Storing the energy from wind is obviously useful. But is it essential? Numerous studies cover the matter both asserting that storage can useful and asserting its not. The practical common result is the continental U.S. could increase wind energy production another ten times before the capacity would merit storage at scale.
It’s just not that simple. In Hawaii where the ocean limits interconnection over a wide area the local conditions rule. To get to high wind use a buffer needs to be in place between the source, the wind and to the consumer. Hawaii has a 70% renewable target and to get there some form of moving energy production from the time it’s generated to the time it’s used has to be in place.
But numerous studies as well as European wind integration experience have demonstrated that in the continental 48 states the use of wind energy could increase by more than 10-fold without energy storage. The opportunity is in using the sources of flexibility that are already present on the electric grid. Every day, grid operators constantly accommodate variability in electricity demand and supply by increasing and decreasing the output of the flexible generators – power plants like hydroelectric dams or natural gas plants that can rapidly change their output of generation.
The peak demand is met by the stored energy in the dammed water or the natural gas in the tank or pipeline. Grid operators also move power from regions with momentary excesses of electricity to other regions that have a need for electricity at that moment. Grid operators use these same flexible resources to accommodate any additional variability introduced by wind energy.
In the U.S. now, demand for electricity can vary by a factor of three or more depending on the time of day and year, which nationwide translates into hundreds of gigawatts of flexibility that are already built into the power system.
Its almost always much cheaper to use the existing flexibility than to build new sources of flexibility like energy storage facilities. When the existing sources of flexibility are eventually saturated, a number of additional low-cost sources of flexibility can be deployed, such as building additional transmission lines, encouraging additional demand response resources, reforming grid operating procedures, or making the generating fleet more flexible.
Continuing advances in energy storage technology can make it more economically competitive as a provider of grid flexibility. Its important to remember that resources like wind energy can already be cost-effectively and reliably integrated with the electric grid without energy storage for quite some time to come.
Compare that to Hawaii’s plan to install a 15-megawatt battery on a new 30-megawatt wind farm. Computers will work to keep the battery exactly half-charged most hours of the day. If the wind suddenly gets stronger or falls off, the batteries will smooth out the flow so that the grid sees only a more gradual increase or decrease, no more than one megawatt per minute at some hours of the day.
The Hawaiian installation is designed to succeed at a crucial but obscure function: frequency regulation. The alternating-current power system has to run at a strict 60 cycles per second, and the battery system can give and take power on a micro scale, changing directions from charge to discharge or vice versa within that 60th of a second, to keep the pace steady.
The battery system can also be used for arbitrage, storing energy at times when prices are low and delivering it when prices are high. It can hold 10 megawatt-hours, which is as much energy as a 30-megawatt wind farm will produce in 20 minutes if it is running at full capacity. That is not much time, but it is huge in terms of storage capacity. The reason for the arbitrage? Publicly disclosed figures put the project in the range of $130 million, with about $10 million for the battery. The Energy Department has provided a $117 million loan guarantee. Folks in Hawaii are going to pay, but the cost of the investment will be lower with all of the U.S. backing the plan up.
Isolated power systems like Hawaii’s seem like highly unique cases, since geography prevents them from sending excess electricity to neighboring regions there is limited access to sources of power system flexibility, the power grid is often weak, and the price of electricity is often high.
The success of countries like Spain, Germany, Denmark, Portugal, and Ireland reliably and cost-effectively obtaining 10% or more of their electricity from wind farms without adding any storage resources is instructive. As well, the main grid operator in Texas has regularly obtained 20% of its electricity from wind energy, also without the use of energy storage.
The National Renewable Energy Laboratory summed the matter up in a remote quote, “At present levels of wind penetration on the electrical grid, storage has not been a priority consideration. But eventually, as system resources and not exclusively due to wind or other renewable resource capacity adds on, the nation’s electrical grid will benefit from energy storage technologies. Essentially, the power system already has storage in the form of hydroelectric reservoirs, gas pipelines, gas storage facilities, and coal piles that can provide energy when needed. Today, storing electricity is more expensive than using dispatchable generation. In the future, through, advances in technologies such as batteries and compressed air, energy storage may become more cost-attractive.
The point is that Hawaii is an isolated set of islands that needs to store back energy production and move it to the time its needed. The other side of the point is, as the renewables become a larger proportion of the total, the continental U.S., as big as it is, is a set of islands as well.
By Brian Westenhaus of NewEnergyandFuel.com
Source: The Wind Power Storage Issue