Solar charging - can it be so?

[obiwancanoli]

I'm still trying to wrap my head around the solar and power issue, but I have learned a lot. In conversation with my RV service tech, an independent guy who takes pride in his knowledge and work, I was listening to him discuss the wiring issue, in conjunction with a new Victron controller (100/50) and Victron 712 Voltmeter he'll be installing this week.

Something my tech said about properly wiring the solar panels - in series, I think - got me to wondering...., rather than the alternative setup, pretty much has a good 5-hour window (10-3) for maximum charging, where in series would allow the panels to begin charging as soon as daylight hits, albeit at a lower rate, of course.

I've always heard that maximum performance of any solar panel was generally limited to the most direct sunlite one can have - about 5 hours. And clouds, trees, buildings, etc., severely reduce their capabilities, if not altogether eliminated them.

Now I'm thinking I heard my tech say that properly wired, panels would recharge batteries as soon as daylight appeared, and through the day until dusk, and I assume he said this knowing a new Voltmeter and MPPT 100/50 Controller (Victron's) would also be installed. He also stated he'd seen solar charge batteries sitting under a flourescent light!

Could it be true?!?!?!

[ajriding]

honestly, In real life, I couldn't tell the difference in PWM parallel or MPPT series with two 100w panels. Both would get the batts charged during the day, and the biggie is using power overnight since the was plenty of available power from the panels during the day.

I would have added more panels, but ran out of roof space.

I like running the panels in series as I can use smaller wire, and use less wire (or if the same wire then at higher volts is a bit less loss).

I have a backup mppt on hand in a faraday cage, n hope the panels can survive the worst.
I am hopeful mass arrst are made Nov 4 and "within" enemies are taken out, but enemies from afar are always a threat.

[3_tons]

time2roll wrote:
So does the 300 produce 2x the 140?

Thats an interesting question...I cannot offer any ‘empirical’ one against the other test data, mostly due to the wattage (and wiring) disparity, though honestly I’ve truly been quite satisfied with the performance of either system. whether operating separately or in tandem.. I seldom if ever have hook-ups, so site selection is what mostly matters, as does a rapid harvest (aided by Li’s high receptivity) - in a race against the sun, shading tends to be my number one harvest adversary...

3 tons

[time2roll]

So does the 300 produce 2x the 140?

[3_tons]

BFL13 wrote:
The earlier start with a higher voltage notion sounds good, but at the time of the earlier start your amps are so low, who cares? Say you get 2 amps from 7-8am that you would not get otherwise. That is 2 AH. My goodness, two whole AH!

On no shade different sets real life--I put three 100w panels (6.2 Isc each) in parallel with a PWM and got 18.6a to the battery by Trimetric when array aimed at high noon. I quickly swapped to MPPT and got 18.x (forget exact amount).

It turned out that panel heating kills off wattage with MPPT to the same degree that PWM "wastes watts" according to MPPT advertising, so it was a wash.

I then tried the panels in series with the MPPT (can't do that with the PWM) and got--ta da-- 18.x to the batts by Trimetric. Same.

So that's what I got in real life. Three 100w panels will do what they do and that's that. You can't get blood out of a stone and wire them funny to get more, or use a different controller. At least I couldn't.

Solar is so variable each day, you can't realize all these so called advantages that you will ever notice. Pick something that makes the most sense and that's your solar. After that it is all up to the weather man what good it does you. Meanwhile keep your generator handy, because you will need it if you don't have one, and might not need it if you do have one (Sod's Law with that)

Agree, many thanks for this sage report from ‘RealVille‘ - I’m all for MPPT (as well as other tweaks), but from my perspective this all has more to do with personal nuance...In the end it’s Mother Nature who is the final photon arbiter...JMHO

3 tons

On edit, I have two systems as follows:

300w MPPT and 140w PWM, both with separate shunts and metering...

[obiwancanoli]

Amazing how the content has diverted from my original post... though I always learn something, even when my mind simply won't wrap itself around the posts sometimes... you guys are amazing!

[CA_Traveler]

Boon Docker wrote:

CA Traveler wrote:
See my 7:03am post today. The bypass diode acts like a direct short with 0V and conducting all amps. Well OK there is a small voltage drop (0.3V) across the diode. The other 2 panel sections are still producing 10V each with the amps.

