Small Off-Grid Solar Setup Questions

SolarShed2014SolarShed2014 Registered Users Posts: 16
BASIC OVERVIEW:
I built a 16ft x 12ft shed last fall with plans all along to have it powered by off-grid solar, really as a means to educate myself on the setup and day-to-day implementation of off-grid concepts.


EXPECTED POWER NEEDS:
LED Lighting (Two 16ft LED Light Strips, supplemented by battery-powered LED Lights)
A box fan
32" LED LCD TV
Lepai Mini Audio Amp driving 2 bookshelf speakers
Battery charging (18V power tools, AA, AAA, 10,000mah portable battery backup, etc)


EQUIPMENT I'VE GOT:
(1) 100 watt 12V solar panel (will add a second one soon, would like a total of 4 eventually)
(1) 20ft pair of 10 AWG MC4 extension cables
(1) 30 amp PWM Charge Controller
(4) Trojan T-605 6V Golf Cart Batteries (About 3.5 years old in uncertain condition, they sat unattended for 8 months in battery boxes while I built the shed. Just topped them up with distilled water yesterday)
(4) 12 volt 55AH Sealed AGM Batteries (About 4.5 years old, had good charge 6 months ago)
(2) 400 Watt 12V inverters
(1) ANL Fuse holder with (2) 100 amp fuses
(1) In-line 10 AWG ATC Fuse holder with assorted Fuses (7.5 - 40amp)
(4) sets of BC-16PN-TP 16-Inch Positive & Negative Battery Cables (unknown gauge)
(2) sets of 3ft length 3AWG Positive & Negative Cables (200 amp ring terminals with soldered ends)


QUESTIONS/CONCERNS:
1: Rather than offer up my theories on the best way to utilize the existing equipment in the most efficient way possible I thought I would reach out and get some opinions on what I might be missing or need improving in order to get the system up and running.

Right now I have the solar panel mounted on the shed, MC4 cabling run into the shed, and all the components sorted on shelves near the Golf Cart batteries (which are sitting 2 each in 2 separate battery boxes) waiting to be hooked up.

I don't particularly plan on using both sets of batteries, just wound up with the AGM batteries on a stroke of luck, but I wouldn't mind making use of both technologies in 2 separate systems down the road if it makes sense in an education/experiential way.


2: With this size system does it need to be grounded?


3: With my single 100 watt panel should I even bother hooking up the (4) 6V batteries in series-parallel to get a 12V-420AH battery bank, or should I only hook up 2 batteries in series for 12V-210AH bank until I get a second panel?
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions

    Welcome to the forum.

    You have only one 100 Watt panel. That is not going to charge those four Trojan batteries. Nor will it charge four 55 Amp hour AGM's. It doesn't need a 30 Amp controller either, as it is only going to output about 5.5 Amps.

    You either need more PV, or you need to downsize to only one of those AGM's. Example: for 420 Amp hours @ 12 Volt you need about 735 Watts of PV and a bigger charge controller.

    Your inverters are probably MSW type, which usually have issues with grounding the AC neutral so don't. Not that they would run very long from a single 55 Amp battery. Otherwise grounding is a good idea for safety reasons.

    I'll suggest you decide on a system size first (how many Watt hours you want to supply) and start adjusting equipment to suit those needs. Otherwise you have a lot of miscellaneous stuff that won't work together.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Welcome to the forum.

    You have only one 100 Watt panel. That is not going to charge those four Trojan batteries. Nor will it charge four 55 Amp hour AGM's. It doesn't need a 30 Amp controller either, as it is only going to output about 5.5 Amps.

    You either need more PV, or you need to downsize to only one of those AGM's. Example: for 420 Amp hours @ 12 Volt you need about 735 Watts of PV and a bigger charge controller.

    Your inverters are probably MSW type, which usually have issues with grounding the AC neutral so don't. Not that they would run very long from a single 55 Amp battery. Otherwise grounding is a good idea for safety reasons.

    I'll suggest you decide on a system size first (how many Watt hours you want to supply) and start adjusting equipment to suit those needs. Otherwise you have a lot of miscellaneous stuff that won't work together.

    Thank you for the response!

    The 30 amp controller came bundled with the panel, along with the MC4 cable and Z-mounts. I knew my eventual goal would be (4) 100 watt panels so I decided that was a decent place to start. The golf cart batteries I acquired before I'd really looked into the sizing of the panels in relation to the batteries. If I'm only using power in the shed 3 or 4 days a week for 2-3 hours would I possibly be putting a low enough draw on the 420 amp hour battery bank that it would have enough time to charge via 400 watts of panels? Or am I missing something in the equation?

    Yes, the inverters are modified sine wave. I'm not sure how much that will affect trying to run the LED TV off the inverters. Any experience with that? The box fan motor may be an issue from what I gather.

    What is the minimum gauge wire I need for running those 6 volt batteries in series and eventually in series-parallel? And the 55AH AGM batteries in parallel?
  • BB.BB. Super Moderators, Administrators Posts: 28,853 admin
    Re: Small Off-Grid Solar Setup Questions

    As Marc says--It is much easier and usually makes more sense to design your system to support your loads than to try and put a system together and see how it works.

