What size panels can my 100/20 Smart Solar handle?

[Photobug]

Based on the numbers 100v 20a, I would guess 2000 Watts of solar but know that can't be right.

Is it 20a at 12v so 240 watts of solar?

What happens if I hook up more than that? If I were to try to use it for 300 Watts of panels, assuming less than 100% efficiency of the panels, would that be safe? If you did put too much wattage through a too small of an MPPT does it blow a fuse, or just not work to the panels potential?

 

[Chris Boyd]

Look at the individual ratings of the solar panels. They will tell you max voltage the panel can produce at max wattage. That’s the limiting factor of the voltage input. Above that the unit will trip internal protections.

Max amperage is the sum of all the wattage of the panels divided by the max voltage of the panels selected. The formula P=IxE (Derived from ohms law)is the best way to do the calculations. In this case I is current (amps). Take wattage (P) divided by voltage (E) to get current.

In practice, none of the panels can do what they’re rated for unless in “perfect conditions” but max voltage should be the initial guide. As long as you don’t exceed that, you’ll likely not exceed the amperage in a single panel configuration. For multiple panels of the same type current is additive, voltage isn’t.

 

[john61ct]

First number is max total voltage **input**, and must be well respected, in fact I would use 80-85Voc as the maximum for reliability / longevity.

Second is Amps actual at **output** voltage, and you can exceed that at peak times in order to get highest **average** output, best value out of your SC dollar. aka overpanelling

Wattage depends on your system voltage, so with a 12V bank nominal 240W, could easily handle a 300W actual measured input in peak conditions - cold, bright, 90° angle to the sun at noon

might get say 10Ah on good days.

I doubt there would be any risk of harm to the SC until past 350-400W input, but the times output could potentially go past that 240W, too much energy is unutilized, so only in the arctic winter. . .

 

[john61ct]

Double the wattages above for a 24V system

 

[Chris Boyd]

Based on the numbers 100v 20a, I would guess 2000 Watts of solar but know that can't be right.

Is it 20a at 12v so 240 watts of solar?

What happens if I hook up more than that? If I were to try to use it for 300 Watts of panels, assuming less than 100% efficiency of the panels, would that be safe? If you did put too much wattage through a too small of an MPPT does it blow a fuse, or just not work to the panels potential?

Here is the data sheet for the 100/20

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20,-100-20_48V-EN.pdf

The 100v is open circuit voltage. Data sheet says 290w nominal Panel (PV) at 12v. 20a is max charge current.

Solar math can be confusing.

 

[john61ct]

Data sheet says 290w nominal Panel (PV) at 12v.

So slight overpanelling at 350W, up to 400W would be fine.

This gets you much higher **average** SC output, only rarely "wasting" some panel output in rare peak conditions, when it doesn't matter.

All solar sizing decisions should be oriented toward worst case conditions, unless it is just supplementary to convenient ICE sources available on demand.

Even then, whatever you can do to reduce ICE runtimes are very worthwhile investments.

Especially in reducing energy consumption.

 

[Photobug]

Thanks guys for the info. My Smart Solar is currently in a DIY box with a LifePo battery.

My plan was/is to carry it between boat truck and picnic table. As I consider upgrading solar and battery capacity in the truck, I was wondering if it had the capacity to handle the extra load. If I do upgrade I will likely put a separate solar charger in the truck.

While i have you here, what do you suggest for reading so I can better understand the complicated math of solar and the acronyms like Voc and ICE sources?

 

[dreadlocks]

I've got 650W of solar hooked up to my 30A SmartSolar, it just caps out at 30A and ~430W.. I need to get another Solar Charger and split the panels, just havent yet.

ICE = Internal Combustion Engine
VOC = Voltage Open Circuit (no loads)

 

[Photobug]

ICE = Internal Combustion Engine
VOC = Voltage Open Circuit (no loads)

I figured out Voc but where can I read about solar math so I can ask less questions and answer more of them?

 

[john61ct]

DC Electrics 101 learning resources

Please do not post or discuss actual topic content here. Only links or references to sites (other than "Battery University"*) and books and other forum threads containing a lot of useful accurate information on Batteries, solar, generators, wiring and circuit protection, ACRs etc, inverters...

www.cheaprvliving.com

EDIT: Wow, got moved or deleted!

Anyone want to try to find it on the Internet Archive's Wayback Machine?


Meantime try this:

One switch - house & engine? - Page 2 - Cruisers & Sailing Forums

Originally Posted by DefinitelyMe I've never understood this approach [dedicated start battery] for a liveaboard cruising yacht. I understand that it's perhaps the most common setup and that people

www.cruisersforum.com

 

[dreadlocks]

Be weary about conventional solar information you find on the internet, those of us using solar in mobile, nomadic configurations are not helped at all by articles and calculators and discussions that outright assume your putting fixed panels in on a fixed location with stable averages long term.

This is what ultimately resulted in my early failures w/solar boondocking, I greatly overestimated how much energy I could harvest and relied too heavily on the solar.. most of the insights you'll find dropped on forums like this are far more useful than some blog for an off the grid cabin that dude chopped down a bunch of trees for.. or a guy on a boat who goes days/weeks/months without seeing a tree and takes great effort to navigate around bad weather.

 

[john61ct]

Yes but for 101-level orientation, learning the jargon and math logic behind the guidelines, places specializing in off-grid mobile living are pretty good

Certainly compared to US oriented communities who think using aircon, plugging into mains 3x a week or running a genset hours every day is normal practice.

The biggest hurdle often is not the technology so much as the concept of treading lightly, sacrificing some mod cons and comfort levels

in order to live within the energy you can produce, rather than thinking you need to bring your appliances along that were designed for cheap mains AC.

 

[dreadlocks]

Oh yeah, all the nomenclature and electrical principles are the same.. its just once you get past that surface level the usefulness starts to drift as most of us run rather unconventional off the grid solar setups, where driving may be the 'generator' and perhaps you have hard personal limits on driving time that those with gensets dont.

For example, as a complete noob way back when.. it took a long time to come to terms with the fact that to operate my ~30W fridge indefinitely boondocking, I needed ~200W of solar to feel comfortable.. where some guy on a boat runs all sorts of things off 200W, the difference being how easy it is for him to get direct light on it from dawn to dusk versus how I gotta eek by with 10-20% output usually with mebe some lucky bursts of full direct sunlight.. Nobody talks about designing a solar setup that sees alot of shade, thats antithetical to solar.. you dont put panels where they get shaded duh.

 

[Photobug]

The biggest hurdle often is not the technology so much as the concept of treading lightly, sacrificing some mod cons and comfort levels. in order to live within the energy you can produce, rather than thinking you need to bring your appliances along that were designed for cheap mains AC.

That is really the gyst of my camping. I keep it really simple and conserve my resources. Ice, good food and beer are about the only luxury I have with me. Now that I think about it, I don't even use the lights in my truck or outside it often, I barely use my headlamp. Up till now I could afford to be without power but if I switch to a fridge, my need for reliable power will change.

 

[john61ct]

Yes for most "normal sized" mostly-solar rigs, even a small fridge is the vast majority consumer of Ah, and to have any chance of only-solar I would reco 200Ah and 2-300W of panels.

Northern winters in PNW type conditions more panels.

IMO ICE power should be there as an occasional backup.

Not that I want to get too holier than thou, just my background is full-timing off grid for years at a stretch since the 80's.

I accept some really need to have the mod cons or they simply can't get away from the S&B home at all.