Any experts on solar to provide an update of things.

JohnShannon · Jul 10, 2014

The basic problem an Mppt controller has with a battery charging application is, that battery and panels are pretty well matched to begin with. Unlike for instance panels and water pumps.

The Vmpp (voltage of maximum power) falls with temperature and if the panels are hot enough could equal the battery voltage, at which point the mppt tracker is really just introducing loss.

So if the panel is cold Vmpp is around 18V and Vbatt is say 13V the mppt controller converts power at 95% efficiency and you will get about 30% more charge current than direct connection.

A hot panel has a vmpp that drops about 2mv times 36 cells per degree C so at 120F the panel Vmpp will have dropped something like 2.5 V down to 15.5V or so. Now with a hot panel the mppt controller stepping to a battery voltage of 13V at 95% efficiency will only boost output something like 15%

The charge curent boost is better with depleted batteries but the phenomenon is the same as the panel heats up the Vmpp falls and the advantage of mppt power conversion diminishes

Maine Sail · Jul 11, 2014

JohnShannon said:
The basic problem an Mppt controller has with a battery charging application is, that battery and panels are pretty well matched to begin with. Unlike for instance panels and water pumps.

The Vmpp (voltage of maximum power) falls with temperature and if the panels are hot enough could equal the battery voltage, at which point the mppt tracker is really just introducing loss.

I have been tracking marine solar installs now for about 6 years and not once seen an MPPT not beat PWM. I've also conducted multiple head to head A/B comparisons with all equal except the controller. My controlled monitoring testing for the week mentioned, here in Maine, for MPPT gains, is 20.8%.. (strong emphasis on "in Maine")

I have also yet to see panel voltage get down to battery voltage on a boat, though I am sure on a hot roof on a land install this is very possible or perhaps in situations where the panel is mounted to the deck in a very hot region with virtually no wind...

JohnShannon said:
So if the panel is cold Vmpp is around 18V and Vbatt is say 13V the mppt controller converts power at 95% efficiency and you will get about 30% more charge current than direct connection.

Absolutely..

JohnShannon said:
A hot panel has a vmpp that drops about 2mv times 36 cells per degree C so at 120F the panel Vmpp will have dropped something like 2.5 V down to 15.5V or so. Now with a hot panel the mppt controller stepping to a battery voltage of 13V at 95% efficiency will only boost output something like 15%

At 126F I have recorded panel voltages on the MPPT side of the controller in the 15.5V range. This gives me a real world installed PV Pmax drop of 0.045V per degree above 77F on a Kyocera 140W panel... 126F - 77F = 49 Degrees - 17.7V @ 77F - 15.5V @ 126F = 2.2V Drop / 49F = .045V per degree (installed). Rarely do I see the panel voltage fall below 15.0V on boats with MPPT. This is likely due to the usually good airflow around the panels on boats. I would need a panel temp of about 152F to have the panel voltage at 14.4V, but in bulk this is still capable of providing some boost.

All this is really not relevant in the whole scheme of total daily net boost, which is occurring.

JohnShannon said:
The charge current boost is better with depleted batteries but the phenomenon is the same as the panel heats up the Vmpp falls and the advantage of mppt power conversion diminishes

Yes as panels heat up MPPT gains do diminish but when averaged out over the day I have not ever seen PWM beat MPPT as installed on a boat.

As you know MPPT gains are only occurring during bulk charging. With solar on boats the vast majority of the time the controller is in bulk mode, this is good for MPPT gains. This is due to the panel area vs. bank Ah size and the panels inability as a current source to drive voltage up until well into the upper 90's as a % charged for most installed systems unless VERY large or on cats with gobs of real estate..... This makes the MPPT gains last longer in duration than on comparable land based systems where they have lots of real estate to devote to solar panels. While a lot of calculations from land can apply, boats are certainly a slightly different model to calculate when it comes to solar..

Brian D · Jul 12, 2014

jbinbi, I have found that based on my electrical requirements on the water, my 50 watt panel provides the needed current to run my VHF, 2 GPS terminals (one for DSC and one for autopilot), and autopilot. It also provides enough current to keep my batteries topped off.

