If you want 100% GHG reduction, for every 1 watt nameplate solar rating, 1 x 0.2 capacity factor x 730 hours a month x 3 months a season = 438 Watt-hour of battery or other energy storage. 80% reduction needs 100 hour vs a whole season, so 20 watt-hour required storage. Dr. Chu of Stanford is my source.