There is only one constraint for the electric system: the power produced needs to exactly match the power consumed at any point of time. If you mismatch those t

There is only one constraint for the electric system: the power produced needs to exactly match the power consumed at any point of time. If you mismatch those two numbers, the grid is going to fail. The baseload is just the number for the power under which the demand never drops in a giving time frame, typically 24 hours. The other number would be the peak load, which is just the maximum load in that timeframe. The actual load will be between these two numbers and at any time the constraint named applies. So "baseload" isn't some expecial part of the electricity. It is an accounting number. The challenge is to provide the correct power to the grid and for that, different technologies are used. Coal and nuclear power plants have a reasonably high availability, but as others have written, far away from 99% uptime. Their downside is, that their output can only be regulated very slowly. Both properties made them ideal for the amount of power which is called baseload. The problem is, they can't deliver much else due to their limitations. That is also the reason, that for decades the architects of the power systems tried to drive the baseload up. To increase demand at night, Belgium installed floodlights on their freeways, Germany for a while pushed electric heaters which would draw their main power at night at a reduced price. Solar and wind behave inverse, they might not be as reliably available, indeed the sun doesn't shine at night, but they can be switched off in an instant. But any time they produce enough electricity, they can carry the baseload. So currently in Germany wind easily provides large parts of the baseload (https://www.electricitymap.org https://www.electricitymap.org). Coal plants are almost shut down, even solar right now produces as much energy as coal. So without coal and nuclear, the challenge still is to match the grid demand. This is independant from the baseload number. And with the shift to reneweables, the baseload number can be driven down quite considerably, if incentives are given to use electricity in times of high supply.