Solar Panel efficiency - Should I upgrade

[socaldmax]

Originally Posted by 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?


Sent from my iPhone using Cruisers Sailing Forum

Here's a video showing how dramatically a little shading affects a normal panel.

https://www.youtube.com/watch?v=-WGU5j7Rh1g

Sunpower panels are not only more efficient, they also lose much less power when partially shaded due to their construction (more connections). They also have a lower temp coefficient, meaning as the temp. rises, they still produce more power. Here's a video.

https://www.youtube.com/watch?v=dlZSL4C0VYQ

As for your question about smaller panels vs larger with partial shading on the larger and no shading on the smaller, here's my opinion.

Under the same conditions, with no shading, a 100w panel will always produce more than twice what a 45w panel will produce. If the 100w panel gets substantial shading (like 50%) it's output will drop to nearly zero.

The following is only how I would do it, not saying everyone should.
Personally, I'd mount the 100w panel where it would very rarely, if ever, get shading. There's a good chance the 45 w panel is a little more than 50% of the size of the 100 w panel, so if it's possible to keep the 45 w in full sun, every effort should be made to do the same for the 100 w.

I wouldn't even bother to drill holes and mount a 45 w panel. The copper cable (especially boat cable) costs as much as the panel, maybe more. As panel prices have been dropping to $1/watt and even lower - 59 cents/watt is what I paid for the last set of 10 230 watt panels, the price of quality copper cable has gone up. So when you factor in low power (and even lower in the AM and PM), same amount of labor to install as a larger panel, same number of screws, same amount of cable, to me, it never makes sense to install a panel under 150 -200w.

[brownoarsman]

That is a great description and super helpful! Thanks socaldmax!


Sent from my iPhone using Cruisers Sailing Forum

[DeepFrz]

posted by tstano: I'm pretty sure they test panels in the desert aimed directly at the sun at a certain temp.

Actually they test them indoors in a "lab" with light and temp. controls.

[cheoah]

Originally Posted by Bulawayo

Monte, with so much solar you still didn't have enough energy? We have 3x 340watt Kyocera panels and 2x 110w panels plus 2x D400 wind gennies and never have an issue. The two smaller panels are on the bimini and one is often shaded. We have 3x Rolls lead acid batteries (12 md 375), new in early 2014, giving 1125A. We swear by these batteries but, boy, are they heavy. I believe that two (750A) would have been adequate.
We also run a chart plotter, three lots of refrigeration, VHF full time, autopilot, a 12v water maker and the usual other stuff. We often run our radar at night or in poorer weather, otherwise it is usually off. We did change all our lights to LED.

Ya, um, I think you have a net surplus. Too bad you can't sell it. Or power a couple small villages.


Sent from my iPad using Tapatalk

[Bulawayo]

Yeah, It has worked for us on our last boat as well, hence installing the same again.

[Capt Gill]

Originally Posted by 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."

You have to dig pretty deep to get this info, it's not readily available.

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.

"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."

"Always" ?
You have to dig pretty deep to get this info, it's not readily available.

[monte]

Originally Posted by Bulawayo

Monte, with so much solar you still didn't have enough energy? We have 3x 340watt Kyocera panels and 2x 110w panels plus 2x D400 wind gennies and never have an issue. The two smaller panels are on the bimini and one is often shaded. We have 3x Rolls lead acid batteries (12 md 375), new in early 2014, giving 1125A. We swear by these batteries but, boy, are they heavy. I believe that two (750A) would have been adequate.
We also run a chart plotter, three lots of refrigeration, VHF full time, autopilot, a 12v water maker and the usual other stuff. We often run our radar at night or in poorer weather, otherwise it is usually off. We did change all our lights to LED.

