Your existing demand is not flat. Not flat over a single day, nor a single week nor a single year.

So you already have some spare capacity on the system.

If your demand peak was summer air con, then adding the solar makes the system more stable. This can be seen in a few grids that issue less grid warnings in summer now.

In the Indian state of Bihar in the current summer season, the grid met the extra demand purely due to smart grid installed on rooftops. That state used to have shortage of electricity during peak summer until 2yrs ago

Not to mention solar contributed to more than 15 % of Indian summer demand which is crazily high due to 40+ degree temperature during the heat wave Solar that too decentralised is a massive boon