Short answerLifting 500 gallons a day through 200 ft of total dynamic head takes about 240 W of panels on a direct-drive pump with 5 peak sun hours. Energy scales with gallons times feet, so 1,000 gallons through 100 ft needs the same 240 W.
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Key takeaways
- Energy scales with gallons times feet: 500 gal through 200 ft costs the same as 1,000 gal through 100 ft.
- At 5 sun hours, about 240 W of panels lifts 500 gallons a day through 200 ft.
- Scale the table by 5 / your design sun hours.
The table
Read across from your total dynamic head (pumping water level plus rise to the tank plus friction, see total dynamic head) to the column nearest your daily water. The figure is panel nameplate watts for a pump wired straight to the panels with no battery.
| Total dynamic head | 250 gal/day | 500 gal/day | 1,000 gal/day | 2,000 gal/day |
|---|---|---|---|---|
| 25 ft | 20 | 30 | 60 | 120 |
| 50 ft | 30 | 60 | 120 | 240 |
| 100 ft | 60 | 120 | 240 | 480 |
| 150 ft | 90 | 180 | 360 | 720 |
| 200 ft | 120 | 240 | 480 | 960 |
| 250 ft | 150 | 300 | 600 | 1,200 |
| 300 ft | 180 | 360 | 720 | 1,440 |
Why gallons times feet is the whole story
Lifting one gallon one foot takes 0.00314 watt-hours of pure work. So 500 gallons through 200 ft is 100,000 gallon-feet, or 314 Wh of water work. A small DC pump turns about a third of its electricity into lift, so it draws about 900 Wh. Spread over 5 peak sun hours that is 180 W at the pump, and about 240 W of panels once heat, dust and wiring losses are taken off the nameplate.
Double either the gallons or the feet and the watts double. That is why the table is a straight line in both directions, and why a deep well with modest daily demand can be cheaper to solarise than a shallow one feeding a big herd.
Adjusting for your sun
The table assumes 5 peak sun hours. Scale it by 5 divided by your design sun hours: with 3.5 hours in your darkest month, multiply by 1.43. Our state pages list every month for every state. Fewer sun hours also means a higher flow rate for the same daily gallons, which can push the pump onto a less efficient part of its curve.
Run your own numbers. The sizing calculator shows every step, for your state, lift and pipe.
Open the calculatorWhen the table stops being useful
- Above about 200 ft of head, small DC pumps rated at 230 to 270 ft maximum head deliver little water. See deep well solar pumps.
- Above about 6 gpm, the 2,000 gallon column at 5 sun hours, you are past the comfortable range of the small DC pumps we list and into larger DC or solar-inverter AC pumps. See DC vs AC solar pumps.
- If the well yields less than the flow rate, more panels cannot help. See well yield and recovery.
Questions
- How many watts does a solar pump need for a 200 ft well?
- For 500 gallons a day at about 200 ft of total dynamic head, roughly 240 W of panels with 5 peak sun hours, assuming 35% wire-to-water efficiency and 75% of nameplate reaching the pump. For 1,000 gallons a day it is about 480 W.
- Does a deeper well always need a bigger pump?
- It needs more energy in proportion to the lift, and a pump whose curve still delivers your flow at that head. Setting the pump deeper below the water does not add lift; only the depth to the pumping water level counts.
Put your own gallons, lift and pipe in and see every step of the working.