USEPA - Technology Innovation and Field Services Division (TIFSD)

Mobile systems provide solar energy in northern climates

The Department of Transportation for Alberta, Canada, is examining innovative strategies to resolve environmental issues in remote areas of the province. Portable units for harnessing solar energy have been demonstrated over the past five years as a viable method for generating the electricity needed to drive remediation systems at several sites in western Canada. The typical mobile system consists of a 21-ft trailer holding a 2-kW PV array and 1,600-amp/ hr storage battery used to power, as needed, a 100-psi air compressor, pneumatic pumps, and air blowers over short durations.

Applications indicate that solar energy availability typical to the climate of southern Alberta (6-8 hours during summer and 4-6 hours in winter) is sufficient to power the low to moderate electricity demands and seasonal work often involved in remote cleanups. Through use of the storage battery, however, ample electricity could be withdrawn for systems requiring 24-hour operation. Mobile solar systems were deployed in western Canada to power equipment such as: Submersible pumps for dewatering and product skimming at a hydrocarbon-impacted site in Beaver River, BC, from July 2002 to December 2004.

Use of the full 2-kW PV array avoided need for a typically high-maintenance diesel generator consuming a large volume of fuel, or alternate installation of electricity lines extending to the utility grid at an infeasible cost. Successful hydrocarbon recovery prompted plans to install a permanent solar system to fully remediate and reclaim the site flow of 250 cfm for SVE addressing residual hydrocarbons from a pipeline break at Rocky Mountain House air base from May to September 2006. Solar energy provided sufficient power to enable the SVE system to increase volatilization and promote biodegradation of hydrocarbons, while eliminating the need for routine maintenance and frequent refuelling of diesel generators. Over the five months of operations, hydrocarbon levels in all wellheads were reduced from concentrations more than double the “lowest effect level” (LEL) targeted by the Alberta Ministry of the Environment to less than 10% of the LEL.

The mobile unit’s existing 5-kW generator for auxiliary power (when insufficient solar energy is available to provide constant battery charge) burns natural gas at a rate of approximately 0.6 m3/hr. Diesel generators becoming available now offer the “autostart” compatibility needed in these applications, at an estimated fuel consumption rate of 1.3 gal/kWh. Diesel cost for transfer of the mobile unit is estimated at approximately $0.80/ mile, or approximately $200 for a typical distance of 250 miles. Rental cost for the unit depends on deployment duration but typically ranges from $1,500 to $1,800 each month.

The 2-kW PV array is estimated to produce approximately 3,650 kWh of electricity annually in 24-volt direct current, 115-volt alternating current, or 240-volt alternating current. Generating the same amount of power with an electricity generator is estimated to produce 512 kg of carbon equivalent or an estimated 12 metric tons of carbon over the typical 25-year lifespan of PV units.

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