Designing new solar system (includes diagram)

[astrocamper]

Originally Posted by astrocamper

I use a breaker disconnect between the panels and the MPPT controller and a disconnect between the MPPT controller and the battery bus bars.

I should have said I have my panels fused and have a disconnect switch between the fused panels and the MPPT controllers. I have a breaker/disconnect between the MPPT controllers and the battery bus bars.

I always shut off my solar panel feed before disconnecting the MPPT controller from the batteries.

[Rocketman3]

Originally Posted by TiffinAlleg

Thanks I should have put the combiner box on there. The way I have it drawn out (in parallel), does it make a difference if I wired the panels as shown or just connected each one directly to the combiner box?

You can create parallel solar runs by either using the MC4 connectors or a parallel combiner box. Pro’s and cons on both sides.

To find out about Victron’s Smart Network (having the BMV Pass the voltage to the MPPT do a google search on “ Victron VE.Smart Network “.

[geordi]

With a controller that can handle it - and you have to look at the ratings of your panels and controller to know for sure - It will almost always be better to wire the panels in series for higher voltage than parallel for higher amperage, because the losses in the wire to the controller will be much worse at lower voltage (and need thicker wire to handle the amperage)

[Pappion]

Coach batteries typically need higher voltage than starter batteries.
That Lithium BIM does not boost the voltage. So low charge rate and partial charge.
DC-DC Chargers can boost the voltage. They can adjust voltage for Lead Acid types or for Lithium. They have current limits, which is good for your alternator.


https://www.victronenergy.com/dc-dc-...t-non-isolated


https://www.renogy.com/12v-dc-to-dc-...SAAEgIPYfD_BwE

[hclarkx]

I agree with those recommending series panels. Lower losses and better MPPT action. And your solar controller may be more efficient at the lower current (mind is). The only reason to go parallel would be if you expect a lot of partial shade, maybe from your own A/C or similar. As others have noted, diodes in the panels pretty much obviate this issue though I think they are not quite as effective as parallel if you have shade often. If your panels are "home" style meant for micro inverters, they may not have diodes. Though I would not let that keep me from doing series unless you expect a lot of shade affecting just one or two panels.

I have no fuses in my system. Only circuit breakers. I use them as disconnects. Two for each solar controller (on input and output) and a large one on the battery (sized based on my inverter). That one completely isolates the battery and facilitates leaving the battery at 50% charge during storage for maximum LFP life. I.e., it removes all parasitic load.

[geordi]

Originally Posted by hclarkx

I have no fuses in my system. Only circuit breakers. I use them as disconnects. Two for each solar controller (on input and output) and a large one on the battery (sized based on my inverter). That one completely isolates the battery and facilitates leaving the battery at 50% charge during storage for maximum LFP life. I.e., it removes all parasitic load.

LFP? Not sure what the acronym is, but batteries going into storage should be fully charged - they WILL self-discharge (all do) at some rate, and if they are any flavor of lead acid chemistry, they will grow sulfates that will ruin the long term performance.

I left my coach in storage just a week ago, after working on it for a week (all new floor) and dry camping for the entire time. I left it with the solar controller as the only thing connected to the batteries and the panels on, so the Victron can manage the batteries and keep them from self-discharging.

[geordi]

Some thoughts about battery capacity and measurement though, this might change the OP's ideas for system design:

I was the only person living in the coach while working on it last week, and where I was parked I had full sun exposure... But the Victron was telling me that I was only making about 2.5 kWh per day. When I started the generator it would say I was in bulk charge (Magnasyne 2812 inverter) for quite a long time.

Continuous loads were the inverter feeding my fridge (kill-a-watt said it was around 60-80 watts most of the time) and my LED TV, Apple TV, laptop, and router which were on pretty much whenever I was awake. The Magnum was reporting about a continuous 18 amp (12v) load, which seems pretty close. The router was directly on the 12v.

The inverter and the Victron controller couldn't seem to agree on the voltage of my array, which is confusing to me. I need to investigate this more, and might be a reason to consider replacing the Magnum if it is threatening to overcharge my batteries... But I'm also concerned that the Victron wasn't fully charging them either. The voltages are set according to Interstate's chart for their GC2 products.

