Solar panels

[dcneuro dcneuro.net]

I am about to upgrade the refrigeration on my 40. It is a sea frost, currently AC and engine driven system. I’m changing it over to DC. I am planning 1 or 2 130W flexible solar panels on top of the bimini. I currently have a 20W flexible panel on top of my dodger, held in place simply by strings which tie off at the corners and are stitched into the canvas. I’m thinking about doing the same thing on the bimini with the larger ones. Anyone have a better system or a better idea?

Thanks.

Sent from my iPad

Dr. S.

[M K]

About 16 years ago, we monitored the power usage on our 35.5c Bristol for about a week, and realized that the engine driven refrigeration was using about half of the power in a 24 hour period.  We changed the refrigeration to a large holding plate, about twice the normal volume, and a small DC compressor.  And added 88 watts of solar power on top of the Bimini.  A year later we added a sensor which turns on the DC Compressor whenever there is sunlight, and less than a fully frozen holding plate.  We usually anchor for 2-3 days maximum,  and then raise the anchor with the engine running the windlass.  Since then we have never had to run the engine to freeze the holding plate.  We turn on the refrigeration system in the Spring, and pull the fuse to turn it off in the Fall.  No hassle Nice!   Bottom line, invest in a bigger holding plate, and you'll need a lot less solar panel output.  

Marilyn 

"Adena" Bristol 35.5c

[M K]

Sensors to optimize refrigeration electric usage

https://www.scadtech.com/sensistat

https://www.practical-sailor.com/wp-content/uploads/2020/02/PS0409_Sensitat.pdf

[Jerry Brisson]

I have to agree with a larger cold plate being much more efficient. This summer I had the opportunity to monitor a 12V refrigeration system which utilizes a below water plate to dump heat. The boat was on the hard all summer so cooling was very inefficient. Often pushing the limits of solar and worn out batteries ready for replacement. 

When the refrigeration temperature was set low enough to keep ice cube trays frozen solar kept up and low temps were maintained.  Raising the temperature setting on the thermostat seemed to increase energy usage to the point where solar, poor heat dispersion and weak batteries could not keep up and the temps kept climbing. Plugging in a battery charger was the only way to cool down the refrigerator. Once down to the lower setting solar would maintain the temperature which was baffling. After watching this occur several times I finally realized at the lower setting ice remained frozen and less energy was used. When raising the thermostat setting ice trays would partially melt and then refreeze every cycle requiring much more energy usage. 

This seems to coincide with the results of your larger cold plate by avoiding phase change from liquid to solid which is very energy intensive. Once launched with new batteries installed I know to keep the refrigerator set fairly low to conserve energy. Counter intuitive to what I would have expected.

Jerry Brisson 

Bristol 32 - Athena 

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