Yes and no, as I mentioned, on passage we ran low. A wind gen averaging 5ah would have been enough to offset the deficit. At anchor, more than enough. In fact enough to run a 8000btu portable Aircon or pressure wash the deck for half a day, heat the boiler from the battery bank, vacuum, electric kettle and make water to spare etc so I wouldn't really recommend more solar. We do have a good space on the Bimini if we decided to add another 240W panel so...maybe...
We did have a wind gen on our last sephina but opted to see how we went with just solar this time. During our 3 week Atlantic crossing we were fine for the first week, then had to run the engines for an hour or so at night to charge for the second week, and were fine again for the last week from the solar. Unfortunately the stock alternators charge at 70A for about 30 mins then output reduces to about 40A as the alternators heat up so one hour engine running only puts in 70A-80A

[socaldmax]

Originally Posted by Bulawayo

Yeah, It has worked for us on our last boat as well, hence installing the same again.

Not to sound flip, and you already know this, but there's no such thing as too much power. More power = more creature comforts = happier wife = happier life, to drastically oversimplify things.

After adding 2 more batteries and another solar panel, I found I was fully charged really early in the morning, despite running the inverter 24/7 and having some constant loads.

I bought an ice maker, and it made a lot more of a difference that I thought it would! Even before the upgrades I didn't make an effort to conserve power (I'd already swapped all lights over to LED) so there was no need to cause any friction by chanting "Turn off the lights", or "Turn that off!" It's the little things that make life a lot easier, starting with plenty of power!

[monte]

Yep, the difference between 1A too much and 1A not enough is huge

[Capt Gill]

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.[/QUOTE]

Your confusion is well warranted, not only to my statement, but to the wealth of info and misinfo. in this thread, also because of the many variables involved
in determining the actual amount of power getting to the reservoir, your battery(s). So, as to not cause any further confusion I'll say that my point was to not take the mfg's power rating on a solar panel as what you'll actually get. The best, easiest to understand (in my opinion,given the subject) info on solar power is found in Nigel Calder's book, Boat Owners Mech. and Electrical Manual (3rd ed. or later)
Some anecdotal info re. my first statement on power ratings: I inquired to a few venders for more spec's and info on how they determined their power ratings, I got only one response that was not spin, Go Power! Solar Flex™, an upstanding company I believe. Below is the email conversation:
------------------------------
From: Jack via Go Power! [webmaster@gpelectric.com]
Sent: 25/04/2015
To: customerservice@carmanah.com
Subject: Form submission from: Contact Go Power!

First Name: Jack
Company: Skill Marine Centre
Details:
Please explain your power ratings, e.g., the below is rated @ 100 watts and
current rating is 5.62 amps, since most batteries won't safely take a
charging voltage much over 14 volts I don't understand how you get a 100 watt
rating (5.62 x 14 = 78.68 watts).
Solar cell type Monocrystalline
Output power 100 W
Rated current 5.62 A
=================================================
Hello Jack,
The open circuit voltage (Voc) of the solar panels are much greater than 14V. This is the unloaded voltage the solar panel will produce when measured under the test conditions they are put under.
For example, the 100 flexible solar panel you're referencing in your email has an open circuit voltage of roughly 18V. The panel also has a short circuit current rating (no load) of ~ 5.6A. The product of these two give you the 100W rating.
The controller can charge your batteries as high as 14.8V if you have flooded batteries. If not, it would be as high as 14.4V and lower depending on how full they are.

Please feel free to contact us if you have any additional questions or concerns.

Regards,
Mike Battagello
Carmanah Customer Support
Toll-free (US & Canada): 1.877.722.8877
Worldwide: +1.250.380.0052
Fax: +1.250.380.0062
=================================================
Thanks, for the speedy response. Yes, I see how you arrived at that rating and will venture to say that if you changed the method to reflect useable power it would put you at a competitive disadvantage as they all use the same method. Useable power, which is the figure one needs to compute for realistic charging assets, e.g., my system uses AGM batts.so, 14.4 v is the highest voltage acceptable which gives approx. 81 watts useable. Is this not correct ? Stating up front the amperage and/or the power at the most common voltages would be useful for deciding the # of panels needed.
"The panel also has a short circuit current rating (no load) of ~ 5.6A" I believe that would be max load as the leads are shorted.
Best regards,
Jack
=================================================
Hello Jack,
You pretty much have it,
The best way to look at it would be to look at the current the panels produce. This is the real world number you can see under ideal conditions (which typically you won't always see all day/every day).
This way you can have an idea how much charging you can expect from the solar system - especially if you start adding multiple panels.
You can also do comparisons between different panels to see the current they can produce.

