I never ran out of permeate inseason. I've only ever needed to supplement my permeate as I first get ready fror the season. Then I draw municiple water, which in my case is from a large open resourvois and has been well filtered, but then they add chlorine. When I use it, I haul a 275 gal IBC tote full, pump it into my permeate tank then I let it set for 3 dys to get rid of most of the chlorine. Then I do the opening for the season proceedure using it in my RO. . Once The season is underway I clean the RO using a blend of what's left from the initial municiple water and my permeate water. I've always had a tank large enough that a cleaning never uses it up. I just run the proceedure by the clock, not until the permeate is gone.
As a general rule you should have storage for 2x what the RO does an hour. In my case, that's 500 gal storage. I'll be using an 850 gal tank for the permeate storage this coming season. Back when I had my 3x8 evaporator, my permeate tank was a 1000 gal tank, I sold that as I cut back in size of my operation, but both then and now, I have and had an RO rated at 250 gph. Thus I need at least 500 gal for permeate storage, I'll have 850.
My potential bottle neck will be sap storage, for 200 min to 500 max (if I tap on the neighbor with permission) I'll only have a 300 gal and a 200 gal storage tank plus a 100 gal head tank. But being retired it shoul pose no problem, I can boil anytime I have enough sap to make enough concentrate.
If your RO does 20 gph, you need 40 gal storage and so forth.
Dave Klish, I recently bought a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.