One of our side projects this summer has been figuring out a better way to get water out of our rain barrel. We have a 30-gallon poly tank, which we placed in a cart to pull with the lawn tractor. The water can gravity-feed from that tank to plants, but we need a way to get water into the tank from the rain barrel. We had been using a combination of using a short length of hose as a siphon and filling buckets from the rain barrel spout.
We decided to build a solar-powered pump, as a way to transfer the water and to play around with solar. Using a coupon card from Northern Tool, I bought a Shu-Flow water pump and a small solar panel. Harbor Freight has solar batteries and solar controllers. The pipes and fittings came from Menards, and I used a spare Rubbermaid tub and scrap wood for the rest.
There are two components that are quite important for solar-based equipment. The first is the battery. Most conventional vehicle batteries are designed to provide a quick burst of power, to engage a starter. These batteries can become damaged if they are drained of power on a regular basis. Deep cycle and solar batteries are designed to be discharged and recharged. The other important component is the solar controller. This unit controls the flow of electricity from the panel to the battery and from the battery to the 'load', which in this case is our pump. Our controller is very simple and cost only $20 or so, but there are more complicated units that can be connected to multiple loads and provide information through an LED display.
I used scrap wood to make a platform to mount the pump and battery and raise them off the base of the tub, in case water accumulates. I built another platform to hold the solar controller and provide better access to the plugs. A third platform holds the solar panel. I added a filter to protect the pump from debris. The pump can be controlled with a switch mounted to the outside of the tub, but the pump is designed to sense pressure differential and start when there is an imbalance. The volume of water we are using has too small of a head to generate a significant pressure, but the pump should work when we build a larger water collection system.
We use the pump to transfer water from the rain barrel to our watering tank, and also to pump water from the watering tank to the plants. So far it has worked well, and gave us some experience on finding components for solar systems. It is portable in the sense that we can pick up the tub and move it where needed, but the battery makes the unit quite heavy. I can see why solar-based equipment tends to be stationary.
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