Solar Panel Efficiency?

Irish Rover

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We've just finished fitting 2 new solar panels which claim to have an output of 625W each connected to a Victron 150/85 MPPT controller. I'm in the Eastern Aegean and it's reasonably sunny here today with occasional cloud. The panels are connected in series, and the maximum output we're seeing around lunchtime is around 750W with a load on the batteries, so around 60% of the claimed output. Even though the panels were relatively cheap around $180 each I was expecting a better output. Would anyone else in the Med especially around Greece or Türkiye have comparative figures, maybe @vas ?
 

lustyd

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What's on the other side of the MPPT? There are many reasons you'd get lower power than rated so useful to cover those off first. Is it a lithium bank (rate of acceptance) is the bank low enough to accept the charge? What's the voltage of the bank? Is anything else providing a charge? Assume you're reading the 750W from the MPPT not the BMS?

These may be covered by your other posts but useful if you note them here too. As a general rule, the stated power of any panel will be just under what you will get from it in good conditions with zero shading if the panel is relatively cool
 

Irish Rover

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My batteries are 3 x 210 Ah AGM plus 2 x 105Ah engine start batteries. Batteries were showing 13.4v when I came to the boat today and I intentionally depleted them by operating a water heater through an inverter. Im reading the output from the panels throught the Victron connect app.
 

lustyd

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It could be that AGMs just can't take the charge fast enough (one of the benefits of Lithium). Can you try leaving the water heater running to max out the load? I imagine a water heater would add a few hundred Watts at least so should be a good test. That's assuming you didn't leave it running?
 

Irish Rover

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It could be that AGMs just can't take the charge fast enough (one of the benefits of Lithium). Can you try leaving the water heater running to max out the load? I imagine a water heater would add a few hundred Watts at least so should be a good test. That's assuming you didn't leave it running?
I did leave the water heater running but the battery voltage continued dropping below 11.8v and I didn't want to leave it low for too long.
 

andsarkit

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Solar panels are rated under standard conditions (STC) of 1000 watts per square meter of sunlight perpe ndicular to the panel at 25 deg C. In real life you will never get ideal conditions so the output will always be less.
Having said that, my house installation on the roof is rated at 3.8kW and I have seen 4.2kW output on a sunny spring day in Devon. I think house installations must be rated differently.
The Victron controls the amount of power going to the batteries depending on the stage of the charging cycle but with your depleted batteries I would expect more output from the panels.
You could disconnect the panels and measure the open circuit voltage and short circuit current on a sunny day. The current measurement could be difficult as most meters top out at 10A so you would need a DC clamp meter. (best to cover the panels when you make the connections to avoid any sparking)
 

B27

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New panels often exceed their labelled power, it's to allow for tolerances and aging. They are often guaranteed to meet a certain output power when they are 20 years old or similar.
It's not impossible for the sun be be brighter than 'standard' either.
I've read elsewhere that some MPPT devices can fail to find the correct power point. Instead of operating the panel where it gives most power, they draw too high or too low a current, because the tracking algorithm gets 'confused' by changes in light or old data from previous panels of a different voltage.
To make any sense of it, you really need to measure things at the panel, but has has been noted the power is quite high, you'll need a clamp meter or a big shunt or something.
You need to know the current and volts as loaded by the MPPT, and ideally the open circuit volts and short circuit current.
Then on the load side, 750W is a lot of 12V amps, some poor wiring could drop a volt or more.
Or there might be a current limit set in the software somewhere. It sometimes seems that no two people use the same Victron firmware!
I'd also be looking at the AC components of voltages.
 

geem

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Solar panels are rated under standard conditions (STC) of 1000 watts per square meter of sunlight perpe ndicular to the panel at 25 deg C. In real life you will never get ideal conditions so the output will always be less.
Having said that, my house installation on the roof is rated at 3.8kW and I have seen 4.2kW output on a sunny spring day in Devon. I think house installations must be rated differently.
The Victron controls the amount of power going to the batteries depending on the stage of the charging cycle but with your depleted batteries I would expect more output from the panels.
You could disconnect the panels and measure the open circuit voltage and short circuit current on a sunny day. The current measurement could be difficult as most meters top out at 10A so you would need a DC clamp meter. (best to cover the panels when you make the connections to avoid any sparking)
On 360W of solar we often see over 420w in the Caribbean. These panels are nothing special either
 

noelex

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If the installation is correct and the solar panels are performing as they should be, you should occasionally see the full rated output of the panels if you are cruising in areas with good solar insolation. We certainly experienced this when we were cruising the eastern Aegean.

