Energy storage will soon become an essential element of the smart grid, especially as more power generation from inherently interimittent sources such as solar and wind come online. So what's so cool about energy storage? Analysts see a strong, upcoming demand for energy storage as part of the grid.

This will likely be a combination of some kind of central storage (i.e., a 20MW flywheel installation near a power generation station) and distributed storage (i.e., batteries or supercapacitors next to the familiar green transformers in people’s yards). These types of energy storage are primarily driven by a need on the part of utilities for load balancing, since it's expensive for them to constantly adjust the output of traditional power generation systems as the load varies. Energy storage may even allow them to offset or delay the requirement of additional power plants, such as a gas-fired "peaker" plants.

According to a report from Pike Research, the demand for energy storage is driven by several trends, including the proliferation of intermittent renewable energy sources such as wind and solar, the move toward smart grids, and the coming rise of plug-in hybrid and electric vehicles, to name just three.  While storing electricity was once thought a practical impossibility, a variety of technologies have now emerged to disprove that theory, and the global energy storage market is poised to grow from $329 million in 2008 to $4.1 billion by 2018, according to Pike.

From the PV perspective, however, experts aren't so sure (unless you're totally off the grid). There may be value for companies and people to buy and store power when it is least expensive, and use the stored power during peak demand when prices are highest. Called “time shifting,” this is an interesting concept, although it may be a bit ahead of its time.

Jaime Smith of SunEdison (Beltsville, MD), who runs the installer/developer’s North American PV commercial operations, said “as far as taking a solar curve and shifting it and it being worth the value of that shift for the cost of the storage, we have not seen that yet. We’re keeping our eyes and ears open for the right technology but we haven’t seen anything yet that is cost-effective.”
 
To a lesser extent, the need for energy storage will also be driven by the inherently intermittent nature of many renewable energy sources, such as solar power and wind. As more of this kind of power generation comes on-line, it makes sense to store the energy for times when the wind isn’t blowing or the sun isn’t shining.

Proponents of solar power, however, like to point out that although PV is intermittent (due to clouds and of course darkness), it’s actually highly predictable. Clouds don’t cause that much variability if the PV is spread out over a wide enough area, and because they are visible, it’s relatively straightforward to predict the impact on power generation on a short-term basis and even easier to predict the amount of power that will be generated the next day based on weather reports. That’s fine because power markets operate on a day to day basis.

Dan Shugar, CEO of Solaria (Fremont, CA), a supplier of PV modules, said: “In PG&E’s territory alone, which is pretty much north of LA up to Oregon, there’s about 30,000 solar plants. If you look at a 10 x 10 mile area, statistically there’s no variability.”

Also, depending on location, peak demand is often in near-perfect sync with demand, since it’s the heat of the sun that creates the need for air conditioners which are the primary source of demand.

“Solar is not available when you want it, but it’s available when you need it,” quips Smith of SunEdison. “It does have intermittency, but the reality is when the demand is the highest – which is when air conditioning demand is the highest – we are the strongest,” he said. Shugar agrees: “Do we need storage today? No. Solar is generating in a very high correlation with when the grid is needing power.”

While that’s true in most of California, it can be a little different in other States. “We’re not perfectly correlated because people come home and flip on their air conditioning in Western States at 5:00 and we’re peaking earlier than that, so storage could be very interesting for us to try to shift that curve,” Smith said.

In the future, 5-10 years from now, when PV and other renewables come to represent a significant percentage of the overall power generated for the grid, energy storage could play an increasingly important role.

“As you go from a scenario where 2% of the peak load is generated by PV to 20-30-40%, you start to get into a situation where you need storage,” Shugar said.

But he also points out that there are many other ways to control demand with a smart grid in place.

“Instead of building dedicated storage systems, there are other things you can do. For example, all the commercial buildings with over 50 kW/h of load have time of use metering now. It’s very simple to install some demand response – there are programs that exist right now that are doing that – where you might let the temperature go from 71 degrees to 72 or 73 when electricity prices are highest.”

Electric vehicles will also come into play, in part by helping to advance battery technology, but also by becoming an integral part of the smart grid. Andy Chu, director of marketing at A123 Systems (Watertown, MA) envisions a time when utilities are so linked into the grid that they can monitor and control electric vehicle battery chargers, and charge them quickly or slowly so as to optimize the load/generation equation.

“Electric cars already have a computer in there that can control the charging rate,” Shugar said. “My car is charging right now out in the parking lot from a solar array coupled with the building. I could easily control the rate at which that car is charging based on the availability of solar or a demand signal from the utility.”

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