Regards,
Mike Battagello
Carmanah Customer Support
Toll-free (US & Canada): 1.877.722.8877
Worldwide: +1.250.380.0052
Fax: +1.250.380.0062
= END of EMAIL=
There you have it or at least what I have, I hope this helps a bit.

[noelex 77]

Originally Posted by Capt Gill

Some anecdotal info re. my first statement on power ratings: I inquired to a few venders for more spec's and info on how they determined their power ratings, I got only one response that was not spin, Go Power! Solar Flex™, an upstanding company I believe. Below is the email conversation:
------------------------------

I can understand your confusion when distributors give wrong, or least misleading information.

By definition at Voc the panel is producing zero power. All companies use Vmp not Voc for their power calculations. This includes Solar Flex. From the Solar flex table you can see if you multiply the Vmp by the Imp you come up with the listed power of solar panel. Exactly as it should be. For example the 100w panel has a Vmp of 17.8v and an Imp of 5.6 A (17.8x5.6=99.7w). If we used the Voc, as you and the company suggest, we would the nonsense rating of 130w (23.3 x 5.6) for a 100w panel.

I think the mistake the company is making in the email is calling 18v Voc when you can see from the table it is actually Vmp (rounded to 2 significant figures).



Your point about the batteries not accepting 17.8v is spot on. That is why MPPT regulators were developed. They will convert the 5.6A @ 17.8v to the lower battery voltage with a consequent increase in current. So 5.6A @17.8v might be converted to 7.1A @14v ( ignoring conversion losses ).

Unfortunately in real world conditions the 17.8v is likely to be seen only very rarely. It will only happen in very cold conditions, or very briefly as the sun pokes out from behind a cloud. The temp statistics for this panel are listed as 0.38% per degree C. Typical cell temperature will be 15-20° above STC in bright conditions, often a bit more for a flexible panel. At 20° the panel Vmp will decrease by 7.6% (0.38x20). So the Vmp under real world summer conditions is likely to be around 16.5v before the wire and switching losses. With 3% voltage loss in the wiring and some losses at contact points the regulator is likely to have a real world Vmp of around 16v in ideal bright conditions with no shaddows.

If we ignore the Imp loss with temperature (because its small). Under real world bright conditions the 100w panel mostly due to the reduced Vmp will be producing 16x5.6= 90w even with an MPPT controller there will be some conversion losses so we might expect around 86w from our 100w panel under very good conditions if the regulators tracking is spot in and the panel has no shaddows.

A non MPPT regulator cannot do any voltage conversion so the panel voltage is the battery voltage (ignoring wire losses). At the reduced voltage current will be slightly higher than the Imp, but the increase is small. If we estimate this at 5.75 A (up from 5.6 A) and the battery voltage is sitting at 14.2v we get almost 82W. As no voltage conversion is necessary the controller losses are typically less than a MPPT controller so the battery might get 80w from our 100w panel with a non MPPT controller.

These are theoretical calculations using the manufacturers supplied figures, but they have close agreement with the real world results.

[socaldmax]

Originally Posted by Capt Gill

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.

Your confusion is well warranted, not only to my statement, but to the wealth of info and misinfo. in this thread, also because of the many variables involved
in determining the actual amount of power getting to the reservoir, your battery(s). So, as to not cause any further confusion I'll say that my point was to not take the mfg's power rating on a solar panel as what you'll actually get. The best, easiest to understand (in my opinion,given the subject) info on solar power is found in Nigel Calder's book, Boat Owners Mech. and Electrical Manual (3rd ed. or later)
Some anecdotal info re. my first statement on power ratings: I inquired to a few venders for more spec's and info on how they determined their power ratings, I got only one response that was not spin, Go Power! Solar Flex™, an upstanding company I believe. Below is the email conversation:
------------------------------
From: Jack via Go Power! [webmaster@gpelectric.com]
Sent: 25/04/2015
To: customerservice@carmanah.com
Subject: Form submission from: Contact Go Power!

