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Please feel free to use the calculator below to do your own calculations for solar arrays and battery backup.

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Equations

Use the following equations to determine solar array size and battery backup requirements based on 12V nominal system voltage.

Power consumption for each piece of equipment Power = voltage × current W = V × A
Daily amp-hour load for each piece of equipment Amp-hour load = power / voltage × hours of operation per day (h) Add up amp-hour load for whole system. Ah = W / V × hours of operation per day (h)
Efficiency and loss-corrected load for whole system Corrected load = amp-hour load / 0.8 Ah(corr) = Ah / 0.8
Worst case equivalent sun hours (ESH) (h) Determine from charts or meteorological data.  
Solar array current requirement (A) Solar current req. = Corrected load / ESH (h) A = Ah(corr) / ESH (h)
Number of solar panels in parallel (N) No. of panels = solar current req. / current output per panel N(panel) = A / A/panel
Autonomy or reserve time (Ah) Autonomy = no. of days × corrected load / % discharge rate Ah(res) = N(days) × Ah(corr) / % discharge rate
Battery bank (backup) size Battery bank = autonomy (Ah) / Ah per battery Bank = Ah(res) / Ah/battery

Calculator

Example

 A permanent station with a Trimble receiver, cellular phone, modem, and computer located in Boulder, Colorado, approximately at latitude 40´02´´ N, 105´14´´ W, elevation 1602 meters.

Power consumption:

Equipment			Power	Hours/day
Trimble 4000SSi receiver	  9W	   24 
Cellular phone			 15W	    4 
Cellular phone modem		 10W	    4 
Computer			 20W	    4

Daily amp-hour load:

Equipment			Calculation	 Ah
Trimble 4000SSi receiver	9W/12V × 24h	18.0 
Cellular phone			15W/12V × 4h	 5.0 
Cellular phone modem		10W/12V × 4h	 3.33
Computer			20W/12V × 4h	 6.67
Total						33.0

Efficiency and loss-corrected load:
33 Ah / 0.8 = 42 Ah.

Worst case equivalent sun hours (ESH) for Boulder, CO:
3.5 hours

Solar array current requirement:
42 Ah / 3.5 h = 12A

Number of solar panels in parallel:
Three solar modules are currently being used in UNAVCO designs:

  • Siemens PC-4JF rated at 75W (4.4 A 17.0 V)
  • Siemens M75 rated at 48W (3.02 A 15.9 V)
  • Solarex MSX-30 rated at 30W (1.68 A 17.8 V)
Choosing the M75 module, four panels are needed to cover the solar array current requirements: 12A / 3.02A per panel = 3.97 panels

Autonomy or reserve time:
Choosing five days of autonomy with 50% maximum discharge:
5 × 42 Ah / 50% = 420Ah battery bank

Battery bank (backup) size:
Three types of sealed deep cycle batteries are currently being used in UNAVCO designs:

  • Deka 90Ah
  • Deka 66Ah
  • Deka 30Ah

As an example, if you choose the Deka 90Ah, five batteries are needed to provide the required autonomy. 420Ah / 90Ah per battery = 4.67 batteries.

Last modified Thursday, 25-Jan-2007 23:56:50 UTC
 

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