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Load balancing: PSE installs wind with PV

Kari Larsen

US, Washington State utility Puget Sound Energy (PSE) is combining solar PV and wind power at its grid-connected Wild Horse Wind and Solar Facility in Kittitas County. Steven St. Clair, Manager, Renewable Assets at PSE, talks to renewable energy focus’ Kari Larsen about the project.

Many critics’ arguments against the commercial viability of wind and PV amount to the fact that neither can be used as baseload power at large scale – and therefore ‘why would a utility, for example, be interested in adopting them’?

But as utilities increasingly seek alternatives to coal and oil, they are prepared to look beyond this viewpoint and investigate the “value” inherent in each of the technologies that a utility could benefit from, maybe as a hedge against rising gas prices, or as a way to help achieve a mandatory renewables generation target.

And one utility in particular, Puget Sound Energy, is even experimenting by using wind and PV in combination, to discover exactly how this could address the variability issues of both sources. Nowhere else in the USA has a utility tried to marry such different sources of electricity generation, but the elements’ uneven temperaments are precisely what the utility finds attractive. They are aiming to track the power profiles of each to see if there’s a way to balance the two, effectively to see if it is viable to fill in the wind gaps with solar PV power. Not to mention raise the profile of renewable energy in the process.


Steven St. Clair, manager, renewable assets at PSE, says that PSE initially decided to put up solar arrays at its Wild Horse Wind Farm because infrastructure and grid connection were already in place. This mitigated costs, particularly as the farm is located only two hours’ drive from Seattle, a major population centre. “We wanted to have the ability to draw people over to see these renewable energy technologies and use that as an opportunity for educational outreach,” St. Clair says.

Despite being further north than sunny California, eastern Washington has a very good solar resource. St. Clair notes, “according to the National Renewable Energy Laboratory (NREL), the solar intensity in eastern Washington is about equal to that of Houston, Texas.”

PSE also decided to place solar arrays at its wind farm in order to boost the local solar market. “Ten per cent of the solar panels that we are going to be using are made in the state of Washington by a company called Silicon Energy,” St. Clair explains. The remaining 2,400 panels are made by Sharp, USA.

The what and the how

Solar panels are being added to the Wild Horse Wind Farm in two phases. The first phase began in October 2007 with the 2,400 solar panels from Sharp USA yielding 450 kW. The second phase will see another 50 kW installed, bringing the total to 500 kW, with an annual output of about 650 MWh.

Project statistics: Wild Horse Wind Farm


  • 127 1.8 MW Vestas wind turbines;

  • 229 MWp capacity;

  • 642,000 MWh annual output;

  • Positioned at 4,000 ft elevation.

Solar PV

  • 2,723 fi xed angle, multicrystalline photovoltaic solar panels (2,408,

  • 0.187 kW panels from Sharp Electronics, 315, 0.165 kW panels

  • from Silicon Energy);

  • 500 kW system;

  • 650,718 kWh annual output.

This makes the Wild Horse solar installation easily the largest in the North West, according to St. Clair. The largest in the US, to his knowledge, is the 14 MW solar PV array at Nellis Air Force Base in the Nevada Desert.

Not surprisingly, erecting solar panels on a wind farm did present some challenges. The wind farm itself was originally planned with a design criterion for a 100miles/h wind speed, but after a wind event of 115-116miles/h, the design criteria had to be increased to 120miles/h.

This also meant that the solar panel stack, which was planned to be 7 feet high, had to be reduced to five feet high.

St. Clair is keen to say that so far, the solar panels at Wild Horse have exceeded production estimates for every month they have been in operation. “Currently we’re running about 11% ahead of where we thought we would be on an energy basis. Now it’s too early to say that we will see that kind of performance for the entire first year of the project and for subsequent years, but certainly it’s been very gratifying to see the kind of generation that we’ve had from it.”

He is aware, though, that this level of performance will ease off. “Solar panels do deteriorate over time, and we would expect to see a drop off of maybe 1%-1.5% each year of the project, but right now we’re so far ahead that I think the future bodes very well.”

