Solar Panel efficiency - Should I upgrade

[monte]

sorry for the confusion, I meant we use 20 Ah continuously, ie 480 A/day
Panels put out around 50 Ah for around 8 hrs/day with the shading and limited November sunlight hours
I think we should be right next passage by cutting back on usage

[socaldmax]

Originally Posted by newhaul

Sorry forgot we are running 2x 100 watt mono panels with a pwm controller IMO not worth the cost of mppt for our needs

That's really good for a PWM controller! With 200w into an MPPT controller, I wouldn't expect to see over 12.5-13A max, you're right, not worth replacing the controller.

I did find a 20A MPPT controller that sells for $102 delivered. I've installed 5 so far, and they produce very close to calculated output. I have one with 410w on it (too much current, but it produces 22A for almost all of the day, as opposed to the normal daily curve) and 2 have a 205w panel ea and 2 have a 230 watt panel ea. Those are all RV installs, so they use less power than a boat at sea with fridge, autopilot, etc.

Even though these systems were all under 20A, I figured $100 was worth it for an MPPT.

[socaldmax]

Originally Posted by monte

sorry for the confusion, I meant we use 20 Ah continuously, ie 480 A/day
Panels put out around 50 Ah for around 8 hrs/day with the shading and limited November sunlight hours
I think we should be right next passage by cutting back on usage

Monte, with a Lagoon 400, wouldn't it be possible to mount your panels on an arch, with no shade?

[monte]

Yup, but unfortunately the spinnaker tended to shade the panels a lot during our Atlantic crossing. That combined with 50% clouds most days limited the output.

[newhaul]

That's with a 30 amp pwm controller so can add up to 200 watts more

[monte]

Efficiency of these panels is around 18% from memory

[Abgreenbank]

Don't know which victron blue solar mppt controller you have but there is a know software issue with some, my 75/50 is producing around a third of the expected amps to the batteries, Victron are replacing it under warrenty.

Regards

Ab


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[Capt Gill]

Keep in mind when calculating the amount of power (watts) to not use the vendor's power rating as most use open circuit voltage which you cannot use to charge your batteries, it's more like 14.2 v , so the arithmetic (not math) is more like: 14.2 X x amps = x watts. I've found the useable power to be about 80% of what is advertised. So far I've only found Ocean Planet to state power ratings realistically, if there are others I'd like to know.

[socaldmax]

Originally Posted by Capt Gill

Keep in mind when calculating the amount of power (watts) to not use the vendor's power rating as most use open circuit voltage which you cannot use to charge your batteries, it's more like 14.2 v , so the arithmetic (not math) is more like: 14.2 X x amps = x watts. I've found the useable power to be about 80% of what is advertised. So far I've only found Ocean Planet to state power ratings realistically, if there are others I'd like to know.

I'm a little confused.

Which vendors? Solar panel or controller? All of my solar panels (4 different brands) all used Vmp for their output calculations, not Voc. Of all of the brands of solar panels I've looked up, all of them have used Vmp, not Voc, to calculate wattage. The main thing I use Voc for is to ensure I don't exceed the max input voltage of the solar controller, either in series or parallel.

Can you give a specific example of this? My 20A solar controller has a max PV wattage of 300w, which comes out to 20 A output @ 15v, not 14.2v.

[noelex 77]

There is some confusion about solar panel ratings.

The good news is that all the solar panel companies measure the output under identical conditions, (STC) so the results can be compared. The wattage is always Vmp x Imp. The bad news is that these conditions are not very representative of average conditions. The panels are measured for this test with very bright flashes of light so the solar cells never get at chance to heat up.

Some panels list the NOCT output, which is more realistic of real world conditions. Unfortunately, fewer manufacturers are listing the results of this test so it usually not possible to use it when comparing panels.

However the solar panel statistics contain a wealth of information. They always list the temperature coefficients for Vmp and Imp so you can calculate the output of various panels in real world temperatures. Some list the output at different luminances. If this is available you can calculate the output under a range of conditions.

The listed STC wattage of the panels will be rarely seen in practice, but you should occasionally see the panels producing this output under ideal conditions with a MPPT controller. This is a good test of healthy well installed system. However, do not rely on the solar panel display for this test. These displays are typically optimistic. Use your battery monitor or better still an accurate multimeter.

If you have a non MPPT controller you should occasionally, under ideal conditions, see an output equal or slightly greater than the sum total of the Imp.

[sailorboy1]

Some impressive power usage and supply being quoted in the thread . Meanwhile its 715am and I'm getting 6.2 amps out of 290 watt panel into my little 460ah bank that is at 92% for running the frig last night


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[kas_1611]

Originally Posted by sailorboy1

Some impressive power usage and supply being quoted in the thread . Meanwhile its 715am and I'm getting 6.2 amps out of 290 watt panel into my little 460ah bank that is at 92% for running the frig last night


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Just checked the input from my ickle 35w flexible panel, currently lying on the coachroof, in front of the spray hood, at completely the wrong angle to the midday sun, with 1 section shaded by the boom and I'm showing 0.9amps. Now the battery is fully charged as I'm in my home marina and have been on mains all month so it's possible the panel could be capable of supplying a little more but the charge control must be kicking in. So I am going to leave it on battery for a couple of hours and see what I get.

Keiron

[kas_1611]

OK, fridge has kicked in and pulled out a few amps and now the same 35w flexible panel, still shaded by the boom, is valiantly putting 1.2amps back in.

Given it is 14:35 CEST and I am at 43º31'N, air temp is 23ºC (shade) and the panel is flat on the roof rather than angled towards the sun (so not an ideal angle of incidence) that's not bad, it works out as 50% of theoretical maximum (35w/14.2v=2.46amps).

Keiron

[brownoarsman]

This is as good a place as any to ask a question that's been bugging me I guess!
I've spent hours reading solar panel threads and websites, and obviously shade is bad, but how much shade is how bad?
Is the shadow of a spinnaker halyard going to drastically cut your solar efficiency? Or does it only start to matter when whole cells are shaded? The Internet suggests that getting shades across the short dimension is the worst due to how the panels are constructed (series run lengthwise, so shade on the short horizontal axis disrupts all the series). But would there ever be an argument to use a smaller 45w panel over a 100w panel if the 45w panel can be kept in full sun and the 100w panel would be partially shaded?


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[tstano]

Your problem is that it's not noon 24 hours a day. Too many variables like temp, humidity, battery condition, cloudiness, and a moving base. I'm pretty sure they test panels in the desert aimed directly at the sun at a certain temp. The Peukert effect on how well your batteries take the charge may also have come into play. What was your SOC during your observations? Lot of good info by previous posters.