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Old 08-09-2012, 01:50   #16
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Re: MPPT vs PWM Solar Regulators

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Originally Posted by haiqu View Post
Be careful with very cheap controlers. This one has a non adjustable absorption voltage of 13.7 which is much too low. The specs suggest its an on /off regulator even though the add mentions PWM.

Your batteries will thank you if you buy something a bit better.
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Old 08-09-2012, 06:25   #17
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Re: MPPT vs PWM solar regulators

Voltage set points were the same for both controllers. Batteries were AGM. PWM was a used BlueSky I borrowed to assess situation before buying MPPT.

We decided to go solar for many reasons, but what we saved in genset fuel, made the controller cost difference moot. Also at $.60 a KW for shore power in the Bahamas, we saved the difference on the controller in less than two months.

We expect the entire installation (installed when tax breaks for solar were available and using 100% our labor) will pay back in 4-5 years, if fuel and fuel derivative prices continue to increase at $.70 per year as they have since we installed.
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Old 08-09-2012, 07:12   #18
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Re: MPPT vs PWM solar regulators

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Voltage set points were the same for both controllers. Batteries were AGM. PWM was a used BlueSky I borrowed to assess situation before buying MPPT.
Bluesky was formed to make MPPT regulators. They have just released their first non MPPT regulator, but it has not hit the market yet.
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Old 08-09-2012, 07:27   #19
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Re: MPPT vs PWM Solar Regulators

You are quite correct. I haven't had my tea yet. The unit we tested was a Morningstar, I don't remember the unit designation but it must have been in the 30a range.

Appreciate you catching this.
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Old 08-09-2012, 09:05   #20
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Re: MPPT vs PWM solar regulators

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Originally Posted by noelex 77 View Post
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.

Noelex--

A PWM controller is not going to increase the output current to the batteries. So any increase in current provided to the batteries using an MTTP over that which the panels provide represents a true current/power gain from that which an PWM would provide.

Yes, I agree there are loses in all converters but those loses should be ignored because in reality the current/power gain is a function of the difference in current provided to the batteries themselves vs the current output from the panels.

Foggy
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Old 08-09-2012, 09:11   #21
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Re: MPPT vs PWM solar regulators

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Originally Posted by noelex 77 View Post
Bluesky was formed to make MPPT regulators. They have just released their first non MPPT regulator, but it has not hit the market yet.
That seems like an odd change in direction. Any idea why they decided to produce a non-MPPT? Just to diversify their product line?
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Old 08-09-2012, 09:18   #22
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Re: MPPT vs PWM Solar Regulators

Sure--- as Noelex and others correctly point out, if one has room for additional panels, adding a panel is the least expensive way to increase output current/power using a less expensive controller.

Yes, I know I seem to be mixing current & power. The reason is there are little changes in the battery's voltage so in my simple analysis I usually treat battery voltage as a constant.
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Old 08-09-2012, 09:20   #23
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Re: MPPT vs PWM solar regulators

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Noelex--


If the panels are low voltage units and of course not connected in series, a PWM controller is not going to increase the output current to the batteries. So any increase in current provided to the batteries over that which the panels provide represents a true current/power gain from that which an PWM would provide.

Yes, I agree there are loses in all converters but those loses should be ignored because in reality the current/power gain is a function of the difference in current provided to the batteries themselves vs the current output from the panels.

Foggy
The I/V curve of solar panels is not a vertical line after the Vmp.

A MPPT regulator will operate the panels at Vmp (for the particular conditions that the panel is experiencing). If the voltage is reduced the current will rise (slightly).

So the input current of a MPPT regulator is lower than the current that would be derived from the panels by a non MPPT regulator.

The effect of this is not large, but the assumption that the current stays constant as the voltage is changed is erroneous, a look at the I/V curve makes this clear.

When talking about the small gain of MPPT these effects need to be considered when comparing outputs.
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Old 08-09-2012, 09:41   #24
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Re: MPPT vs PWM solar regulators

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Originally Posted by noelex 77 View Post
The I/V curve of solar panels is not a vertical line after the Vmp.

A MPPT regulator will operate the panels at Vmp (for the particular conditions that the panel is experiencing). If the voltage is reduced the current will rise (slightly).

So the input current of a MPPT regulator is lower than the current that would be derived from the panels by a non MPPT regulator.

The effect of this is not large, but the assumption that the current stays constant as the voltage is changed is erroneous, a look at the I/V curve makes this clear.

When talking about the small gain of MPPT these effects need to be considered when comparing outputs.

Noelex--

I am looking at current (NOT POWER IN THIS CASE) goes-into controller vs goes-into battery. You can forget all the power positions on the MTTP curve for this approach. If the total current available to the battery is greater than the current provided to the controller that is the basis for making measurements. This is independent to the panel output wattage.
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Old 08-09-2012, 09:59   #25
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Re: MPPT vs PWM Solar Regulators

Morningstar TriStar TS-45, PWM Charge Controller, 45 Amp, 12/24/48 Volt

This is what I am looking at, robust build and with capacity to expand. The Pro star controllers are a bit cheaper, but this looks more versatile. Also read through Pro star manual and it appears there is an automatic equalization program in it with no way to turn it off-an unexpected equalization voltage could be hard on my electronics. The Tri-star is completely user adjustable and at 45 amp rating has all the capacity I may need as there will be more/larger panels added in the future.
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Old 08-09-2012, 10:02   #26
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Re: MPPT vs PWM solar regulators

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Originally Posted by foggysail View Post
Noelex--

I am looking at current (NOT POWER IN THIS CASE) goes-into controller vs goes-into battery. You can forget all the power positions on the MTTP curve for this approach. If the total current available to the battery is greater than the current provided to the controller that is the basis for making measurements. This is independent to the panel output wattage.
Yes I am talking about current as well.
Perhaps a simple example will illustrate the point.

Let's assume the input to a MPPT controler is 20A @ at 16v
The output is 22.2A @14.4v

Many people assume that means the MPPT regulator has gained 2.2/20 or 11% more current over a non MPPT regulator.

However the current will rise (slightly) as the voltage is reduced.(the exact amount can be found by consulting the I/V curve)

So a non MPPT regulator operating at an input voltage of 14.4v would have extracted not 20A but say 20.5A under identical conditions. So the real gain is 1.7/20 or 8.5%
(Note I have assumed zero conversion losses and identical self consumption)
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Old 08-09-2012, 10:16   #27
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Re: MPPT vs PWM Solar Regulators

OK! I see your point. Makes sense!

Foggy
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Old 09-09-2012, 10:22   #28
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Re: MPPT vs PWM solar regulators

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Originally Posted by belizesailor View Post
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.
+1 (I use Moringstar ProStar model)

MPPT is less an advantage as the voltage increases, ie, if you keep your batteries charge, as you should, there is much less advantage.
Tom
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Old 09-09-2012, 10:33   #29
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Mppt always provides some advantages especially where the panel optimum operating point differs greatly from the nominal battery voltage with PWM if there is a large voltage difference the panel output can be severely reduced with PWM

Dave
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Old 09-09-2012, 10:44   #30
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Re: MPPT vs PWM Solar Regulators

I had the absolute cheapest Chinese junk regulator that I could find on ebay. I replaced it with a Blue Sky MPPT and gained almost 30%. It was worth it to me, equal to a 4th panel in my case.
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