    For example, 4x 6 volt 210 AH batteries should be charged at 5% to 13% rate of charge (minimum to typical cost effective maximum). A solar array would look like:
    • 420 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 395 Watt array minimum
    • 420 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 791 Watt array nominal
    • 420 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,028 Watt array cost effective maximum

    The minimum rate is useful for weekend/seasonal usage. The nominal is good for daily usage. And the cost effective maximum is about the largest array that usually makes sense for a "balanced" system design (you can go larger, but only if you have very heavy day time loads, etc.).

    And how much energy would such an array produce? Using PV Watts for Norfolk VA, fixed array with array tilted to latitude:



    Month
    Solar Radiation
    (kWh/m 2/day)


    1
    3.84


    2
    4.53


    3
    4.69


    4
    5.47


    5
    5.40


    6
    5.69


    7
    5.44


    8
    5.61


    9
    5.02


    10
    4.95


    11
    4.04


    12
    3.37


    Year
    4.84




    So if we toss the bottom three months, you get somewhere around 4.53 hours of "noon time equivalent sun" per day (February). If we take the 10% array of 791 Watts:
    • 791 Watts * 0.52 end to end AC solar system efficiency * 4.53 hours of sun = 1,863 Watt*Hours of 120 VAC energy (February average day)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    Thank you for the response!

    The 30 amp controller came bundled with the panel, along with the MC4 cable and Z-mounts. I knew my eventual goal would be (4) 100 watt panels so I decided that was a decent place to start. The golf cart batteries I acquired before I'd really looked into the sizing of the panels in relation to the batteries. If I'm only using power in the shed 3 or 4 days a week for 2-3 hours would I possibly be putting a low enough draw on the 420 amp hour battery bank that it would have enough time to charge via 400 watts of panels? Or am I missing something in the equation?

    Yes, the inverters are modified sine wave. I'm not sure how much that will affect trying to run the LED TV off the inverters. Any experience with that? The box fan motor may be an issue from what I gather.

    What is the minimum gauge wire I need for running those 6 volt batteries in series and eventually in series-parallel? And the 55AH AGM batteries in parallel?

    Oh boy; equipment bundles. "Let us sell you what we make the most profit on" is the real description there. Four 100 Watt panels would be just over 20 Amps so you're good with a 30 Amp controller then. But four 100 Watt panels are going to cost you more per Watt than buying larger panels. In fact at 400 Watts you're at the 'tipping point' between using standard panels & PWM controller and switching up to GT style panels & MPPT controller: the $1 per Watt or so difference in panel price comes to around $400 which when added to the cost of the PWM controller makes MPPT feasible. This has become even more so with the introduction of MidNite's Kid 30 Amp MPPT at <$300. Expanding a system is rarely easy or cheap.

    The problem with putting 5 Amps to 420 Amp hours of battery is that it will be fairly ineffectual no matter how long you leave it on. It's about maintenance level; it will keep the batteries charged but it won't actually bring them up from discharged state. Unfortunately battery charging isn't as simple as replaced used Amp hours by apply 'X' Amps for 'Y' hours. With four of the panels you'd be applying perhaps 22 Amps (with PWM charger the exact panel specs will matter) which is the minimum 5% rate so over time that could recharge 420 Amp hours.

    A couple of things: first, the batteries aren't being charged now which means they are slowly dying as they wait. Second, if you use power from them while they are charging once the panels are installed that rate falls below minimum and becomes less effective. It's a good thing they are used batteries you haven't got much in to.

    The problem with using MSW inverters with anything is that the inverters' outputs aren't all alike. Some are just square wave, some are pretty close to sine. You can pretty much bet that low cost = low quality waveform. Then there's the other unknown: the power supply of what you are trying to run. Motors won't like it, that's a guarantee. They will draw more power and run hotter, slower. In some cases so much so as to be ineffectual. Other types of power supplies are a gamble. Maybe it will work, maybe it will burn up. There's no way to know in advance. At the very least expect noise in any audio/visual equipment and be very pleased if there isn't any.

    Wire sizing depends on how much current is expected and how much Voltage drop can be tolerated. You could pull 100 Amps from a 420 Amp hour battery bank for a short time. You could pull 5 Amps for a long time. Depending on which is your intent you would use either 1 AWG or 14 AWG, each fused according to its capacity. Where Voltage sag is a concern you use larger size to reduce that (longer length and/or greater Amps = larger Voltage drop requiring bigger wire).

    Take one 400 Watt inverter. It will probably draw about 40 Amps maximum at minimum input Voltage. The instructions that came with it should have recommended wire and fuse sizes, and the wire size may be different according to length. It will say something like "Use 8 AWG wire up to five feet. Use 6 AWG wire up to eight feet." If you skip that and go to standard 4 AWG auto battery wiring it should handle 50 Amps up to 15 feet with minimal Voltage drop for 400 Watts on 12 Volts.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Oh boy; equipment bundles. "Let us sell you what we make the most profit on" is the real description there. Four 100 Watt panels would be just over 20 Amps so you're good with a 30 Amp controller then. But four 100 Watt panels are going to cost you more per Watt than buying larger panels. In fact at 400 Watts you're at the 'tipping point' between using standard panels & PWM controller and switching up to GT style panels & MPPT controller: the $1 per Watt or so difference in panel price comes to around $400 which when added to the cost of the PWM controller makes MPPT feasible. This has become even more so with the introduction of MidNite's Kid 30 Amp MPPT at <$300. Expanding a system is rarely easy or cheap.

