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Magnolia 08-17-2013 09:12 AM

Solar Panel
Hi ya!!

How do I determine what size solar panel we need for an Engel MT35?

Also, would it be smart to buy/install a solar panel that is dedicated only for the Engel, or, install a larger one and then use the power for other uses?


Mariner62 08-17-2013 12:05 PM

Solar Panel
Dont just power the fridge from a panel. Use the panel to charge a battery and power the fridge, and whatever else you want to power, from the battery. That way the fridge will be powered even when the sun is not available.

You'll need to size your panel based on the average current draw of your fridge (and other gear). You'll need to check the specs for the current in amps, and also estimate the cycle on/off of the fridge - this will vary a lot depending on whether the ambient temp is warm or cold.

For example, if your fridge draws 2 Amps and runs for 30 minutes in every hour, that's an average load of 1A. In a 24 hour period that's a total of 24Ah. So you need a panel which can put at least 24Ah into your battery in a day. If you estimate 6 hours of peak solar generation per day, then you need a panel that can produce 4Amps (4 amps x 6 hours = 24Ah)

A typical '12V' panel runs at about 17volts, so that's a requirement for a 68 Watt panel.

If you're powering more gizmos, then you'd need to up the capacity.

You'll need a charge regulator too so the battery doesn't get boiled.

There are many losses in the electronics and unknowns in the insolation effects, so these are all just estimates, and of course it all goes to custard when the sun don't shine :-)

Hope that helps!

Magnolia 08-17-2013 04:49 PM

Re: Solar Panel
Hey Mariner62 - thanks for the help!

Ok - I was following until you went from Ah to Volts. LOL Is there a book that tells me that 17volts requires at least a 68 Watt panel?

Alex W 08-17-2013 06:22 PM

Re: Solar Panel
Get a battery monitor first and keep track of your power consumption over an average day. This is a very useful tool to have on the boat anyway and will give you a lot of insight into your battery usage.

Then get a panel large enough to cover that consumption plus 20%.

Mariner62 08-18-2013 01:19 AM

Solar Panel
Power is volts x amps. So 17 x 4 = 68.

Couldn't agree more about the battery monitor. I have a BMV-600, but there are many others available. Absolutely invaluable.

Magnolia 08-18-2013 07:36 AM

Re: Solar Panel
Thank you, Alex W and Mariner62 - we will get a battery monitor. Currently we have two batteries. Fairly new. I need to write down what they are. But...will one monitor work for both?

Mariner - thanks for spelling out the math equation for me. I'll write it down so I can remember is. LOL

hydrodog 08-18-2013 09:24 AM

Re: Solar Panel
Practically speaking you want as many panels as you have space for .... you can use all the power that you have then some.... most everyone even with panels needs to recharge their batteries just not so often.
Good Cheap panels can be had from Sun Electronic out of Miami....

Alex W 08-18-2013 11:16 AM

Re: Solar Panel
The battery monitor will work for two batteries that are tied in parallel, but it won't work for two batteries on different sides of a battery switch (where one is used for the house battery, and one is used for the starter).

If you only buy one monitor you want it on the house battery.

Magnolia 08-19-2013 08:40 AM

Re: Solar Panel
Thanks again everyone for your help. It is greatly appreciated. :)

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