MPPT vs. Shunting Solar Controller

[Maine Sail]

Regarding the current limit power supply to simulate a solar panel (which I think is clever), MS can correct me if wrong but the power supply was first setup with a voltage at 17.4 and then the current limit was adjusted to be .4 amps. This means that the supply will put out 17.4 volts as long as the load current is below .4 amps. If the load increases past the .4 amp point, the power supply voltage will begin to drop in order to limit the current.

If you look at the video in the first post, at about 2.36 minutes in, you can see the mppt controller search algorithm in action and it actually looks like it works nicely. When the switch is flipped connecting the current limited power supply to the controller solar input, the current first starts at zero but then quickly ramps up. If you look to the left side of the supply, you can see the current limit display light come on but the controller is still able to cause an overshoot in the current just for a fraction of a second before the power supply stabilized at .4 amps - and the current limit light stays on. The controller did a nice job as it put the power supply in current limit but just barely as it allowed the maximum voltage the supply was set at. The controller did find the maximum power output from the supply, found it quickly and seemed to hold it stable. I can’t see anything wrong with this setup..

I pulled this from the Genasun web site
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The MPPT benefit is:
10% additional power in the summer. (Hot panels have a Vmp closer to battery Voltage.)
30% additional power in the winter (Cold panels have a higher Vmp.)
50% in partial shading (Partial shade causes a dramatic increase in Vmp. We have consistently seen 50-60% increase in energy harvest from partially shaded panels.)
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What I wanted to point out is the 10% additional power in the summer from the manufactures web site and this is what we are likely to see for a sailboat application (not the great numbers from this experiment). If you’re using a panel when it’s warm and sunny out, the panel is maybe 15% efficient for electricity but they are much more efficient for collecting heat (nice dark color). Sometime just feel how hot a panel gets. The maximum power point is temperature dependent and drops with temp - mostly due to voltage drop.

The 50% increase in partial shading condition is interesting however.. but I wonder if this occurs when the power output is very low to begin with and 50% increase of a low number is still a low number??

Walt,

It was actually set to 4.0A not 0.4A. That said this is a "best case" scenario. As you stated solar panels have worse performance when hot and better when cold. In the "real world" I see average performance increases of 7-15% with MPPT not the 20-30% often bantered around.....

I only used the power supply because it is consistent and I can set it to maintain its consistent output where a solar panel in an A/B is dependent upon the sun and sky which change, especially here in Maine.. I used the power supply for a cleaner "apples to apples"....

 

[Witzend]

Interesting video showing the effects of cooling the panel with water.
http://www.youtube.com/watch?v=5IG1HThEOS0

Not sure what other variable are in effect though.

 

[Maine Sail]

Interesting video showing the effects of cooling the panel with water.
http://www.youtube.com/watch?v=5IG1HThEOS0

Not sure what other variable are in effect though.

We have some benefit on boats that the panels can often have a breeze cooling them off top and bottom. They can still get hot, though not as hot as they do on a black asphalt roof....

 

[JohnShannon]

Detailed panel data sheets will give you temperature data.
The important ones being temp coefficient of peak power voltage and of peak power.

As the panel heats the Vmpp drops (which is why panels intended for 12V charging are at such a high voltage) and max power drops as well.

Here are the ultimate water cooled solar panels, claim about 85% recovery of solar energy

http://www.cogenra.com/

Not really suited for marine use.

 

[walt]

It was actually set to 4.0A not 0.4A.

woops.. I was only a factor of 10 off . I edited my post to fix this..

 

[gettinthere]

OK, let me try this question...
Why do we need a charge controller at all?

Recently we discussed how battery acceptance will limit or restrict the charge. I probably botched this description but you get the drift. It had to do with alternators & solar panels operating at 14.7 vs 14.2, etc. The voltage couldn't get to 14.7 as long as the battery was in bulk mode.

So if the battery is hungry for recharging, why can't it take 17 volts? As it comes up the acceptance rate should limit this. I'm sure I'm still missing part of all this, no surprise there!

 

[Witzend]

The Mitsubishi PV-MLU255HC mono crystalline panels I chose for my home system are spec to provide up to 90% Pmax @50deg.C. We will see next summer how they really preform.

 

[Maine Sail]

OK, let me try this question...
Why do we need a charge controller at all?