    The problem with putting 5 Amps to 420 Amp hours of battery is that it will be fairly ineffectual no matter how long you leave it on. It's about maintenance level; it will keep the batteries charged but it won't actually bring them up from discharged state. Unfortunately battery charging isn't as simple as replaced used Amp hours by apply 'X' Amps for 'Y' hours. With four of the panels you'd be applying perhaps 22 Amps (with PWM charger the exact panel specs will matter) which is the minimum 5% rate so over time that could recharge 420 Amp hours.

    A couple of things: first, the batteries aren't being charged now which means they are slowly dying as they wait. Second, if you use power from them while they are charging once the panels are installed that rate falls below minimum and becomes less effective. It's a good thing they are used batteries you haven't got much in to.

    The problem with using MSW inverters with anything is that the inverters' outputs aren't all alike. Some are just square wave, some are pretty close to sine. You can pretty much bet that low cost = low quality waveform. Then there's the other unknown: the power supply of what you are trying to run. Motors won't like it, that's a guarantee. They will draw more power and run hotter, slower. In some cases so much so as to be ineffectual. Other types of power supplies are a gamble. Maybe it will work, maybe it will burn up. There's no way to know in advance. At the very least expect noise in any audio/visual equipment and be very pleased if there isn't any.

    Wire sizing depends on how much current is expected and how much Voltage drop can be tolerated. You could pull 100 Amps from a 420 Amp hour battery bank for a short time. You could pull 5 Amps for a long time. Depending on which is your intent you would use either 1 AWG or 14 AWG, each fused according to its capacity. Where Voltage sag is a concern you use larger size to reduce that (longer length and/or greater Amps = larger Voltage drop requiring bigger wire).

    Take one 400 Watt inverter. It will probably draw about 40 Amps maximum at minimum input Voltage. The instructions that came with it should have recommended wire and fuse sizes, and the wire size may be different according to length. It will say something like "Use 8 AWG wire up to five feet. Use 6 AWG wire up to eight feet." If you skip that and go to standard 4 AWG auto battery wiring it should handle 50 Amps up to 15 feet with minimal Voltage drop for 400 Watts on 12 Volts.


    The insight is *greatly* appreciated. It's clearing up a lot of issues.

    As for the equipment bundle, the panel alone would have been $150. The additional cost of the bundle (which included the charge controller, (2) 20ft 10awg MC4 cables and 4 Z-mounts) was only $35 over the cost of the panel itself. I'm fully prepared to replace the charge controller if/when needed but reviews were positive enough that I was willing to get my feet wet with the bundled unit.

    For the scope of my project I thought the 100 watt 12 volt panels would be the simplest way to start and gradually expand over the course of a few months. I've got an 8 foot wide by 4 foot deep porch angled at 35 degrees that will perfectly fit (4) of the 100 watt panels.

    So I've got the 3ft 3 AWG inverter cables. The inverter will be within 3 feet of the batteries, so that should be more than sufficient for my current inverter, but at up to what size inverter could I support with the 420AH battery bank and 3ft 3 AWG cables?

    I've been trying to find examples/pictures of a good, clean solar installation that's near/equivalent to my setup so I can get a visual guideline to go off of to get ideas of fusing, cable routing, etc. but haven't had much luck. Any ideas where I might find some?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    So I've got the 3ft 3 AWG inverter cables. The inverter will be within 3 feet of the batteries, so that should be more than sufficient for my current inverter, but at up to what size inverter could I support with the 420AH battery bank and 3ft 3 AWG cables?

    420 Amp hours @ 12 Volts is a respectable amount of power. There's a couple of things you have to understand about "how much inverter it can support". Inverter size is in maximum Watts (actually Volt Amps) which corresponds to the maximum current draw from a battery bank at a given moment. Normally for flooded cell batteries this should not exceed 25% of the Amp hour rating. In this case that's 105 Amps or 1260 Watts DC. The inverter will take some power to run itself and there is some conversion loss in converting to AC power. So the battery bank should be good for a maximum of 1000 Watts AC. That's a pretty standard size inverter for a 12 Volt system. You may even run a bit over that without too many difficulties. But, and this is important, it won't support it for long.

    Here's the other thing to understand: Watt hours. It's Amp hours with Volts. That same 420 Amp hours at its maximum safe DOD multiplied by nominal system Voltage amounts to 2520 Watt hours. See the difference? One is the biggest load it can handle at a moment without 'going flat' the other is the quantity of power it can supply over time.

    And then they intermix. In theory that 2520 Watt hours could be 5 Watts for 500 hours or 500 Watts for 5 hours. In practice the real capacity diminishes as the load demand at the moment increases. So the maximum 1 kW load would not actually last for 2.5 hours. Complicated, isn't it?

    Usually you only have to worry about maximum Watts for something like getting a motor started and the demand doesn't last long enough to make a difference. The average load over time (Watt hour capacity) becomes the more important aspect.
    I've been trying to find examples/pictures of a good, clean solar installation that's near/equivalent to my setup so I can get a visual guideline to go off of to get ideas of fusing, cable routing, etc. but haven't had much luck. Any ideas where I might find some?

    Nope. That is a problem with solar: every install is unique to the particular location. You may be able to copy basic specs and equipment, but most of the unique aspect is in the wiring. Two systems may have the same PV, controller, batteries, et cetera but because one's array if 20 feet further off it will have different wiring.

