by Windy Dankoff, Dankoff Solar Products, Inc.
VERTICAL LIFT (HEAD) is measured from the SURFACE of the water source to
the pump outlet or the water level in the storage tank (whichever is higher)
TOTAL DYNAMIC HEAD (TDH) = Vertical Lift + pipe friction loss + any
back-pressure due to flow restriction or pressure accumulation.
HORIZONTAL DISTANCE of piping does NOT effect the load on the pump, except
in terms of friction loss in the pipe. Refer to Pipe Sizing Chart.
VOLUME OF WATER in pipe or tank does NOT effect pressure or the load on the
pump.
This can be used to calculate the load on a pump OR the pressure available
from an elevated water tank. Be sure to add the friction loss from piping.
VERTICAL FEET = PSI X 2.31
PSI is pounds per square inch
METRIC: 1 bar = 1 kg/sq cm = 10 vert. meters = 14.22 PSI
This is useful for estimating the cost and feasibility of any pumping system, even if the specific pump is unknown.
In American Units:
WATTS =
FEET X GPM X 18.8
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PUMP EFFICIENCY %
In Metric Units:
WATTS =
METERS X LPM X 16
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PUMP EFFICIENCY %
Feet or Meters = Total Dynamic Head
Pump Efficiency is "wire to water" (includes motor and pump losses)
Average efficiency for solar pumps is ~ 45% (varies 30 to 60%)
Enter Efficiency as a whole number: For 45% enter "45"
TO DETERMINE THE EFFICIENCY of a proposed or existing pump system, invert
the above equation to solve for pump efficiency.
PV ARRAY RATED WATTS (minumum) = WATTS REQUIRED TO PUMP WATER X 1.25
This "oversizing" is necessary is because most PV modules will not deliver
full rated power under high temperature conditions and with dust
accumulation and aging. Manufacturer's tolerances per warranty may be +/-
10%. There are also small losses in controllers and wiring.
TYPICAL INSTALLED PRICE of PV ARRAY =
PV ARRAY RATED WATTS X US$10
This is for rough estimation only, based on typical 1999 prices and not
including the pump and controller.
1 HP = 746 Watts (theoretical, at 100% conversion efficiency)
Typical solar pump motor efficiency is ~ 80%, so typically:
Motor draw per HP (80% efficient motor) = 746 / .80 = 932 Watts
Combustion engine HP rating = approximately True HP X 2.5
Electric motors are rated by true HP
POWER: WATTS = VOLTS X AMPS
ENERGY CONSUMPTION: WATT-HOURS = WATTS X HOURS
If system voltage is doubled, current = 1/2 and power loss in wiring = 1/4.
Or, for equal power loss, wire size (cross-sectional area) = 1/4.
Refer to Wire Sizing Chart.
Copyright © 1999 by Dankoff
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