Yes they fluctuate enough that you can make a profit even with a "20% loss". Here [1] you can see today's prices on the electricity spot market for Europe (Changing the date does not work in my browser though)
Another way to say this is that there is a real economical value for storage because of the increase in renewables
Another way to say this is that there is a real economical value for storage because of the increase in renewables
[1] https://www.rte-france.com/eco2mix/les-donnees-de-marche