Renewable Integration: Solving the Volatility of a Smart Grid

Chris Campbell, A123 Systems
June 27, 2011 | 3 Comments

With Storage Week 2011 just around the corner, I thought it would be appropriate to discuss the challenges of renewable integration and provide some insight on the opportunities currently on the horizon.

In addition to frequency regulation and spinning reserve, advanced energy storage technology, including lithium ion battery systems, helps facilitate the increased penetration of renewable energy sources to the grid. Energy storage addresses the inherent variability of wind and solar, which is one of the key remaining hurdles to renewable adoption within the current power infrastructure. With the increased penetration of renewable generation, the grid is experiencing a shift from predictable dispatchable generation to variable non-dispatchable generation. This adds a new level of uncertainty and volatility to the grid that causes an array of problems as the relative proportion of variable generation vs. traditional dispatchable generation increases.

Since generation from renewable sources is unpredictable, it becomes difficult to schedule and manage traditional generation assets to compensate. Renewable sources also tend to be geographically concentrated and isolated, causing problems related to transmission constraints. Furthermore, the continuous change in generation results in imbalances and volatility, increasing the area control error (ACE), which measures the generation and demand imbalance usually on a second-by-second basis.

Grid and renewable operators are struggling to respond to these changes. Options such as adding additional gas turbines to compensate for the variability of renewables are being discussed, but these are imperfect solutions given that they essentially counteract the benefits and purpose of deploying renewable sources. Wind farm operators can curtail their output to reduce the impact, but doing so forgoes generation and reduces the value of wind output.

Advanced energy storage can be used to address the unpredictability of renewable generation, and meet operational performance standards being established to mitigate the effects of increased amounts of variable generation. Technically, storage can address most of the issues associated with intermittent generation. Short-term, fast-response storage has already been demonstrated as a viable means of managing grid imbalances and volatility through the regulation service. In the longer term, storage can be deployed to shift energy in time to “smooth” the output of renewable generation or reduce the peak load on constrained transmission assets.

In addition, inverters used to connect large scale battery systems to electrical grids can provide reactive power as a coincident service that can help support improved voltage, and related performance requirements. One utility taking advantage of these benefits is Southern California Edison, which is deploying energy storage systems based on lithium-ion technology at the Tehachapi wind farm.

An important factor to take into account is whether advanced energy storage can provide an economically viable solution. While regulation services using short-duration storage produce measurable return on investment, increasing the duration of storage increases the cost.

Renewable energy and power grid operators should therefore consider multiple functions for storage assets—for example, performing both shifting and regulation—or taking advantage of price differences during the day, often referred to as inter-temporal arbitrage. Combining multiple functions can provide multiple revenue streams, making the economic benefits of advanced energy storage for renewable integration more prominent.

3 Comments

marc metteauer
July 1, 2011

One new technology that would address the storage issue is the RPM, which was on the wire yesterday with a new patent. It can store AC power as real AC, without conversion, and be instantaneously available. If it's scalable, this could be a huge part of the storage equation. I would like to see more about it. http://www.prweb.com/releases/2011/6/prweb8605066.htm

Garth Barker
June 28, 2011

Right on. The only stumbling block in the way of storage is the assignment of a dollar value to the benefits; California is working on it, the FERC needs to finish the task they started and when done there will be another market created - a two way market based on sub-hourly pricing; a boon for the energy system but not so much for fossil fueled generation that's primarily used for integration of variable resources.

Gary Tulie
June 28, 2011

There are essentially two main factors affecting the management of power grids with large penetration of intermittent generation.

1. The risk of excess generation

In extreme conditions, power generated by wind and solar can exceed demand on the local grid even before any contribution is made from traditional generation. This has occasionally happened on windy summer nights in Western Denmark (Denmark has 2 power grids).

2. Variation from prediction

This in the more common problem and relates to errors in predicting wind or solar power, and consequent increases in spinning reserve which must be maintained to ensure grid stability. Usually error bars across a region are around +/- 10% from prediction 4 hours ahead.

Both of the above can be mitigated by one of three techniques

a. Adding power storage to the system

This enables any excess power to be absorbed and released next time there is a deficit.

b. Management of load

In the case of areas with district heating, this can direct any excess electricity to heat pumps (factor 1), or with the same heat pumps act as a swing - scheduling power production up to the bottom of the error bar to the grid and directing any electricity above this production level to heat so eliminating most of the net variation from predicted output (factor 2)

Note:- There are other loads which are not time critical which can substitute for heat pumps on district heating networks

c. Improve grid infrastructure

Develop more and bigger electrical interconnections allowing power to be shared over a much bigger area. This will greatly reduce the risk of excess power production and tend to reduce the percentage size of the error bars on predicted power output (variations tend to even out over a large area).

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Chris Campbell

Chris Campbell is responsible for A123 Systems’ global go-to-market strategy for the Energy Solutions Group business unit. He is defining and developing the worldwide markets for A123's energy storage solutions, exploiting a rapidly expanding...