Pumping water for free
Pumping water uphill can be “almost free” when you use photovoltaic (PV) panels and a DC pump. This can be a great convenience if you happen to live on a hilly lot where it might be cost-prohibitive to run electricity to a tank, or you really want to reduce your reliance on the grid. Let gravity do the work.
DC pumps are a little more expensive than the standard AC, but they can run directly off your PV array so require no grid-tied electricity. With the dramatic decrease in the cost of photovoltaic panels, the increased interest in reducing one’s carbon footprint, and/or the desire to become more self-sufficient, these systems are now being installed in areas where the power grid is readily available.
I recently worked on this type of system in the foothills south of Santa Fe. The client has a rainwater storage tank next to the house at the bottom of a sloping lot. The garden is about 200 feet away and up about 25 feet in elevation. It would have been very costly to trench an electrical line. The cost of running the pump every day to getwater to the garden seemed counterproductive to the goal of increasing sustainability with a large garden.
The simple solution was to install a DC pump with the rainwater tank next to the house connected directly to a properly sized solar panel as a power source. An additional tank was installed slightly uphill of the garden. On every sunny day, water is pumped up to this tank to keep it full, and it provides water to the garden via gravity. A float in the upper tank signals the DC pump when to pump water and when to stop.
Acequia Madre Elementary School has a DC-based rainwater system equipped with a battery. In this case, the PV panel keeps the battery fully charged so that on cloudy days, water is fully accessible.
The technology to do this has been around for decades, but what has changed is the price. Both PV panels andDC pumps have dropped dramatically in price. Additionally, today there are many more sizes of pumps and panels, so matching up these two components ismuch easier. The components must match! Not just any PV panelwill power any DC pump. Almost all 120-volt AC pumps can use a standard wall outlet. The output provided by a photovoltaic panel must match the power requirements of the DC pump.
Now for a one-time fee of a fewhundred dollars for a single, small PV panel and a DC pump, you can pump water without having to pay an electric bill. This same setup would have been thousands of dollars not too long ago. In an area with lots of sun, this is a perfect low-cost, longtermsolution. It’s an example of newer technologies and lower prices enabling solutions not feasible just a short while ago: a small change that can provide years ofwater delivery for free.
Doug Pushard, founder of the website www.HarvestH2o.com, has designed and installed residential rainwater systems for over a decade. He is a member of the Santa FeWater Conservation Committee, a lifetime member of the American Rainwater Catchment Systems Association, and an EPAWaterSense Partner. He can be reached at doug@HarvestH2o.com.