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Old 04-02-2018, 06:14   #1
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How do you measure Solar Output to system

I keep seeing comparisons of efficiency of various solar panels and claims of so many amp hours for an installation. Can anyone explain to a non-electrician how to simply measure output of solar panels?
Can it be as simple as just putting an ammeter in series with the panels and the battery?
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Old 04-02-2018, 06:19   #2
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Re: How do you measure Solar Output to system

An ammeter will give you instantaneous current. To know exactly how many amp hours your array is producing youíll need an amp hour meter on the solar output.
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Old 04-02-2018, 06:22   #3
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Re: How do you measure Solar Output to system

I laid mine out and hooked a multimeter to them. Check out www.marinehowto.com he tells you how to do most everything.
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Old 04-02-2018, 06:24   #4
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Re: How do you measure Solar Output to system

Do you have a battery monitor that shows net amps?
If so switch off the solar panels or disconnect the solar feed to the battery. Amps should read close to 0 with all other items switched off. Then switch on the solar feed and you should see positive amps (in daylight). You can then cover each solar panel one at a time with a blanket and see if they are all contributing a charge. You can do this with different angles to the sun to see difference that makes too. Try putting the blanket on half a panel and see what that does too.
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Old 04-02-2018, 06:46   #5
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Re: How do you measure Solar Output to system

Our solar charge controller has a display of Amps. It continuously alternates between voltage and current (about 5 seconds at a time) so you can see at a glance what the panels are putting out.

If your controller does not have this feature then an ammeter will work. As noted above this will measure Amps, not Amp-hours.

Cheers!

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Old 04-02-2018, 10:35   #6
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Re: How do you measure Solar Output to system

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An ammeter will give you instantaneous current. To know exactly how many amp hours your array is producing youíll need an amp hour meter on the solar output.
Exactly. I fit an amp hour meter in the charge circuit to accumulate the total. I also fit a timer to reset the AH meter each night so I could see results for the current day.
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Old 04-02-2018, 11:48   #7
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Re: How do you measure Solar Output to system

"Can it be as simple as just putting an ammeter in series with the panels and the battery?"
Well, actually? An accumulating WATT meter. The amps and volts will vary, what you want to know is the total power, the wattage, of the panels. R/C hobbyists have made little gadgets like the "Watt Meter" very popular under many brand names:

https://www.amazon.com/Power-Analyze...rds=watt+meter

All of $15-20 and most will handle more power than your typical panel will put out.

Depending on your controller (MPPT, PWM, none) you will either be able to use the full power, in watts, that your panel puts out. Or, with a cheaper controller you'll be limited to something like 14.4 volts at whatever amperage you can get, and excess voltage (and power) gets thrown away.

Rule of thumb, if a panel is rated "100 watts" you'll get five hours worth of full power (that's rated as noon sunlight) in a typical 12-hour day. So, 500 watt-hours per day from a 100W panel. More in the tropics, substantially less in Anchorage during the winter.

You really can find all the definitions and standards and calculators for that online, courtesy of Uncle Sam and others. But $15 and a pencil will get you close fast.
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Old 04-02-2018, 11:54   #8
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Re: How do you measure Solar Output to system

Itís usually as simple as looking at your controller.
My Outback 80 gives all kind of information, way more than I know what to do with, or truthfully have a use for.
Iíd say fit as much Solar as you either physically can, can afford or are willing to have appearance wise. Iíve never met someone yet that had more Solar than they could use, not yet anyway. Reason is if you have the power, youíll find a use for it, yes you can live with less, but why if you donít have to?
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Old 04-02-2018, 12:16   #9
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Re: How do you measure Solar Output to system

Pacific Yacht Systems just published an interesting series on solar installations that addresses the OP’s question. Here is the most recent: https://youtu.be/HyAvQD8Z6dQ
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Old 04-02-2018, 12:18   #10
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Re: How do you measure Solar Output to system

Momentary output is measured in watt, total output measured in watt hours.

you need to multiply the voltage with the current to get the watts.

Voltage fluctuates with the state of charge, so you need to run the numbers every few moments to be somewhat accurate in your total output figure.



