Putting PV and energy storage together

July 12, 2011 - A solar PV testbed in Arizona is widening its reach to investigate integration of different energy storage technologies with PV onto the grid.

Attached to a 1.6MW solar plant located at the U. of Arizona’s Science and Technology Park (owned by Tucson Electric Power), built by Solon, the energy storage research and testing site will have four phases: the first will implement compress air energy (designed by UA faculty and students in the AzRISE program), followed by a second phase with lithium ion. Solon’s Supervisory Control and Data Acquisition (SCADA) system will manage it all. The UA’s overall SolarZone is a ~14MW combined testbed incorporating various types of solar tech in 2-5MW chunks: multijunction CPV; "more conventional PV"; and concentrated thermal storage for CSP.

PV variability isn’t so much of an issue now, but as it scales from what is "large" today (~20MW) to "large" in the future (multiple hundreds of MW sites), intermittency will have a definable cost for utilities, explained Bill Richardson, Solon director of R&D. (He’s also at Intersolar North America this week, speaking about energy storage.) By pairing solar PV with energy storage, "there’s an opportunity beyond just fixing intermittency" to other things storage brings to the table: shifting when output happens, frequency/voltage control, transmission/distribution deferral. "Customers in different places have different needs," he noted, so Solon wants to get familiar with and know how to integrate different kinds of energy storage technologies. Put another way, Solon’s in the business of managing energy systems, and then handing it off to customers, including control of everything (generation to storage). For TEP, they get an up-close look "how to control these things, what works in what situations," Richardson said. And for UA, well, it’s full of really smart people who want to try out different things, such as algorithms for energy management.

For example, compressed air, the first-stage candidate in the Solon-TEP-UA experiment. TEP thinks compressed air "is interesting on a large scale" to help shift the load, Richardson said. (And UA happens to also have developed prototype of a system that makes compressed air more efficient, he added.) On the flip side, Li ion is better for short-term power, and TEP is interested in this angle too. It’s simply being able to address energy management from both sides (generation and storage) with whatever’s needed for the grid at that time, "and have control over the whole thing," he said. The pieces will be slightly bigger than 100kW, and it’s "more interesting to have smaller demo pieces to practice on, gather data, then scale up," he said — because for some customers that small size could be just right.

The CAES will be introduced in August, and Li ion added in 4Q11. Two more are slated beyond that, with help from partners, but without specific guidelines. Beyond that, the site won’t be maxed out; it’s a test site to look at long-term effects, so there’s the ability to continue to put in new technologies from new partners.

And to that point, there’s not really an endpoint in the project; e.g. they may quickly learn what CAES efficiency is and its cycle times, but there will still be value in validating technical and economic models. UA is working on algorithms to help storage make decisions on its own: e.g. taking into account grid rates and weather forecasts to determine if the system should charge or discharge. Then compare what the model says the utility could save, run it with real PV for a month and see if the numbers line up.

And data on that modeling is critical for funding as well, Richardson added, showing financers a field-proven working model.

Richardson noted Solon is open to other demos, with utilities or even banks (and hinted they indeed are, but wouldn’t specify with what partners or technologies). "There are lots of different companies and storage out there to be investigated," he said, "and we’re willing to work with all of them."

Bottom line: future turnkey PV systems will come attached with energy storage of some type(s). "We want to be able to hand the keys over, the control for all of it," Richardson said.

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