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Storing Solar Energy for the Grid

published: 2011-08-23 9:58

Whether it is utility-scale or residential, storing solar power from PV panels in the form of electricity is currently the subject of millions of dollars of R&D in the United States where several large-scale PV power plant farms are being built or planned. Banking this electric power for release at times when the PV panels are not producing is essential to avoid grid fluctuations.

The U.S. federal and state governments have approved billions of dollars for research on a variety of energy-storage technologies in the past two years. This funding for storage technologies has not gone unnoticed by venture capitalists. Many of these projects are targeting energy from concentrating solar power (CSP), such as underground compressed air and thermal storage (molten salt).

CSP has an absolute storage advantage over PV through the ability to store thermal energy for up to 15 hours after the sun is no longer shinning. For CSP, the storage process involves storing the heat energy - through thermal storage – and releasing it to drive the generators that produce the electricity.

But for PV systems, the energy that needs to be stored is the actual electricity destined for the grid. Technologies for PV energy storage, such as super capacitors, hydrogen generation and fuel cells, are still under development to work out a variety of issues before they can be deployed for grid storage.

Meanwhile, batteries (Li-ion, sodium sulfur and flow batteries) are currently the technology of choice.

2012 Grid Storage Market

In April 2011, the U.S-based Electric Power Research Institute released a report that lays out 10 energy storage applications EPRI thinks will serve the energy storage market and support wholesale renewable producers. The EPRI research also identifies 21 benefits of energy storage, including power quality, power reliability, retail time and retail demand charges.

EPRI pegs 2012 as the real turning point for the grid energy storage market because most of those U.S. companies that received the bulk of the DOE federal stimulus funding for storage projects are expected to move into pilot project testing stages.

“Despite the large need for energy storage solutions, very few grid-integrated storage installations are in actual operation in the United States. This landscape is expected to change around 2012, when a host of new storage options supported by U.S. stimulus funding begins to emerge and, in turn, catalyzes a portfolio of new energy storage demonstrations. Such tests in real-world trials will provide needed data and information on the robustness of such systems, including performance and durability, cycle life costs, and risks,“ states the report.

According to the EPRI report, the total U.S. energy grid storage market could support as much as 14 GW of capacity if these energy storage systems could be installed for about $700 to $750 per kilowatt-hour.

Grid Storage Batteries Advances

Flow batteries, basically large tanks of liquid that produce and store an electric charge, is one of the new technologies being explored for large-scale grid storage.

Silicon Valley-startup EnerVault has completed the design of a prototype of such a battery and is launching a demonstration project at an almond farm in the California Central Valley town of Turlock in late 2012. If all goes well, the company - with the help of $3.5 million it raised from venture capitalists – says they will make the technology available in 2013.

Meanwhile, California-based Primus Power is using a $14 million DOE grant and $11 million in venture capital to build a 25 MW zinc flow battery farm in the California Central Valley town of Modesto beginning in early 2012.

Aquion Energy is developing a sodium ion battery as an alternative to lithium ion batteries for grid storage. The advantage of sodium, basically salt, is that it is much more abundant than lithium. The company plans to use low-voltage cells that would operate between 12 volts and 48 volts. Strung together into a shipping-container-size box, the batteries would produce 500 to 1,000 volts.

A spinoff from Carnegie Mellon research and originally funded with $5 million from the DOE, the company expects to start producing its battery packs for testing by the end of the year and begin manufacturing by 2013.

AzRISE Storage Project

In Arizona, Solon has partnered with Tucson Electric Power and Arizona Research Institute for Solar Energy (AzRISE) at the University of Arizona for the development of an energy storage management research and testing (SMRT) site next to the 1.6MW solar plant Solon previously built at the University’s Science and Technology Park to study different energy storage technologies. It is the latest of six storage research sites AzRISE has established around Arizona to tackle various storage issues.

Research at AzRISE is addressing “the goal of baseload through peak load electrical generation with solar energy and energy storage technology solutions.”

One problem utilities have today is managing energy reserves to avoid higher costs that can occur with maintaining an oversupply of power as well as the risk of blackouts from a loss of power.

Small Scale Storage Spin-Offs

While most of the research and pilot projects are targeting utility-scale energy, there is also an opportunity for smaller-scale energy storage behind the meter at individual commercial or housing sites. Currently, there is no way for individual power users to locally store off-peak power in order to benefit from any cost savings they may receive from reduced dependence on peak load utility costs, as well as secure a reliable source of power during an emergency.

This form of individual energy storage would allow businesses to manage spikes in their power usage that can drive their electric costs higher during peak hours. This type of energy storage application does not require the enormous amount of energy storage capacity that a utility grid-scale storage project would require. Residential projects, such as a community battery storage project, would also alleviate hardships of wide ranging blackouts that can occur during natural disasters.

One project started in 2010 involves using 16-kWh lithium-ion batteries from the Chevy Volt, which still have up to 70 percent of useful life after their specs are to low for automotive power. General Motors and ABB, maker of grid-tied inverters, have created a battery pack for 25 kW storage applications, which would power about five U.S. homes.

American Electric Power and S&C have also begun a DOE-funded community energy storage pilot project using 25 kWh lithium-ion battery packs that will be put in communities next to transformers that would feed three to five houses with 80 25-kW units on one circuit.

Combining and Sharing Technology

The technologies that seem to be making it to the market place the fastest are those technologies targeting the need to store energy for only short periods of time.

According to the current research trend at AzRISE and elsewhere, the issue of energy storage will probably be resolved on the utility-scale by using a mix of different energy storage technologies, including super capacitors, batteries and underground, high-capacity compressed air. Like most technology applications with a host of variables, different energy storage options will work for different specific applications and needs.

There also seems to be a consensus that, unlike other energy technology breakthroughs that tend to remain proprietary, information sharing among the energy storage players will be open since the need to solve the grid storage issue is immediate.

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