Max Overpanelling for Victron MPPT 100/50

[Rumbledethumps]

Hi All,

Quick noob question:

I'm still putting together a 12v system and have a Victron Smartsolar MPPT 100/50 and 3x Renogy 200W panels which each have a Voc of 27v and an Isc of 9.66A.

My intention was to wire the 3 panels in series (combined Voc of 81v) as this would be comfortably under the max volts of the controller and at 600W, also under the max recommended PV input watts for the controller of 700W.

However I've subsequently seen some posts regarding overpanelling which is of interest to me as I live in cloudy England....

In one post on the Victron forums a poster with 4 panels wired in parallel asked if they could add an extra panel to achieve just under the max amps input of the 100/50 charge controller. An Expert Answer suggested not only doing this but also adding a second bank of 5 panels in a 2S5P configuration, more than doubling the input watts to around 1400W, adding that as long as the input voltage was comfortably under the max of the controller the amps would be throttled, effectively maxing out the out the wattage going to the batteries.

So my first question is; is this correct and if not, why not? Why do Victron state only to use panels up to 700W total input if it's OK to significantly exceed this with certain panel configurations?

My second question is, based on the panels that I'm using, what would be the max number of panels that you would use for overpanelling and in which configuration?

Thanks.

 

[littleharbor2]

If you really want to over panel you could step up in nominal battery voltage. Sounds like you are referring to a 12 volt system. If you step up to 24 volts you can double the wattage coming into the controller without endangering the controller or associated wiring.

 

[timselectric]

You could easily double your output, with 6 panels.
3s2p = VOC 81 and ISC 19.32
This is great for cloudy days, and the CC will hold it at 50 output amps on sunny days.

 

[Phil.g00]

At the risk of sounding facetious, you can add a 1000 panels, as long as you keep them in a cupboard.
But to answer the question yes, you will probably be able to add more panels comfortably if you are not using the ideal slope, direction in cloudy England.
How do I do it?
Like adding salt to food.
I put up my best conservative guess, see what I get, then add more to taste.
If I pair an East string with a West string I can practically double the recommended number and that's in sunny South Africa.

 

[timselectric]

When over paneling, you can't go over on the voltage. But, you can go over on the amperage.
Just realize that at some point, it just becomes wasteful.

 

[Rumbledethumps]

Thanks all,

Littleharbour; I corrected the post to show that it is a 12V system. Tim; as you suggest I was thinking of a 3s2p configuration as that would keep me comfortably under on volts and well under on amps. Phil; I'm currently checking panel positions in various spots of the garden to maximise the areas that get the most sun.

One other noob question I have is; say I do go for the 3S2P configuration (ie 1200w total) and there are certain conditions that allow the panels to put out close to this level of power, what happens to the excess power when it has been fed into the charge controller? If the max that the controller can put out is say 14.4V x 50A = 720W, what happens to the excess power? Does this mean that in theory you could put 3S4P configuration together for 2400W and the controller would still handle it? If so why do Victron give the 700W input limit?

Sorry if this is basic but I want to learn the theory thoroughly before I start messing with stuff.

 

[timselectric]

Thanks all,

Littleharbour; I corrected the post to show that it is a 12V system. Tim; as you suggest I was thinking of a 3s2p configuration as that would keep me comfortably under on volts and well under on amps. Phil; I'm currently checking panel positions in various spots of the garden to maximise the areas that get the most sun.

One other noob question I have is; say I do go for the 3S2P configuration (ie 1200w total) and there are certain conditions that allow the panels to put out close to this level of power, what happens to the excess power when it has been fed into the charge controller? If the max that the controller can put out is say 14.4V x 50A = 720W, what happens to the excess power? Does this mean that in theory you could put 3S4P configuration together for 2400W and the controller would still handle it? If so why do Victron give the 700W input limit?

Sorry if this is basic but I want to learn the theory thoroughly before I start messing with stuff.

The charge controller, will only put out its maximum power. The rest is just wasted/ not utilized.

 

[Rumbledethumps]

The charge controller, will only put out its maximum power. The rest is just wasted/ not utilized.

Thanks Tim, but is that to say that I could theoretically use a 3S4P configuration (not that I would as I'm not that wasteful) and it wouldn't cause damage to the controller having 2400W of power being routed to it? Does the excess power just stay in the panels somehow?

 

[timselectric]

The available power of the solar panels, isn't feed into the charge controller. The charge controller draws from the available power. It's only capable of drawing its limit. The panels don't care if you use their power or not. They just make it available.

 

[Rumbledethumps]

The available power of the solar panels, isn't feed into the charge controller. The charge controller draws from the available power. It's only capable of drawing its limit. The panels don't care if you use their power or not. They just make it available

Perfect thanks Tim, that makes total sense; just so I'm 100% sure I won't cause any damage by adding as many panels as I wish, as long as I don't exceed the input voltage?

 

[Phil.g00]

and there are certain conditions that allow the panels to put out close to this level of power, what happens to the excess power when it has been fed into the charge controller? If the max that the controller can put out is say 14.4V x 50A = 720W, what happens to the excess power?

Think of the MPPT as being able to present to the panels as a variable resistor. If it can only deliver X amount of power it presents as a resistance that will only allow the panels to make X amount of power. The excess power just doesn't get made.
My understanding is that Victron units have reverse polarity protection. This protection, however, is only able to protect up to certain current magnitudes and if you exceed these values and then also get the polarity wrong as well the unit will be kaput.

 

[timselectric]

Think of a stream or creek. If you put a pipe into the water, you can divert water to another location. If the creek is low, you won't get as much water flow.
If the creek is high, you will get more flow. But, no matter how high the creek gets, your pipe can only flow so much water.

 

[Rumbledethumps]

Think of a stream or creek. If you put a pipe into the water, you can divert water to another location. If the creek is low, you won't get as much water flow.
If the creek is high, you will get more flow. But, no matter how high the creek gets, your pipe can only flow so much water.

The perfect analogy; thanks Tim that's really clarified things in my mind. Thanks for helping me.

 

[Rumbledethumps]

Think of the MPPT as being able to present to the panels as a variable resistor. If it can only deliver X amount of power it presents as a resistance that will only allow the panels to make X amount of power. The excess power just doesn't get made.
My understanding is that Victron units have reverse polarity protection. This protection, however, is only able to protect up to certain current magnitudes and if you exceed these values and then also get the polarity wrong as well the unit will be kaput.

Thanks Phil; this is all really helping my understanding of things. I appreciate it.