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Old 14-08-2017, 19:18   #361
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Re: Challenges with Solar on boats

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Originally Posted by foggysail View Post
I installed a Victron 150/70 controller before I upgaded my panels. Later I realized I should have stuck with my original plan to purchase the 150/85. I thought I would never ever see a charge current over 70 amperes. I was incorrect.

My new panels are 4 each 295 watt 32Vmp mono panels for a total of 1180 potential watts. Now I am controller limited to about 980 watt using a battery voltage of 14 for calculation.

I have seen 69 amperes! OK, so I suffer from over paneling, should have purchased the panels prior to the controller. The world has not come to an end however. I may not get peak performance but I do get better performance during cloudy days. For batteries I have 860AH bank of golf carts. There are other considerations helping to limit their output such a sun/panel angle, cleanliness for example.

After the season ends, I plan selling this controller, maybe in the $300-325 range and correct my mistake with a 150/85 next season.

Maybe upgrading my controller needs more thought. More on this later
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Old 15-08-2017, 09:59   #362
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Re: Challenges with Solar on boats

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Originally Posted by arsenelupiga View Post
I like your idea of oversized panels. thinking to replace 2 x 180 w with 2x 360 w - sunpower. Will be straight replacement and size will fit nicely.

Already have victron 100/15 x 2.

Do you have any issues with your oversized panels setup ?

On sunny day have no issue with current setup but new setup would provide double power on substandard days.
Just to make sure we are on the same page. I have 2x 280W (no 360w, that was just a thought experiment) and 2x 75/15

360w panels work as long as the panel's maximum voltage and current is below the controller's limits (100v / 20A according to the english manual and 100v / 15A according to the German manual, maybe ask Victron which one is correct).
You will have some oversized panels then, which will give you more current on cloudy days and outside noontime.

To unleash the potential peak power you need bigger controllers.
A bigger charger will make a difference in peak power, but how often do you need this peak power? Peak power will mostly happen on sunny days when there is plenty of non-peak power available to fully charge the batteries anyway. Using the full peak power won't help on cloudy days, using higher average power does help.


Why not just give it a try and see if it works for you. You can still upgrade one controller and see how much difference this makes.
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Old 15-08-2017, 14:36   #363
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Re: Challenges with Solar on boats

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Originally Posted by rabbi View Post
Just to make sure we are on the same page. I have 2x 280W (no 360w, that was just a thought experiment) and 2x 75/15

360w panels work as long as the panel's maximum voltage and current is below the controller's limits (100v / 20A according to the english manual and 100v / 15A according to the German manual, maybe ask Victron which one is correct).
You will have some oversized panels then, which will give you more current on cloudy days and outside noontime.

To unleash the potential peak power you need bigger controllers.
A bigger charger will make a difference in peak power, but how often do you need this peak power? Peak power will mostly happen on sunny days when there is plenty of non-peak power available to fully charge the batteries anyway. Using the full peak power won't help on cloudy days, using higher average power does help.


Why not just give it a try and see if it works for you. You can still upgrade one controller and see how much difference this makes.
Yes, that is my thinking. However what I am really after is best - low light per square area - panel performance. That is not necessary equal to best - optimum conditions - panel performance which seem to be sunpower 360.
Sunpower does not have many bypass diodes so I expect low light performance may not be up there.

Will dig on actual low light performance of panels see what do I get.
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Old 15-08-2017, 15:49   #364
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Re: Challenges with Solar on boats

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Originally Posted by arsenelupiga View Post
Yes, that is my thinking. However what I am really after is best - low light per square area - panel performance. That is not necessary equal to best - optimum conditions - panel performance which seem to be sunpower 360.
Sunpower does not have many bypass diodes so I expect low light performance may not be up there.

Will dig on actual low light performance of panels see what do I get.
Arsenelupiga,

Worth talking to someone who knows Sunpower panels and installs them.
Jim Gray from Odyessy Marine Electronics located at the Boatworks at Coomera has and is currently doing 3 jobs the same as yours using 3 and 4 360w Sunpower panels.

I believe he will recommend you change your MMPT controller.

Outback Marine has a download link to a Vitron Solar calculator.

Power Generation Solar Controllers Victron Blue Solar MPPT Controller

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Old 15-08-2017, 16:35   #365
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Re: Challenges with Solar on boats

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Arsenelupiga,

Worth talking to someone who knows Sunpower panels and installs them.
Jim Gray from Odyessy Marine Electronics located at the Boatworks at Coomera has and is currently doing 3 jobs the same as yours using 3 and 4 360w Sunpower panels.

