Pumping Water For Free
by Doug Pushard
Pumping water uphill can be “almost free” when you using photovoltaic (PV) panels and DC pumps. 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.
Today most pumps are Alternating Current (AC) pumps, which are designed to run off ordinary electricity. You plug them into a wall outlet and they run. On the other hand, Direct Current (DC) pumps use a different type of energy. This is the type of electricity generated directly from photovoltaic (PV) panels or stored in batteries (i.e. have a positive and negative terminal). Both pump water with DC pumps being a little more expensive then AC pumps. However, unlike AC pumps, DC can be repaired consequently having a longer overall life and are more energy efficient. In areas where there is plentiful sunshine, DC pumps used with properly sized PV panels can generate good water pressure and require no grid-tied electricity.
These types of systems have been installed in off the grid homes for decades. For these locations it has been the only viable solution. 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. This client has a rain water storage tank next to their 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. Additionally, the cost of running the pump every day to get water to the garden seemed counterproductive to increasing one’s sustainability provided by a large garden.
The simple solution was to install a DC pump with the rain water 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. This higher elevation tank then 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.
The Santa Fe’s 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 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 and DC pumps have dropped dramatically in price. Additionally, today there are many more sizes of pumps and panels so matching these two components up are much easier. The components must match! Not any PV panel will 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. Fortunately, there are many sources available to help you with this issue.
Now for a one-time fee of a few hundred dollars for materials (PV panels and 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 long-term solution. This solution is an example of newer technologies and lower prices enabling solutions not feasible just a short while ago, saving both electricity and water (i.e. the water required to generate the electricity). A small change that can save money long-term and provide years of water delivery for free.