    This is why you need to understand the reasoning behind the choices made, instead of just using a given wire. There are two main factors is choosing wire size: current handling and Voltage drop. The first is a minimum that must be met: if it can't handle the expected current it will fry. The second is to reduce power loss through Voltage sag which may be present depending on Voltage, current, and distance. The largest problem here occurs between panels and controller due to long distances usually involved. The second most likely trouble spot is between batteries and inverter due to the high currents usually involved.

    After the wire sizing is worked out the fuse or breaker can be selected according to the current expected. These are the things figured out last, once the basic equipment and locations have been worked out. And if you are planning on future expansion it helps to wire for it at the start, rather than have to change it all out later to accommodate greater current.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    420 Amp hours @ 12 Volts is a respectable amount of power. There's a couple of things you have to understand about "how much inverter it can support". Inverter size is in maximum Watts (actually Volt Amps) which corresponds to the maximum current draw from a battery bank at a given moment. Normally for flooded cell batteries this should not exceed 25% of the Amp hour rating. In this case that's 105 Amps or 1260 Watts DC. The inverter will take some power to run itself and there is some conversion loss in converting to AC power. So the battery bank should be good for a maximum of 1000 Watts AC. That's a pretty standard size inverter for a 12 Volt system. You may even run a bit over that without too many difficulties. But, and this is important, it won't support it for long.

    Here's the other thing to understand: Watt hours. It's Amp hours with Volts. That same 420 Amp hours at its maximum safe DOD multiplied by nominal system Voltage amounts to 2520 Watt hours. See the difference? One is the biggest load it can handle at a moment without 'going flat' the other is the quantity of power it can supply over time.

    And then they intermix. In theory that 2520 Watt hours could be 5 Watts for 500 hours or 500 Watts for 5 hours. In practice the real capacity diminishes as the load demand at the moment increases. So the maximum 1 kW load would not actually last for 2.5 hours. Complicated, isn't it?

    Usually you only have to worry about maximum Watts for something like getting a motor started and the demand doesn't last long enough to make a difference. The average load over time (Watt hour capacity) becomes the more important aspect.



    Nope. That is a problem with solar: every install is unique to the particular location. You may be able to copy basic specs and equipment, but most of the unique aspect is in the wiring. Two systems may have the same PV, controller, batteries, et cetera but because one's array if 20 feet further off it will have different wiring.

    This is why you need to understand the reasoning behind the choices made, instead of just using a given wire. There are two main factors is choosing wire size: current handling and Voltage drop. The first is a minimum that must be met: if it can't handle the expected current it will fry. The second is to reduce power loss through Voltage sag which may be present depending on Voltage, current, and distance. The largest problem here occurs between panels and controller due to long distances usually involved. The second most likely trouble spot is between batteries and inverter due to the high currents usually involved.

    After the wire sizing is worked out the fuse or breaker can be selected according to the current expected. These are the things figured out last, once the basic equipment and locations have been worked out. And if you are planning on future expansion it helps to wire for it at the start, rather than have to change it all out later to accommodate greater current.


    OK, I figured I'd try my hand at a diagram of my proposed equipment layout/configuration.

    Should I be installing a fused disconnect switch between the panels and the charge controller? Any additional fusing needed?

    I've got a 7.5-30V DC LED voltmeter display, what would be the best way to incorporate that into the system (or should I not bother)?

    Any other comments? This has been a huge help on this project. Thanks again.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions

    Here's the disconnect switch I was considering placing between the solar panels and the charge controller:
    http://www.lowes.com/pd_92606-296-L211N_4294722479__?productId=3365260
    (Square D 30-Amp Fusible Metallic Disconnect)

    Would this be the right one to use?

    And if so, would I use (2) 30 Amp fuses?

    Which of the following types of plug fuses should I use?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions

    Okay, issues.

    The array will be configured how? It makes a difference. With more than two panels in parallel each should have a fuse or breaker on it.

    A disconnect and/or over-current protection on the combined panel output to the charge controller is not necessary unless required by code. If code required it has to be DC rated for the Voltage and current involved. You can't just use a standard AC disconnect box (well maybe you can but whether or not it will be right or accepted is another issue).

    The output of the charge controller should have a fuse or breaker on it. This is more important than the input: panels are self-limiting in current, batteries are not. If PV output is shorted and the wiring is sized properly they can push Isc into a dead short indefinitely without anything going wrong. If the charge controller should short the batteries can dump huge amounts of current into it in an instant; far more than the output wiring would be designed to handle.

    Your links are all to standard AC equipment. This is not suitable nor recognized for DC equipment. DC is more difficult to safely interrupt and proper fuses/breakers/disconnects need to be used. Some examples here: http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1.html
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Okay, issues.

    The array will be configured how? It makes a difference. With more than two panels in parallel each should have a fuse or breaker on it.

    A disconnect and/or over-current protection on the combined panel output to the charge controller is not necessary unless required by code. If code required it has to be DC rated for the Voltage and current involved. You can't just use a standard AC disconnect box (well maybe you can but whether or not it will be right or accepted is another issue).

    The output of the charge controller should have a fuse or breaker on it. This is more important than the input: panels are self-limiting in current, batteries are not. If PV output is shorted and the wiring is sized properly they can push Isc into a dead short indefinitely without anything going wrong. If the charge controller should short the batteries can dump huge amounts of current into it in an instant; far more than the output wiring would be designed to handle.

