Solar power and MPPT controllers

[Georgio]

A question to the solar experts…

I have a 25W solar panel that when I fitted last year worked well with no charge controller and helped keep the batts topped up with on a 600+ mile passage. In preparation for a longer trips this year (2 x 10 days or so) I have bought a further 20W panel that will be fitted at the stern and was planning to wire this up in much the same way as the existing panel as I can easily switch it off if the batts are showing full on the monitor (unlikely).

I’m wondering if I should also fit a MPPT controller as the theory is that it alters (lowers) the output voltage of the panel and converts this into additional amps (apologies if that is over simplified) and would like to hear real-life experiences of how this effects the charging ability of solar panels. MPPT controllers are not cheap so are they worth it?

Thoughts appreciated...

 

[obarut]

I bought a charge controller last month. In its prospectus it says that charge controller is not necessary if the current flows through it is less than %1 of the current capacity of the battery which is to be charged.

 

[FullCircle]

Well, once its fitted and forgotten, the price will fade from your mind.
I like the principle, as it is much more efficient.
I have the Marlec one, which is fitted with both my solar and wind generator inputs.
Easy to fit, good display.

 

[VicS]

Well, once its fitted and forgotten, the price will fade from your mind.
I like the principle, as it is much more efficient.
I have the Marlec one, which is fitted with both my solar and wind generator inputs.
Easy to fit, good display.

The Marlec regulators for wind generators are just PWM regulators aren't they?

Isn't MPPT only applicable to solar panel controllers?

Actually I dont see MPPT mentioned in connection with any of the solar regulators on Marlec's website.

Which one do you have?

 

[FullCircle]

Actually, now I look, it does not specifically mention MPPT.

I have the HRDi unit, with a remote repeater display unit.

http://www.marlec.co.uk/products/windchargers/windcharger-controllers/hrdi/

 

[noelex]

I think the likely gains on a boat system from MPPT are usually greatly exaggerated. Some real world data would be helpful and should not be difficult to collect. Hopefull someone will oblige.
A single MPPT regulator will work best when all panels have are identical and see the same condition. With one old panel and a new one at of these conditions are being met. Good MPPT are expensive and cheap ones not worth bothering with. The extra cost per gained watt (assuming there is any gain in your case)is going to be very expensive given your small panel size.
I would get at least a simple regulator however. You can leave the boat unattended when regulation is needed. If it’s a very cheap regulator you will get better performance by using a bypass switch when you can carefully monitor voltage, but with multistage PWM regulator (still cheap) the bypass switch is not worthwhile.

 

[charles_reed]

A question to the solar experts…

I have a 25W solar panel that when I fitted last year worked well with no charge controller and helped keep the batts topped up with on a 600+ mile passage. In preparation for a longer trips this year (2 x 10 days or so) I have bought a further 20W panel that will be fitted at the stern and was planning to wire this up in much the same way as the existing panel as I can easily switch it off if the batts are showing full on the monitor (unlikely).

I’m wondering if I should also fit a MPPT controller as the theory is that it alters (lowers) the output voltage of the panel and converts this into additional amps (apologies if that is over simplified) and would like to hear real-life experiences of how this effects the charging ability of solar panels. MPPT controllers are not cheap so are they worth it?

Thoughts appreciated...

With the input you refer to, 35 watts, I doubt any MPPT controller will be justified and it's doubtful you even need a cut-out regulator.

I've a BZ500 MPPT controller fed by a nominal 428 watts of PV panels pair-wired in in series to put out a nominal 24 volts to feed about 400 ah of 12v batteries. It certainly has improved the input from the panels by 10-12%.
It would have been theoretically more efficient, but impractical, to make the input voltage a theoretical 48 volts.

 

[noelex]

With the input you refer to, 35 watts, I doubt any MPPT controller will be justified and it's doubtful you even need a cut-out regulator.

I've a BZ500 MPPT controller fed by a nominal 428 watts of PV panels pair-wired in in series to put out a nominal 24 volts to feed about 400 ah of 12v batteries. It certainly has improved the input from the panels by 10-12%.
It would have been theoretically more efficient, but impractical, to make the input voltage a theoretical 48 volts.

