backchannel: island of misfit [solar] toys

Our unfortunate fellow has already spent hundreds on some stuff that won’t play well together.  Each component is fine on its own, interestingly enough.

good news first

The setup (other than the oversized inverter) is sized rather well.  200w of panel, 20A of b2b charging, and 100Ah of battery.   Good.

the less good news

Renogy needs to be horsewhipped for selling a kit with mono panels on a PWM controller.  It’s a mismatch that costs about 6% yield for no reason at all.

Sell poly panels with PWM controllers for the same price, if you must.  Better yet, sell the better-performing combo at the slight discount the poly panels would suggest.  Bastids.  I chalk this up to a product manager wanting to include the MONO!!!!! buzzword rather than any desire to thwart the consumer.

Gel batteries are not a good choice for vandwellers.  They have all the cost of AGM without the throughput advantages.  Gel will put out about C/5, the same as flooded.   In this case that’s 20A, or about 240w.

Gel batts also demand slightly lower voltage, which frustrates our desire to tweak battery voltage to attenuate the mono/pwm mismatch problem.  In this case (ha!) the battery shell says 14.4v is max Vabs.   If I’m reading the manual correctly, s/he could set the DIPs to: S1 ON S2 ON S3 ON S4 ON S5 ON to get maximum allowed Vabs (14.4v, yielding 152.352w) and Vfloat (13.8v yielding 146.004w).

A DC-DC charger is probably overkill when solar is present.  A $25 solenoid or $50 voltage sensing relay would have sufficed. OP also spent $260+ on a 1500w inverter when the battery can only provide ~240w.  Even if we consider the solar’s max contribution we’d still be up to only about 400w.  That same inverter is offered in a 500w model for less than $100.


IMO, these would be better spends for less money

  • solar

    • 2x100 poly + 20A pwm; or

    • 2x100 poly/mono + 20A mppt

  • 100Ah Renogy AGM if s/he really wants VRLA.  Same price, but it can take 14.8v and will crank C/3 (400W).  If OP is willing to go flooded s/he could have over 2x the capacity, 1.25x the throughput, and about 4x the useful life from something like a set of T-105s for the same money. (sorry for hollaring but this gets frustrating)

  • a plain constant duty solenoid

  • 1000w inverter if s/he must, since our combined bank + solar will now make ~600w under excellent conditions.  The 500w should also suffice.

Note:  by swapping AGM for the Gel and poly for the mono we get a max of 166.352w rather than the prior cap of 152.352w.  This is due to it being 14.8v x 5.62A instead of 14.4v x 5.29A.  That’s a 9.2% solar power increase for free.  Do you want 9.2% more solar power for free?  (this is not a trick question)