    Your links are all to standard AC equipment. This is not suitable nor recognized for DC equipment. DC is more difficult to safely interrupt and proper fuses/breakers/disconnects need to be used. Some examples here: http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1.html


    The array will be configured with (4) 100 watt panels in parallel.

    So then, could I use something like this (www.amazon.com/In-line-ACT-Water-resistant-Fuse-Holder/dp/B0002KR88A/) with 7.5(?) amp fuses in between the 100 watt solar panels?

    And then the same fuse holder with a 30 amp fuse between the charge controller and the batteries?

    And would I then need a fuse between the solar panel array and the charge controller?

    Thanks!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    The array will be configured with (4) 100 watt panels in parallel.

    Okay, so the current would be 4*Isc for sizing wire. That's probably going to be around 24 Amps. The individual panel fuses would be sized for the maximum series fuse rating, or if that's not given then Isc * 1.56 or probably 10 Amps.
    So then, could I use something like this (www.amazon.com/In-line-ACT-Water-resistant-Fuse-Holder/dp/B0002KR88A/) with 7.5(?) amp fuses in between the 100 watt solar panels?

    Automotive style fuse holders are generally not good enough quality for RE use. They tend to burn up even when not stressed. Look for a more robust unit; I think Blue Sea makes a module capable of multiple fuses. This will have to be weather-proofed because it will likely be outside. The Blue Sea equipment is for marine use and they may have something suitable as-is. (This to avoid going with the more expensive RE equipment such as MidNite combiner boxes.)
    And then the same fuse holder with a 30 amp fuse between the charge controller and the batteries?

    There should definitely be a fuse between the charge controller output and the battery. You may even want to use a circuit breaker here. It appears 30 Amps would be right providing no further expansion is planned.
    And would I then need a fuse between the solar panel array and the charge controller?

    Thanks!

    You don't really need any form of over-current protection between the array and the controller as PV is self-limiting on current. People will put a circuit breaker on that line but it functions only as a disconnect.
  • DavidOHDavidOH Solar Expert Posts: 109 ✭✭✭
    Great start up

    I'm (still) working on something similar. Check out "My Solar Project" http://forum.solar-electric.com/showthread.php?10461-My-Solar-Project
    Mine is about 500 watts. 4 panels, 4-6 batteries. The guys here picked through it and helped me refine it somewhat.

    I have a suggestion on powering your TV through the inverter. DON'T ! Get a 12 volt TV !
    http://www.backwoodshome.com/forum/vb/showthread.php?t=24424

    There are a LOT of TV's that have a 12 volt power input. Check the back of them for the voltage input. Get one with the 12 volt EXTERNAL power supply.


    Keep us informed on your building project. I love reading how others are doing. Thanks, David
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Okay, so the current would be 4*Isc for sizing wire. That's probably going to be around 24 Amps. The individual panel fuses would be sized for the maximum series fuse rating, or if that's not given then Isc * 1.56 or probably 10 Amps.

    Question:
    I looked back at the manufacturer's diagram/recommendations to make sure I hadn't read it wrong and they recommend, when connecting (4) 100 watt panels in parallel, to use (3) MC4 branch connectors with no mention of fusing:

    Attachment not found.

    Are they presenting an unsafe situation with this recommendation?


    Automotive style fuse holders are generally not good enough quality for RE use. They tend to burn up even when not stressed. Look for a more robust unit; I think Blue Sea makes a module capable of multiple fuses. This will have to be weather-proofed because it will likely be outside. The Blue Sea equipment is for marine use and they may have something suitable as-is. (This to avoid going with the more expensive RE equipment such as MidNite combiner boxes.)



    There should definitely be a fuse between the charge controller output and the battery. You may even want to use a circuit breaker here. It appears 30 Amps would be right providing no further expansion is planned.

    What would be the most efficient/least expensive way of implementing a circuit breaker between the charge controller and the battery?

    You don't really need any form of over-current protection between the array and the controller as PV is self-limiting on current. People will put a circuit breaker on that line but it functions only as a disconnect.

    Also on this last point, the diagrams provided in the owners manual show a fuse in-line between the panel and the charge controller (but they do list it as optional):
    Attachment not found.


    And another question regarding battery wiring. If I'll be attaching a 1000 watt inverter to the battery bank (4 Trojan T-605s wired in Series/Parallel) what would the amperage ratings be as far as determining the gauge of wiring to be used for interconnects between the batteries?
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Great start up
    DavidOH wrote: »
    I'm (still) working on something similar. Check out "My Solar Project" http://forum.solar-electric.com/showthread.php?10461-My-Solar-Project
    Mine is about 500 watts. 4 panels, 4-6 batteries. The guys here picked through it and helped me refine it somewhat.

    I have a suggestion on powering your TV through the inverter. DON'T ! Get a 12 volt TV !
    http://www.backwoodshome.com/forum/vb/showthread.php?t=24424

    There are a LOT of TV's that have a 12 volt power input. Check the back of them for the voltage input. Get one with the 12 volt EXTERNAL power supply.


