Hello,
since the panels and accumulators have the same multiplication factor you can use the vanilla factor that somebody figured out already: https://wiki.factorio.com/Power_production#:~:text=The%20optimal%20ratio%20is%200.84,needed%20to%20charge%20the%20accumulators).
"The optimal ratio is 0.84 (21:25) accumulators per solar panel, and 23.8 solar panels per megawatt required by your factory (this ratio accounts for solar panels needed to charge the accumulators)"
You can also get a normal solar blueprint with correct ratios and use the upgrade planner tool to upgrade to elite panels and accumulators. The ratio will be correct then.
