# How to wire panels for water pump series or parallel?

Registered Users Posts: 4
Hi Dear engineers:
I have an AC water pump (optimum voltage = 600 volts, Imax = 33 amps), day length = 7 , how many panels should I buy and how to wire them in series and parallel connections

• Super Moderators, Administrators Posts: 31,684 admin
Really need more information than this... DC Solar panels cannot connect directly to a AC powered pump (typically 3 phase at this power level). Normally there would be an AC inverter (DC in, AC out) or a VFD (Variable Frequency Drive--Which, at its most basic level, takes DC or AC power in and outputs variable frequency 3 phase power).

VFDs are very nice... They "soft start" the motors, and can (if designed and programmed correctly) vary the pump RPM based on amount of sun and maximum allowed water pressure.

Just to size a solar array:
• 33 Amps * 600 Volts = 19,800 (if you want single phase DC)
Most large format solar panels are around Vmp~30 to 36 VDC... So, if you could get (for example) 250 Watt panels @ Vmp~30 volts and (250W/30v=) 8.33 Amps Imp...

So, nominally, that would be 20x panels in series (for Vmp-array~600 VDC) and 3x parallel strings (4x 8.33a=) for 40 Amps Imp-array.

Solar panels tend to be not "very good" batteries--They are really current sources. Solar panel current pretty closely equal to the amount of solar energy falling on the panel(s).

Voltage wise, the Voc-cold to Vmp-hot can be almost a range of 2:1...
• 30 Vmp * 0.8 = ~24 VDC Vmp-hot (hot climate, no wind)
• 24 VDC * 2 = ~48 VDC Voc (voltage open circuit) in sub freezing weather.
So, a 20x panel string would range from ~480 VDC Vmp-hot-array to ~960 VDC Voc-cold-array

Need to understand the connection (and electronics) between the array and the motor (electrical requirements).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 4
Mr. Bill:
Thanks a lot from your quick and satisfying replay.