i dealt with something similar to this in the southeast US...
you might want to check your electric company for different billing plans...
the default plan, that you get when you sign up is usually a tiered, variable rate...
you know about the tiers... but there is also a peak season (summer) where all the tiered rates go up... where i live, it goes from $.05/KWhr in the winter to over $.12 in the summer...
i changed my billing plan to one more suitable for high-useage... i pay a higher rate to be connected to the grid.. (based on previous useage) - then i pay a fixed $.05c per KWhr for as much power as i need... it comes out to about $.08 or $.09/KWhr after i pay for everything... (taxes, street light fee, other BS)
with the old plan i hit $900 one month (about triple my normal bill), then i got wise and called them - just to see what they would do... they didnt give a shit - they just wanted their money. then i asked about other plans, and they told me if i had the one i have now it would have only been $350 or some shit...
anyways, call them and see if you are on the "stupid plan"...
just my $.02 / KWhr