Well, it probably can be done for even less than $4,000 DIY. I would use 4 SOK lithiums which are highly rated by Will Prowse at $570 each. Then four 100 watt HQST panels for $85 each and a $120 Renogy 40A MPPT controller. The main parts add up to $2,700 plus a few hundred for brackets and wire. Add $1,000 or so for Battleborns.
But you probably also want to upgrade the converter to a Progressive Dynamics 9180 ALV and swap out the BIM for a BIM-Li 225, all for about $500.
David
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