Monday, October 26, 2009 at 4:07:52 AM - by Danny Vo

Helios Energy Partners proposal for a 200-megawatt solar photovoltaic (PV) installation (solar farm) got a thumbs down recently from Xcel Energy.

Xcel, which invites bidding on an annual list of Request for Proposals (RFPs) for renewable energy, turned down the PV farm, slated for Pueblo, Colorado, about 150 miles due south of Denver.

Xcel, headquartered in Minneapolis, Minnesota, serves 3.4 million electricity consumers and 1.9 million natural gas consumers in Minnesota, Wisconsin, Michigan, North and South Dakota, Colorado, New Mexico and Texas.

Once listed as one of the “dirty dozen” for its coal-fired generation (largely for mercury emissions in Minnesota), today Xcel Energy is ranked first in wind energy, and fifth in solar capacity among U.S. power companies.

Instead of the Helios project, Xcel Energy officials are eyeing the San Luis Valley in southern Colorado for a 330-plus-megawatt solar thermal installation, depending on approval from the Colorado Public Utilities Commission. One megawatt of solar thermal energy has been shown capable (by the Solar Electricity Generating Station, 1991, in California’s Mojave Desert) of powering about 290 homes.

Solar thermal plants often require cooling systems, many of which rely on water, so their siting in areas where water supplies are limited, or even precarious, is a tough proposition.

This is particularly true in the San Luis Valley, where the Colorado Water Conservation Board (CWCB) is still working out policy on water remaining for development. The problem is complicated by old water rulings and allocations, which leaves reserves in doubt. They could be as much as 1.4 acre-feet, or as little as 400,000 acre-feet, and few San Luis Valley residents – whose main occupations is growing potatoes, and whose wells are now metered – are willing to part with enough to cool a solar thermal installation.

Local officials are hoping for an air-cooled plant, for which the area – with its low daytime temperatures – is ideally suited. This is good news, because Xcel Energy has reportedly already spent $100,000 to purchase 82 acres in the Valley.

Kent Scholl, a senior analyst for Xcel Energy, said the company is not looking to build water-cooled plants, and said the proposed installation would require, at most, about 300 acre-feet of water per year, leaving lots for potatoes and other Valley crops.

Meanwhile, Pueblo County and the Depot Reuse Authority will continue their efforts to get some land from the U.S. Department of Defense in hopes of attracting future solar projects, including a pending RFP (2010) from Colorado’s other major utility, Tri-State Generation.