Can I use a solar pump to pressurize a tank for domestic use?
Maybe. Keep in mind that 1 psi = 2.31 feet of head so pressurizing a tank up to 50 psi adds about 115′ of head that the pump must push against so be sure that your pump can handle it. I would not recommend using a diaphragm pump for this application because you run the risk of rupturing the diaphragm if your pressure switch malfunctions. Another reason not to use a solar direct pump to pressurize a tank is that your tank might get low in the early morning or late evening when there isn’t enough sunlight for the pump to operate. Pressurizing a tank is best left to a separate booster pump or an AC centrifugal submersible pump running off of your inverter/battery bank, generator or utility power. Better yet, pump to an elevated tank and gravity feed down to your home or wherever you need the water.
