Questions about setting up my solar panel array

[yambine]

I will have 4 Battleborns for my 24v battery bank.
Will 8pcs of 100w hqst be enough? What's the best way to arrange it with 10AWG cables?
If I need to order 4 more to make it 12pcs, will 10AWG cables still be good enough and how to best arrange it?
thanks in advance guys!

 

[rmaddy]

4 12.8V 100Ah batteries is 5120Wh. How much of that do you plan to use each day? Let's assume you use 80%. That's 4096Wh. If we assume 5 solar hours each day then you need 820W of solar to fully recharge the batteries in a day. A 1000W of panels might get you that depending on how they are mounted (flat on an RV roof or mounted at the ideal angle for the given time of year).

More solar is almost always better. 1200W will help in the winter and on cloudy days.

1200W at 24V would be 50A of charging power. 800W would only be 33A.

The arrangement depends on the charge controller you have and how much shading you might need to deal with. More in series is slightly better performance if there are no shading issues. It also allows for smaller wires due to lower amps.

You can't decide on wire size until you finalize the panel choice and their arrangement. Then you will know how many amps you have to deal with and whether you need a combiner box and fuses.

Also consider large panels. Why 100W panels? Why not 200W, 300W, or even 400W panels? How and where will these panels be used/mounted?

 

[MisterSandals]

Will 8pcs of 100w hqst be enough?

Why 100W panels? Why not 200W, 300W, or even 400W panels?

Mounting a bunch of panels is a pain in the butt and the hardware and wiring can get spendy. Mounting 3-4 bigger panels is a LOT easier than 8 little panels.
Look for big cheap panels on craigslist or local marketplace websites. If you post your location (city or zip), maybe someone here can point you to a good source for panels in your area.

 

[schmism]

10AWG cables still be good enough and how to best arrange it?

10awg is rated for ~30amps. so for 800-1000w PV array your going to need a string of panels pushing 26-33v

 

[yambine]

4 12.8V 100Ah batteries is 5120Wh. How much of that do you plan to use each day? Let's assume you use 80%. That's 4096Wh. If we assume 5 solar hours each day then you need 820W of solar to fully recharge the batteries in a day. A 1000W of panels might get you that depending on how they are mounted (flat on an RV roof or mounted at the ideal angle for the given time of year).

More solar is almost always better. 1200W will help in the winter and on cloudy days.

1200W at 24V would be 50A of charging power. 800W would only be 33A.

The arrangement depends on the charge controller you have and how much shading you might need to deal with. More in series is slightly better performance if there are no shading issues. It also allows for smaller wires due to lower amps.

You can't decide on wire size until you finalize the panel choice and their arrangement. Then you will know how many amps you have to deal with and whether you need a combiner box and fuses.

Also consider large panels. Why 100W panels? Why not 200W, 300W, or even 400W panels? How and where will these panels be used/mounted?

Thanks for the advise again rmaddy!

I do understand where you are coming from. Here's my current situation. I'm living in LA but I'm planning to go off-grid or semi off-grid in 1 or 2 years after I move out of here. Right now I'm building a solar system at my house to gain knowledge and experience so I'm building a 24v four battery system. Below are some aspects of my planning process, feel free to correct me if you think otherwise.

1. I'm using 100w panels because they are easier to move. For example like I can temporally move them to a storage or another city with my SUV. I don't mind using bigger panels in the future but only until I have situated.

2. Currently I'm not considering A/C as a component of my current system as it takes up too much power and the area of LA I'm living in does not require AC most of the time. As far as I know a 5000 BTU A/C will use up 2000wh or more within 4 hours. I will need more than 4 batteries to accommodate that. If I have to move to an area that requires AC my thinking is I will have to build another 24v four battery system later on just to run the AC. I prefer two 24v than one 48v system due to it's flexibility and safety features. Turning a 24v into a 48v system will also mean I have to replace a lot of the components and wirings which will not be economical.

