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The Role of Storage with Variable Energy Sources Like Wind and Solar

by November 8, 2011

In a recent post, I asked What’s Going To Happen To Your Vehicle’s Lithium Battery At the End Of Its Life? One of the options discussed in the NY Times article about the fate of batteries that sparked my post was as a means for storing electricity generated by wind turbines. A couple of other recent articles about energy storage caught my eye—both related to wind energy.

Why might storage play a key role in a grid that has a lot of wind turbines?

In early October, Mark Ahlstrom, the CEO of WindLogics, gave an excellent presentation as part of Frontiers in the Environment series at the U of MN’s Institute on the Environment (view the video here). He explained how our variable demand for electricity over the course of a typical day is met by a range of generation sources, from base load to “peakers.” Base load is met by nuclear, coal, and hyrdo—depending on location. Base load plants are meant to run 24/7, and adjustments to their output need to be scheduled well in advance. On the other end of the spectrum are peakers, which are small electrical generators that can be turned on with little notice and do not need to run for a minimum period of, say, a day. The figure below is based on a slide from Ahlstrom’s slides.

ahlstrom-sys-load-combo

Ahlstrom went on to explain how things get interesting when a substantial amount of wind generators are added to the mix. In the figure below, the bright green line represents the reduced daily load that results by adding a number of wind turbines to this hypothetical typical energy demand. He goes on to explain how the rest of the electricity generators need to adapt to this new load curve, which can have more spikes and other challenges, such as a faster ramp-up in the early morning hours—challenges that the current energy system wasn’t set up to tackle.

ahlstrom-sys-load-combo-2

Here’s a good piece by the ClimateWire group that landed in the NY Times: Fickle Winds, Intermittent Sunshine Start to Stress U.S. Power System. It dives into detail about the policy challenges that blending intermittent energy sources with our traditional electrical generation system.

Back to storage. A recent piece in the NY Times described how Batteries at a Wind Farm Help Control Output. In the largest battery installation connected to the grid in the U.S., they’ll use over a million batteries to provide storage for a few minutes of generated electricity from a large wind farm in West Virginia. The idea is that this stored electricity can be fed into the grid to help smooth things out when output from the wind turbines drops off momentarily. It is not designed to even out longer periods when the wind is calm. Significant storage on the time scale of hours and possibly days would most likely require a solution such as pumping water uphill or compressing air when the wind blows, and then using this stored energy to run a generator when the wind is quiet (here’s a project underway to study pumped hydro in conjunction with wind farms in northern Minnesota). There may also be options to store electricity in electric vehicles integrated with a smart grid of the future.

Finally, another NY Times piece that gave me some pause had to do using water heaters and electrical space heaters to store excess electricity brought about in part from excessive winds in the Pacific Northwest. The idea is that automated, shorter-term storage of excess electricity in homes that already have electric hot water heaters and heat with electricity could bleed off excess electricity pouring into the grid during storms when wind generators are running at maximum output (note that the situation was further complicated because hydropower operators were unable to reduce output from their generators for fear of creating conditions that might kill fish).

At a gut level, this strikes me as a good way to avert disaster, but probably not a great strategy from an energy efficiency standpoint. My sense is that using electricity for water heating and space heating is not nearly as efficient as, say, natural gas. The standard reason for arguing this point is that the efficiency of traditional energy plants is much less than 50%, whereas a high-efficiency hot water tank can exceed 90%. However, maybe this standard reasoning needs to be updated in a situation where electricity comes from wind or solar. This is a topic that merits further consideration.


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