backchannel: PWM makes more power at 80% state of charge than at 50%

a continuation of this reddit post:

Because I drank more coffee than usual this morning: PWM power output fluctuates with voltage because amps * volts = watts, and panel current stays pretty stable under normal insolation. Using the Renogy 100w mono at 70F ambient again, and some crude assumptions about voltage/SoC: > > > * MPPT output: **82w**. Much like the honey badger, "MPPT don't GAF about Vbatt". > > * PWM output at a high-ish Vabs (14.8v): 5.29A x 14.8v = **78w** <-- very close to mppt! Hmmm.... > > * PWM output at Vfloat (13.6v): 5.29A x 13.6v = **72w** > > * PWM output at 100% state of charge: 5.29A x 12.8v = **68w** > > * PWM output at 80% state of charge: 5.29A x 12.5v = **66w** > > * PWM output at 50% state of charge: 5.29A x 12.1v = **64w** <-- PWM is hating life down here > **Corollary 1**: one could [tweak PWM](http://rvwiki.mousetrap.net/doku.php?id=electrical:solar:pwm_tweaking) to get a bit more power by configuring setpoint voltages, while still staying within battery manufacturer recommendations. With PWM and similar controllers, higher battery voltages directly relates to higher overall output. **Corollary 2**: This one isn't obvious, but other things being equal **PWM will typically get more power from poly panels** than from mono due to the latter's higher voltage (and necessarily lower current for the same 100w rating). In the case of the Renogy 100w examples PWM makes about 6% more power on poly than mono.