Panel Output -- Early and Late in the day...

[Sumner]

Probably a rather boring post but a recent discussion on solar panels and charge controllers on another board got me wondering how our solar panels and charge controller were working early in the morning as far as output. We are working on the Endeavour currently in Florida and have the panels and controller connected to the 12 volt start battery as we are waiting to buy and install four 6 volt Trojan T105's when we are ready to go in the water. We are running the 12 volt fridge, one laptop and additional monitor, 12 volt fans and some of the lights off that battery so I also have a charger on the battery to make sure it stays up during the night.

We have 6 -- 80 watt panels (480 watts total) and the panels are 12v panels rated at 4.4 amps at 18 volts and are all connected in parallel. One thing to remember is that a panel can be putting out 18 volts but just a fraction of an amp depending on sun angle. I have a Blue Sky 3024i MPPT controller and it can only use the amperage the panel is making, which depends on the sun angle to the panel. So only 4.4 amps are available at full sun close to 90 degrees to the panel. So the 6 panels have a potential of around 30+ amps at maximum sun input using a MPPT controller vs. a PWM one. Most solar sites show that for the first daylight hours and the last daylight hours there isn't much power to be harvested from the sun. I wanted to see how much in our case.

Since we have the 110 volt charge on the battery overnight the battery was pretty much topped off at the beginning of the test when I removed the charger leaving only the panels as a source of power.

With the battery topped off I was able to add the following loads to see if the panels could keep up at the low sun angles.

2 -- 12 volt fans drawing about .5 amp each for a total of 1 amp.
1 -- Laptop computer with a larger external monitor for a total of 4 amps.
1 -- 12 volt Fridge that draws about 4.5 amps.

I could put loads on from .5 amp to 9.5 amps with the above. The voltages and amps that will be noted were output from the MPPT controller and not the input to it from the panels as I only have the volt meter on the battery side and the amp meter shows a net value of the input amps from the controller and load amps.

7:10 -- Sunrise

7:55 -- The sun is about 10 deg above the horizon and not really on the panels at this point.

7:55 -- Test starts with a voltage to the batteries of 13.4 volts and no loads with the amp meter at 0.0. The charge controller was showing that it was in bulk mode. The panels must of been putting out 15-18 volts but no amps at this point. It doesn't take much light on them to show a 17+ volt output but without amps nothing good is happening.

7:55 -- I turned one fan on, .5 amp load. Charging volts remained at 13.4 but the amps went to a negative .6 amp. This was another indicator that although the panels were generating voltage there was no amperage to be gained.

8:00 -- Almost an hour after sunrise and just a bit of sun on the panels. No load and 13.5 volts and 0.0 amps.

8:11 -- No loads. 14.0 volts and 1.1 amps. Remember this is 1 amp from 480 watts of panels.

8:11 -- 2 fans on, 1 amp load. 13.8 volts and .1 amp. So panels are now generating about 1 amp as before.

8:14 -- Fans off. Fridge turns on (4.5 load). 13.5 volts and a negative -2.7 amps. Panels might be making close to 2 amps now.

8:18 -- Nothing on. 13.8 volts and +2.5 amps.

8:20 -- Nothing on. 14.3 volts and 2.5 amps. Remember that battery was pretty much fully charged at start of test.

8:21 -- Charge controller goes from 'Bulk' mode to 'Acceptance Mode'. Amps go down to 1.8 and keep decreasing as battery is topped off. This is good as we can still see pretty well what the panels are able to produce.

9:00 -- Turn computer and 2nd monitor on and both fans, 5 amp load. 14.3 volts and +.4 amp. Panels are keeping up with the 5 amp load.

9:04 -- Fridge comes on and I turn the fans off for a load of about 8.5 amps. 14.3 volts and +.2 amps. Panels are now keeping up with a 8.5 load.

9:04 -- I add the 2 fans to the load for a total of 9.5 amps. 14.1 volts and -.1 amp. This indicates that the panels could handle the 8.5 amp load but not quite the 9.5 amp load.

I stopped the test at this point, as the battery was topped off and I couldn't load the panels enough to see what they were producing.

My personal conclusion is, the solar sites are pretty much right, that in the first couple hours of the day and the last couple hours your solar panels don't contribute much. Especially if your panels are not oriented towards the sun and even then some of the sun's power is loss, as it is going through more atmosphere.