    Keep us informed on your building project. I love reading how others are doing. Thanks, David

    Very interesting idea. I do already have an old spare HP 19" monitor that uses a 12V 5A power adapter, but that wouldn't work for what I had planned. The usage of the TV should be fairly low, so not sure it's going to make a large impact on my power usage. I think I'm probably better off putting that $150-$200 towards an extra 100 watt panel :)

    I'm looking through your solar project now, thanks for the link!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    Question:
    I looked back at the manufacturer's diagram/recommendations to make sure I hadn't read it wrong and they recommend, when connecting (4) 100 watt panels in parallel, to use (3) MC4 branch connectors with no mention of fusing:

    Are they presenting an unsafe situation with this recommendation?

    Yes.
    A panel has an Isc rating and a maximum series fuse rating. The former is how much current it can produce, the latter is how much it can conduct - as in if it shorts and is being fed current from other panels in parallel with it. Usually the fuse rating is 10-15 Amps. With an Isc in the 5-6 Amp range two panels feeding into one can exceed the maximum current rating and set it on fire.
    What would be the most efficient/least expensive way of implementing a circuit breaker between the charge controller and the battery?

    A very good question. What do you consider to be "least expensive"? You can run any sort that meet the ratings needed for DC current and Voltage involved. Some options: http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/stfubr1.html
    Also on this last point, the diagrams provided in the owners manual show a fuse in-line between the panel and the charge controller (but they do list it as optional)

    Of no value since the circuit should be designed for the maximum the panels will put out. Their current will never go above that. "Isc" means current at short circuit ("I" is "Intensity"; an old term for Amperes).
    And another question regarding battery wiring. If I'll be attaching a 1000 watt inverter to the battery bank (4 Trojan T-605s wired in Series/Parallel) what would the amperage ratings be as far as determining the gauge of wiring to be used for interconnects between the batteries?

    Well it would be maximum output Watts divided by minimum input Voltage plus inverter tare and conversion loss. Or roughly 1000 Watts / 12 = 83 Amps if you can keep the Voltage above 12 and the power demand below 1kW. At the low end of things it gets interesting: some inverters go down to 10.5 Volts before shutdown, and that is 95 Amps for the 1kW. If you add in the conversion loss and perhaps 2 Amps for the inverter you're now at 108 Amps. Oh and some people will insist on using the surge rating, but surge is only for seconds and can not be considered 'continuous'. All wire and OCP can handle momentary current above the continuous rating.

    This is why it's handy to get the manufacturer's recommendations for wire and fuse sizes.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Yes.
    A panel has an Isc rating and a maximum series fuse rating. The former is how much current it can produce, the latter is how much it can conduct - as in if it shorts and is being fed current from other panels in parallel with it. Usually the fuse rating is 10-15 Amps. With an Isc in the 5-6 Amp range two panels feeding into one can exceed the maximum current rating and set it on fire.

    So would it be possible/safe to connect 2 pairs of 2 panels together in parallel, with an MC4 branch connector, and then each pair have a short pigtail with a 15 amp fuse on it leading to the final MC4 branch connector that connects the 2 pairs together in parallel running into the shed going the charge controller? I'm just thinking of ways to simplify the wiring with the MC4 connectors involved while still keeping everything from going up in smoke.


    A very good question. What do you consider to be "least expensive"? You can run any sort that meet the ratings needed for DC current and Voltage involved. Some options: http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/stfubr1.html

    So 30 amp circuit breaker inside one of these http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/baby-box.html mounted on the wall between the charge controller and the battery. Am I missing anything?


    Of no value since the circuit should be designed for the maximum the panels will put out. Their current will never go above that. "Isc" means current at short circuit ("I" is "Intensity"; an old term for Amperes).

    Got it. No fuse between panels and charge controller. Just fused between panels with more than 2 in parallel.

    Well it would be maximum output Watts divided by minimum input Voltage plus inverter tare and conversion loss. Or roughly 1000 Watts / 12 = 83 Amps if you can keep the Voltage above 12 and the power demand below 1kW. At the low end of things it gets interesting: some inverters go down to 10.5 Volts before shutdown, and that is 95 Amps for the 1kW. If you add in the conversion loss and perhaps 2 Amps for the inverter you're now at 108 Amps. Oh and some people will insist on using the surge rating, but surge is only for seconds and can not be considered 'continuous'. All wire and OCP can handle momentary current above the continuous rating.

    This is why it's handy to get the manufacturer's recommendations for wire and fuse sizes.

    So I would be sizing the wiring between the batteries based on the capacity to handle the total of 108 amps for a 1 foot distance for interconnects? Or is the current flow from one battery to the next going to be less than the total draw from the entire bank in the series-parallel configuration?
  • BB.BB. Super Moderators, Administrators Posts: 28,853 admin
    Re: Small Off-Grid Solar Setup Questions

    ore
    So would it be possible/safe to connect 2 pairs of 2 panels together in parallel, with an MC4 branch connector, and then each pair have a short pigtail with a 15 amp fuse on it leading to the final MC4 branch connector that connects the 2 pairs together in parallel running into the shed going the charge controller? I'm just thinking of ways to simplify the wiring with the MC4 connectors involved while still keeping everything from going up in smoke.
    I am not quite sure I understand your connections. The traditional wiring method would be to wire two panels in series, and put a fuse (or breaker) in that string. Then tank the 2 series panels + breaker (or fuse), and then put the X strings together in parallel.

    You want the fuse/breaker to protect a single shorted string from the rest of the panels (i.e., 2 or more parallel strings feeding a single shorted string).

