They are not "cut", those industrial users ( mostly in chemistry) get paid to power down. They could receive more money to power down than to work, so they do

They are not "cut", those industrial users ( mostly in chemistry) get paid to power down. They could receive more money to power down than to work, so they do that when it's interesting enough.. The electricity net is really fragile. You need to guess averages to the system as a whole, so there's not much flunctuation. Renewable energy is an extra variable too. Some additional reserves can be powered on/off to make the system stable. Ps. If you cross those averages by 5% for example, you get a hefty fine, so monitoring your power outage is really important. Source: worked at a company monitoring this for multiple countries.