Design Review

[mike616]

Hey everyone. I've been doing some research for the last few weeks planning out my first solar build. This will be going on my 42 foot fifth wheel which me and my family are living in full-time.

I work remote and we are doing a long (3 month) trip across the country this summer. My goals are to be able to run at least one AC unit for 6-8 hours per day as well as all the other normal stuff (fridge, computer, monitor, lights, fans).

My RV uses a 50A, split phase system. I'm planning to use the following components:

2x Growatt Inverter, 3000W, 24V
3x Server Rack Battery 24V 200 Ah
12x 250W Santan Solar Panels
24v to 12v converter
PV Combiner Box
Victron Orion DC - DC Charger

Attached is my wiring diagram. I'm not totally sure on the fuse or wire sizes. I'd really appreciate if anyone can look this over and let me know where I can make corrections, improvements.

Also, I may do this in phases. One or two batteries to start. I may also start with only 9 panels, so 3S2P on one side and 3S1P on the other. Would there be any issues with this?

 

[rodrick]

You might need a soft start for the ac circuit

 

[SamDeleted]

12x 250W Santan Solar Panels

That's 3kw of panels

In summer, flat on a roof , I'd guess you'd make about 12-15kwh a day

Is that enough power for your needs ?

 

[mike616]

You might need a soft start for the ac circuit

Agreed. I'm considering these: https://www.amazon.com/dp/B098NJ6W2K/ref=twister_B0BRKWMN7Y?_encoding=UTF8&th=1

 

[mike616]

That's 3kw of panels

In summer, flat on a roof , I'd guess you'd make about 12-15kwh a day

Is that enough power for your needs ?

I'm not sure actually. I'll have about 14.4 KWh of batteries if I get three batts. Six hours of one AC unit running will be around 9.4 KWh. I'm just not sure if I can get more panels on my roof. I'll be up there taking measurements tomorrow.

 

[SamDeleted]

I'm not sure actually. I'll have about 14.4 KWh of batteries if I get three batts. Six hours of one AC unit running will be around 9.4 KWh. I'm just not sure if I can get more panels on my roof. I'll be up there taking measurements tomorrow.

Looking at it you've got at least a couple more KWh in loads lights, fans, fridge ect. Maybe 12-13kwh a day usage ?


Are the batteries going to be charged from your trucks engine as well while moving ? Cause that could make up the difference


If you've not already bought the panels, you could go for higher efficiency panels that make more power per square foot , I have new 425w panels that are roughly the same size as my old 250ws

 

[mike616]

<snip>

I'll take a look at other panel options. I kinda just picked whatever the cheapest I could get on Santan solar at the moment.

At most, I can get about 4kW of PV in the Growatts (~2kW each). And yes, I'm planning to charge from the truck while driving but there will be many days where I'm stationary so I can't always count on that making up the deficit.

Have you had a chance to look at my wiring diagram? I'm curious if I've got the right idea about hooking everything up.

 

[pollenface]

I'm not sure actually. I'll have about 14.4 KWh of batteries if I get three batts. Six hours of one AC unit running will be around 9.4 KWh. I'm just not sure if I can get more panels on my roof. I'll be up there taking measurements tomorrow.

The dc-dc charger will help a lot also.

 

[mike616]

Okay I just took measurements of the roof. It looks like best case, I can get 3.5kW of panels using a hodgepodge of 400W, 325W and 100W panels. It looks like most panels are about 40 inches wide so I can't fit them between my ACs and the edge of the roof without them hanging off. So I'm squeezing a few 100W panels in there.

I used the PV calculator at https://pvwatts.nrel.gov. It says I can expect about 9 kWh per day in winter and 20 kWh per day in summer. Does that sound reasonable (I used my zip code in southern California).

 

[SamDeleted]

Okay I just took measurements of the roof. It looks like best case, I can get 3.5kW of panels using a hodgepodge of 400W, 325W and 100W panels. It looks like most panels are about 40 inches wide so I can't fit them between my ACs and the edge of the roof without them hanging off. So I'm squeezing a few 100W panels in there.

I used the PV calculator at https://pvwatts.nrel.gov. It says I can expect about 9 kWh per day in winter and 20 kWh per day in summer. Does that sound reasonable (I used my zip code in southern California).

