The grid can be balanced by the application of market forces. (If there's an electrical shortage, prices go up. If there's a surplus, prices go down. The incentives are all there to encourage producers to produce power during shortages.)

I was thinking more about pollution or nuclear waste management. A coal plant that just buys coal at market prices and sells electricity at market prices isn't paying for externalities unless they're taxed on CO2 and particulate emissions.

You could balance it that way but people don't like it when there is a power out, nor do they like when a electrical shortage causes prices to rice 10-20x that of normal prices. At that point people will vote on politicians that will fix the problem using tax money to bail out the situation, similar to how people expect government to fix the problem when banks crashes.