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Grid Storage a Key to Success of Renewables

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Matthew Shapiro
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Iron
Re: Yet another infrastructure problem?
Matthew Shapiro   4/26/2012 11:22:38 PM
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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). 

Scott Orlosky
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Platinum
Re: Yet another infrastructure problem?
Scott Orlosky   4/29/2012 11:08:20 PM
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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.

Rob Spiegel
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Blogger
Re: Yet another infrastructure problem?
Rob Spiegel   4/30/2012 12:30:31 PM
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Interesting, Geoff. I would think the degradation on battery storage would be greater and that pumped hydro would be more efficient.

Rob Spiegel
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Re: Yet another infrastructure problem?
Rob Spiegel   4/30/2012 1:28:55 PM
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I agree it's a good thread, Scott. Facing the storage problem certainly indicates that renewable energy sources have reached the point where storage is a problem that needs attention. 

Kevin
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Re: Yet another infrastructure problem?
Kevin   8/19/2012 4:00:08 PM
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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.

 

Kevin

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