Recently we discussed how battery acceptance will limit or restrict the charge. I probably botched this description but you get the drift. It had to do with alternators & solar panels operating at 14.7 vs 14.2, etc. The voltage couldn't get to 14.7 as long as the battery was in bulk mode.

So if the battery is hungry for recharging, why can't it take 17 volts? As it comes up the acceptance rate should limit this. I'm sure I'm still missing part of all this, no surprise there!

The batteries limit the current as they get more full not the voltage. Too much current at "full" pushes the voltage and is what causes the gassing.

So if you don't limit the voltage with a controller and there is enough current to "push" the voltage you can still "cook" the batteries..

Sounds like I need to do another video...

 

[gettinthere]

Can you do a video on confusion?
Maybe if I drop my chainhook on my head, it will sink in!

 

[Maine Sail]

Can you do a video on confusion?
Maybe if I drop my chainhook on my head, it will sink in!

This stuff is confusing for many and you're not alone...

As a point of reference I have two group 27 batteries on my bench right now, these are same batts in the video.

At 100% full just a measly 0.2A of current is enough to push the voltage to 14.4 volts. This is a 160Ah bank. Even a 10W solar panel has 0.6A of current capability..

If a 10W panel can produce upwards of 0.6A it would push the voltage even higher.. These batteries when full should be "floated" no higher than 13.2V - 13.8V.

In the morning I will make a video with that 160Ah bank raising the voltage to 30V (getting it out of the way/no controller) but limiting the current to show the voltages at certain current levels to full batteries.

 

[Maine Sail]

OK, let me try this question...
Why do we need a charge controller at all?

Recently we discussed how battery acceptance will limit or restrict the charge. I probably botched this description but you get the drift. It had to do with alternators & solar panels operating at 14.7 vs 14.2, etc. The voltage couldn't get to 14.7 as long as the battery was in bulk mode.

So if the battery is hungry for recharging, why can't it take 17 volts? As it comes up the acceptance rate should limit this. I'm sure I'm still missing part of all this, no surprise there!

Here you go...

 

[justsomeguy]

This stuff is confusing for many and you're not alone... -snip-
In the morning I will make a video with that 160Ah bank raising the voltage to 30V (getting it out of the way/no controller) but limiting the current to show the voltages at certain current levels to full batteries.

Thanks for the video. I noticed when you cranked up the voltage, the battery seemed to limit it to around 16 or so volts.
What might happen if I connected a small solar array that's putting out about 28 volts, but only about .07-.08 amps, to my 12 volt/85 Ah battery?
Without a charge controller, will I kill it with this little trickle charger?

Yep, I'm ascared...

 

[weinie]

Not to venture too far off topic, but after reading the post and looking at the videos, I tried to find out the type of solar controller that a previous owner had installed in my boat. I could not find any instruction manual, but was able to find this spec sheet which does indicate it is a PWM. It is connected to a 36W panel and either one of 2 group 24 sealed starting batteries (also from a previous owner, which I plan to upgrade when they start to die out.) My concern was the "regulation" voltage specified in the spec sheet. If this is the same as the floating charge, I would think it is too high? What I do love about the controller, though, is the digital readout on the front which tells me the voltage and the current too.

 

[Maine Sail]

Not to venture too far off topic, but after reading the post and looking at the videos, I tried to find out the type of solar controller that a previous owner had installed in my boat. I could not find any instruction manual, but was able to find this spec sheet which does indicate it is a PWM. It is connected to a 36W panel and either one of 2 group 24 sealed starting batteries (also from a previous owner, which I plan to upgrade when they start to die out.) My concern was the "regulation" voltage specified in the spec sheet. If this is the same as the floating charge, I would think it is too high? What I do love about the controller, though, is the digital readout on the front which tells me the voltage and the current too.

That is not a bad controller at all through it does lack a float level voltage. Ideally you do want the batteries to go into a lower voltage when they get full. You'd use less water using the 14.1V setting than the 14.4V but you'd "finish" charge slightly slower and lack any "gassing" which gets the electrolyte moving around in the battery to prevent stratification. Many of these controller are designed with daily cycles in mind for off grid applications so even if you got to 14.4V it would be for a minimal amount of time each day. On boats that are often left unattended for long periods we do get the banks back to 100% so a float voltage becomes more important than in a controller designed for off grid work where they array will have a tough time ever getting to 100%..