    The "nice" way to do this would be to get a "combiner box" with breakers. The breakers can be turned off (servicing/debugging a failing string, etc.). The wires are all combined together and then fed on a pair of cables to the PV input of the controller. Normally the combined current of the panels (Isc*1.56 if you follow NEC) should exceed the cabling back to the controller--And you do not need a second breaker to protect that wiring (the array can never exceed the wire current rating).
    So 30 amp circuit breaker inside one of these http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/baby-box.html mounted on the wall between the charge controller and the battery. Am I missing anything?

    Back to basics--What exactly is the charge controller (PWM or MPPT) and its current rating. And what is the exact rating of the array.

    If the charge controller is a 30 amp MPPT charge controller, then the wiring between the controller and the battery should be:

    30 amps * 1.25 NEC derating = 37.5 amps ~ 40 amp rated breaker/fuse minimum

    The 1.25 derating is used because fuses and breakers if they carry more than 80% (1/1.25) of their rated current, they can trip.
    Got it. No fuse between panels and charge controller. Just fused between panels with more than 2 in parallel.

    In general, that is the correct answer. When you have 3 or more parallel strings of panels, the total output current of two of the parallel panels in the array exceeds the "series fuse rating" of the third string of panels (if they are shorted).
    So I would be sizing the wiring between the batteries based on the capacity to handle the total of 108 amps for a 1 foot distance for interconnects? Or is the current flow from one battery to the next going to be less than the total draw from the entire bank in the series-parallel configuration?

    More or less, the battery cables need to be rated for 1.25x the maximum expected continuous current you want to send through the battery string(s) (feeding loads and/or charging, which ever is worse case).

    It usally makes mores sense to do the actual calculations for your design. So, now that you have a handle on your equipment power power requirements... Can you give us a list:

    X solar panels (Vmp/Imp rating)
    Brand/Model of ABC charge controller
    Brand/Model of Battery bank (number of batteries, AH/voltage of batteries/cells, battery bank voltage)
    Brand/Model of AC inverter (or inverter/charger)
    Brand/Mode of AC battery charger (if used)

    We can then step through the process and help with the calculations/section of wiring/breakers and double check hardware (controllers, battery bank, etc.).

    We try for a "balanced system" that will meet your needs. It does get a bit iterative as you make a selection of a piece of equipment and see how that changes the parts needed around it.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    So would it be possible/safe to connect 2 pairs of 2 panels together in parallel, with an MC4 branch connector, and then each pair have a short pigtail with a 15 amp fuse on it leading to the final MC4 branch connector that connects the 2 pairs together in parallel running into the shed going the charge controller? I'm just thinking of ways to simplify the wiring with the MC4 connectors involved while still keeping everything from going up in smoke.

    No.
    Connecting two panels in parallel with no fuse and then connecting the third with a fuse offers no protection: you still have three panels in parallel. EACH panel must have a fuse or breaker when connecting more than two in parallel. There's no shortcut for this.
    So 30 amp circuit breaker inside one of these http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/baby-box.html mounted on the wall between the charge controller and the battery. Am I missing anything?

    If you're using a 30 Amp controller and running current under 30 Amps using at least 10 AWG wire that will work fine.
    So I would be sizing the wiring between the batteries based on the capacity to handle the total of 108 amps for a 1 foot distance for interconnects? Or is the current flow from one battery to the next going to be less than the total draw from the entire bank in the series-parallel configuration?

    Wires between batteries are usually the same size as those from batteries to inverter. They don't necessarily need to be (depends on the situation) but that's just easier to remember and do. Another factor that affects battery to inverter wiring is distance: longer distances increase Voltage sag under heavy load so it is necessary to put in larger wire than is actually needed for the current in order to keep the inverter from shutting down due to low Voltage at its input (even though the batteries aren't low). This depends on the size of the inverter, expected current, and wire length required.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    BB. wrote: »
    ore
    I am not quite sure I understand your connections. The traditional wiring method would be to wire two panels in series, and put a fuse (or breaker) in that string. Then tank the 2 series panels + breaker (or fuse), and then put the X strings together in parallel.

    You want the fuse/breaker to protect a single shorted string from the rest of the panels (i.e., 2 or more parallel strings feeding a single shorted string).

    The "nice" way to do this would be to get a "combiner box" with breakers. The breakers can be turned off (servicing/debugging a failing string, etc.). The wires are all combined together and then fed on a pair of cables to the PV input of the controller. Normally the combined current of the panels (Isc*1.56 if you follow NEC) should exceed the cabling back to the controller--And you do not need a second breaker to protect that wiring (the array can never exceed the wire current rating).

    My description was based on the wiring diagram provided by the manufacturer here:
    Attachment not found.


    BB. wrote: »
    Back to basics--What exactly is the charge controller (PWM or MPPT) and its current rating. And what is the exact rating of the array.

    If the charge controller is a 30 amp MPPT charge controller, then the wiring between the controller and the battery should be:

    30 amps * 1.25 NEC derating = 37.5 amps ~ 40 amp rated breaker/fuse minimum

    The 1.25 derating is used because fuses and breakers if they carry more than 80% (1/1.25) of their rated current, they can trip.

    It is a 30 amp PWM charge controller. Additional details in the summary below.


