The usual wholesale price of electricity is around $0.11 per kWh. The retail price of electricity is around $0.16 per kWh. So you save about $0.05 per kWh used in an average month -- not bad! That's a free $20!
Until a "100 year" storm comes along, and makes the wholesale price of electricity $9 per kWh. Now instead of saving $20, you owe $8,800 more than usual.