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Old 07-09-2012, 09:11   #1
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MPPT vs PWM Solar Regulators

Is the $80-100 price difference for the MPPT vs the old PWM style charge regulators worth it? I have read through most manufacturer's info on these and am not sure I would gain much. The old PWM style regulator I had for 12 years and 2 boats has done a fine job, but finally died and needs to be replaced. Looking at Morningstar regulators, they have a good reputation and warranty. I have 2 Kyocera 80 watt panels that max out(with the old regulator) at about 9 amps.
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Old 07-09-2012, 10:48   #2
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Re: MPPT vs PWM solar regulators

Are these KC80 panels? If so, Vmp is 15.3-17.4Volts depending on conditions. When your batteries are discharged the PWM is closed 100% of the time and the panels operate at 13.8 to 14.4V (depending on PWM settings). The panels would produce more power if they were operating at Vmp. If you estimate that as 2V above where they currently operate that means about 14% more energy from the panels using an MPPT controller. That only applies when the sun is bright enough to reach Vmp and the batteries are low enough to accept the full amount. So, ballpark, you might see about 1 to 1.5A increase for maybe 2-5 hours/day. Is that worth it?
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Old 07-09-2012, 10:59   #3
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Re: MPPT vs PWM solar regulators

The gain from MPPT is quite small on a yacht.
If you are going to get a MPPT regulator get a good one.
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Old 07-09-2012, 12:24   #4
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Re: MPPT vs PWM solar regulators

I like my BlueSky 2512 with the Pro Remote.
Input current from the panels/MPPT output to the batteries.
This photo was taken on a sunny day after I ran the 1KW hot water tank element from the inverter for a half hour and the 200 aH battery bank was at about 60%.
The panel array is 320 watts, and recharged the batteries to 100% by late afternoon.
We were on vacation in Canada when this photo was taken, so the usual loads (refrigeration etc) were in place at the time.
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Old 07-09-2012, 12:40   #5
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Re: MPPT vs PWM solar regulators

If you don't have the room to add more panels (or bigger ones) and absolutely need the extra 10-15% power output, then MPPT controllers are ok.

Otherwise, buy more or bigger panels. Panels are relatively cheap and MPPT controllers are relatively expensive.

But if you want high output panels, more than 150 watts each, you have to go with an MPPT controller because the panel voltage will be 35 or so and they need the MPPT controller to match the battery voltage. Otherwise you are wasting more than half of your panel's output.

David
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Old 07-09-2012, 12:41   #6
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Re: MPPT vs PWM solar regulators

Be a bit wary of trusting the controlers display a lot of them are not accurate.

However gains of this sort of order, and greater, are possible, but there are times when there are losses as well. The average gain is not very high.

About 5-10 % is typical, from the very best controlers, in my experience. Cheap MPPT controlers are poor, frequently worse than simple non MPPT regulators.
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Old 07-09-2012, 13:28   #7
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Re: MPPT vs PWM solar regulators

We run three 135 watt Kyoceras through a BlueSky 2412. We burn about 75-100 Ah a night in the Bahamas. We get it all back by about 1400 and then run net 0aH until sundown. The meter on our BlueSky produced the same numbers as the independently shunted ammeter we used to check the system during set up. The heat dispersion is entirely passive and within a locker where it helps keep things dried out. We believe we are 15-20% ahead of the curve with MPPT based on daily data collected for 16 months.
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Old 07-09-2012, 13:52   #8
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Re: MPPT vs PWM solar regulators

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Originally Posted by brilliantstar View Post
We get it all back by - We believe we are 15-20% ahead of the curve with MPPT based on daily data collected for 16 months.
There are some dangers directly comparing the input and output figures from the regulator. Even if these are accurate, which is unusual.
The current produced from a solar Panel at at a lower voltage will be higher. This makes a direct conversion of input watts and output watts on a MPPT regulator display to be flawed.

The self consumption of the MPPT regulator is higher, and there are some conversion inefficiencies.

If you account for these factors I think you will find your 15-20% gain is very close to my figure of 5-10%.

The gain from MPPT is a very hotly debated topic and least we are in reasonably agreement, but 10% is still important, so any raw data, from practical experience is always helpful.

I think a carefully analysis of this data will see the gain you report drop to closer to the 5-10% level.
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Old 07-09-2012, 14:24   #9
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Re: MPPT vs PWM solar regulators

Our improvement is not based on the BlueSky meter. It is based on the time of day we hit the 0 AH point on our Link 2000. On average we get to 0 AH at least 60 minutes and sometimes 90 minutes earlier than we once did. A parallel battery condition meter reports the same outcome.
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Old 07-09-2012, 14:38   #10
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Re: MPPT vs PWM solar regulators

Quote:
Originally Posted by brilliantstar View Post
Our improvement is not based on the BlueSky meter. It is based on the time of day we hit the 0 AH point on our Link 2000. On average we get to 0 AH at least 60 minutes and sometimes 90 minutes earlier than we once did. A parallel battery condition meter reports the same outcome.
That is a useful date point. What were the voltage set points with the old and new regulator set points ?
What was the old regulator?
Sorry for the questions, but even these minor 10% differences are important or cruising sailors.
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Old 07-09-2012, 15:25   #11
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Re: MPPT vs PWM solar regulators

To OP's original question, I think we are all pretty much in agreement that MPPT will likely provide some improvement, that the bottom end of that is around 5%, top end around 20%, and consensus around 10-12%.

Only our sailor from Texas can answer whether or not that kind of improvement is worth the money. If you have the room, might be better spent on an additional panel, but absent room 10% might pay itself back relatively quickly depending on what the other options are for making that power.
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Old 07-09-2012, 16:38   #12
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Re: MPPT vs PWM solar regulators

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Originally Posted by Sailormantx View Post
.... Looking at Morningstar regulators, they have a good reputation and warranty. I have 2 Kyocera 80 watt panels that max out(with the old regulator) at about 9 amps.
My experience with Morningstar Sunsaver series of controllers (PWM) is excellent. Simple and bullet proof. Have run one at home and on the boat for about 5 years.

I've had the same debate about switching to MPPT, but these basic PWM controllers are still getting the job done for me. And when I run the numbers the likely gains always seem small. Would be nice if I could hook them up side by side in my installation and test first.
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Old 07-09-2012, 17:20   #13
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Re: MPPT vs PWM solar regulators

Well, you can buy a more expensive regulator or else you can buy another solar panel. Just go for whichever option gives you more Watts per invested buck!

If there is no deck space left, MPPT may be the only way to squeeze out some extra Amps from what you might have there. Just remember modifying panel mounts so that you can angle them may give you more extra Amps than any regulator.

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Old 07-09-2012, 20:54   #14
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Re: MPPT vs PWM solar regulators

Thanks for all the input, it confirms my original thought the there is not a big enough gain for my situation. There is plenty of DC available at anchor unless there is no sun for several days, but I run far short, approximately 25 amps/day underway if not careful with electronics use. I need to order a regulator this weekend, switching the panels off manually is too risky, one distraction away from overcharging my batteries.
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Old 07-09-2012, 22:53   #15
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Re: MPPT vs PWM Solar Regulators

Here ya go:

New 10A Solar Panel Charge Regulator Controller 12V/24V CMP for Solar System BLK | eBay

AU$11.38 each. Buy two, keep a spare.

Rob
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