For the past month (March 2013) we've been producing about 130kWh per day.  I switched from time-of-day rates to flat so that there will not be a repeat of last summer, when night-time AC usage exceeded my off-peak co-generation surplus.  That meant that I had to pay roughly 60 dollars per month extra for those off-peak kWh even though I was making and banking more on-peak than I used.  With flat rates I'll always be able to use from my surplus.  The winter rates are used to settle up at the last meter reading of the year so that means there's almost no monetary difference between on-peak, off-peak, or flat rate surplus when it comes to getting paid.