Devil is in the details. Peaker plants are almost always natural gas, and I'd expect an electric oven (high power appliance that immediately turns on when you turn it on, and immediately turns off when turned off) is most likely using electricity from a peaker plant, rather than a baseload plant.
Time is the more important thing here.
If you turn on your electric stove at 3pm, when the grid is stressed from the afternoon sun, your electricity is almost certainly coming from a peaker plant (unless you're in California, at which point the peaker-plants are coming on at 6pm or so).
If you turn on your electric stove at 2am in the middle of the night, the grid is almost not being used at all, and cheaper nuclear power / baseload plants are probably what powers your stove.
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Its not so much "The Grid has 30% renewable energy on the average". Its "At 2pm, the grid is mostly non-renewable due to the number of peaker plants" and "at 2am the grid is mostly renewable nuclear"
As solar panels get deployed, the times will change, but the concept won't change. Peaker plants are the only plants that can respond to consumers. Anyone using electricity at times outside of what renewable energies can provide will effectively be using natural gas.
For California, you can check the actual generation mix:
https://www.caiso.com/TodaysOutlook/Pages/supply.html
For today:
| MW @ 2AM | MW @ 3PM
------------+----------+---------
Renewables | 5337 | 17228
Natural Gas | 10339 | 9568
Hydro | 1529 | 1178
Imports | 6216 | 778
Batteries | -23 | 183
Nuclear | 2241 | 2240
Coal | 7 | 2
California has a lot of solar panels.
The natural gas peakers come on at 6pm as the sun sets, but the day is still hot so AC is on.
At 6pm (1800) today, its reporting:
* 8983 Renewables
* 11933 Nat Gas
* 3403 Hydro
* 5948 Imports
* 1351 Batteries
* 2235 Nuclear
* 1 Coal
There’s also the potential for demand smoothing.