My panel sits flat on the starboard side aft cockpit rail. I had thought about mounting a satellite TV pole and rotating AzEl (azimuth and elevation) head to allow the panel to point towards the sun, but I don't think I will gain anything by that. I did not do any testing to confirm, just a hunch. It seems the majority of sailors (or boaters) have their panels flat. Being in SoCal we have a very high angle sun all year round.

Having installed a lot of satellite systems on ships I can tell you the cost factor auto tracking is not worth adding to solar panels. There is too much involved in trying to get the motors (two motors) going and would probably require more power from the batteries than you would get to replenish them. Manual tracking is more efficient unless you do a lot of tacking.

walt · Jul 13, 2014

The 20 percent of gain for MPPT in post 15 is interesting (early May in the NE so probably cooler conditions). I couldn’t tell for sure but it sounded like you had two panels, two controllers and one battery - so each controller saw the same exact battery voltage over the whole day - which is a nicely controlled test..

Was there any significance to the charging algorithm for each of those controllers with the final 13.4 battery voltage? Likely both were still in bulk charging mode?

Maine Sail · Jul 13, 2014

walt said:
The 20 percent of gain for MPPT in post 15 is interesting (early May in the NE so probably cooler conditions). I couldn’t tell for sure but it sounded like you had two panels, two controllers and one battery - so each controller saw the same exact battery voltage over the whole day - which is a nicely controlled test..

Yes each controller was fed to the same LiFePO4 battery so they were treated equally.

walt said:
Was there any significance to the charging algorithm for each of those controllers with the final 13.4 battery voltage? Likely both were still in bulk charging mode?

No significance at all because both controllers were in "bulk" the entire time. They were both set for GEL but there was no way they were raising the voltage of the Li bank much above 13.5V until about 99% SOC.... Bank was 400Ah discharged to 80% DOD. At midweek I discharged again. The voltage ranged between 13.3V and 13.4V all week and would occasionally ping 13.5V. Li batteries have an extremely flat charge & discharge curve.

There is no MPPT gain in absorption or float mode as the battery determines current at voltage...

-------------MPPT------PWM---------------
Day 1 ---- 16.99 ---- 13.73 Pouring Rain
Day 2 ---- 42.15 ---- 36.08 Mostly Clear
Day 3 ---- 45.12 ---- 37.73 Clear
Day 4 ---- 33.07 ---- 27.39 Rain Morning - Afternoon Overcast/Clearing
Day 5 ---- 26.80 ---- 20.44 Rain/Drizzle
Day 6 ---- 23.87 ---- 19.99 Rain/ Drizzle
Day 7 ---- 32.44 ---- 27.12 Overcast to Clearing
Week --- 220.44 - 182.48

walt · Jul 13, 2014

Also interesting about those numbers..

When someone is doing a power study to see what size panel they need, it is common to use a rule of thumb that tells about what amp hours you can expect from a certain size panel (in watts).

And.. you can find numbers on the internet out to three digits for this..

If we want to use your numbers for the rule of thumb..

For PWM, you saw between 13.73 to 37.7 amp hours from 140 w panel
For MPPT, you saw between 16.99 to 45.12 amp hours from 140 w panel

So the amp hours / panel watt rule of thumb (example, the MPPT max number is 45.12 / 140 = .32)

PWM .1 to .269
MPPT .12 to .32

The average daily amp hours for MPPT is 31.49 and 26.12 for PWM. So the same "average" rule of thumb for estimating amp hours woud be

MPPT 31.49/140 w panel = .225
PWM 26.12 / 140 = .186

Example, if you had a 50 watt panel and used the Genasun MPPT controller, you could expect..

Average amp hours per day - 50W * .225 = 11.25 amp hours.

The expected range might be 50*.12 = 6 amp hours to 50*.32 = 16 amp hours.

Ie, using Maine Sails data, a 50 watt panel might give you a daily range from 6 to 16 amp hours with an average of about 11.25 amp hours.

Maine Sail · Jul 13, 2014

walt said:
Also interesting about those numbers..

When someone is doing a power study to see what size panel they need, it is common to use a rule of thumb that tells about what amp hours you can expect from a certain size panel (in watts).

And.. you can find numbers on the internet out to three digits for this..

If we want to use your numbers for the rule of thumb..