Thanks for the input Charles. There is a shortage of any real world data on boats so your figures are useful. There has been some criticism of MPPT regulators exaggerating the measurement of the Amphours in data.
If you could elaborate on how you arrived at the 10-15% it would be helpful.

BTW I think you would find the output would decrease if you went up to 48V.

 

[Georgio]

Thanks for all the posts, most interesting. Given a total wattage of circa 45 watts, the cost of a "good" MPPT controller and the likely increase in charging efficiency 10-15% I will stick with having them wired direct without a controller.

 

[VicS]

I will stick with having them wired direct without a controller.

I don't think you have told us the battery capacity.

The rule of thumb is that up to 10watts of solar power per 100Ah of capacity does not require a regulator. Above that it does.
It is generally advised that panels in excess of 10 watts should have a regulator anyway.
That's a regulator to control max charging not necessarily an MPPT controller.

There are simple controllers about ( Maplin ) not as fancy as PWM which simply disconnect/reconnect the solar panel as required. Also some slightly cleverer ones which can also disconnect/reconnect a load when the battery voltage falls.

http://www.maplin.co.uk/power/alternative-energy/charge-regulators

 

[Georgio]

Quite right Vic, the batt bank size does have an impact on this, it is 2 x 110 A/hr.

FYI, I will not be leaving the boat with the pannels charging. They are only used while onboard, particularly on longer trips so I don't have to run the engine. When cruising locally the engine (with smart regulator) is more than man-enough to keep the boat powered.

 

[Roberto]

mppt feedback

I have an mppt controller fitted to 2x90W solar panels.

There is a bit of increase in output, we had a boat with similar panels but with PWM controller and tried to check the difference: in hazy/cloudy days the MPPT gives a lot more, in sunshine days they are more or less equivalent.
Basically, MPPT seem to work best when solar panels are supposed to work worse.

To be sure about what we are talking about, percentages of "10% better" mean that instead of 9A you roughly get 10A, and this for the few hours when the panels output their best. That may mean a few Ah a day of difference...

A lot, lot more important IMHO is the possibility of varying the inclination of panels: during the first few hours in the morning, if I adjust my panel inclination I can easily get "300%more". Again, to be sure what we are talking about, this means that I can get 6A instead of 2 for a few hours :smile:

Anyway, I would personally suggest fitting an MPPT controller when there is no physical place for other panels

 

[noelex]

I have an mppt controller fitted to 2x90W solar panels.

There is a bit of increase in output, we had a boat with similar panels but with PWM controller and tried to check the difference: in hazy/cloudy days the MPPT gives a lot more, in sunshine days they are more or less equivalent.
Basically, MPPT seem to work best when solar panels are supposed to work worse.

To be sure about what we are talking about, percentages of "10% better" mean that instead of 9A you roughly get 10A, and this for the few hours when the panels output their best. That may mean a few Ah a day of difference...

A lot, lot more important IMHO is the possibility of varying the inclination of panels: during the first few hours in the morning, if I adjust my panel inclination I can easily get "300%more". Again, to be sure what we are talking about, this means that I can get 6A instead of 2 for a few hours :smile:

Anyway, I would personally suggest fitting an MPPT controller when there is no physical place for other panels

Thanks for the feedback, but the difference with or without MPPT is small and is always going to lost in the more significant differences between panels, installation, wiring etc so we really need measurements taken on the same boat.
For those with a MPPT controller its worth thinking how you would bypass the regulator if it fails. (there seem to be a lot of regulator failures on boats) Why not give the bypass system a practical try and tell us the results.

 

[steveallan]

Jacar MPPT Kit

from the same company that sells the ultrasound kit

https://secure.vividcluster.crox.ne...View.asp?ID=KC5500&keywords=mppt&form=KEYWORD

Silicon Chip article here
http://siliconchip.com.au/cms/A_112335/article.html

You will need to pay if you want to view the full article.