With the better panels you can see a significantly higher output than the rating.

These brief peak outputs do not contribute a great deal to the total output, but they show the system is healthy.

I would test each panel separately. This can be done using a multimeter with each panel disconnected from your system. Measure Voc and Isc (for this latter measurement a clamp on multimeter is safer) and see how this matches with the specifications. There are videos online showing how to do this.
 

vas

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IR,
I assume they are flat on the coachroof?
600odd W must be 2.5X1.something is size right?
In series means that you bring down to the mppt something like 90V.
How long are the runs and are the cable sizes ok so there's no serious voltage drop (not that it would matter much @90V)
No mast, no sails, so no shadows (even tiny ones drop massively!)
No open array radar nearby casting shadow either, right?
Lastly, were these values in port, and did you by any chance had a sailing boat either side (well on the sun path side!) casting shadow to the panels?
I'd discard AGM and other arguments as you've emptied them enough to be in bulk mode.

anyway, assuming you're OK with the above, my stats say that on 8yo 600W panels (2X300) END OF SEPTEMBER with the sun burning indeed BUT fairly low nowadays in the horizon, I didn't get more than 380W peak at 1:00pm over the last week. most days was in anchor nicely facing south (not that it maters as panels are flat on the h/t) and was wall to wall sunshine.

So I'd say your values match mine (although for brand new panels I'd expect a bit more tbh - mine are some AXOR iirc, german design, chinese made most likely).
Obvs if they were facing south 25-28deg and stable you'd get more out of them, but that doesn't work on a boat as you know!
I expect that you get the values from the Victorn MPPT app, check history tab for the next few days, but making sure batteries need charging and mppt is in bulk mode by 1pm

Highest output season for us is July, fullstop.

cheers

V.
 

noelex

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BTW an interesting comparison of series v parallel connection of solar panels that was posted recently. Unfortunately they did not test the most efficient system of multiple solar controllers:

 

lustyd

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I'd discard AGM and other arguments as you've emptied them enough to be in bulk mode
I wouldn’t. Lead batteries don’t take as much current as lithium when charging. These are taking 21A each while presumably quite warm which is a fair amount for lead.
 

vas

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I wouldn’t. Lead batteries don’t take as much current as lithium when charging. These are taking 21A each while presumably quite warm which is a fair amount for lead.
haven't noticed anything like that, first 4yrs were with Trojans, next 4 are with LifePO4, same behaviour, maybe because my batteries are usually at 50% SoC :)
even now with lithium I rarely manage to get them up to 90% (which I know is a good thing) I just tend to run the watermaker more, or whatever else...
 

noelex

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I wouldn’t. Lead batteries don’t take as much current as lithium when charging. These are taking 21A each while presumably quite warm which is a fair amount for lead.
If the charging is in bulk mode by definition the batteries are taking all the current (at the particular voltage) the solar controller can deliver.
 
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rogerthebodger

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Firstly, I would like to know what you mean by efficiency of a solar panel.

Efficiency is as I understand it is input compared with output.

In an ICE its the energy in the fuel input compared with the mechanical energy that is output.

I think the efficiency of the resulting collection and storage efficiency is what you are looking for which in my view quite different.

Just a question
 

lustyd

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haven't noticed anything like that, first 4yrs were with Trojans, next 4 are with LifePO4, same behaviour, maybe because my batteries are usually at 50% SoC :)
even now with lithium I rarely manage to get them up to 90% (which I know is a good thing) I just tend to run the watermaker more, or whatever else...
The power you consume is different, hence my suggestion to leave the heater on to get maximum solar output. Many posts on here talking about increased solar due to higher acceptance rates. Lead is just a slower chemistry alongside more basic battery designs.
 

lustyd

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If the charging is in bulk mode by definition the batteries are taking all the current the solar panels can deliver.
No, the batteries would be taking all the charge they can accept. It’s not the same thing, and the solar reduces production to match consumption not the other way around.
 

lustyd

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Not in bulk mode.
Yes in any mode. Acceptance rate is a hard limit on the battery. you can’t just ram more juice in to a battery. Chemistry doesn’t work like that. For normal installs you won’t usually notice but as solar banks get larger it’s a huge issue for small lead banks.
 
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