An article from
Waste Advantage Magazine
January 2014

Landfills

In the Dead of Winter, The Little Solar Pump That Could

A four–month test in Iowa shows that solar–alone power can boost recovery rates of landfill gas in new and closed cells, at lower costs.

Mark Bertane

As the number of landfill gas–collection systems has grown in recent years, so to have groans from many engineers and operators when they discover that methane production from their wells isn’t meeting projections. This puts owners who have contracted to provide gas in a tough spot.

Unrelated but noteworthy in the gas–system expansion is a greater possibility of threats to nearby groundwater from fugitive leachate and subsurface–gas migration. A third issue, always hovering, is the cost of providing electrical and/or pneumatic power to new or closed landfill cells, particularly at remote sites.

One solution to all three that has been grabbing attention lately revolves around solar power, specifically solar pumps. But how practical are they outside the Sun Belt?

A Problem in Iowa

The Cedar Rapids/Linn County Solid Waste Agency, which serves Iowa’s second largest county, installed gas–collection systems in 2010 for both active and closed landfill cells as an expected revenue generator. Methane production, however, came up short of the results predicted by modeling.

In 2011, close monitoring determined that high levels of liquid from one of the Agency’s landfills was filling the wells and negatively impacting gas production. In addition, the Agency suspected that leachate might be migrating slowly toward groundwater.

Agency executive director Karmin McShane contacted regional engineers with The Foth Companies to investigate as well as offer and implement solutions. The firm prepared a preliminary assessment and controlled–measures study in October 2011 to gather data for planning and implementing corrective measures.

Foth engineers postulated that lower liquid levels in the collection wells would improve the efficiency of the gas system and, secondarily, reduce potential groundwater impacts. The study suggested the use of low–flow pumps to reduce levels. Lead engineer, Brian Harthun, further suggested testing the viability of pumping with solar power for efficiency and cost savings.

One Tough Test

Foth initiated the test in December 2011. Four months in the dead of winter—at 42° North latitude (roughly equivalent to Toronto), with 65 to 76 percent cloudy days and only 10 to 11 hours of sunlight a day—proved a rough challenge.

Linear–rod reciprocating–piston drive motors employed by the engineers were identical, but each used a different power source: 1) In the first well, direct electric power was converted from 220–volt AC to 24–volt DC, 2) in well #2, direct power came from 12–volt DC batteries charged through a mounted solar panel, and 3) in the third well, the motor was driven simply by a solar panel with no backup assistance.

The pumping flow rates were between 1 and 2 gallons (3.78 to 7.57 liters) per minute. Pump intakes were set 1 to 3 feet above well bottom to avoid accumulated silt or debris. Liquid levels were measured periodically through March 2012, and pressure transducers were installed March 6, 2012 to measure liquid elevations every 15 minutes. Percentages of methane and oxygen were measured periodically before and during pump operations.

Results: Up to 20 Percent More Gas

By early April 2012, the results were in. The analyses showed that the low–flow pumps reduced average 24–hour liquid levels sufficiently to remedy the migration issue, and that those lower levels were consistently maintained by all power options, including solar only. Although overnight liquid levels increased somewhat at the solar–alone well, they dropped again in the morning when the pump "woke up."

At the same time, the lower liquid levels from all three power options exposed an additional 15–18 feet of screen in each well—between 75 and 90 percent more—which resulted in additional gas flows of 15 to 20 percent. “We were quite pleased both with the operational and financial performance of the solar pump," said Harthun, the Lead Engineer. He cited steady, uninterrupted performance and lower costs of installing and maintenance. He said that eliminating the need to run electric or pneumatic lines to the closed cell was a major attraction.

At the time of this writing, two years after the test was initiated, the solar pump continues to operate as expected, with no downtime. Its test success prompted the Agency to purchase and install several other solar–alone pumps at the site, all of which have been performing well.

Benefits of Solar