Optimal ratio: 21:25.
"Close enough" ratio: 20:24.

For 200 accumulators:
optimal: 200:210*250 = 238 solar panels.
"close enough": 200:200*240 = 240 solar panels.

We need to put away 2 (with rounding to whole numbers) solar panels instead of adding 20.

Link to the article: https://wiki.factorio ...