By Lisa Buchanan
Posted: 06/30/2011 01:00:00 AM MDT

Xcel Energy presented its proposal to the Boulder City Council on June 7. Under this plan, Boulder would sign a 20-year power purchase agreement for Renewable Energy Credits (RECs) with Xcel and a wind developer in eastern Colorado; power generated at this wind farm would be dedicated to providing Boulder`s energy needs. Boulder`s REC costs equal the cost of wind minus Xcel`s avoided costs; costs that Xcel would have spent to provide the power from one of their coal or gas fired power plants. Boulder would also pay Xcel for power provided to the City when the wind was not blowing (integration) and for “curtailed” wind; when turbines are shut down because wind generation is greater than the grid capacity and/or the power demand.

I have been working as a volunteer with a large group of modelers and advisors analyzing renewable/natural gas system configurations for Boulder`s power supply that achieve various carbon emission levels. We used actual hourly demand, wind, solar, and other data to model solutions for Boulder`s electrical needs. Based on this work I have the following concerns with Xcel`s proposal.

1. The 70 to 90 percent renewables promised by Xcel is not feasible with wind alone and does not translate into a similar reduction in carbon emissions because when the wind is not blowing fossil fueled power is used to meet the electrical demand. A mix of complimentary energy sources (wind and solar) is required to maintain more than 40 percent renewable penetration because solar power peaks at mid-day when the wind dies down.

2. It is preferable to obtain wind power from several different locations, as opposed to one location, as wind speeds and power generation vary geographically. Power purchased from separate wind farms, when combined, provides a more consistent power source.

3. Paying for “curtailed” wind is perhaps the least defined and riskiest cost because, based on actual wind speed data and model results, curtailment is likely to occur frequently in all seasons except summer. Also, Boulder has no control over which of Xcel`s power sources will be curtailed. It is likely Xcel would favor operating their coal-fired plants over the wind farms since coal plants are not easily shut down. Curtailment is typically a risk assumed by the wind farm operator and utility, not the customer. Xcel`s proposal provides no incentive to distribute the extra wind power to other customers.

4. Though some long term contracting is necessary; given how quickly renewable energy technologies are changing, a 20 year contract with one wind farm would be extremely limiting. Also, a competitive bid process would likely reduce the overall cost to the City of Boulder.

5. Boulder assumes all the risk in this agreement and may end up with a system that doesn`t achieve the desired carbon reduction or renewables penetration.

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