Sunday, August 11, 2013

Hawai`i Energy Storage: Many storage technologies compete to back up intermittent renewables

You can’t run a 24/7 power system on intermittent renewables like wind and solar.

They won’t keep the lights on.

But the Islands are building intermittent renewables like mad, and leaving legacy fossil fuel plants to back them up. Ultimately, that’s neither sustainable nor in line with state policy.

The next few RaisingIslands posts will review how the paradigm is changing. The key to the change is the fast-moving new world of energy storage.

With appropriate storage, intermittent power becomes firm power. Oil and coal plants can go away.

Our primary sources for this series are a four-day conference on utility-scale energy storage research and a new industry/government report, the DOE/EPRI/NRECAElectricity Storage Handbook for 2013, which was released earlier this summer.

If you’re interested, you should read the report, as we’re only going to summarize pieces of it here.

As little as 10 years ago, there was very little choice available in terms of energy storage—most folks were getting by with lead-acid batteries, although there was a lot of “potential” out there for different storage technologies.

That has changed.

“Storage for frequency regulation has become fully commercial and facilities are being built to explore renewable integration, PV smoothing, peak shifting, load following and the use of storage for emergency preparedness,” wrote Imre Gyuk, of the U.S. Department of Energy’s Energy Storage Program, in the foreword to the report.

The Hawai`i Clean Energy Initiative plays a role in the story, and is cited in the report.

What quickly becomes clear when you pay attention to energy storage is that this field is dense, complex and difficult to summarize, other than to say there’s a lot going on.

Most folks think about storage and think batteries, and indeed, batteries are a key piece—perhaps the biggest piece. But they’re certainly not all of it. There is also, flywheel energy storage, compressed air energy storage (CAES), pumped hydropower, thermal storage, and hydrogen.

Each of these technologies has strengths and most also have significant weaknesses. Some are appropriate for certain applications but not for others. Balancing those features is both difficult and necessary to move forward.

There are many issues in deciding whether a new system is ready for prime time. Here are some of them, which I drew from my participation in a June conference in Newport Beach, “Massive Energy Storage for the Broader Use of Renewable Energy Sources.”

This list is largely designed to rank battery storage systems, but much of it can be applied to any storage technology.

The dream energy storage system of the future needs to be:
Made of cheap materials;
Efficient, in that you get nearly as much energy out as you put in—preferably 80 percent round-trip efficiency or better;
Safe, in that it won’t explode, leak, or otherwise endanger those in the immediate vicinity;
Have charge-discharge capacities of approaching 10,000 times;
Energy dense, so it is compact (although this is more important for mobile systems like electric car batteries than stationary utility-scale storage, it can't take up too much acreage);
Made of non-toxic compounds;
Recyclable at the end of its useful life;
Able to operate at ambient temperatures.

Oh, and it needs to be far cheaper than anything available today. The U.S. Department of Energy’s ARPA-E program is looking for batteries in the $100 per kilowatt-hour range. Most of the cheapest technologies available today are in the range of 5 to 10 times that...or more.

Can we get there? In this series we’ll take a look.

(ARPA-E stands for Advanced Research Projects Agency-Energy. It is a Department of Energy program modeled on the Department of Defense's DARPA, the Defense Advanced Research Projects Agency.)

© Jan TenBruggencate 2013

1 comment:

Jonathan Cole said...

Energy storage is a complex subject and there are many ways to calculate its value.

There is the capacity per cycle times its lifetime # of cycles. Or there is the actual cost per kWh stored regardless of the capacity of the storage medium.

In distributed solar energy systems, the important cost is the cost of lifetime kWh capacity, because it is very difficult to actually calculate how much electricity is actually stored, because it is going in and out of the battery under many complex sets of conditions. The solar PV feeds the battery but it also feeds the inverter for ongoing electrical use during the day.

The most important thing about storage is how little do you actually need in order to maximize self-consumption and autonomy while also maximizing the life of the battery.

FYI, I just purchased four L16 flooded lead acid batteries for ~300 each. Together they amount to a nominal 10.08 kWh of storage (12 VDC x 840 AH at the 20 hour rate - more at a slower rate).

With these batteries you have to de-rate them by 50% in order to maximize their life so it is more realistically ~5 kWh of storage.

My last set lasted for 7 years at about 250 50% cycles annually. That comes out to about 8750 kWh stored or $0.13/kWh stored.

However, I cannot supply exact figure as to how much was stored and how much was used during the day. That is an automatic balancing act based on very complex and varying conditions.

That is why I have instead learned to size the battery according to optimal operating conditions. Experience demonstrates that it is a ratio of generated energy to stored energy that gives the best and most cost-effective solution.