You can mix and match panels into one charge controller if you do it carefully, have a look at this:

Mixing solar panels – Dos and Don’ts • SOLAR POWER SECRETS

Mixing Solar Panels: Discover Now Dos and Dont's of Mixing the Same Types or Different Types of Solar Panels. Act Now to Save Your Money!

solarpanelsvenue.com

And try this calculator:

Solar Panel Series & Parallel Calculator - Footprint Hero

Use our solar panel series and parallel calculator to easily find the wiring configuration that maximizes the power output of your solar panels.

footprinthero.com

You're other option is separate charge controllers for each type of panel, or a combination of both ideas

 

[mike616]

Thanks for these resources. Believe it or not, I took a few circuits classes in college and should have known this stuff.

There will be two MPPTs (one on each Growatt) which have a max PV input voltage of 150V.

The panels I'm considering have these stats:

Qty​	Power (W)​	V_oc (V)​	V_mp (V)​	C_mp (A)​
4	400	40.1	40.16	9.96
4	325	69.6	57.6	5.64
6	100	21.3	18.15	5.51

The 325W and the 100W panels have similar operating currents so I shouldn't see too much power loss if I string those in series. It's the 400W panels that throw things off. I can do a 2S2P setup with those and get 1600W out of them. But I can't see a way to arrange the remainder of the panels (4x 315W and 6x 100W) without going over the 150V max input of the MPPTs.

If there's another all-in-one inverter with a higher PV input voltage, that might work. Or I drop the 100W panels and settle with a 2900W system.

 

[SamDeleted]

Thanks for these resources. Believe it or not, I took a few circuits classes in college and should have known this stuff.

There will be two MPPTs (one on each Growatt) which have a max PV input voltage of 150V.

The panels I'm considering have these stats:

Qty​	Power (W)​	V_oc	V_mp (V)​	C_mp (A)​
4	400	40.1	40.16	9.96
4	325	69.6	57.6	5.64
6	100	21.3	18.15	5.51

The 325W and the 100W panels have similar operating currents so I shouldn't see too much power loss if I string those in series. It's the 400W panels that throw things off. I can do a 2S2P setup with those and get 1600W out of them. But I can't see a way to arrange the remainder of the panels (4x 315W and 6x 100W) without going over the 150V max input of the MPPTs.

If there's another all-in-one inverter with a higher PV input voltage, that might work. Or I drop the 100W panels and settle with a 2900W system.

You can get all in ones upto 450v/550v PV input, I haven't got any recommendations that side of the pond others might help

4s on the 100w matches voltage almost perfect with 2s2p on the 400ws

I think you don't have to match the amps up, just the volts , different amps levels should just combine smoothly

 

[SamDeleted]

Those 325ws are very high voltage @60v , it's going to make them difficult to match with anything, also max string of 1 with your growwatt ... So all would have to be in parallel

 

[mike616]

One of those links you sent says that all the panels in a string will operate at the current of the lowest current panel. So if I put the 400W panel which maxes 10A and the 325W panel which maxes 5.6A in series, then the 400W panel will only operate at 5.6A or 226W max.

The voltages don't have to match up in series right? I just need them to sum up to less than the 150V max of the MPPTs. They should have similar operating currents though to minimize loss.

My other thought is to use a second PV combiner box to arrange the 325W and 100W panels in a second series/parallel array:


325W -- 100W -- 100W -- 100W

325W -- 100W -- 100W -- 100W


And the 400W panels would just be 2S2P:

400W -- 400W

400W -- 400W

 

[SamDeleted]

One of those links you sent says that all the panels in a string will operate at the current of the lowest current panel. So if I put the 400W panel which maxes 10A and the 325W panel which maxes 5.6A in series, then the 400W panel will only operate at 5.6A or 226W max.

The voltages don't have to match up in series right? I just need them to sum up to less than the 150V max of the MPPTs. They should have similar operating currents though to minimize loss.

It's getting complicated and I don't want to guide you wrong here, don't take what I say as gospel. So others pls feel free to correct me if I am wrong.

Each string wants to be made up of one single type of panel, no mixing in strings (unless panels are very closely matched spec)


You can have different amp voltage panels (or strings of panels) in parallel if similar voltage amps....


Eg:

String one:
100w 4 series = 85v~ @ 5.5amps (400w total)


String two:
400w 2s2p = 80v @ 20amps (1600w total)


Paralleled together would output:
80v @ 25.5amps (2000w total)


rough maths ...

 

[mike616]

Yeah it's getting complicated but I think I'm following the right methodology:

One string combined 325W and 100W panels which both have the same operating current.

Another string of 400W panels which are all the same current and voltage.


In series, all panels in the string have the same current.

In parallel, each string has the same voltage.

The other option is to switch to a 48V system and just to go with a single inverter capable of split phase output like the MPP LVX6048WP.

 

[SamDeleted]

One string combined 325W and 100W panels which both have the same operating current.

Seems viable