I believe he will recommend you change your MMPT controller.

Outback Marine has a download link to a Vitron Solar calculator.

Power Generation Solar Controllers Victron Blue Solar MPPT Controller

Thanks for details. I want to convince myself first that low light performance will actually be improved enough to warrant change. My current victron solar panels seem to do quite good job in overcast. But everyone claims great low light performance.


Looking at alternatives, kaneka 3 x 120V hybrid EU panels, fit nicely on my davits, would produce same power in ideal conditions as currently, but shading becomes non-issue and also overcast days performance improves considerably.

Cant find any hard numbers on internet though....
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Old 15-08-2017, 22:59   #366
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Re: Challenges with Solar on boats

There seems to an assumption in recent solar threads that undersizing the controller will only result in a loss of power when the batteries are going to be fully charged anyway.

This assumption is not correct.

The maximium current occurs when the battery voltage is low. Peak power from the panels tends to occur in intermittent cloudy weather when the panels cool down.

Having an undersized controller does not have have an effect on the output on days where there is uniform heavy cloud all day, but it does have a significant impact on days where there intermittent cloud and sun. This applies to days where there may be some sun for portions of the day, but especially on days where the sun periodically pokes out between clouds. In the latter case the solar output is likely to be the highest recorded, especially in terms of amps into the battery. In a good installation it is not unusual to record an output equal too or even exceeding the STC rating of the panel, providing the controller can handle this power.
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Old 15-08-2017, 23:03   #367
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Re: Challenges with Solar on boats

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Originally Posted by arsenelupiga View Post
Sunpower does not have many bypass diodes so I expect low light performance may not be up there.
Bypass diodes have an influence on a panel's performance when partially shaded. It is not related to low light performance.

Sunpower claim the best low light performance in the business. The type of cell they use is slightly different and I think there is some justification for their claims, although the effect is only slight.
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Old 16-08-2017, 12:26   #368
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Re: Challenges with Solar on boats

Quote:
Originally Posted by arsenelupiga View Post
Thanks for details. I want to convince myself first that low light performance will actually be improved enough to warrant change. My current victron solar panels seem to do quite good job in overcast. But everyone claims great low light performance.


Looking at alternatives, kaneka 3 x 120V hybrid EU panels, fit nicely on my davits, would produce same power in ideal conditions as currently, but shading becomes non-issue and also overcast days performance improves considerably.

Cant find any hard numbers on internet though....
Oversizing panels makes most sense if the panels are reasonably cheap in my view. The special brand you mentioned doesn't sound cheap.
But if you oversize by doubling your maximum power per panel, you should expect double the output during morning hours / overcast days (up to maximum Amps per MPPT controller, of course)


If you want to oversize, here is an official Victron FAQ which supports the point that you just need to take care of Isc and Voc (and can ignore maximum power).

https://www.victronenergy.com/live/drafts:mppt_faq

Quote:
Q4: I want to over dimension the PV array, how can I calculate the maximum?

Over-dimensioning a PV array is installing more Watt-peak than the maximum charge power of the chosen MPPT charge controller. A common reason to over dimension is to cater for winter time.
How to determine how far you can over dimension the PV array?
There are two limits, when determining the maximum array size that can be connected to an MPPT:
The Maximum PV open circuit voltage (Voc at STC)
The Maximum PV short circuit current (Isc at STC)
Both values are specified in the datasheets of all our MPPT Solar Chargers. Those two ratings of the PV array must not exceed these MPPT limits.
Note that these two maximum ratings must not be multiplied to determine the maximum installable Watt-peak. Instead, each of them needs to checked by itself:

Determining the maximum PV open circuit voltage
First look on the datasheets of the solar panels to see what their maximum open circuit voltage is. Then multiply that by the number of panels that are in series in the array. The result of the multiplication must not be higher than the Maximum PV open circuit voltage as listed on the MPPT Datasheet. Make sure to not forget taking the coldest expected temperature into account. Because the colder it is, the higher the open circuit voltage on a PV array will be.

Determining the maximum PV short circuit current
Get the maximum PV short circuit current from the PV Panel datasheet. Multiply by the number of panels in parallel in the array. Having more panels in series does not change the number.
The result of the calculation may not exceed the Max PV short circuit current as specified on the MPPT Datasheet.
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