By Bob Moser, Americas correspondent

With North America's Western Interconnection serving more than 77 million people - many of whom are located in coastal load centers - burgeoning demand for peak-hour electricity is increasingly sourced from renewable sources such as wind power.

But issues presented by off-peak production and distance from energy-thirsty cities have led to growing demand for the development of short-term storage options, as well as new ways to move energy efficiently.

The question of whether the Western Interconnection is nearing saturation for new sources of energy is a very location-specific issue. Certain areas of the grid are highly utilized and may be near capacity, explains Bradley Nickell, director of transmission planning for the Western Electricity Coordinating Council (WECC). Meanwhile, other areas are ripe with capacity to fill, but lack the demand.

“The challenge is really where the wind is, not where the load is,” says Nickell.

Wind is a geography-constrained renewable, with the highest wind levels available in Wyoming, Montana and the Columbia River gorge-area of Oregon and Washington, according to WECC, which manages and facilitates interconnection-wide transmission planning activities for the Western Interconnection. The Western Interconnection includes 14 Western US states, Canada's Alberta and British Columbia and northern Baha Mexico.

Long-distance cables, long-term thinking

In terms of energy lost through long-distance cables, superconducting cables deliver a significant improvement over the more common high-voltage transmission lines used today.

While the implementation of superconducting cables requires long-term planning with a correspondingly long-term return on investment, these cables clearly create an opportunity to connect remote energy resources like wind from the Midwest to more needy load centers on the coast through advanced long-distance transmission, says Frank Schmidt, head of the HTS Systems business unit at Nexans, a global leader in the cable industry.

Nexans recently completed a successful test of the world's first HVDC high temperature superconductor power transmission cable, designed for 200 KV. It's an important step towards showing how these cables can transfer the bulk power required by proposed supergrid projects like the Tres Amigas renewable energy hub in the US.

Tres Amigas plans to link the Western, Eastern and Texas interconnections via HVDC and VCS AC/DC converters, forming a 9.6 km triangular electricity circuit that could transfer and balance gigawatts of renewable power between the grids.

Need for energy storage?  

Integrating renewable energy sources into the Western Interconnection arguably comes with a responsibility to ensure that flexibility has been built in to deal with fluctuations in generation.

Fluctuation and ramp control issues are compelling producers to consider energy storage applications, particularly as renewables come closer to making up a penetration rate of 20% or more. Storing energy generated at night for peak day hours in an affordable way will help make wind and solar more competitive against traditional baseload energies.

“New advanced batteries, pumped hydro systems with ranges of 200MW or more, and compressed air energy storage with the potential of 300-plus MW are options that KEMA favors”, says Richard Fioravanti, director of storage applications at KEMA, a global leader in energy consulting, testing and certification.

These types of storage are also being looked at in the Western Interconnection by utilities and independent power producers alike. “Diurnal storage options that would hold that energy for around eight hours would be really effective”, adds Fioravanti.

Each storage solution offers different pros and cons, explains WECC’s Nickell. Flywheel energy storage is fairly low-energy, but fast acting and compact, making it easy to place near the load.

While batteries and flywheels are usually located closer to the load, and therefore meant to resolve problems closer to the operator, hydro and CAE rely on location, explains Nickell. Hydro and CAEs only prove feasible when placed where a dam is appropriate (in hydro's case) or where air can be stored underground (the norm with CAE). Those two options offer large energy storage capability for energy generated at night to be saved for peak day hours.

According to Nickell, the bulk of investor interest is in these latter two areas. Similarly, WECC is focusing on hydro and CAE development.

But debate remains in the US over whether energy storage solutions are even needed. "It's not a universally-accepted concept," says Fioravanti.

"A lot depends on what side of the equation you are on. In the end, it's more equipment that somebody has to pay for. We've got to find a way to finance the addition of this equipment."

"Some still say that isn't necessary. Wind farms are spread across such a large geographic region that you never see them all stop at the same time," says Fioravanti. "Others say wind is such a small overall percentage of the grid, that it's just a hiccup if it stops producing.

The reality is that some states, such as California, are targeting up to 30% renewables. This in itself may necessitate more renewable energy storage options.

“It's a debated concept right now, the necessity of having ramping control, but KEMA believes it is an issue that folks should start preparing for,"  Fioravanti adds.

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