W/ solar running near $1 a watt, and a $15 controller, how is that a good deal at $500 ?
'01 31' Rexall Vision, Generac 5.5k, 1000 watt Honda, PD 9245 conv, 300 watts Solar, 400 watt inv, 2 12v batts, ammeters, led voltmeters all over the place, KingDome/sat, 2 Oly Cat heaters, and towing a Dodge GCV, or a Lowe bass boat, or a Kawi Mule.
The usual rule for PWM is you need 20% margin over your rated Isc amps for sizing the controller and the fuse that goes on the pos line near the battery.
300w pointed at a high sun can get you 300/130 x 8.2 = 19a (which should be about twice the Isc of a 150w panel) so the 20a controller supplied is inadequate for amps size.
Also that controller has been noted on this forum in other kits as a poor one for some reason can't remember so you will need a better controller anyway. Lots of 25 and 30a PWM controllers on ebay at low cost, so no problem there.
As to that kit's price, just take off the "free" shipping and go with what they really cost and it looks better.
An alternative to consider is a single 24v panel in the 250w range and the 20a Eco-worthy ($102) or Tracer $130) MPPT controller.
2003 Chev 2500HD Gas, 2003 Komfort 26FS 5er,
1981 Frontier 11ft Truck Camper
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Don't know where BFL got his 130 in that formula, but 19A total Isc is really too close to the rated 20A PWM limit. For 300W array I would go for 25A controller.
The price - to me this kit has only one useful item: 2*150w panel. Possibly, 2*MC4 Y-connectors, they are expensive but you only need them if you run a parallel without a roof junction box. Everything else is either wrong item or wrong quantity. 40ft #10 wire is too short for on-rig installations, this is mere 20ft one way run. Z-brackets are a cr-p. Controller is too weak for this setup. And yes, there was a negative feedback on Phocos 30 - which in itself doesn't mean much, but the brand is not popular in RV.