Refrigeration and Solar Panels: Can solar panels supply all the necessary current?

Solbian solar panels on Bimini

An increasingly popular question we hear at Boat Shows is "What size solar panel do I need to run the refrigeration on my boat?" Of course, this begs the question "What is your refrigeration's current draw?" which in itself may not have a set answer.

The current consumption of any refrigeration system is meaningless unless all the conditions are specified; i.e. box temperature, ambient temperature, water temperature, compressor speed, voltage, etc. The manufacturer's figures are simply average numbers; some, like Frigoboat, attempt at a true average figure, while others are more a marketing tool. Making use of variable compressor speed, as Frigoboat does with the Merlin and Guardian speed controls, and others do with the Danfoss/Secop AEO control module, brings even higher efficiency and lower overall power consumption in air- and keel-cooled systems, but is counter-productive in a pumped-water system. This is because the pump adds 25% to 35% extra current draw, and so it is best to run the compressor at full speed and get the job done as quickly as possible. The most efficient system is one using the Keel Cooler; no pump, no fan, and variable compressor speed can be used to gain even higher efficiency.

Daily consumption is measured in amp/hours per day, and you can get an idea of what to expect by using a watts meter, like Watts Up, on your refrigerator leads. These meters can tell you how many amp/hours per day a device is using, and it's best to use it over several days to get a daily average. The running consumption will vary dependent on conditions, as will the on/off cycle time, so you will need to be able to come up with an average daily amp/hr draw.

As a general rule of thumb, a solar panel with SunPower® cells will give approximately 1/3 of its rated wattage as a daily yield in amp/hrs. A panel with regular monocrystalline cells will produce about ¼ of its wattage as daily amp/hrs, and a polycrystalline panel produces around 1/5 of its wattage rating in amp/hrs per day.

Let's take an example:

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Marine Cooling, Refrigeration, Monitoring, And Solar Solutions

Are you a boat owner, or soon-to-be boat owner, with questions about your vessel's systems? Let us help you find those answers. For example:

    • Want to know how many amp/hours your solar panel is putting into your battery bank? Philippi's PSM System Monitor can help you there.
    • Water-cooled vs air-cooled refrigeration, see "Which Condensing unit should I use" in Refrigeration > Planning.
    • Where does one begin when planning for solar panels on a boat? With "Marine Solar Panels Planning and Installation Guide in Solar > Planning.
    • Can you have air-conditioning on your boat without running a generator, or the engine, or being plugged into 115v power? (Hint: Yes!)

If you don't see the answer to your questions in our website, blog, facebook, or twitter posts, then contact us directly. We will respond as soon as possible.


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