July 5, 2007
Is Grid-Scale Storage Finally for Real?
Smart Grid Newsletter
By Mark Fitzgerald, a consultant and Contributing Editor at GlobalSmartEnergy
We all know the party line when it comes to electricity storage for the T&D infrastructure. In theory, it could be the ultimate game changer. In practice, it is too expensive. It can't be done at the size and scale needed. It hasn't seen any fundamental breakthroughs in decades.
Hang on just a minute.
While we've been distracted by all the commotion around smart meters and BPL and the digitization of the infrastructure, storage technologies have slowly, quietly, incrementally improved to the point that they now deserve our attention.
To be sure, we're still a long way from storage nirvana. We're not going to be sending the output of the Grand Coulee Dam to a giant stack of Duracells to be stored for a month until we need it. Not in this century.
And to be sure, we still haven't seen any radical breakthroughs. Instead, existing technologies have improved to the point – and costs have dropped to the point – that storing electricity now makes economic sense for certain specialized applications.
For utilities, electricity storage can enhance power quality, help with peak loads, and support renewables. The technologies are ready, say storage advocates, and have the potential to help our under-funded and over-stressed power grids.
At Smart Grid Newsletter, we believe it is time for North American utilities to seriously consider electricity storage as they plan their updates and upgrades. In some cases, it is the best and most economical option. To help you along, we've compiled this quick overview of existing technologies, given you a snapshot of the drivers and barriers, and included links to additional resources at the end.
Technologies and Capacities
Pumped hydro, which generates electricity by reversing water flow between reservoirs, is the most widespread energy storage system on power networks. With an efficiency rate of more than 70%, pumped storage accounts for over 90GW worldwide, according to the Electricity Storage Association (ESA).
Flywheel systems, which utilize a massive rotating cylinder, boast effective load following characteristics and a wide-range of short and long-term capabilities. Beacon Power has refined low-cost commercial flywheel designs for operation that could last up to several hours and experts estimate that forty 25kW (25kWh) wheels can efficiently store 1MW for one hour.
Super capacitors, or electrochemical capacitors, possess swift charge and discharge capabilities. More powerful than batteries, they can be cycled tens of thousands of times. Those with energy densities under 20kWh/m3 have been successfully developed, and work is underway to expand the effectiveness of larger units.
Flow batteries have low energy density, but they offer high capacity and independent power and energy ratings. Technologies in use include polysulfide bromide (PSB), vanadium redox (VRB), and zinc bromide (ZnBr). The Tennessee Valley Authority recently built a 12 MW, 120 MWh PSB storage plant. VRB installations offer up to 500kW, 10 hrs (5MWh). In 1991, Meidisha unveiled a 1MW/4MWh ZnBr battery and numerous multi-kWh ZnBr batteries have been built and tested over the years.
Vehicle-to-grid. The idea of using the batteries of electric vehicles as an energy storage resource -- a concept called Vehicle to Grid (V2G) -- is still in its infancy, but may have potential as a quick-response, high-value service to balance fluctuations in load. By connecting enough vehicles to the grid and transmitting power back and forth as needed, utilities could one day save billions per year, some experts predict.
Storage Drivers
According to Electricity Storage Association chairman Jim McDowall, installation of electricity storage is accelerating. Demonstrations are popping up around the country and confidence is building. Some of the benefits of electricity storage include:
- Protection from long outages, voltage sags, and surges
- Effective on-site generation for peak shaving customers (GridPoint has developed an energy management portal that informs customers about the most cost-effective time to run appliances and allows the to control energy consumption and costs.)
- Streamlining supply during peak periods by coalescing storage capabilities with renewable resources (Ice Energy has patented an energy storage module that can reduce building peak demand by up to 95 percent while providing 7.5 tons of cooling capacity for six continuous hours.)
- Complementary optimization of photovoltaic and wind-generated electricity
- Favorable life-cycle cost, including capital and installation cost, operation and maintenance cost, and disposal cost
- Versatility for transitioning to microgrids and decentralization
Storage Blockers
The storage industry has been working work with governments, regulators, utilities, and operators to address and attempt to overcome the challenges to the proliferation of electricity storage. Some of these include:
- A lack of government subsidies and incentives to encourage investment
- Regulatory constraints and limitations
- The uncertainty of selling electricity storage systems at a price that will allow both developers and customers to profit
- Political will (it will take time to influence decision-makers. Will the window of opportunity stay open long enough for that to happen?)