First Name: Jack
Company: Skill Marine Centre
Details:
Please explain your power ratings, e.g., the below is rated @ 100 watts and
current rating is 5.62 amps, since most batteries won't safely take a
charging voltage much over 14 volts I don't understand how you get a 100 watt
rating (5.62 x 14 = 78.68 watts).
Solar cell type Monocrystalline
Output power 100 W
Rated current 5.62 A
=================================================
Hello Jack,
The open circuit voltage (Voc) of the solar panels are much greater than 14V. This is the unloaded voltage the solar panel will produce when measured under the test conditions they are put under.
For example, the 100 flexible solar panel you're referencing in your email has an open circuit voltage of roughly 18V. The panel also has a short circuit current rating (no load) of ~ 5.6A. The product of these two give you the 100W rating.
The controller can charge your batteries as high as 14.8V if you have flooded batteries. If not, it would be as high as 14.4V and lower depending on how full they are.

Please feel free to contact us if you have any additional questions or concerns.

Regards,
Mike Battagello
Carmanah Customer Support
Toll-free (US & Canada): 1.877.722.8877
Worldwide: +1.250.380.0052
Fax: +1.250.380.0062
=================================================
Thanks, for the speedy response. Yes, I see how you arrived at that rating and will venture to say that if you changed the method to reflect useable power it would put you at a competitive disadvantage as they all use the same method. Useable power, which is the figure one needs to compute for realistic charging assets, e.g., my system uses AGM batts.so, 14.4 v is the highest voltage acceptable which gives approx. 81 watts useable. Is this not correct ? Stating up front the amperage and/or the power at the most common voltages would be useful for deciding the # of panels needed.
"The panel also has a short circuit current rating (no load) of ~ 5.6A" I believe that would be max load as the leads are shorted.
Best regards,
Jack
=================================================
Hello Jack,
You pretty much have it,
The best way to look at it would be to look at the current the panels produce. This is the real world number you can see under ideal conditions (which typically you won't always see all day/every day).
This way you can have an idea how much charging you can expect from the solar system - especially if you start adding multiple panels.
You can also do comparisons between different panels to see the current they can produce.

Regards,
Mike Battagello
Carmanah Customer Support
Toll-free (US & Canada): 1.877.722.8877
Worldwide: +1.250.380.0052
Fax: +1.250.380.0062
= END of EMAIL=
There you have it or at least what I have, I hope this helps a bit.[/QUOTE]


I was trying to be polite. I'm afraid you are mistaken. The method used to measure and publish rated power output has been posted twice above.

All solar panels are rated exactly as noelex and I posted earlier. They are subjected to a flash in a controlled lab environment, called STC and all measurements are derived from that.

When any company mfrs solar panels, they group their cells by efficiency and build sets of panels using these tightly grouped cells. The best cells might all go into their 300 w panels. The next group make up their 295 w panels, next = 290 w panels, and so forth. The panels are all identical size and construction, it's just that the cells are better in the 300 w panel vs the 295 w panel due to production tolerances.

When you buy a solar panel, it will produce 3 to 5% MORE than rated output for a few weeks, and slowly drop as it ages with power output guarantees at future dates, like 10 yrs and 20 yrs, for example.

The rated power output of a solar panel is always based upon Rated Voltage (Vmp) x Rated Current (Imp) = Rated Power (Pmax)

This example is from the Sunpower 327 w panel:

Rated Voltage (Vmp) = 54.7V (obviously NOT battery charging voltage!)
Rated Current (Imp) = 5.98A
Rated Power = 54.7 x 5.98 = 327.106w

Ratings are so tightly controlled that their next rated panel is 315 w with:
Vmp = 54.7V
Imp = 5.76A
Rated Power = 54.7 x 5.76 = 315.072w.

All specs for solar panel output are published by the mfr, not vendors. All solar panel mfrs rate their panels in exactly the same method, using the exact same specs: Vmp and Imp.