So a panel that produces 6 amps at 30v (full sun) would produce with partial shading 6 amps at 20v. How is it possible that a panel operating at 2/3 can still produce 6 amps.

Panels contain constant voltage devices. 6A at 30V = 180W and 6V at 20V = 120W or 2/3 of that panel power.

MPPT controllers convert power (watts) for the load, PWM controllers pass amps to the load.

Hope this helps.

[BFL13]

The earlier start with a higher voltage notion sounds good, but at the time of the earlier start your amps are so low, who cares? Say you get 2 amps from 7-8am that you would not get otherwise. That is 2 AH. My goodness, two whole AH!

On no shade different sets real life--I put three 100w panels (6.2 Isc each) in parallel with a PWM and got 18.6a to the battery by Trimetric when array aimed at high noon. I quickly swapped to MPPT and got 18.x (forget exact amount).

It turned out that panel heating kills off wattage with MPPT to the same degree that PWM "wastes watts" according to MPPT advertising, so it was a wash.

I then tried the panels in series with the MPPT (can't do that with the PWM) and got--ta da-- 18.x to the batts by Trimetric. Same.

So that's what I got in real life. Three 100w panels will do what they do and that's that. You can't get blood out of a stone and wire them funny to get more, or use a different controller. At least I couldn't.

Solar is so variable each day, you can't realize all these so called advantages that you will ever notice. Pick something that makes the most sense and that's your solar. After that it is all up to the weather man what good it does you. Meanwhile keep your generator handy, because you will need it if you don't have one, and might not need it if you do have one (Sod's Law with that)

[Boon_Docker]

CA Traveler wrote:
See my 7:03am post today. The bypass diode acts like a direct short with 0V and conducting all amps. Well OK there is a small voltage drop (0.3V) across the diode. The other 2 panel sections are still producing 10V each with the amps.

So a panel that produces 6 amps at 30v (full sun) would produce with partial shading 6 amps at 20v. How is it possible that a panel operating at 2/3 can still produce 6 amps.

[phemens]

CA Traveler wrote:

red31 wrote:
For me the purpose of a controller is to limit power going to a battery (trailer storage), that and 'sleep' or night mode were it prevents batt drainage. 'Full by noon' means the controller was limiting power before noon and the rest of the day unless you have some other use of the excess power.

In active use many things limit power, location, calendar, orientation, temperature, overcast, smog, shade, bird poop, dirt ...

Once the batteries are full the unused solar power is available for house loads, ie keep the batteries full until sunset. Some have used the excess power for say hot water but I'm not sure how well that works out.

I'm one of them. After noon, everything I get from solar is bonus, so I do run the electric water heater - free money! 😉

[joshuajim]

Here's a graph for my ground mount solar at the S&B. Sunrise yesterday was at 6:36 and power was produced at 7:00. Sunset was at 6:43 with power production ending at at 6:36. This was a totally clear day in the desert.

[CA_Traveler]

See my 7:03am post today. The bypass diode acts like a direct short with 0V and conducting all amps. Well OK there is a small voltage drop (0.3V) across the diode. The other 2 panel sections are still producing 10V each with the amps.

[Boon_Docker]

CA Traveler wrote:
Check your panels IV graphs and you'll see the amps drop with reduced light for the panel. That is not the same as partial shade that triggers a bypass diode to conduct reducing the voltage but not the amps for that panel - think an A/C shadow on part of a panel.

How is that possible that the voltage is reduced, but the amperage is not reduced?

[CA_Traveler]

Check your panels IV graphs and you'll see the amps drop with reduced light for the panel. That is not the same as partial shade that triggers a bypass diode to conduct reducing the voltage but not the amps for that panel - think an A/C shadow on part of a panel.

The effect of shadows on the controller output is dependent upon how the panels are wired and the type of controller. These days with low panel prices the trend is to just add another panel and enjoy camping.

[time2roll]

If you run parallel you can use a PWM controller that just clips the voltage. If you run series you need the better MPPT controller that converts all amps and volts to the proper voltage and maximum amps. This holds watts or total power constant.

There’s a lot to know.