March 24, 2013

Bulk Wind Generation to Distributed Storage

Executive Summary

A significant challenge for grid operators is effective integration of an increasing amount renewable energy (RE) fueled generation whose output varies. Variation occurs year-to-year, season-to-season, throughout each day and minute-to-minute. Variable RE generation types include wind, solar (especially photovoltaics), ocean wave and tidal power.

For the foreseeable future, much or even most variable RE electricity production is expected to be from wind generation. Coincidentally, there is increasing interest in distributed energy resources (DERs). This value proposition combines wind generation integration electricity storage benefits with “locational” benefits associated with distributed storage (storage located in the utility distribution system, at or near where electricity is used).

Specifically, this value proposition entails use of distributed storage to store energy from bulk/central wind generation. The benefits and synergies are numerous. For example, at night, when most wind generation occurs, the demand for the energy and thus the value of the energy are low. By storing that low value energy for later use when demand is higher, its value is enhanced. Coincidentally, the utility transmission system is underutilized and most efficient at night, so charging distributed storage with bulk wind during this time increases utilization of the utility transmission and distribution (T&D) infrastructures. Using distributed storage to provide power closer to end-users provides more benefits than the same amount of power located further from end-users.

Discussion

Integration of wind generation into the electric supply and transmission systems poses some well-characterized challenges. First, as shown in Figure 1, a significant portion of wind generation occurs at night, when the value is low. Second, electric energy produced by wind generation at night contributes to an increasing number of hours during which “negative prices” prevail. This is because electricity supply exceeds demand and output from the generation that is on-line cannot be reduced without significant cost or performance penalties.

An especially attractive response is to use distributed electricity storage systems (DESS) to store the low value energy generated at night, by large central wind farms (see Figure 1). Coincidentally, the energy is transmitted and distributed to the storage when the T&D systems are lightly loaded so they operate more efficiently.That increases utilization of those T&D assets because more energy is transmitted and delivered using the same amount of capacity throughout the year. Conversely, that T&D capacity is freed up to transmit and deliver more energy, real-time, during peak demand times.By reducing T&D energy losses during peak, less total generation, transmission and distribution capacity is needed to offset the energy losses.

The same storage system could also be used to provide most of the “ancillary services” needed by grid system operators to keep the electricity grid operating in a stable and reliable manner. Depending on the location of the storage, it may also provide benefits related to improved local electric service reliability and power quality. By accommodating the variability of the wind generation, the storage also improves the overall performance of the electrical generation fleet because generation output does not have to be varied to accommodate (i.e., offset) wind generation variability. 

Two notable examples of regions in the United States with excellent potential for this value proposition include New York and California. In New York, there is significant potential for wind generation located “up-state” near the Great Lakes of Lake Ontario and Lake Erie. The potential is significant because of what is often called “lake-effect” winds that occur at night and that are relatively steady and predictable. Furthermore, transmission corridors into the New York City area are heavily loaded during the day and “in-city” generation is limited. In that case, storing energy from up-state lake-effect wind generation in distributed storage (located in New York City) offers compelling benefits. Similarly, transmission into the “Los Angeles basin” (L.A. basin) in Southern California is increasingly congested while a significant portion of RE generation development – including wind generation – is in less populated areas to the North and East of the L.A. basin. Adding more generation in the L.A. basin is challenging due in part to air emissions related siting challenges. So, charging in-basin distributed energy storage using off-peak energy from remote wind generation may be quite attractive.

This value proposition could involve a bilateral contract between: a) the wind generation owner and the storage owner or b) the wind generator and “aggregators” of distributed storage or possibly even wing generators and utilities.

Conclusions and Observations

Large scale wind generation is poised to be a significant future electric supply resource. As such, there are looming challenges related to integrating wind generation whose output varies throughout the day and from minute-to-minute. Coupling that variable wind generation with distributed electricity storage – especially within generation and/or transmission constrained “load pockets” – may be quite attractive.

In addition to increasing the value of the output from wind generation, numerous other benefits are possible, including: increased utilization of T&D assets, using the same storage to provide ancillary services, enabling less variable operation of the conventional generation fleet, reduced fuel use, air emissions and equipment wear, improved localized power quality and electrical service reliability.


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