Solar show pushes for energy storage

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The U.S. Intersolar show took place in July in San Francisco with over 22,000 attendees and 800 exhibitors. Initial keynotes dwelled upon what it will take in terms of policy and infrastructure to create a 10 GW annual market in the U.S., solar expansion (growing 67% in 2010 and demand for photo-voltaics in Q1 2011 up 66% over Q1 2010), The U.S. Department of Energy’s (DOE) SunShot Initiative which targets 50 cents per watt module manufacturing costs, and the success of the California Solar Initiative (CSI) (19,877 PV systems installed in 2010 amounting to 194 MW). After the initial fanfare, attendees serious about achieving utility-scale solar broached the subject of twinning renewables with some means of energy storage.

Eric Cutter, Lead Analyst at Energy + Environmental Economics (E3) explored the value proposition of integrated solar photovoltaic (PV) and energy storage systems.

“Costs may be high, but they are declining rapidly,” he said. “The question is whether the combination can become cost effective in the near future.”

On the plus side of the ledger, he cited solar’s provision of on-peak generation, lack of emissions, distributed architecture. When twinned with storage, power delivery would be reliable and dispatchable with fast response. However, the analyst confirmed that even considering all possible benefits of PV/storage to the utility and the customer, that does not outweigh the costs.

To make matters worse, he noted that more efficient and flexible turbines and cheap gas presented an even steeper challenge to the renewable movement. 

To bridge the gap by 2014, he expected 20% in cost reductions for PV, a 40% drop in storage battery prices (or other storage technologies) and a cut in the size and balance of system costs for solar.


“The key to bridging the gap is to provide high penetration and distribution of PV, better integration of renewables and further evolution of existing business models,” said Cutter.

Janice Lin, Managing Partner of Strategen Consulting and Director/Co-Founder of the California Energy Storage Alliance (CESA) said energy storage was fundamental to many key California policy initiatives. The state has already passed legislation to procure workable energy storage for renewables while rolling out a series of mandates to utilities and incentives to consumers to adopt solar and wind. As a result, several new storage projects are already underway in the Golden State. These mainly fall along the lines of already existing facilities and cover a broad range: sodium sulfur batteries which have been adopted in the form of a 34 MW battery being used at a wind farm in Japan; producing ice at night using excess energy in order to provide additional daytime cooling at lower cost – Napa Community College currently has a 12 KW thermal storage system; high-speed flywheels which convert electrical to kinetic energy and back again such as a 3 MW unit used by New England ISO; below ground compressed air such as the 115MW compressed air energy storage (CAES) plant in McIntosh, AL; and pumped hydro, such as the Tennessee Valley Authority’s Raccoon Mountain.

To get over the cost hump, she saw another approach than purely incremental improvements in storage technology: offset or even eliminate other planned expenditures.

“New required transmission to meet the state’s 33% renewable portfolio standard goal will cost around $12 billion,” said Lin. “Closer examination may identify areas where storage can provide cost-effective transmission and distribution deferral benefit.’

Meanwhile, a company known as Xtreme Power has developed a solid-sate dry cell battery that provides 1 MWh of storage. It smoothes output to plus/minus 100 kW/min and controls ramps to within 1 MW per minute. The latest version is under construction will provide 10 MHh for a 30 MW wind farm in Hawaii.

The Sacramento Municipal Utillity District (SMUD) is an example of a utility developing its own energy storage due to the timing of renewable output.

“Solar’s intermittency, forecast difficult and slight mismatch with our peaks are challenging,” said Obadiah Bartholomy, Project Manager for SMUD. “Our wind resource blows well, but mostly at night.”

It has grand plans to virtually eliminate natural gas generation by 2050. But this leaves a massive energy gap that renewables only go partway to closing.

“Solar with storage could solve our peak problems,” said Bartholomy. “Without storage or control, however, it could well create problems.”

SMUD is installing two 500 kW zinc bromine 6-hour battery systems in one demonstration project as part of a micro-grid which includes a combined heat and power (CHP) plant. It is also evaluating a 400 MW (10 hours capacity) pumped hydro project at Iowa Hill and the Solano CAES project which has a 25 to 200 MW potential. It would depend upon natural gas for return energy.

Tom Stepien, Chief Executive Officer at Primus Power, made the point that renewable sources had to match the steady advancements in flexibility being demonstrated by gas turbine generation sources. This is where grid storage can help, he said. He pointed out that storage technology is almost wholly using a centralized model with pumped hydro accounting for 99% (127,000 MW). In comparison, CAES has 440 MW, various battery technologies account for 401 MW and flywheels 25 MW.

Per his analysis, energy storage would have slightly lower capital costs than utilized gas generators for energy firming, would not consume water or pollute, would require a smaller footprint and could be installed in a few months rather than several years. Primus Power is advocating EnergyPods consisting of banks these battery pods which could be placed on site at wind and solar farms, or even individual cells deployed in houses.