One afternoon on a particularly muggy day, a power outage has suddenly struck in a large metropolis. Shortly thereafter, that same evening, somewhere in the depths of the power utility’s grid computer system, an internet alert was regionally generated to countless Tesla Model S vehicles whose auto-pilots immediately set course via GPS for the affected grid sub-stations. At once, garage doors opened, electronic drives sprung to life, autonomous vehicles reversed onto suburban streets and in a seemingly dream-like trance, but fully aware of their surroundings, entered highway on-ramps in a journey to become veritable power sources through banks of power inverters to the blacked-out region (Figure 1). Each of these vehicles, with their 85 kW-hr capabilities, now provided emergency power to hospitals, businesses, and homes in the region until utility crews could restore power.

Teslaroadx600 Figure 1: Teslas on the road with automatic steering and traffic aware cruise control. (Image courtesy of Tesla Motors)

And there was a bonus to these electric vehicles (EV) owners who availed themselves to this opportunity: They are selling back their energy and gaining a nice margin over what it cost them to charge their vehicles at night---as much as a 6x return-on-investment. Where else can you get that kind of return on your money?

This is Nuvation’s Mike Worry’s fantasy of a Hollywood movie-like, science fiction to become a reality in the next five years or less. Think this is still a fantasy? Well Nissan just announced on May 10 a new trial scheme allowing electric vehicle owners in the U.K. to sell power from their vehicles back to the grid. Under the vehicle-to-grid (V2G) pilot project, developed in partnership with Italian utility Enel and U.K.’s National Grid, 100 Nissan LEAF vehicle owners in the U.K. will use special bi-directional charging points to sell stored power from their vehicles back to the grid at peak times.

There are currently about 18,000 electric Nissan LEAFs running on U.K. roads. If all were connected, they would have a capacity of 180 MW of energy.

__Ask the experts __ I recently called upon Mike Worry, CEO of Nuvation Engineering and Martin Mills, Regional Sales Manager of Maxwell Technologies for their expertise in bringing to the EDN audience, a clear picture of large scale energy storage and the Ultracapacitor’s place in this technology.

__Daily Energy cycling __

I began our discussion with a question regarding the use of batteries and ultracapacitors in smoothing out solar and wind-powered generators’ output fluctuations over time. Worry commented that this was a good example of a hybrid application working well to combine the high power of ultracapacitors with the high energy of batteries. In applications such as this, the need for a great deal of energy that a battery can supply in a function such hours-long electricity demand reduction is combined with the exceptional response time and cycle life of an ultracapacitor measured in millions of cycles vs. the battery’s thousands of cycle capability.

If there are wind gusts occurring 10s of times per day, then you will consume a battery’s life in under a year. See Figure 2. Whereas, if you hybridise with ultracapacitors, you now have a quality system that is able to handle the frequent high power surges with ultracaps and the slower but longer duration outages with a battery.

WindFarmCaithnessx600 Figure 2: Wind Farms taking flight (Image courtesy of Caithness Energy)

This is both good for operations and good for cost. Worry said that what Nuvation, as an engineering company, finds in these energy storage systems is that to each part of a problem you build a different solution, so ultracaps and batteries work really well in such situations.

Mills added that from Maxwell’s perspective, ultracaps in these types of hybrid systems really are a great complement to batteries. They help extend life expectancy as well as reduce the potential size of the batteries required. The operational temperature range also give ultracaps an advantage, even though most of these systems will have some sort of thermal management capability. Ultracaps are exceptional at extreme cold temperatures as compared to batteries, so thermal management design, if implemented, need not be too elaborate or costly.

I commented that I had written an article in which ultracaps supplemented batteries in a light rail transportation system in extremely hot climates like Arizona where I live. A Maxwell expert gave some great insights into this type of design challenge.

Mills said that there are two different market segments where ultracaps are used in transportation and grid applications: When an ultracap is deployed on the light rail vehicle itself, that is a transportation market area; when it is used to store wayside energy captured through recuperative or regenerative braking, we call that a grid application.

Rate-payers concerned with the cost of using the utility

I posed the question asking how stacked utility services could be implemented using smart-storage electronics. I wondered how services such as demand charge reduction could save rate-payers money by using energy during low demand times and providing energy back to the grid during peak times. And how ultracaps would fit into this scenario.

Worry exclaimed that the fascinating part of the emerging energy storage industry is that we’re taking a resource of energy that used to only be instantaneous and transactional and we are inventing the concept of being able to store it and then apply that stored energy using energy management software.

By analogy, imagine what money was like before we had the ability to store money in banks or before we had the ability to store information in written form. We are now doing that with energy. There is a whole new economic model that has emerged from that.

The ability to stack these services is really in a software layer and the ones that make for quick returns and justify return on investment (ROI), like demand charge reduction and load shifting or behind-the-meter applications, are all about how the utility prices electricity. If they charge a premium for your highest amount of power draw, then of course that will motivate the industry to figure out what they can put in place in the way of energy storage to reduce that demand charge, and equally if there are different charges for different times of the day, then that will motivate the industry to use energy for time-of-use shifting. Worry thinks we will see emerging residential energy storage systems that basically make decisions, stacking those different types of algorithms to figure out the best way to apply energy storage in order to reduce your electric bill.

Then on the utility side of the meter you see stacked services that are making different decisions because on the utility level there are things such as renewables integration and frequency regulation that are operating at a larger level and making different decisions; this would be another set of algorithm-stacked services that run on the grid level.

Easing the financial burden

I live in Arizona where there are many people with residential solar installations that are taking advantage of the abundant sunshine here in the desert. So many homeowners think they can get off the grid easily here. Without energy storage, that is going to be difficult because there are still cloudy days during the monsoon season as well as other times of the year. ROI is in the order of an average of 10 years or so for these types of installations to recoup their initial investment. (See this Solar ROI calculator app) So stacked usage would help lessen the financial burden of the homeowner utility bill.

RPSmapx600 Figure 3: RPS policies are in 29 states and Washington, DC (Image courtesy of Berkeley Lab)

Mike Worry thinks we will see some energy storage rollout in high quantity, small energy storage systems on the residential side in order to have people optimize their electric bills. The largest driver for energy storage will be on the utility scale, and he thinks it will be the very high Renewable Portfolio Standards (RPS) targets of many utilities. See also California RPS website California RPS website (Figure 3).

Learn about Solar Curtailment in the second part of the article.