Under load (nearly constant 18 amps) the Magnum battery monitor said it was fully charged at 12.6 and like 75% at 12.0 volts... Not sure I agree with that, but that WAS under load. I will be interested to see what the Victron reports for maximum voltage when I go back and can check the history on that.

One of the upgrades I was making while doing the floor was to ensure all the cables were clean and pretty (and all are 2/0 welding wire), and set up several bus-bars with all the loads (house and chassis) and grounds on their respective bars, so there is only ONE continuous path from the batteries to the loads. I discovered a possible power loop between the chassis side that was somehow providing power to the coach, not sure which circuit is wired wrong but that's for another day. I also discovered that my GUEST brand cut-off switches had a partial-contact failure, so replaced them with one new Perko. Hopefully that will contain any spurious power losses... But these are the gremlins that need to be chased in any power system.

[rarebear.nm]

Different opinion on series vs parallel panels. I believe the proposed panels are rated at about 34V each. When using standard 12v panels you need to run in series to get voltage up for the MPPT controllers.

The solar on my 5th has three 350watt panels producing 44.4 volts as metered, rated voltage is little higher. At that level I ran them parallel to better isolate any shading problems. My panels are arranged one forward, one rear and third one midship. Very good success with this design. At 34V you somewhat in the middle ground of going series vs parallel. It can always be changed if you use heavy enough wire for the down haul in the first place.

I think I'd go with a parallel design with those panels.

I totally agree with adding a good battery monitor. Without it you never really know what's happening.

In addition to breakers either side of the controller I added fuses in the roof top combiner box sized for the wire between the combiner and the panels. I don't like having smaller wire attached to a larger wire without proper protection at the interface point.

[Pappion]

My take on series panels and shading.
Yes, the bypass diodes help, but they have a voltage drop 0.3v ~ 0.5v. So it's not as helpful for two 18V panels. It's better when there is more voltage overhead to play with.


Some people do 2 series strings in parallel. Which works well for curved roofs.

BTW: My MPPT controller data shows slightly lower efficiency for higher series voltage vs parallel higher current. So what? There is likely more loss in the wiring related to higher current.

[geordi]

An MPPT controller means that the relationship of solar voltage to battery voltage doesn't matter, it doesn't HAVE to be higher, and having it significantly higher does not help or hurt the conversion. You have W number of watts to put to the batteries, and the controller can handle A amperage and V voltage from the panels. W=VA so if either voltage or amperage rises, the other drops.

Now in the case of transmission from the panels, think about water in a pipe. Amperage is the total amount of water being delivered, voltage is the flow rate. The restrictions (losses) are pressure. You want to deliver as much as possible with as few restrictions... BUT doing it at higher amperage and lower voltage means for each unit of time, more amperage (amount) is being delivered which raises the pressure and creates heat - losses. You can counter this with a bigger pipe, but only to an extent. But then there are losses to distance at lower voltage too.

Delivering lower volumes much faster (lower amperage and higher voltage) is less amperage per unit time, which is easier - less losses.

[beach house]

Originally Posted by geordi

An MPPT controller means that the relationship of solar voltage to battery voltage doesn't matter, it doesn't HAVE to be higher, and having it significantly higher does not help or hurt the conversion. You have W number of watts to put to the batteries, and the controller can handle A amperage and V voltage from the panels. W=VA so if either voltage or amperage rises, the other drops.

Now in the case of transmission from the panels, think about water in a pipe. Amperage is the total amount of water being delivered, voltage is the flow rate. The restrictions (losses) are pressure. You want to deliver as much as possible with as few restrictions... BUT doing it at higher amperage and lower voltage means for each unit of time, more amperage (amount) is being delivered which raises the pressure and creates heat - losses. You can counter this with a bigger pipe, but only to an extent. But then there are losses to distance at lower voltage too.

Delivering lower volumes much faster (lower amperage and higher voltage) is less amperage per unit time, which is easier - less losses.

