Bulk Wind Generation to Distributed Storage

Executive Summary

A significant challenge for grid operators is effective integration of an increasing amount renewable energy1. Energy is the potential of a physical system to perform work. (A common unit of work is foot-pound—the amount of energy needed to lift one pound up a distance of one foot.) Energy exists in several forms such as electromagnetic radiation ... (RE) fueled generationThe manner in which electricity is generated. The electricity that flows through California 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 powerThe rate at which energy is generated, converted, transmitted, distributed or delivered..

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 propositionOne or more individual benefits associated with a specific use. A value proposition is said to be attractive if the total value of all benefits exceeds all costs, including required return on investment, if any. combines wind generation integration electricity storage benefits with “locational” benefits associated with distributed storage (storage located in the utility distributionThe practice of and infrastructure for distribution of electricity to end-users by utilities. Typical voltages range from 12 to 138 kiloVolts (kV) 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 demand1. The rate at which electricAn adjective meaning “needing electricity to operate” such as electric motor or wire. IEEE: Containing, producing , arising from, actuated by or carrying electricity. energy is delivered to or by a system or part of a system, generally expressed in kilowatts or megawatts, at a given instant or averaged over any designated interval of time. 2. The rate at which energy is being used by... 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 transmissionAn interconnected group of lines and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to customers or is delivered to other electric systems. 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 supplyA source of electric energy and/or capacity, possibly including generation facilities and purchases. 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 capacityThe rate at which equipment can either generate, convert or transfer energy. throughout the year. Conversely, that T&D capacity is freed up to transmit and deliver more energy, real-timePresent time as opposed to future time. (From Interconnection ReliabilityThe degree of performance of the elements of the bulk electric system that results in electricity being delivered to customers within accepted standards and in the amount desired. May be measured by the frequency, duration and magnitude of adverse... Operating Limits standard.), during peak demandThe maximum power draw from end-user loads during specified times. For example, most utilities experience peak demand during hot summer afternoons. 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 qualityA measure of the level of voltage and/or frequency disturbances.. By accommodating the variability of the wind generation, the storage also improves the overall performance of the electrical1. An adjective meaning “pertaining to electricity”. Electrical Engineer. 2. Related to, pertaining to or associated with electricity but not having its properties or characteristics. 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-peakThose hours or other periods defined by NAESB business practices, contract, agreements, or guides as periods of lower electrical demand. 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 resourceA source of electricity and/or demand reductionA chemical process that results in the acceptance of electrons by an electrode’s active material. The opposite of oxidation. that is included in a utility’s electric supply portfolio.. 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.