What size solar panels (electric) and inverter do I need for 1 1/2 horse power water pump?
We live in a remote location and get our water from rainwater captured in cisterns.
I would like to also run our water pump, which creates the water pressure in the house, on solar electric panels.
So we would use a large bank of batteries to collect solar power in the batteries, and then an inverter powered by the batteries to actually run the pump.
The water pump says that it is 1 1/2 horsepower, which is a lot. It is a very big house.
The pump only runs intermittently. It charges a pressure tank and only comes on when the pressure drops. So there is a period of time when the solar panels can recharge between uses of the pump. It might be several hours or (if the washing machine or clothes washer is running) every 5 to 10 minutes).
How can I figure out what size solar panels I need and how big of an inverter I need?
We would also need some kind of back-up power from the grid which does not automatically prefer the grid over the solar panels. Adding back-up power from the grid is easy. Giving the solar panels time to work before drawing from the grid is the hard part. We don't want the grid to charge the batteries leaving the solar panels nothing to do.
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That size & rating of pump is typically going to pull 15 to 20 amps of power at 120VAC, or very roughly 1500 Watts. You should budget for about ten panels sized 60″ x 30″ . Your inverter simply needs to be able to deliver 1500W.
Big project
the pump will draw about 1000 watts. Lets say it runs 25% of the time 12 hours per day (you do sleep?) so thats about 4 hours per day. SO 1000 * 4 / 1000 = 4 kw-hrs per day. You should plan for 3 days of power, so a 12 kw-hr system. Since the sun only shines 3 full hours in the wintwr, you will a 12/3 = 4 kw system a 3 would be close.
The system with batteries will run $30,000 to 40,000. If you don’t use that much water, ie 25% of the time, and you don’t mind water if the sun doesn’t shine, get a 1.5 kw system for $15,000. I’d meter the water for a month then calculate your useage to size the system exactly.
Perhaps I misunderstand, but do you already have grid power there? If so, you could get a grid-tied solar system. No batteries to worry about at all, and if the pump needs more than the panels can supply instantaneously, no problem. With a grid-tied system, every bit of energy from the solar panels will be used, either to power the home, or build up a credit towards future electric usage.
You may be better off getting a booster pump that is designed to work directly off solar. They are more efficient, use less power, and would not suffer power loss from batteries and an inverter. http://www.altestore.com/store/Solar-Water-Pumps/Surface-Pumps/Flowlight-Booster-Pump/c534/
As far as a grid-tied battery backup system, you would need an inverter that is designed to do this. It is programmable so you can set the preference for the power source, so it will first fill the batteries from the solar. http://www.altestore.com/store/Inverters/Grid-Tie-Off-Grid-Capable-Inverters/c561/