I'd buy Tesla Powerwalls¹ and charge 'em up. One of them can store upto 13.5 kWh of energy and going by your comment below (190 kWh/30 days = 6.3 kWh/day, which seems in line with "I have an extra KW of power generation for ~8 hours" for peak days), it seems two of them costing $14k as per their calculator can handle 4 days worth of surplus.

Not sure if the economics would work out in your favor² but I personally consider going off-the-grid worth the cost.

¹https://www.tesla.com/powerwall

²subsidies: https://www.tesla.com/support/energy/powerwall/learn/incenti... (could potentially knock off 50% of the cost if you qualify)