For PWM, you saw between 13.73 to 37.7 amp hours from 140 w panel
For MPPT, you saw between 16.99 to 45.12 amp hours from 140 w panel

So the amp hours / panel watt rule of thumb (example, the MPPT max number is 45.12 / 140 = .32)

PWM .1 to .269
MPPT .12 to .32

The average daily amp hours for MPPT is 31.49 and 26.12 for PWM. So the same "average" rule of thumb for estimating amp hours woud be

MPPT 31.49/140 w panel = .225
PWM 26.12 / 140 = .186

Example, if you had a 50 watt panel and used the Genasun MPPT controller, you could expect..

Average amp hours per day - 50W * .225 = 11.25 amp hours.

The expected range might be 50*.12 = 6 amp hours to 50*.32 = 16 amp hours.

Ie, using Maine Sails data, a 50 watt panel might give you a daily range from 6 to 16 amp hours with an average of about 11.25 amp hours.

Yep that works too..

In Maine I have just been advising my customers to plan on about 4 - 4.5 hours at max panel current. Not all panels list 45C so the 25C number gets pretty close when multiplied X 4 in a Maine. I install very little PWM these days as pretty much every boat is real estate challenged....

Also keep in mind we had a very rainy spring here. That performance, while decent, can be improved on with better weather. I average closer to 35Ah/day over the season with our Kyocera 140W.. That 16 Ah day IIRC was like a Noah's Ark rain day..

Graycruiser · Jul 14, 2014

Interested too

Bill Roosa said:
and on a related note, would there be interest in a pole mounted solar panel that automajicaly tracks the sun. I'm working on one with about 144 watts (12 amps) that will track the sun when it is up and then safe itself during darkness. This would (I'm hoping) also work while sailing and healing-tacking but I don't know if the motors I'm using are up to slew rates that high. also don't know the energy consumed in that mode and wither it would be worth it. I do know that it is worth it, energy wise, when you are at anchor as my back of the envelope calculations show a 45-50 increase in collection over a flat panel.

I don't know that slew rate would be all that much of an issue. So, if it took a minute or longer to re-focus, what's the problem. Perhaps a rate and/or dampening parameter would allow configuration for the type of sailing. Even if it couldn't keep spot-on and you lose 10 or even 20% would it be a big deal? Most sailing I do the heel angle is fairly constant while on the same tack. Perhaps, if sailing on a constant swell (ocean) could be more of an issue; but, then, so would the energy consumed by the motors themselves. Do keep us informed. We gear-heads are interested.

Brian D · Jul 16, 2014

The key to easy tracking is to have a 2-axis stabilized system. This will keep the motor skew rate to a minimum. Unless one is in rolling seas, a 2-axis stabilized system will always keep the panels pointed at the sun on any point of sail. The only other concern would be shadowing and there is nothing that can be done about that except a change of point of sail.

sea_casper · Jul 22, 2014

Forget tracking, it makes no sense, reliability would be an issue, and its not cost effective, compared to fixed panels. Go with the largest panel you can fit, the fixed frame will cost far less than any movable frame. panels in the 250w range are less than a dollar/watt. I put on a 235w panel last year, I have a 3.6a fridge/freezer that runs 24 hrs, 7days/week in the summer. Since last year we have not used shorepower, needed to run our honda gen, or start the engine soley to charge batteries. We tend to cruise for 1 to 2 weeks at a time.and sometimes its rainy or overcast for days, even under those circumstances we still get some gain out of the panel. Our setup is documented here

We have about 330ah of battery and have converted interior lights and the anchor light to LEDs.

Forget calculating angles, temperatures etc., and get the biggest panel that physically fits your boat. With full sun you propably won't use all the panel can put out all of the time, but under less optimum conditions you will get more than a smaller panel optimized. Also since these panels have higher voltages, use a MPPT controller.

