If you don’t have access to clean water in your off grid home, nothing else will matter. Some will be fortunate enough to have crystal clear and potable water directly from a spring or well but most of us will need some type of water filter or purification system.
The problem is most of the water filters sold at your local building supply store or water filtration store are not made to be energy efficient. Something as simple as a backwash valve on an iron filter can waste a lot of your hard earned kWhs as they use power 24 hours per day.
In this article we will discuss some of the common water filter systems and how to make them more efficient.
Iron, Manganese and other Media (Sand) Filters
Most water filtration systems rely on a regular backwash cycle to clean and maintain the filter media (sand).
These backwash valves keep time by using power from the grid via a wall wart so they can automatically backwash every day, two days, week etc.
Some models consume up to 15-20 watts 24 hours a day and add kWhs to your bill for a little bit of convenience.
The best way to reduce this consumption is to plug your filter into a timed electrical outlet, similar to the way a Jacuzzi tub is wired.
When you want to perform a backwash for your filter, simply turn the timer on for an hour and press the backwash button on the water filter valve.
The backwash will cycle in 20-40 minutes. In another 20-40 minutes the timer will power off the filter until the next time you need it. No waste.
Use the wiring diagram below for installing your iron, manganese or sand filter.
UV Water Sterilization Light
Another very common water purification system found in a solar home is the UV light. UV lights kill bacteria such as E coli and coli form but they present a major challenge for the off the grid home.
These UV lights can use 20-100 watts continuously. This will add up to 0.48-2.40 kWhs per day to your energy requirements.
For your off grid home this could add $4500-$6000 to the initial cost of your solar electric system.
UV lights work by killing bacteria as the water passes by the light. It is instant. By the time the water sees the light, the bacteria are dead.
The problem with these lights is that they stay on all day even if water is not passing thru them. This is unnecessary waste.
The correction for this waste is to add a flow switch that operates your UV light. Plumb the flow switch into your main water supply line. Wire your electrical supply through the flow switch and then to the UV light. When you open a faucet, the flow switch will automatically turn the UV light on. When you close the faucet, the flow switch will turn the UV light off.
This has been tested and works very well. Remember the UV light kills bacteria instantly. There will be a tiny delay between the water flowing and the flow switch activating the light. In our experience, the delay is not enough to allow water to pass thru unsterilized. If this really concerns you or you have high bacteria counts, you can add a second UV light somewhere else in the line to be sure every liter of water has been treated. Running two UV lights for a few minutes a day will be far less energy than operating one unit 24 hours per day.