Transition - 14/November/2017

No compromise on security of supply

In green and flexible power systems, services like rapid cures for hiccups in grid frequency can be valuable

NEW APPROACH TO ANCILLARY SERVICES

As provision of electricity moves away from command-and-control governance to become a multi-faceted business subject to the rules of demand and supply, specific sub-markets for vital grid support services are emerging. The new approach means services like rapid response to deviations in grid frequency become products in their own right

Electricity grid operators have a tough job. Not only do they oversee the most vital delivery system in the world, the product they distribute has to exactly match demand for it at all times, down to split second intervals. Should supply fall short of demand, or exceed demand, grid frequency would wobble off target (60 Hertz in America and 50 Hz in most other regions) and risk collapse of the whole system.

The second-by-second matching of supply and demand to maintain frequency is achieved through frequency regulation, a largely automated process in which the dispatch of electricity from generators is constantly increased and decreased in tiny amounts. This dispatchable generation comes as part-and-parcel of the bulk supply of electricity from thermal capacity, hydro and other plant. Integral to the delivered package, it is an “ancillary service” and provides essential support to the primary activity.

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A NEW APPROACH

The increasing proportion of renewable energy in today’s power systems carries the risk that the electricity for frequency control may not always be available. As the head of the Australian Electricity Market Operator, Audrey Zibelman, recently put it, a higher level of renewables on the system means the provision of frequency control and other ancillary services needs a new approach, “Not because it is a bad thing, but because it was bundled previously with the big generators.”

The emerging approach, whether in Australia, Europe or across America, is to treat the electricity needed for frequency regulation as a product in its own right and subject it to the forces of demand and supply in a specific services sub-market. The UK system operator recently held a specific auction for ultra fast frequency response, which was won by bidders offering instantaneous power from batteries. In the wide Pennsylvania-Jersey-Maryland area of the United States, PJM Interconnection, a regional transmission organisation, now operates a frequency control market for fast ramping resources to bid into tenders to provide grid services.

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supply-01

Modelling by Danish researchers of various volumes of wind generation in the power system demonstrates that maintenance of grid frequency and power quality is not a problem

PLENTY OF OPTIONS

Batteries are beginning to demonstrate a market edge for provision of instantaneous bursts of power now their prices have dropped, particularly the price of lithium-ion technology. But they are not the only contenders for frequency regulation. Batteries face competition from electricity generators and also from electricity consumers. Consumption can be turned off at the flick of a switch to restore frequency and users who are unaffected by a dip in power supply are often prepared to accept relatively low payment for the demand response service they provide.

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“Modern wind turbines can draw
on the kinetic energy in their rotating
blades to deliver fast-acting power
injection into the grid”

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Generators will continue to provide frequency response, wind turbines among them, if for no other reason than it conveniently comes from the inertia inherent in the kinetic energy of many rotating generators. In Canada, the Hydro Quebec power utility has equipped hundreds of wind turbines with grid-responsive technology, as Tom Butler at the Clean Energy Council, Australia’s main green lobby group, points out. “Modern wind turbines can draw on the kinetic energy in their rotating blades to deliver fast-acting power injection into the grid if triggered by an event. They can also be flexibly controlled to deliver the correct response to suit the local grid conditions and requirements,” he states. In the US, the Public Service of Colorado also draws on wind energy for frequency regulation.

Admittedly the practice requires careful coordination of all the many clusters of wind turbines, especially on a power system running almost entirely on wind energy, as researchers at the Technical University of Denmark (DTU) and Denmark’s Aalborg University point out in a study from 2016, Provision of Enhanced Ancillary Services from Wind Power Plants. Their modelling of various volumes of wind generation in a power system demonstrates that maintenance of grid frequency and power quality is not a problem.

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FROM SOLAR TOO

Solar photovoltaic power can also be tapped to balance the grid. First Solar and the California Independent System Operator (CAISO) partnered for a series of tests in summer 2016 demonstrating that a 300 MW utility-scale PV plant outfitted with standard inverters and software controls could respond to CAISO’s automatic generation control signals and frequency response commands. By curtailing the facility’s output slightly, it was in a position to demonstrate its ability to meet and even exceed frequency regulation response normally provided by gas plant. The inverters proved they could respond faster than spinning generators. “The plant demonstrated fast and accurate frequency performance,” the project partners report, also in cloudy conditions and to correct both positive or negative frequency deviations. “Data from these tests will be used by the CAISO in the future ancillary service market design,” state the partners in their project report.

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supply-02

By the end of 2016, two million electric vehicles were on the road globally, according to the International Energy Agency.

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AND BATTERIES

The attraction to a grid operator of obtaining full access at all times to an instantaneous store of electricity for fine-tune adjustments is undeniable. Battery energy storage systems (BESS), long held to be too expensive for other than some niche applications in grid power supply, are showing strong signs of living up to their long held promise.

Experiments with embedding battery storage in renewable energy projects, as well as at commercial and industrial facilities, are also multiplying. Denmark’s Ørsted (formerly DONG Energy), a world leader in operation of offshore wind power facilities, is installing a 2 MW battery at the Burbo Bank offshore wind farm in the UK. By using the wind farm’s grid connection it can offer frequency response and contribute, in a small way, to maintaining it locally.

For commercial and industrial players looking for market opportunities to sell electricity stored in batteries, frequency regulation is one of the options to “stack” several streams of revenue to help pay for the capital and running costs of battery ownership.

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supply-03
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GOOD IN THEORY

Looking ahead, mainstream adoption of battery electric vehicles (EVs) will in theory enable consumers everywhere to participate in frequency regulation markets. Every EV battery can potentially be a grid-balancing asset. “By varying its charge level, controlled charging can provide any ancillary service, including frequency regulation,” states a California Public Utilities Commission report as far back as 2013.

In practice, the value of the service to a power system may not be sufficient to provide revenue enough to the EV owner to make participation in the frequency response market worthwhile. Neither does the volume of storage offered by even millions of EVs connected to a power system look impressive. If every car on the road in Denmark were an EV, the storage offered would make up a tiny proportion of the total available, according to research by scientists at Aalborg University (see graph above).

As with all electricity users, EVs can provide a flexible means for reducing or increasing demand, as demonstrated in an 18-month pilot project in the San Francisco Bay Area. One hundred BMW i3 owners were paid up to $1540 by electricity provider Pacific Gas & Electric to allow the utility to control home vehicle charging during times of high demand on the grid. Load reductions of up to 100 kilowatts were achieved via targeted delayed charging of vehicles. The PJM frequency regulation market allows bids in increments as low as 100 kW, meaning as few as nine EVs can provide grid services when their reduction in demand is aggregated, states the International Council on Clean Transportation (ICCT).

Commercialisation of vehicle-to-grid (V2G) technology would permit EVs to both draw from and dispatch to the grid economically, according to Zhenpo Wang and Shuo Wang, engineers with China’s National Engineering Laboratory for Electric Vehicles. “Compared with other peak-shaving and valley-filling methods, V2G can be a more economical and effective solution, with the added advantage of rapid response to grid-demand variations,” they state. •

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TEXT Justin Gerdes

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