3. Without a A/C system, a 5120Wh system with 1 small fridge, 1 freezer chest and other basic electronic devices my estimate is around 2500 to 3000wh daily consumption which should be enough. What do you think?

4. 8 100w hqst panels in sunny LA I know is still cutting it close. I will test it but likely need 4 more to be safe. They will now be mounted on top of the house with no shades. I'm assuming 10AWG will be enough for 8 panels and thicker for 12 panels but I could be wrong. In that case I may just have to go with a thicker wire regardless to accommodate 12 panels. Do you know a legit website to get thicker solar-proof wires because I need a lot to pull it from the roof to the house because most them I can find on Amazon are 10AWG? Also I currently have a 40amp solar controller, will one be enough for 8 panels or I need to get one more? And how about 12 panels?

5. Can you advise on how to most efficiently arrange a 8 panel and 12 panel array?

6. Basically I'm trying to plan this out as economical as possible as my current solar budge is limited. So I'm trying to avoid replacing or throwing away any components or wires if I decided to expand my system in the future as I gain more budget.

Thanks!!

 

[rmaddy]

Without a A/C system, a 5120Wh system with 1 small fridge, 1 freezer chest and other basic electronic devices my estimate is around 2500 to 3000wh daily consumption which should be enough. What do you think?

Your battery could power your stuff for a day and a half before being depleted. That's enough if you can guarantee you will get enough solar in that same amount of time to fully recharge the batteries. That's really tough this time of year with the low sun angle. You might want a backup charging plan just in case your initial setup falls a little short some days. You can always add more battery and/or more solar if you find the need.

I'm assuming 10AWG will be enough for 8 panels and thicker for 12 panels but I could be wrong.

Wire gauge is based on the current. We don't know the current because you haven't posted the full specs of your panels nor do we yet know how the panels will be arranged. Let's say you start with 8 at 4S2P and then later go with 12 at 4S3P. The latter will have 50% more current. 10AWG may or may not be enough but we won't know until the numbers are available.

I currently have a 40amp solar controller, will one be enough for 8 panels or I need to get one more? And how about 12 panels?

You have a 24V system. 8 panels is 800W. 800W / 24V = 33A. 12 panels is 1200W. 1200W / 24V = 50A. Your SCC is plenty for 8 panels but is a bit small for 12 panels. 40A at about 26V is 1040W. Since that isn't that much below the possible 1200W of 12 panels, it will work but you might lose some potential on some days. If you find that the one 40A SCC is proving to waste too much power when you have 12 panels you could add a second smaller SCC. Run 8 on the 40A and run 4 panels on the 2nd smaller SCC. But the gain may be minimal and not worth it.

Can you advise on how to most efficiently arrange a 8 panel and 12 panel array?

Again, this depends on the full specs of the panels and of the SCC. Post those details. But most likely you will end up with 4S2P and 4S3P. Do note that when you have 3P or more you need a combiner box and each string needs to be fused.

Basically I'm trying to plan this out as economical as possible as my current solar budge is limited. So I'm trying to avoid replacing or throwing away any components or wires if I decided to expand my system in the future as I gain more budget.

Good plan. I think if you assume 12 panels and wire for that now, you can start with 8 and then it will be an easy addition for the 4 extra panels later without having to replace anything.

 

[yambine]

Wire gauge is based on the current. We don't know the current because you haven't posted the full specs of your panels nor do we yet know how the panels will be arranged. Let's say you start with 8 at 4S2P and then later go with 12 at 4S3P. The latter will have 50% more current. 10AWG may or may not be enough but we won't know until the numbers are available.

So let's assume my final numbers will be 12 panels and below are the hqst panel stats. What's the gauge I should go by?