At about 2 hours after sunrise panels capable of 30 amps were finally generating about 10 amps. The panels were producing their rated voltage for most of the test but not much amperage for the MPPT controller to work with. Still it was doing a better job than a PWM controller would of been doing.

I also recognize this test wasn't done under an optimal test procedure format but feel that is still relevant to panel output during the early sun hours of the day.

Sumner
=================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[rgranger]

Lot of good info.... thnx for sharing.

 

[jssailem]

Thanks Sumner. Even anecdotal data has relevance. It gives us a glimpse at in field conditions. The science is for the lab the report you provided gives us field players some meat to chew. Thanks.

 

[walt]

My personal conclusion is, the solar sites are pretty much right, that in the first couple hours of the day and the last couple hours your solar panels don't contribute much. Especially if your panels are not oriented towards the sun and even then some of the sun's power is loss, as it is going through more atmosphere.

At about 2 hours after sunrise panels capable of 30 amps were finally generating about 10 amps. The panels were producing their rated voltage for most of the test but not much amperage for the MPPT controller to work with. Still it was doing a better job than a PWM controller would of been doing.

If one of those mast from other boats is creating a shadow on your panel, that will also reduce power. I would often see this when my boat was in a slip last winter. FYI, in your case where two hours after the sun came up (assume its good sunlight), if you are only producing 1/3 of what the panels are capable of and with your case of a single battery that is already fully charged, its most likely the charge algorithm that is limiting the current. Doesn't matter if you had MPPT or PWM in this case, likely the same current. MPPT only gives you an advantage when the algorithm senses that the every bit of power from the panel needs to get put into the battery/ load. You might have been getting 10 amps as that is about what your max load is. The charge controller would have only been taking from the panel what it needed for that load since the battery was full.

 

[Brian D]

I agree with your conclusions. For the most part, solar is really only good for about 5 hours during the day. Before that and after that we really are not getting usable light. Now, one might improve upon these results if one were to use a sun tracking system, like telescopes use. This will keep the panel pointing at the sun the whole day.

Did you ever think about installing lunar panels?

 

[Sumner]

. You might have been getting 10 amps as that is about what your max load is. The charge controller would have only been taking from the panel what it needed for that load since the battery was full.

Yes, that is why I stopped the test as I didn't have enough loads to see the output any longer. Before that I feel the controller and panels were responding to the load, but again not enough test equipment to really know??

Sumner

 

[Sumner]

Did you ever think about installing lunar panels?

We had them on the boat until someone came along with a sky hook one night and stole them ,

Sumner

 

[viper]

Given that you have 80 watt panels, I will make the assumption that they are Poly Crystaline and not the newer Mono Crystaline panels which work in much lower light, angles are not as important. Of course we all know what happens when you assume...

With newer panels running 180 watts (140 bucks) and with 6 of them... you could sell power to the other boats...lol
Regards

 

[Ron20324]

Wouldn't this have been a better thing to do when the batteries were more depleted- not charged before testing? On overnights anchored out (with solar panels) I use about 40Ah, 50 if we use the fans.

 

[Hafa]

Insolation calculators such as this one can help determine the actual kWh/m2/day.

 

[Sumner]

Wouldn't this have been a better thing to do when the batteries were more depleted- not charged before testing? .

The test was kind of a 'spur of the moment thing'. If the battery would of been depleted I would of run into the situation of how discharged was it and what was its acceptance rate I believe. I knew the load values pretty accurately and it looked like the charger was trying to keep up with them and would either show a small charge or a 0.0 charge if it was able to produce more than what they were and a negative charge value of what I would of expected when the loads where more than what the panels could handle at that moment.

For sure not a perfect test, but I think one that showed what they are capable of in early light.

I'll have to look into some of the newer technology panels in case I live long enough where I have to replace what I have. I did buy one extra 80 watt panel....

... just in case one breaks or quits working so that I have one that will fit the framework ok. I learned on the other boat that panels can be the same wattage but change in dimensions from the same supplier over time and ... maybe not fit your mounts like the old ones.

Sumner
==============================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[mauruuru]

If you want to determine the effect of azimuth, angle of tilt and lattitude on your panel output you can use PVWatts from the National Renewable Energy Lab (NREL)