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Integrating Renewables

Opportunity for advancement or exercise in futility?

Fortnightly Magazine - March 2010

in the United States.

Not all sources of renewables present significant problems involving integration into the market and operations. For example, small hydroelectric, biomass and geothermal generation are more predictable in terms of production levels. The major challenges will come from solar and wind energy.

Photovoltaic (PV)-based generation is an intermittent source of renewable energy, generally deployed in local situations. Thanks in part to limited use of PV up to this point, integration hasn’t posed major problems. While the amount of concentrated solar generation is expected to increase significantly over the next 15 to 20 years, its impact as a percentage of the overall generation mix will remain low in most locations. As a result, while integration standards for the local distribution grid are required, no serious system operating issues are expected with the expansion of market penetration by the current generation of solar power.

New wind generating facilities are the fastest renewable resource to install and interconnect to the power grid. Wind generation, however, also presents the most significant operational and planning challenges. The penetration of wind-generated power is anticipated even in largely urbanized regions of the United States during the next decade.

The challenges of wind integration at scale can be viewed as seven associated, but distinct, attributes that are characteristic of intermittent wind energy sources:

• Intermittency: Wind generation energy production is extremely variable. In many places, it often produces its highest energy output when the demand for power is at a low point. During periods of favorable wind conditions, it’s possible that all wind projects in an area will be at their full energy output. If that happens, the transmission line could become overloaded and wind generation on that line would need to be curtailed.

• Ability to dispatch: Unlike traditional forms of generation, renewable forms of energy (especially wind and solar) will generate only when the wind is blowing or the sun is shining. Controlling their output, in these instances, is an obvious challenge.

• Remote siting: Wind projects tend to cluster mainly in rural areas not supported by strong transmission systems, and remote from major load centers. Consequently, wind projects have tended to cluster along unfavorable locations, often on lower voltage transmission lines.

• Ability to Forecast: Wind generation is difficult to forecast because it doesn’t always follow a predictable production pattern and forecast technologies aren’t well developed. Solar has similar limitations as a localized cloud cover can suddenly reduce or eliminate the power output.

• Land Requirements: In general, both wind and solar need expansive land area to generate the equivalent power of one normal fossil-fired generating unit. Over time, this will be a limiting factor in how much overall generating capacity can be expected from wind and solar.

• Expensive: Cost is still a significant issue with most renewable forms of generation. They are at an order of magnitude of about 10 to 50 times the cost of free venting, fossil-fired generation. However with appropriate incentives, with innovation in their design and some form of carbon taxation, at least wind likely will be cost