Friday, 22 April 2016

Solar panel output...

Sunny day and a voltmeter - what else are you going to do??

Panel spec.:
  • Open-circuit voltage (Voc) Av 21.6V, sd 0.3 (I see 21.8, so good)
  • Voltage at maximum power (Vmp) Av 17.5V, sd 0.2 
  • Short-circuit current (Isc) Av 0.31A, sd 0.01 
  • Current at maximum power (Imp) Av 0.26A (I see 182.2 mA so a little low but although it was full sun, it's not strong mid-Summer sun so I guess that's good)
  • Maximum power at STC (Wp) 5W ±3%
  •  Operating temperature -40oC to +85oC 
  • Maximum system voltage 1000Vdc Power tolerance ±3%


  1. Solar Panel Specs are always a bit optimistic because they'll specify a certain output with the maximum number of photons the panel can accept at right angles to the panel, etc. to make them seem better than they really are.
    I find real world figures where the panel isn't at 90 degrees to the Sun, dirt on the panel, haze and cloud, etc. amount to about half to two thirds of the rated specs.
    But as I don't constantly consume electricity on my boat, a 10W panel is enough to top my battery charge up over the week ready for a few hours of action at the weekend.

    Do you have a charge controller in circuit, or is the panel connected directly to the battery?

    1. Mark - agree with all of that... this will be directly attached to battery as the battery is 74aH and the panel is only 5w...

    2. Steve, the only thing I'd say is keep an eye on the battery voltage over the summer. I had my 10W panel on a 75Ah battery and over the summer it eventually dried out as the electrolyte evaporated off. I've got my controller set to unhook the solar panel when the battery gets to 14.1v so it charges, but doesn't get to the point of gassing.

  2. Mark - will do.... a long time ago I picked up on the 10% rule*, that providing the panel/charge was less than 10% in Watts, of the battery capacity in aH, you didn't need a charge controller... with the old battery I'd agree there was an issue (only 40aH), the new one is 75, and I think at best the new panel is only putting out 4w (from those readings the other day) so I should be OK, but I'll keep an eye on it as you suggest.... mind you, got to wire in the new solar panel first, and for that I'll be using a soldering iron for the first time in years!

    *which I probably need to check/test is still valid....