Better alternative:
Some solar chargers give you the total output in watt hours.

Or just get a battery monitor that does this for you. Gives you all kind of numbers. Volt, Amps, Watts, Watt hours, Amp hours, state of charge, ...
If you really want accurate information you need to switch off all loads.

And empty batteries, as a full battery doesn't accept much energy.


We have a Victron BMV battery monitor and Victron MPPT chargers. Both give all kind of numbers, and support a smartphone interface. Benefit bside a new toy to play with: no additional holes in the boat panels for displays
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Old 04-02-2018, 12:21   #11
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Re: How do you measure Solar Output to system

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Originally Posted by a64pilot View Post
Itís usually as simple as looking at your controller.
My Outback 80 gives all kind of information, way more than I know what to do with, or truthfully have a use for.
Iíd say fit as much Solar as you either physically can, can afford or are willing to have appearance wise. Iíve never met someone yet that had more Solar than they could use, not yet anyway. Reason is if you have the power, youíll find a use for it, yes you can live with less, but why if you donít have to?
Yup.. Our Victron controllers show all sorts of data if you hook up the optional Bluetooth module. The controller stores 30 days of data, but you can export and keep as much data as you like.

As to having enough solar.. Hi, I'm Travis, and I'm going to be the first guy a64pilot met that has enough solar. We have 900W aboard for our family of five and its more than enough. Most days we do not use all our power. Some days, when we aren't lazy, we will heat water with the excess (electric element through inverter), but %90 of the time, just can't be bothered. So yes, you can actually have enough solar.
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Old 04-02-2018, 12:28   #12
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Re: How do you measure Solar Output to system

QUOTE "we will heat water with the excess (electric element through inverter), but %90 of the time, just can't be bothered."

Can you please explain what the bother is?
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Old 04-02-2018, 13:17   #13
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Re: How do you measure Solar Output to system

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Exactly. I fit an amp hour meter in the charge circuit to accumulate the total. I also fit a timer to reset the AH meter each night so I could see results for the current day.
This is an excellent solution (above) with the least amount of complexity.

Be aware that simply measuring the current directly across the solar panel output terminals (short-circuiting the panel with an ammeter) will yield an amperage that is higher than the actual current supplied by the panel in normal operation. It will display short circuit current, which could be misleadingly high. This procedure is fine for troubleshooting, but not for capacity measurements.

You will also measure a current that is less than the manufacture's short-current rating, unless you are at the equator, with a clear sky, at noon, in cold weather, on the first day of spring or fall.
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Old 04-02-2018, 15:01   #14
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Re: How do you measure Solar Output to system

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QUOTE "we will heat water with the excess (electric element through inverter), but %90 of the time, just can't be bothered."

Can you please explain what the bother is?
Its really because I have been too lazy to finish the install. I wired everything up through a standard wall mounted timer (like for a bathroom fan, but with a higher Amp rating). I originally wired it up to test the concept and ensure it works and draws what I expect. I just never completed it and it requires taking apart our settee and removing a panel so I can set the timer for 30 min. Eventually I will finish the install and mount the timer switch in a better location.

Most days I'm just too lazy to do that (ya cruising life is tough). Also.. We just don't care that much about hot water. Here in the Caribbean, a cold water shower is actually nice most days. Lately with winter flu season, we have been heating water more often (family really likes a hot water shower when sick).
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Old 04-02-2018, 16:43   #15
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Re: How do you measure Solar Output to system

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Originally Posted by travellerw View Post
Yup.. Our Victron controllers show all sorts of data if you hook up the optional Bluetooth module. The controller stores 30 days of data, but you can export and keep as much data as you like.



As to having enough solar.. Hi, I'm Travis, and I'm going to be the first guy a64pilot met that has enough solar. We have 900W aboard for our family of five and its more than enough. Most days we do not use all our power. Some days, when we aren't lazy, we will heat water with the excess (electric element through inverter), but %90 of the time, just can't be bothered. So yes, you can actually have enough solar.


I have a kilowatt, and have to run the generator most days since itís winter and usually overcast, so my kilowatt isnít enough.
Summer is different.
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