Some times I see the relative thermal coefficient of solar cells Isc (called "alpha" or α) written as 1/K, other times as %/K.

I think that %/K can be seen as 0.01/K, but I am not sure.

Is it correct that 0.000555 1/K = 0.0555 %/K?

PS: absolute Isc,stc of the solar cell = 149.6 mA and I would like to output temperature compensated irradiance with formula:

G = (Isc,meas ÷ (1 + αIsc (Tcell-Tref))) × (Gref ÷ Isc,ref)

thus G = (Isc,meas ÷ (1 + αIsc (Tcell-25))) × (1000 ÷ 149.6)

I think that αIsc needs to be filled out here as 1/K (=%/K divided by 100) and not as %/K, otherwise the temperature correction seems too high.


1 Answer 1


You need to know the actual value being converted to convert between systems.
That is the 1/K and %/K values do NOT have a constant ratio - it depends on the actual value under consideration. eg

  • 1A change in 100A = 1%.
  • 1A change in 40A = 2.5%
  • 1A change in 10A = 10%

For variable "N" where N may be watts or amps or volts:

N/K means absolute change in N per degree K (or per degree C)

%N/K means percentage change in N per degree K change.

The conversion depends on the current (or voltage or power)
For eg I_25C = current at 25 degrees C.

  • %N/K value = (100 / I_25C) x N/K value

  • N/K value = %N/K value x (I_25C / 100)


So eg "40A - 0.2A/K" means current would decrease by 0.2A for every degree K (or C) that temperature rose. So eg 50K rise = 50 x 0.2 = 10A so current would decrease from 40A to 30A.

"40A - 0.5%/K" would be the same as the above as 40 x 0.5/100 = 0.2A.

The same applies to figures for Voltage or Power where applicable.

  • \$\begingroup\$ @Russell_McMahon I already knew that %/K is the relative form. I didn't know that 1/K is its absolute counterpart. Thanks for making me learn. For me, your answer can start with "1/K means absolute..." and as second sentence your example "For eg I_25C...". The rest is more background knowlegde and could be the last paragraph of the answer. \$\endgroup\$
    – Pro Backup
    Nov 8, 2019 at 8:48
  • \$\begingroup\$ What I really needed is: %/K = 1/K ÷ (I_25C÷100); your answer helped me to get there. \$\endgroup\$
    – Pro Backup
    Nov 8, 2019 at 8:59
  • \$\begingroup\$ "1/K" is the wrong unit in the case of absolute numbers - it has to be "A/K". \$\endgroup\$
    – asdfex
    Nov 8, 2019 at 9:26
  • 1
    \$\begingroup\$ @asdfex Read carefully. 1/K is a contraction for "per degree K". And if one did this (I now have) you'd also want %A/K. || If one wished to do it real-proper-like you'd want to put X/K where X is the variable being considered - which in this case is usually current or Voltage or power (all of which have temperature dependencies. ). || Sometimes aiming at understanding trumps pedantic correctitude. Sometimes not :-). || I've edited the post to try and convey N/k and %N/k concepts better. That it will not please all is a given. \$\endgroup\$
    – Russell McMahon
    Nov 8, 2019 at 13:32
  • 1
    \$\begingroup\$ Nope, that's wrong. The absolute value is an addition as in 40A - 0.2A/KT and needs the 'A' unit. The relative value is a factor as in 40A * 0.1%/KT and therefore does not carry the 'A' unit. (T is the temperature) You did exactly this in the last section of your post! \$\endgroup\$
    – asdfex
    Nov 8, 2019 at 13:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.