Charles - succintly put. Pumped hydro energy storage is great - but most geographically viable locations have already been built. Also, the environmental impact and large amount of water (and replacement due to evaporation) will be increasingly large barriers. Water shortages are another brewing issue like our energy problems. Compressed air storage is even MORE tied to specific geographical features (large salt caverns)...a niche at best, and efficiency and ease of energy conversion is not that good.
I've come to the conclusion after much study and thought that there are only a few likely vectors to success in grid-scale energy storage. Of course, always open to unexpected breakthroughs!
1. Solar Thermal - these powerplants store solar energy as heat (in molten salt or even large stores of sand or concrete). For short-term energy storage this is a pretty good system, since the power plant already is designed to run on solar heat. Also, this approach allows a "backup mode" using natural gas (or other fuel) if the heat storage runs out. We need to be building more of these plants NOW. However, note that heat is not the most best way to store ELECTRIC energy (such as from wind turbines), since round-trip efficiency will be only ~30%.
2. Solar (or Wind / electric) generation of a synthetic liquid (or gas) fuel. This approach needs more development work, but has great potential because you can store as much "fuel" as you want, and could be high efficiency. The "obvious" fuel is hydrogen, but I've come to believe this is not the best choice due to so many practical issues. Ammonia (3 hydrogens bonded to a nitrogen) is my favorite but methane / methanol / ethanol are OK too (but would prefer to avoid carbon in the molecule). Also, if a synthetic fuel is created - this fuel can be transported and used for many things (cars, other transportation) in addition to grid-power storage. It should be added that biofuels have this advantage...but aren't actually a way to store the grid's ELECTRIC power.
3. Flow Batteries. Conventional batteries don't have enough capacity vs. cost. Flow batteries size the battery to the POWER RATE needed, then you store as much of the reagents as you need to provide the total ENERGY STORAGE you need. Redflow (mentioned by someone else) is one, but there are others. General Atomics is studying a lead-acid flow battery that uses conventional / low cost chemicals and has no semi-permeable membrane (the power-limiting and most "finicky" part of most flow batteries).
Flywheel energy storage has been tried and proven not cost-effective (eg: Beacon Power), Conventional batteries and also distributed EV batteries are not likely to be practical.
Good discussion thread. Obviously there are lots of storage options. It will take a bit of business and risk analysis to sort it all out. The issue is that no one entity has the overall view and each industry has their personal agenda. It will take a consortium of many disciplines to steer the correct path. In the meantime, what an exciting time to live. We are at the start of a whole new way of looking at the world's power needs.
In response to Geoff, the figure for pumped storage total round-trip efficiency today is about 80%, although it will vary some from site to site. I think it's also important to point out that you wouldn't have reason to put all of your renewable energy into storage, but strategically use the minimum ratio of storage capacity to renewable capacity to create the greatest benefit.
When we run wind-storage integration models using pumped storage to create a firm, intermediate-level capacity product between the two, only about 20% to 33% of renewable output goes through storage; the rest goes straight to the grid, with the storage release following flexibly up and down.
In summary, you don't need to add 1 MW storage per 1 MW renewable, nor do you lose 20% of all renewable; you lose 20% x 25% or 30% or about 5% to 6%.
Also, in partial response to Jerry, while wind does have the most to gain from storage, solar PV also is surprisingly intermittent and can stand to gain a great deal of firm capacity value from storage. One can also shift morning output to the afternoon, when peak is generally highest (at least in the summer).
In regard to Pumped Hydro, in situations where there is constant river flow with spare energy it is agreat idea, but where the energy is all coming from the renewable source just to be stored, efficiencies can be a bit low, - the Pump will not be much beter than 80% and the Generator also, particularly adding pipe losses etc. so suddenly the cost of the renewable energy jumps alarmingly due to the wastage.
With Batteries, particularly lead acid, - preferably Tubular Positive plates, efficiency of 98% and large Inverter efficiencies also of 98% are achievable so most of your power is still there. Cheers, Geoff Thomas.
Lux and Pike don'tknow what they are talking about. Both write papers that most always are wrong. Same for the EIA, IEA which past data is good but can't predict worth a dam ;^P
Take this one. They left out the recent tech that makes GS at least by utilities moot. It's NG turbine Cogen units that can throttle to 50% eff reming the need for storage.
Next RE doesn't need storage on uility level because RE mostly happens when needed, solar or on call, hydro, CSP, biomass. The only truly intermitent RE is wind and only big wind far away has that.
So just where is this great demand other than armchair experts dreaming it up?
We already have batteries for under $1/kwhr and have for more than 10 yrs yet they haven't been deployed. Why?
Fact is no market because the utilities already handle massively changing demand and have for over 100 yrs and that in reality is the same as intermitant supply, both handled the same way rather easily.
The only extra cost was running enough equipment to handle expected surges but the changed with throttlable Gas turbines and retrofit kits for older ones.
That plus demand like controlling when EV charger charge, etc solves 99.9% of grid needs. Fact is you can't build enough capacity to make a real difference due to volume of power used.
Get a sub to Pennenergy newsletters of your choice is the actual utility experts info and utility people running the plants instead of those who talk about things they no little.
Well, sometimes pumped storage reservoirs (the really big ones) can be used for recreation. Others may not be, as the fluctuations and currents as the project drains and then re-fills don't make the best environments for fish. Plus most new pumped storage sites are quite far from urban areas.
Thanks for the info, Matthew. I would think pumped hydro would lend itself to public/private projects, since lakes provide recreational opportunities for cities. Any city could use an extra lake. Have you seen public/private projects?
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