Grid connection/balancing

In addition to Wild Horse, PSE has another wind farm, the 150 MW Hopkins Ridge. The annual capacity factor between the two is nominally 32%-35%, operating 65%-70% of the time. With added solar, this profile could improve further due to the different power profiles. Wind tends to blow in the evening, throughout the night and early morning, whereas solar is a mid-day resource.

However, the solar PV does not fully balance the wind, nor can it fully meet peak demand. As PSE does not use energy storage in the form of batteries or pump storage to balance its system, the utility is drawing on the multiple resources of its grid-connected system, with hydro the most prominent.

“In the Pacific North West of the US, we have the huge advantage of the Columbia River system,” St. Clair says. “There’s a tremendous amount of hydro power development on the Columbia River, and all of our balancing of wind farms, load, and multiple resources are done off the Columbia system.

“We like to say that we have virtual storage using the Columbia River, so when the wind farms are up producing, we can back off a little bit on our hydro system and store the water upstream from the dams, holding it in our reservoirs,” St. Clair explains.

As PSE also has gas and coal plants, so far it has been able to integrate the variability within its system, but the company is aware of the challenge of adding more renewables to its power make-up: “I think over time, as we add more and more wind power, it’s going to be increasingly difficult, but there are a number of strategies available. We may choose regional storage, pump storage, or some kind of control area pooling.”

St. Clair is clear, however, that more wind is coming.


St. Clair is fully aware of renewables still being a relatively expensive energy source, with solar PV being even more expensive than wind, but says this is largely due to solar being at the same stage as wind was some years ago. “A great many benefits and breakthroughs in manufacturing and design have allowed wind power to be competitive with alternative sources, and solar PV will get there too, as the price of silicon comes down and some of the newer thin fi lm technologies really begin to take hold in the market,” he says. 

PSE in merger with Macquarie Infrastructure Partners

PSE is currently engaged in a merger with the Australian bank Macquarie, which has put together a group of six investor funds that are buying all shares in PSE. The funds are said to look for long term growth rather than short term benefi ts, something which matches PSE’s strategy, St. Clair says.

The merger will bring extra funds to PSE, which needs to replace ageing infrastructure, but also add additional electric-generating resources – both renewable and conventional.

“It gives us that access to money, to make those investments, and I think you’ll see a number of additional wind farms and probably some other renewable investments from us as we go through time,” St. Clair adds.

The activity of “early adopters” such as PSE can itself help bring prices down, St. Clair believes. Price supports, as seen with wind, could also help put downward pressure on solar prices. Google presents one example, as the company has installed a 1.6 MW system in California.

According to St. Clair, it is possible to see a pay-back period of only 6-7 years if an extra tax credit (ITC), not available to utilities, is taken into account. Local incentives, which reduce demand from the utility and energy bills to the utility, are also important.

Looking at PSE’s own installation, St. Clair admits the project is not yet yielding financial benefits: “we call the Wild Horse solar PV array a demonstration project because we have seen a number of benefits that are not strictly financial benefits. However, these benefits can help us develop our industry here in the State of Washington, and we can provide an opportunity for our customers, in effect it is an investment in the future,” he says.


As a utility, PSE does not qualify for many of the incentives in place for renewable energy. However, as a wind farm operator, PSE is following the efforts to renew the US Production Tax Credit (PTC), which is set to expire at the end of this year.

St. Clair does not believe the failure [up to this point] to renew the PTC will have heavy long-term consequences. “If history is a teacher, what we see is a dramatic change in the market place in the year following an expiration of a tax credit. Wind development proceeds very strongly until the tax expires, and then development activities drop off significantly until the tax credits are re-instated or re-established.

“I’m not sure that we will see a huge drop, quite honestly, this year, because there are many, many projects now in the pipeline that developers and various companies have already bought into,” St. Clair says.

However, there is “still hope that the PTC will be approved before the end of the year.”

When it comes to solar, the picture is slightly different as there is no PTC. There is an investment tax credit, but this is not available to utilities. “That’s something we’re currently working with our legislative team back in the Federal congress to try to change,” St. Clair concludes.

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Energy infrastructure  •  Other marine energy and hydropower  •  Photovoltaics (PV)  •  Solar electricity  •  Wind power