• Max Power at STC (Pmax): 100W
• Max System Voltage: 600VDC (UL)
• Optimum Operating Voltage (Vmp): 18.0 V
• Open-Circuit Voltage (Voc): 21.6V
• Optimum Operating Current (Imp): 5.56 A
• Short-Circuit Current (Isc): 6.5A
• Temp Coefficient of Pmax: -0.23%/0C
• Temp Coefficient of Voc: -0.33%/0C
• Temp Coefficient of Isc: 0.05%/0C
• Dimensions: 32.5 x 26.4 x 1.18 inches
• Weight: 12.1lbs
  

You have a 24V system. 8 panels is 800W. 800W / 24V = 33A. 12 panels is 1200W. 1200W / 24V = 50A. Your SCC is plenty for 8 panels but is a bit small for 12 panels. 40A at about 26V is 1040W. Since that isn't that much below the possible 1200W of 12 panels, it will work but you might lose some potential on some days. If you find that the one 40A SCC is proving to waste too much power when you have 12 panels you could add a second smaller SCC. Run 8 on the 40A and run 4 panels on the 2nd smaller SCC. But the gain may be minimal and not worth it.

I may just go with another 40amp SCC. I know it's overkill but will there be any serious consequence? Because my thinking is that I could always use the 2nd SCC for my second 24v system if needed and stay with two 8 panel solar arrays for two 24v system for whatever reason.

 

[rmaddy]

You still need to post details about your charge controller. What make and model? What is the max input voltage?

 

[yambine]

You still need to post details about your charge controller. What make and model? What is the max input voltage?

https://www.amazon.com/gp/product/B07429RK43/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1

• Negative Grounding MPPT Solar Charge Controller Tracer4215BN, The Advanced MPPT Control Algorithm makes this 40 Amp MPPT Controller Tracking Efficiency higher than 99.5%
• 150V Max PV Input Allow this Charge Controller Handles More Solar Panels Wiring in Series to minimize PV current, 5 x 12V Solar Panel Connecting in Series will be applicable
• Work with all Lead Acid Batteries, Sealed AGM GEL and Flooded Battery, User mode allows buyer setting their own charging parameters.
• RS-485 communication bus interface and Standard MODBUS interface available to meet various communication requirements, Temperature Sensor and PC monitoring Cable Attached
• This 40 amp MPPT Solar Panel Charger works with 600W Solar Panel on 12V Battery System and 1200W on 24V Battery. Max Solar Panel 1560W, multiple load mode allow you set the load on/off in different situation. A Solid State Relay is recommended if you are using a Power Inverter

 

[rmaddy]

With a max input voltage of 150V and a panel Voc of 21.6V you could put up to 6 in series as long as you never expose the panels to a temperature below 3ºF (-16ºC).

Since you now have 8 panels and may later have 12, putting the panels in series strings of 4 makes for an easier layout. And you will never have to worry about the temperature.

So my original idea of putting your 8 panels in 4S2P and then later putting 12 in 4S3P still makes sense with that controller. At 3P the panels could be about 20A. You will need a combiner box and fuses when you have 12 panels. You can use a simple Y connector when you have just 8 panels. 10AWG will work with the 12 panels. Though the length of wire will affect the amount of voltage loss. If the wire length from the combiner box to the charge controller is more than about 60 feet then you should probably go with 8AWG wire for that section. That will keep the voltage loss low.

 

[yambine]

With a max input voltage of 150V and a panel Voc of 21.6V you could put up to 6 in series as long as you never expose the panels to a temperature below 3ºF (-16ºC).

Since you now have 8 panels and may later have 12, putting the panels in series strings of 4 makes for an easier layout. And you will never have to worry about the temperature.

So my original idea of putting your 8 panels in 4S2P and then later putting 12 in 4S3P still makes sense with that controller. At 3P the panels could be about 20A. You will need a combiner box and fuses when you have 12 panels. You can use a simple Y connector when you have just 8 panels. 10AWG will work with the 12 panels. Though the length of wire will affect the amount of voltage loss. If the wire length from the combiner box to the charge controller is more than about 60 feet then you should probably go with 8AWG wire for that section. That will keep the voltage loss low.

