35% of power needs being covered over the time measured ((98/116)×(10/24)).

can be higher. Daytime hours have higher demand, and stat can mean that demand was covered for x hours, instead of production equal to 10/24th of demand.

So if we assume that the 18 days not covered had 0 hours of coverage

unlikely. But a reason the spring period is being highlighted is that there is no heating or cooling demand. There is more room for improvement for sure.