Your confusion came in when you tried to figure out how 14 volts entered into the picture. It doesn't. Solar panels don't charge your batteries. They produce current at a higher voltage to the solar charge controller, which converts that higher voltage current down to (nominally) 14.8V at a higher current to the batteries.

In the case of the Sunpower 327w panel, if it's connected to a good MPPT controller, in perfect conditions you'll see close to 21-22A going into the batteries, much higher than the current posted right on the back of the panel.

54.7V @ 5.98A going into the solar controller @ 96% efficiency gets converted down to 14.8V @ 21.21A. The voltage is lower, but the current goes up, drastically in this example.


Now a little word about Go Power! Out of over a dozen RV solar system installs I've done, 3 were to rip out the Go Power system and install a system that actually works. All 3 owners complained that their Go Power solar system never produced rated output and gradually dropped lower and lower over a very short time. Go Power doesn't mfr anything, they buy no-name products and slap their sticker on it, then jack up the price. Their solar controller isn't even an MPPT controller. All 3 of the controllers I pulled out were flat black panels with a very cheap PWM (like $25 unit from China) mounted to the back of the panel, with a single line battery voltage display on the front.

In one case, the solar panel was shot, virtually no output. I replaced it with a single 230w panel and a 20A MPPT controller and they were getting far more power than they ever saw, even when the system was new.

The other 2 cases, I tested solar panel output, it wasn't in spec, but not too bad. The owners wanted to keep the panel, add another and upgrade to the 20A MPPT controller. Again, they saw more than double the power output than they ever saw new.

I've never seen anything like that with any other brand - never saw a failed solar panel (yet) and certainly not such low output from a solar controller. 2 other issues about those controllers - they only allow 2 absorption voltages - 14.1 or 14.4 - both too low for many brands of batteries. Even their equalization voltage is too low, 14.8v. My normal charge voltage is 15.3v, Go Power isn't even close! At 14.4v, most batteries are only 80% charged, thus the owners complaining of low battery performance.

The other issue was false readings on the front panel display. I understand that a small amount of error can occur from production tolerances, but in all 3 cases, the battery voltage was reading 1.5V-2V HIGHER than actual battery voltage, current readings were also higher than actual, with actual current being almost nil.

Go Power is the only brand I've warned people off from. I'd recommend taking a calibrated (or accurate, if not calibrated) DMM and taking your own measurements of voltage and current in peak sun and compare them to the displayed values. If they're anywhere close, you're very fortunate. I've ony seen 3 Go Power systems, and that was only because I was asked to figure out why they produced almost nothing and replace them with something that produced rated output.

[hellosailor]

Guys-
You know, there ARE standard conditions and ratings for solar panels? Standards for temperature and lighting and all that too?


If a panel vendor is NOT using the standards, or isn't able to say if they have used any standards, you can presume it was made by two guys in a basement of Shenzhen sometime after school and before homework, with about an equal level of competency and reliability. Or, by a couple of slightly older thieves who know damn well that they're playing a numbers game.


Either way...solar panels, and standards for rating them, have been around long enough (and readily accessible, and unlike ABYC regs anyone can find them) that if a vendor can't be bothered with conforming to them...maybe that's a good clue that you should be looking elsewhere?

[redsky49]

"...In the case of the Sunpower 327w panel, if it's connected to a good MPPT controller, in perfect conditions you'll see close to 21-22A going into the batteries, much higher than the current posted right on the back of the panel...".

You mention Sunpower frequently.

I am not very knowledgeable on photovoltaics, but I thought that Sunpower panels were not marine approved by manufacturer. Don't they also only sell to vendors/installers, and not directly to users?

And what is the $100 MPPT controller you mention?

Please pardon the thread drift.

Thanks!

[mitiempo]

Originally Posted by socaldmax

In the case of the Sunpower 327w panel, if it's connected to a good MPPT controller, in perfect conditions you'll see close to 21-22A going into the batteries, much higher than the current posted right on the back of the panel.

With a good quality MPPT controller I would expect 21-22 amps @14.4 from any quality 327 watt panel.