The MorningStar Sun Saver 6/12V sells for $39.00 or so, is PWM and does absorption, float and also has a 14.9V (equalizing) feature. They are also sealed and designed to survive in the marine environment. They will also temp compensate for ambient air temp. This does mean the controller needs to be right near the batts for the best 'temp sensing"... A jump up from the Sun Saver's is the ProStar series. These offer remote displays and other features not found in the SunSaver..

 

[Maine Sail]

Thanks for the video. I noticed when you cranked up the voltage, the battery seemed to limit it to around 16 or so volts.
What might happen if I connected a small solar array that's putting out about 28 volts, but only about .07-.08 amps, to my 12 volt/85 Ah battery?
Without a charge controller, will I kill it with this little trickle charger?

Yep, I'm ascared...

.07 -.08 is very, very small and not even likely to be able to "charge" the battery. It is likely only enough to get the bank to 13.9 - 14.1V even when they are full.. That is a "maintainer" at best but not a good "charging" solar panel....

Also with most any controller they do have standby draws of 0.9mA - 20 mA or 0.0009A - 0.02A.. So that would need to get deducted before you could begin to charge. and reduces your output.. As I said in the video there are "caveats"..

 

[justsomeguy]

.07 -.08 is very, very small and not even likely to be able to "charge" the battery. It is likely only enough to get the bank to 13.9 - 14.1V even when they are full.. That is a "maintainer" at best but not a good "charging" solar panel....

Thanks. I suspect I'll be in the market for a bigger, better panel when out sailing.
Trying to find uses for all the stuff I've got lying around here, and these little Sanyos have been wasting space on my miter saw table for much too long, so they've served as a primer, of sorts. If I do install a charge controller, I'd like it to be accomodating of future upgrades.

I appreciate your efforts in this forum. Thanks again!

 

[Bill Roosa]

MS
Great video!!
how does the fact that my panels are not directly aimed at the sun and that night time diode thingy factor in to all this?

 

[Maine Sail]

MS
Great video!!
how does the fact that my panels are not directly aimed at the sun and that night time diode thingy factor in to all this?

Not aimed at the sun reduces the efficiency of Ah's per day and if you don't have a blocking diode you can lose some of your daily gains at night. Controllers have back flow prevention built in as do some panels. diodes are cheap though...

Still I install many panels that are situated flat that still see full output, based on their rating, a good portion of the day. On our own boat we average 4-5 hours per day at the full rated output so that is the calculation I most often use for "flat panels"..

 

[Albanach]

"Here you go..."

MS.Many thanks for going to the trouble to enlighten us uninitiated a bit more. A great video.
It has me now convinced to buy a Morningstar Sunguard Regulator for my 10W panel - just in case. However its specs show ‘Regulation voltage 14.1 (sealed battery).Would this be ok for a 300A bank? I noticed that you recommended a float charge of up to 13.8V.
I am also puzzled about one thing, probably something taught, when I had a day off in school: As your AMPs increase, so does the Voltage – which I can relate to on a common sense basis. Why do calculators generally show the reverse happening, ie. an increase in one factor leads to the decrease in the other?

 

[Maine Sail]

"Here you go..."

MS.Many thanks for going to the trouble to enlighten us uninitiated a bit more. A great video.
It has me now convinced to buy a Morningstar Sunguard Regulator for my 10W panel - just in case. However its specs show ‘Regulation voltage 14.1 (sealed battery).Would this be ok for a 300A bank? I noticed that you recommended a float charge of up to 13.8V.
I am also puzzled about one thing, probably something taught, when I had a day off in school: As your AMPs increase, so does the Voltage – which I can relate to on a common sense basis. Why do calculators generally show the reverse happening, ie. an increase in one factor leads to the decrease in the other?

In terms of battery charging lets look at it this way:

VOLTAGE = PRESSURE

The higher the voltage moves away from the battery resting voltage the more current can flow into it. This is why when I turned the voltage up to 30V the power supply went into "bulk" and supplied all the current it had or 30A.. Eventually the voltage would have risen to 17V+ but it never would have gotten to 30V before something bad happened.....

Conversely if we lower the voltage to say .2V above the batteries resting voltage very, very little current will flow no matter how much current we have available in the charger.

Also the current available at the charge source drives or pushes the voltage if the voltage is "unregulated". So in this case when I set the voltage to 30V and adjusted the current from 0.2A to 1.0A we saw the voltage climb from 14.4V to 15.1V with just a 0.8A change in available current. This is because the voltage "limit" was 30V and the battery voltage was being controlled solely by the available current.