Downside to using residential solar panels (on top of a RTT)

[dwh]

I was looking into that Victron controller, but according to their website, I need the 30-amp model. Is this the case? I'm having a bit of trouble figuring out exactly how much MPPT I need for my panel. (specs below)

View attachment 548442

I use a 100|30 for my 305w panel. The first number (100) is the max input voltage. Mine has a Vmp of 36v, yours is 55v. No worries there. The second number (30) is max amps out to the battery. 305w ÷ 12v (battery at 50%) = 25a.

As John says, you could save a few bucks and get by with a 75|15, since you'll rately, if ever, see full output from the panel to the battery (mostly due to the battery). But I've got 400ah worth of battery to suck up power, so I figured I'd go with the 100|30 just to make sure I'd get all the solar can produce.

 

[dwh]

Victron Energy SmartSolar MPPT 100/20 Solar Charge Controller 12/24VDC at 20 Amps

Part Number: SCC110020060R Note: This part is being discontinue, please look at the Victron SmartSolar 100/20-48

www.solar-electric.com

There may be some old stock BlueSolar models around if someone wants to give up Bluetooth to save a little more.

You don't have to give up Bluetooth. The BlueSolar has a jack that can accept either a plugin meter or a plugin BT dongle. So it's either/or.

 

[Alloy]

I was looking into that Victron controller, but according to their website, I need the 30-amp model. Is this the case? I'm having a bit of trouble figuring out exactly how much MPPT I need for my panel. (specs below)

View attachment 548442

Below is the NEC 690.7 temper correction chart


My panels have a VOC of 69V. The system was designed to be used at -10F (1.2) so the VOC becomes 82V which requires a Victorn 100/ controller


A larger controller would allow a 2nd portable panel to be used.

For storage both panels could be stacked one on top of the other.

 

[john61ct]

Better to get the portables their own MPPT optimization.

And for shade handling, ideal is one SC per panel.

But at least, all panels per SC should match

 

[Alloy]

Better to get the portables their own MPPT optimization.

And for shade handling, ideal is one SC per panel.

But at least, all panels per SC should match

Better yes but not nessary for just 2 panel that are the same make/model.

Two panels on the roof or two panels on the ground or one up or one down any of them could be shaded. The worst performing panel can always be unplugged.

 

[dreadlocks]

I bought a 30A Smart solar for my fixed roof 325W HIT, it went over 20A and saw ~25A a few times this summer when I managed to get max output from a high sun.. but other than that, vast majority of the time was 20A or less.. If I'd of put a 20A SC on it nothing much would have been lost.. and I've got a LFP battery, with a lead battery.. you'd certainly never get everything aligned you would see that output.

 

[shade]

You don't have to give up Bluetooth. The BlueSolar has a jack that can accept either a plugin meter or a plugin BT dongle. So it's either/or.

No, but that wasn't my point. I was addressing the cost of the unit.

My point was that a BlueSolar should cost less that a SmartSolar. If someone wants to buy a BlueSolar+BT dongle, that's probably not going to save money.

 

[dreadlocks]

With the Smart Solar you can also get Bluetooth, and a Remote Display.. or Bluetooth and a Remote switch, or Bluetooth and Load IO, or Bluetooth and VE.Direct to USB.. with BlueSolar, if you want bluetooth.. you loose all the rest and end up paying the same.. the Bluetooth app is worth the money, having historical stats/graphs/etc are worth their weight in gold when boondocking.. helps you plan/predict when variables are always changing on you.

Keep an eye on Amazon for "Used" SmartSolars, I got my 100/30 for like $190 in a damaged box.. it arrived, box looked fine, nothing damaged or repackaged.. yay savings (~$40)

 

[Alloy]

I bought a 30A Smart solar for my fixed roof 325W HIT, it went over 20A and saw ~25A a few times this summer when I managed to get max output from a high sun.. but other than that, vast majority of the time was 20A or less.. If I'd of put a 20A SC on it nothing much would have been lost.. and I've got a LFP battery, with a lead battery.. you'd certainly never get everything aligned you would see that output.

When designing a system to NEC an addition 25% is added to the rated panel output for snow, high altitude and reflection.

 

[dreadlocks]

you can overload the input side quite significantly w/house panels, at least w/a SmartSolar so as long as your input voltages stay within spec, it will cap amperage on the output.. meaning input amps is always lower.

My Panel is 70v, the Victron takes 100v.. I've got enough overhead..

I'm just saying, if you have a small lead battery bank that will never take the panels full output in the first place, for example designing for poor solar conditions.. then you can save some serious money, at least w/SmartSolar's by sizing the controller more appropriately to the battery size.. which IMO is about 0.15C for FLA and 0.2C for AGM.. no point hooking a 0.3C SmartSolar up to a FLA just because the panel is that size, as it'll be a miracle if you ever see that output..

Now if your future proofing, mebe thinking of a 2nd battery in future or something.. then yeah sure, go for it.. it'll be better than selling this one used and buying the other one new later.

 

[bajarat]

Where did you score your 305w panel from?

 

[john61ct]

When designing a system to NEC an addition 25% is added to the rated panel output for snow, high altitude and reflection.

Not that I think that's relevant, I bet applies to Volts, as in input to the SC.

Those conditions rarely affect Amps output from the SC.

But yes for Victron voltage rating (75, 100, etc) definitely should be conservative and leave some headroom there if those cold/bright conditions apply.

But for the amps part of the spec (15, 20, 30) your **input** potential can go way over, and in order to get max value per SC indeed **should** be overpaneled, as that's called.

 

[monkeyodeath]

Aaaaah, I see, didn't realize that the capacity of the MPPT had more to do with my power bank's charging needs than the panel itself. That makes a lot of sense

Given that I'm starting my setup with a 50ah AGM battery, I think I'll just go with the 100/15 Victron MPPT. That way at least I won't be as nervous in cold temps and it sounds like the 100V model has a beefier heatsink which might be better for my summertime desert use.

It's what I was originally planning on getting and budgeted for. Sounds like I'm not losing much going that route.

Wouldn't surprise me if my needs/power bank end up growing over time, but I'd rather have some gas money left over to actually go enjoy my rig!

 

[monkeyodeath]

Where did you score your 305w panel from?

Picked it up from some folks in SoCal selling a bunch of panels that were removed from a building. Price was right.
(https://losangeles.craigslist.org/lgb/ele/d/santa-fe-springs-preowned-sunpower-305w/7005403529.html)

The only thing that sucks is that instead of being a normal metal frame, these panels have a plastic frame with a huge hinge-type thing on them. I've had to spend a bit of time with an angle grinder cutting it down so that it's relatively square and isn't sticking 8" above my rooftop tent.

 

[dwh]

no point hooking a 0.3C SmartSolar up to a FLA just because the panel is that size, as it'll be a miracle if you ever see that output.

But...

If there are other loads running while battery charging, you might want all the solar can produce, even if the battery alone can't suck it all up.