Air Conditioning With Solar Power? Yes, With FPB 78-1 Cochise


We are about to demonstrate the holy grail of solar energy. But first, the backstory…


Bruce Farrand, head honcho at Circa, sitting next to Linda, is visiting, (more on this later) and even though it is very hot outside we decided lunch on land was in order. We three, along with FPB pro Steve Parsons, ventured forth, and were rewarded with a pleasant interlude ashore.

The norm when leaving the boat has always been to shut everything down. We would not consider leaving a genset running, for example. As it is raining off and on, we would also normally close the hatches. Given sun load, 83F water, 88/92F air, and high humidity, this would guarantee an oven when we returned after lunch.

But Cochise opens up new horizons for us. We left the great room air con running. “No genset=flat batteries,” you are thinking.

Take a look at the lead photo, which we took upon return. Cochise was 81F in the great room, the air was quite dry, and the batteries weren’t only up, but receiving a slight positive charge. Upper left is the net into or out of the batteries, in this case positive 39.7 amps. Upper right is the solar array output, 136 amps. The difference between the two is the power needed to run the air conditioning. Voltage was 25.1.

And we have not yet installed solar film on the windows or arranged for exterior shade clothes, or foredeck awnings. With that, we think we can cut the great room heat load by half.

DSC3656 2

We are collecting between 575 and 720 amp hours a day now, or about 18kW. Total depends on cloud cover, haze, and our alignment relative to the sun. The original estimate of a 30% reduction of theoretical output for shading and alignment losses seems about right.

This is only part of the comfort equation. Air flow, natural and forced, insulation, and heat load reducers as mentioned are all a big part of the puzzle. We will go into detail when we have some more free time. Right now we are getting ready to go…Somewhere.

Posted by Steve Dashew  (September 29, 2016)

2 Responses to “Air Conditioning With Solar Power? Yes, With FPB 78-1 Cochise”

  1. bill Says:

    Hi Steve,

    What was the AC unit?


  2. Steve Dashew Says:

    Hi Bill:
    A pair o 12,000 BTU direct expansion evaps with remote compressors.