Solar Y Branch Connectors MMF+FFM Pair

Solar Y Branch Connectors are used for parallel wiring solar panels (PV modules).

www.renogy.com

is this what you meant by y connectors? Also just want to make sure for 8 panel 4s2p configuration I don't need to have combiner box or fuses, correct?

Since I may eventually go with the 12 panel configuration, can I mind as well get this 3 to 1 connectors showing below instead? Do I need to cover the third connector for the time being if I'm not using it for safety reasons?

3 to 1 Solar Branch Connectors MMMF+FFFM Pair

Renogy 3 to 1 Solar Branch Connectors are used for parallel connection between solar panels. This Connectors come with one male (MMF) and one female (FFM) connection. Renogy Store sells the best solar accessories perfect for your solar application!

www.renogy.com

And for 12 panels, can I later reconfigure it to 6s2p instead? If yes do I still need combiner box and fuses?

Thanks!

 

[rmaddy]

Yes, those are the Y connectors. If you setup 8 panels at 4S2P and then later you setup 12 panels in 6S2P then you never need a combiner or fuses and you can reuse the same pair of Y connectors. Your amps won't change adding the 4 extra panels so that would allow for 10AWG for both setups. But make sure you temperatures never get below 5ºF or the 6 panels in series will be too much for the charge controller.

 

[yambine]

Yes, those are the Y connectors. If you setup 8 panels at 4S2P and then later you setup 12 panels in 6S2P then you never need a combiner or fuses and you can reuse the same pair of Y connectors. Your amps won't change adding the 4 extra panels so that would allow for 10AWG for both setups. But make sure you temperatures never get below 5ºF or the 6 panels in series will be too much for the charge controller.

thanks a bunch!

 

[yambine]

Yes, those are the Y connectors. If you setup 8 panels at 4S2P and then later you setup 12 panels in 6S2P then you never need a combiner or fuses and you can reuse the same pair of Y connectors. Your amps won't change adding the 4 extra panels so that would allow for 10AWG for both setups. But make sure you temperatures never get below 5ºF or the 6 panels in series will be too much for the charge controller.

Hi rmaddy,
Sorry to bother you again. I got a couple more questions so I can understand the fundamentals correctly if you don't mind.

1. For 12 panels in 6S2P, my calculation is for Vol it's 129.6 (21.6voc x 6) which is below 150v max PV input. For Amp it's amp it's 11.12 (5.56A x 2). correct?
2. Why for 6 series the temperature cannot go below 5degree F? Will it cause serious damages to the system or if it's just not efficient?
3. What's the temperate threshold for 4 series?
4. When you mentioned for 12 panels in 6S2P there's no need for a combiner or fuse, why is that? What's the purpose to require a combine or fuse for panel array?

Thanks!

 

[yambine]

So my original idea of putting your 8 panels in 4S2P and then later putting 12 in 4S3P still makes sense with that controller. At 3P the panels could be about 20A. You will need a combiner box and fuses when you have 12 panels. You can use a simple Y connector when you have just 8 panels. 10AWG will work with the 12 panels. Though the length of wire will affect the amount of voltage loss. If the wire length from the combiner box to the charge controller is more than about 60 feet then you should probably go with 8AWG wire for that section. That will keep the voltage loss low.

Since according to you if I do a 4s2p or 6s2p configuration, I don't need a combiner box I assume the length will be from the y connectors to the solar controller (with the PV breaker in between). My current estimate is from 45 to 50 ft in total length. Will that be ok or too much power lost?

Thanks!

