Hey Rich,
I think you have a point, but given that the solar panel I'm starting with won't run the fan(s) the battery I'm hoping will be a sort of buffer.
I started out with mercury thermostats but found that thier good for "heating" applications, where I need fans turned on below a specific temp, but the issue of engaging the fans to cool didn't have an obvious solution (shy of mounting upside-down...)
The digital themostat, uses relays (barely audible when they are activated) and can handle 1Amp @ up to 30V AC/DC. It even has a "Compressor" delay feature that inserts a 5 minute delay between successive cooling cycles.