That's my two cents, its worked for us into our second season, and kept the batteries charged and "burped" over the winter.

gettinthere · Jul 26, 2014

https://www.renogy-store.com/mobile...:443/100watts-bendable-panel-p/rng-100db.htm=

Anyone know anything about this panel?
Sounds too good to be true...

seadaddler · Jul 26, 2014

panels

I went with 2 190watt panels mounted off my arch on my 2007 H-36 and have no problem running 1 ref 1 freezer 24/7 when out cruising with 4-6 volt Trojans.
I also charge 2-cell phones and run TV at night and also use microwave.
I went with 2 large panels which are over the top of bimini and have plenty of charging all day long and panels I got from supplier in Miami,fl and blue sky controller.
Nick

Bill Roosa · Jul 27, 2014

But guys!!!!
I'm a tinkerer and cheap as heck! The tracking system does add complexity (1 opamp, 9 LEDs, two small dc motors, and an H-bridge) but most of that stuff fits on a 3x3 circuit board. The real engineering challenge I'm having is the wind. for the size panel I'm considering the wind loading at 70 MPH (seen that once while sailing BTW) is something like 300 lb on the panel and 270 on the mast/pole structure. Not at all sure that the stern rail could take that kind of load once it gets magnified by the moment arms involved.
I'm thinking that super fast tracking is not needed and as long as the panel can be brought into alignement in 15 seconds or so that would be sufficient for this application.
I'm almost done with the home remodel and will be (if I remember to) taking pics of the build.

justsomeguy · Jul 27, 2014

As before, I'm looking forward to your photos.

Illegitimi non carborundum!

IStream · Jul 27, 2014

gettinthere said:
https://www.renogy-store.com/mobile...:443/100watts-bendable-panel-p/rng-100db.htm=

Anyone know anything about this panel?
Sounds too good to be true...

Renogy has very good prices and a solid warranty on their rigid panels but the warranty coverage on the flexis seems to be much thinner. I don't know whether it's the cells themselves or the polymer encapsulate but I suspect the latter. I'd like to see some test data on how the encapsulate degrades over time with UV exposure.

Of course, all the warranty in the world won't help you if the company goes bust. Not an issue with Kyocera, Siemens, etc. but it can be with the smaller outfits. If the upfront cost is cheap enough, it can be worth the risk but it's always worth keeping in mind that the risk is there.

mitiempo · Jul 27, 2014

The Renogy flex panels are similar to the Go Power flex panels I sell. The Go Power are durable enough to drive a truck over - it has been done. I don't see any issue with durability. Same output as the same wattage fixed panel. Great for installs on canvas or a panel you want to remove and store. For mounting permanently I would use rigid panels.

gettinthere · Jul 27, 2014

mitiempo said:
The Renogy flex panels are similar to the Go Power flex panels I sell. The Go Power are durable enough to drive a truck over - it has been done. I don't see any issue with durability. Same output as the same wattage fixed panel. Great for installs on canvas or a panel you want to remove and store. For mounting permanently I would use rigid panels.

Renogy selling at $200.
Went to gopower website and none of the pages worked.
Saw gopower 100 flex panel on amazon for $650. That did include a charge controller. But $450 for a small controller?

Should I be looking elsewhere?

I dont need flex but I do need thin. I want to mount one or 2 as flip ups on the rail and if they are thick, they will protrude past the toe rail. These are very thin. I can fab a frame to mount them on to facilitate the flipping horizontal for collection and vert for docking.

mitiempo · Jul 27, 2014

gettinthere said:
Renogy selling at $200.
Went to gopower website and none of the pages worked.
Saw gopower 100 flex panel on amazon for $650. That did include a charge controller. But $450 for a small controller?

Should I be looking elsewhere?

I dont need flex but I do need thin. I want to mount one or 2 as flip ups on the rail and if they are thick, they will protrude past the toe rail. These are very thin. I can fab a frame to mount them on to facilitate the flipping horizontal for collection and vert for docking.

Go Power works fine for me. http://gpelectric.com/

I sell 100 watt Go Power flex panels for $399 Cdn every day. Controller not included but most customers buy a Genasun MPPT. Something very wrong with 650.

The rail is one location I would not install a flex panel. One with a solid frame works better there in my experience. I usually use Magma bbq mounts that can be locked in any position with a quarter turn so additional rod supports are not needed.

gettinthere · Jul 28, 2014

Re solid frame...thats why I mentioned fabbing a frame for the flex panel. With a frame the thickness would be less than 1/2" vs 1" for most rigid panels. In my application that diff is important