It is not quite that simple. On the lower voltage panels (12v panels), where the panel voltage output is between 18 and 21 volts (depending on brand of panel), the small gain on these lower voltage panels is usually not enough to overcome the efficiency loss in the MPPT transformer. So very often a good PWM charge controller coupled with the 12v panels will outperform the MPPT controlers, due to that efficiency loss. Most, if not all MPPT manufacturers fail to mention that, but the shunt based amp meters and amp probes don't lie. Also, most of the transformers have peak efficiency bands, where they perform more efficiently at a certain voltage, and going with a considerably higher voltage can lower the efficiency a bit, like Papion noted. It may not be a lot, but during the short, low output, winter solar days, efficiency really counts. Now of course, if one has high voltage panels, or connects the 12v panels in series, then the MPPT is the only way to go. With higher voltage, the transformer losses are overcome by much higher voltage gains, so in those cases, the relationship between the solar voltage and battery voltage would not matter, like you stated.


I fully agree on the voltage loss in smaller gauge wiring, and going with a higher voltage if one has to use smaller gauge wire. That said, when one considers the small cost increase of going with a heavier gauge wire, compared to the cost of the whole system, it is just the wrong place to cheap out and nickle and dime. Plus if the system is overbuilt, there is room for expansion without needing to run new wiring. The same could be said for up sizing the charge controllers.
You get what you pay for.

[beach house]

Originally Posted by TiffinAlleg

Hi all. We've been full timing for about 18 months and we've learned we could benefit from getting some solar for our rig. I consider myself handy and a diy'er but have had limited knowledge about electricity until I started investigating solar. Six months ago, I couldn't have told you that Amps*Volts=Watts. I've spent many hours reading and learning and looking at other people's setups. I plan to do this install myself. I already have the batteries installed and we live well on the 300 AH, but run the generator far too long when it is time to charge. I'm sure I've missed something or could be doing something better. I have attached a diagram of my proposed system (sorry for the handwriting). Any thoughts and comments would be greatly appreciated!

TiffinAlleg,
The only things I would suggest to consider on top of what other have said, don't skimp out on wiring. If you run heavier wiring, not only will it lessen the voltage line loss (increase your efficiency), but if you every want to add more solar panels to your system, you won't have to run new wiring. Same goes for the charge controller, consider going with a higher capacity controller, as with what you have mentioned, you will be close to maxed out. So, not only will the controller be working close to max all the time, but if you want to expand the system in the future, you will have to buy a higher capacity controller. You spend a little extra now, and save a lot down the road. Just something to consider...

[jcussen]

Just an example, I am running series/parallel 2600 watts at 240 volts to a 250 volt solar controller. This is less than 10 amps, through 8 awg wire, so I do have room for some expansion, and it is a fairly long run. Many grid tie installers run panels in series up to 600 volts with no problems.

[geordi]

Originally Posted by jcussen

Just an example, I am running series/parallel 2600 watts at 240 volts to a 250 volt solar controller. This is less than 10 amps, through 8 awg wire, so I do have room for some expansion, and it is a fairly long run. Many grid tie installers run panels in series up to 600 volts with no problems.

My math says you should be seeing 10.8 amps in a perfect system - if you are losing more than that .8 amps in full sun, you have losses somewhere in the system.

My controller is a Victron 150/85 (150 max incoming solar volts, 85 amp max outgoing charge @12v) and I've got 1020 watts in 3 panels at about 45 volts each in series. Even on a cloudy day, I see at least 120 volts, and I have seen the system hit a full 1000 watts in clear full sun. I'm using 10 gauge from the roof and have a TON of extra capacity in that, b/c I'm only around 7.5 amps at the theoretical max. I used the 10 gauge b/c I just happened to have it laying around - it was an old shore power cord from a travel trailer.

But I could have easily gotten away with just a 12 or even 14 gauge extension cord for this voltage. At parallel configuration, I would be losing more power and need at least 8 gauge if not bigger, b/c 24 amps is nothing to sneeze at.