 

[rmaddy]

1. Correct
2. Never exceed a solar charge controller's max PV input voltage. In this case that is 150V. Panel Voc goes up as the temperature goes down. The 129.6V will reach 150V when the temperature gets down to 5ºF. This is determined by looking at the spec sheet for your panels and finding the "temperature coefficient Voc". Your panels have a value of -0.33%/ºC. Based on that value you can work out the temperature that your panels can exceed a certain voltage. If you exceed the 150V you might fry the charge controller or it will just shutdown.
3. 4 in series would be 86.4V. To reach 150V the temperature would need to get down to -324ºF. If you get that cold you have other issues to worry about more than your charge controller.
4. The general rule is that you only need to fuse parallel strings when you have 3 or more strings in parallel. A combiner box allows for higher currents. Most MC4 connectors can only handle up to 30A. You don't use MC4 connectors when using a combiner box so you can handle more than 30A if needed. Your array with 2 in parallel won't get anywhere near 30A.

 

[rmaddy]

Since according to you if I do a 4s2p or 6s2p configuration, I don't need a combiner box I assume the length will be from the y connectors to the solar controller (with the PV breaker in between). My current estimate is from 45 to 50 ft in total length. Will that be ok or too much power lost?

As long as you choose the proper wire size from the Y connector to the SCC that can handle the 11.12A with minimal voltage drop then you will be fine. You can use 10AWG to easily handle 11A over that distance with almost no voltage drop since the voltage is so high.

 

[Rednecktek]

What about a 5s2p? Just throwing it out there, but that would max out the voltage with plenty of cold weather space, you wouldn't need combiners/fuses, and still manageable string sizes if they're bolted together in a frame.

Just a thought.

 

[yambine]

As long as you choose the proper wire size from the Y connector to the SCC that can handle the 11.12A with minimal voltage drop then you will be fine. You can use 10AWG to easily handle 11A over that distance with almost no voltage drop since the voltage is so high.

1. Which elements could damage the panels when they are installed on the top of the roof? In LA, the one thing that I can think of will be hail. The occasional hail comes and goes too quickly for me to react. I know you may not have personal experience handling HQST solar panels so it's unfair to ask but I just like to know generally speaking for solar panels if hail will not be an issue unless they are the size of golf balls. And if there's any prevention method other than taking them down.
2. If something create a small crack on the panel will it be out of commission completely or still able to be used but with a lesser capacity?
3. What other elements could be a major issue for the panels? Since I will eventually be moving out of LA, it's better I have that knowledge in advance
4. For a 6s2p configuration, if one panel is down I assume I will have to take out a total of two instead of just that damaged panel to make it into a 5s2p configuration in order to make the array work properly again, correct?

Thanks!

 

[rmaddy]

Which elements could damage the panels when they are installed on the top of the roof? In LA, the one thing that I can think of will be hail. The occasional hail comes and goes too quickly for me to react. I know you may not have personal experience handling HQST solar panels so it's unfair to ask but I just like to know generally speaking for solar panels if hail will not be an issue unless they are the size of golf balls. And if there's any prevention method other than taking them down.

Being in LA you need to worry about stray bullets, hail, earthquakes, and coconut laden swallows.

Seriously, good panels can handle some hail. Hail damage may be covered by your insurance. Look into your coverage.

If something create a small crack on the panel will it be out of commission completely or still able to be used but with a lesser capacity?

If the panels have bypass diodes then some damage may only impact some output of that one panel without affecting the others.

What other elements could be a major issue for the panels? Since I will eventually be moving out of LA, it's better I have that knowledge in advance

If you go somewhere with the fluffy white stuff in winter then snow loading can be a potential issue. But properly sloped panels should prevent too much of a buildup unless you are in a really snowy area. If that's the case then choose panels with a high surface load rating.

For a 6s2p configuration, if one panel is down I assume I will have to take out a total of two instead of just that damaged panel to make it into a 5s2p configuration in order to make the array work properly again, correct?

Correct.

6S2P is 12 panels. 6 in series. Another 6 in series. Then those two strings put in parallel.

If one panel is ruined it can make that whole string of 6 panels become ineffective. Or it may have minimal impact if the panels have bypass diodes.

If the damaged panel is affecting the whole string then you will want to remove that one from its string. And, as you stated, you will need to remove one from the other string to keep the array balanced as 5S2P.