, then use some type of heat engine (sterling engine maybe on a smaller scale, steam engine for something big) to convert the heat back to electricity. A lot of small energy plants are using molten salt for heat storage and seem to be doing quite well with that technology.
There are lots of answers to this, none of them very satisfactory. They all have serious disadvantages. Stored water is one viable solution, provided you have a mountain and a lake and a lot of cash.
We have no ‘big battery’ solution that is ready for widescale deployment.
It is one of the great missing inventions of the modern era and a pressing concern for the renewable energy business.
Well, aside from what’s already been noted, I suppose you could use the excess energy to produce hydrogen, then either burn it or use fuel cells to get the energy back when it’s dark. I doubt this is the most efficient way, but it would work (there would be some technical issue with storage and such). For a small solar farm, I’m guessing batteries in series would be the most efficient verse the engineering costs (it’s what I did with my own roof top solar…I always wanted to try the hydrogen thing, but I don’t have that level of expertise, and the wife wouldn’t go for storing hydrogen in our shed :p).
What if a company specialized in harnessing the energy of heavy loads harvested in mountains or highlands and then had to be transported downhill. Logging, mining, etc. They could go around to any large downhill operations and engineer out a way of recovering some energy at a minimum investment. It might be enough energy to warrant some degree of infrastructure in some places.
Similar to what is being discussed in this thread: Offsetting Excess Wind and Solar Power Generation. I would so love there to be an easy solution. I will say that for both storage and transport, liquid hydrocarbons are hard to beat. If you are considering only energy solutions where electrical energy is to be fed into the grid, then there storage is problematic. I will repost the TED talk I linked in the other thread. Donald Sadoway: The missing link to renewable energy | TED Talk. Given that the talk is a couple of years old and I have not heard anything further on it, I suspect it is a great idea but a dead end (for probably obvious reasons.)
Keep in mind that *efficiency *is not necessarily the most important parameter. As an example, an certain energy vessel may be 99% efficient, but is completely impractical for large-scale use because you can’t transfer more than 10 joules per second to/from it. In other words, power is also important.
Can I piggy-back on your question, or is that hijacking?
I was wondering today what the most efficient way would be for me to store all this excess heat I’m pumping out of my house today for release in the winter months. Can I pump weights uphill to do that?
A huge pool of water.
You freeze it in the winter, and use it as a heat sink for a heat pump in the summer. Then, when it’s nice and warm, you reverse the process to heat the house in the winter.
Don’t remember where I saw that figure. But your number is incorrect as well. It’s about 1MWh per day per acre - 1GWh divided by 365 days divided by 2.8 acres. So - off by a factor of 7. Divide my result accordingly.
Details for an answer to the op would vary on specifics of location and needs
The linked wiki article is not bad.
Deserts can get cold at night. Storing as heat and using it for your town’s heating needs makes the most sense. Have a fleet of hydrogen cars? Producing hydrogen then. Flywheels are also an option. Space no problem (it is a desert), new liquid flow batteries in development might be a good bet. Near a large salt water body? Use the excess to desal instead.
This is a fanatastic method, simply storing charged electrolite that can be cycled back into batteries as needed. My favorite so far and so simple ( I think)
More on flow batteries from a recent Science article (April 25 2014 but behind the wall).
Lots more in the article if you can get to a library to read it.
One other battery option might emerge as EV batteries age out of their useful lives. An EV battery becomes inadequate for the task when it gets down to something like 70 to 80% of original capacity (range gets too limited) - but repurposing these used batteries into large arrays (when they become available in another decade or two) may find utility in utility applications.
Indeed. Capacitors are as near as no difference to 100% efficient, but with current tech it would take way too many of them to store a useful amount of energy. This may change in the not-too-distant future, since capacitor technology is advancing at a ludicrously fast rate, but it’s not there yet.
Based on what power companies are actually doing now, it looks like in most circumstances pumped water storage is the most practical, though as stated this depends on your precise situation. Ideally, you’d find some customer that can tolerate the intermittent supply, and sell to them.