Apollo solar, electric models pump through Iowa winter: More methane, lower risks

Methods

The engineers initiated the test during December 2011. Linear-rod reciprocating-piston drive motors were identical, but each utilized a different power source: Direct electric power converting 220-volt AC to 24-volt DC in well GW-01, direct power from 12-volt DC batteries charged through a mounted solar panel in GW-02, and power from a solar panel alone in GW-05.

The pumping flow rates were a maximum of 2.25 gallons (8.5 liters) per minute. Pump intakes were set 1 to 3 feet above well bottom to avoid accumulated silt or debris. GW-02 began operating on Dec. 13, 2011, followed by the other two wells on Dec. 21.

Liquid levels were measured periodically through March 2012, and pressure transducers were installed March 6. The transducers recorded liquid elevations every 15 minutes. Percentages of methane and oxygen were measured periodically before and during pump operations.

Results

Average 24-hour groundwater levels were satisfactorily reduced and consistently maintained at pump intake by all three power options, including the solar-only system. Depending upon the well, between 15.6 and 18.4 feet of additional screen was exposed -- between 75% and 93.6% -- equating to methane-flow increases of at least 15% at GW-01 and GW-02 and approximately 20% at GW-05.

Solar-only power at GW-05 produced minor fluctuating liquid levels corresponding with the on/off cycle during daylight/nighttime hours. Approximately 3 to 4 feet of liquid accumulated while the pump was not running. The pump switched on during daylight hours, removing the liquid and maintaining liquid level at intake. The degree of daily fluctuation in GW-05 was relatively minor compared with length of additional screen exposed (17.0 feet).