>99% still means 3 full days of blackout every year. Or using some excess wind capacity to generate some windgas at and keeping it stored using existing natgas

>99% still means 3 full days of blackout every year. Or using some excess wind capacity to generate some windgas at and keeping it stored using existing natgas infrastructure. The windgas process is only 50% efficient at converting electricity so it's only cost effective if it's used for say, <1% of electrical needs. These calculations also dont take into account demand shaping. If you can convince people to stop smelting aluminium so much and charging their cars on the off day that reduces storage needs still further.