    BB. wrote: »
    In general, that is the correct answer. When you have 3 or more parallel strings of panels, the total output current of two of the parallel panels in the array exceeds the "series fuse rating" of the third string of panels (if they are shorted).



    More or less, the battery cables need to be rated for 1.25x the maximum expected continuous current you want to send through the battery string(s) (feeding loads and/or charging, which ever is worse case).

    It usally makes mores sense to do the actual calculations for your design. So, now that you have a handle on your equipment power power requirements... Can you give us a list:

    X solar panels (Vmp/Imp rating)
    Brand/Model of ABC charge controller
    Brand/Model of Battery bank (number of batteries, AH/voltage of batteries/cells, battery bank voltage)
    Brand/Model of AC inverter (or inverter/charger)
    Brand/Mode of AC battery charger (if used)

    We can then step through the process and help with the calculations/section of wiring/breakers and double check hardware (controllers, battery bank, etc.).

    We try for a "balanced system" that will meet your needs. It does get a bit iterative as you make a selection of a piece of equipment and see how that changes the parts needed around it.

    -Bill

    The end result will be the following:
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    No.
    Connecting two panels in parallel with no fuse and then connecting the third with a fuse offers no protection: you still have three panels in parallel. EACH panel must have a fuse or breaker when connecting more than two in parallel. There's no shortcut for this.

    This got me thinking... I was already considering going with an MPPT Charge Controller. If I got a Tracer-2210RN 20A MPPT controller would I be able to set up the following?:
    -(4) 100 Watt 12V solar panels wired in Series-Parallel outputting 24V, having only 2 parallel strings with no fusing required.
    -Tracer 20A MPPT Charge Controller receiving 24V panel input and outputting 12V to the battery bank of T-605s wired in Series-Parallel.


    If you're using a 30 Amp controller and running current under 30 Amps using at least 10 AWG wire that will work fine.
    If I switched to a 20A MPPT Controller that was receiving 24V input from the (4) 100 watt panels but outputting 12V then I'd still be sizing the fusing for 30 amps, correct?


    Wires between batteries are usually the same size as those from batteries to inverter. They don't necessarily need to be (depends on the situation) but that's just easier to remember and do. Another factor that affects battery to inverter wiring is distance: longer distances increase Voltage sag under heavy load so it is necessary to put in larger wire than is actually needed for the current in order to keep the inverter from shutting down due to low Voltage at its input (even though the batteries aren't low). This depends on the size of the inverter, expected current, and wire length required.
    The document at the bottom of this link (http://www.jamestowndistributors.com/userportal/pdfs/howtos/Tech_Wiring_Voltage_Sizes.pdf) shows 4 gauge cable used for 105-125 amps all the way up to ten feet. So it would appear 4 gauge cable would be sufficient if I was using a Xantrex ProWatt SW1000 inverter 3 feet away from the battery bank?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    This got me thinking... I was already considering going with an MPPT Charge Controller. If I got a Tracer-2210RN 20A MPPT controller would I be able to set up the following?:
    -(4) 100 Watt 12V solar panels wired in Series-Parallel outputting 24V, having only 2 parallel strings with no fusing required.
    -Tracer 20A MPPT Charge Controller receiving 24V panel input and outputting 12V to the battery bank of T-605s wired in Series-Parallel.

    If I switched to a 20A MPPT Controller that was receiving 24V input from the (4) 100 watt panels but outputting 12V then I'd still be sizing the fusing for 30 amps, correct?

    No.
    Four 100 Watt panels with an Imp of 5.3 on a PWM controller produce 21.2 Amps.
    Same four panels on an MPPT controller could produce 26 Amps.
    Neither arrangement will work on a 20 Amp controller of either type as the controller will limit the output to 20 Amps.
    The document at the bottom of this link (http://www.jamestowndistributors.com/userportal/pdfs/howtos/Tech_Wiring_Voltage_Sizes.pdf) shows 4 gauge cable used for 105-125 amps all the way up to ten feet. So it would appear 4 gauge cable would be sufficient if I was using a Xantrex ProWatt SW1000 inverter 3 feet away from the battery bank?

    4 AWG is only good to 100 Amps in my experience. Pushing it beyond that will give greater loss and more heat. At that current over 3 feet it should work, especially if you don't heavily load the inverter. If you plan on using it near its maximum, increase the wire size. For 3 feet of copper going up to 2 AWG or even 0 AWG won't bankrupt you.
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    No.
    Four 100 Watt panels with an Imp of 5.3 on a PWM controller produce 21.2 Amps.
    Same four panels on an MPPT controller could produce 26 Amps.
    Neither arrangement will work on a 20 Amp controller of either type as the controller will limit the output to 20 Amps.

    Ah, yes, bonehead moment. I'd have to be running a 24 Volt battery bank and 24 volt inverter in order for that controller to work.


    4 AWG is only good to 100 Amps in my experience. Pushing it beyond that will give greater loss and more heat. At that current over 3 feet it should work, especially if you don't heavily load the inverter. If you plan on using it near its maximum, increase the wire size. For 3 feet of copper going up to 2 AWG or even 0 AWG won't bankrupt you.

    I picked up a set of 2 pairs of 3ft long inverter cables a while back (http://www.northerntool.com/shop/tools/product_200422347_200422347). They're listed as "#3 AWG" which I haven't really seen anywhere else. I had considered using 1 set of the inverter cables to go from the battery to the inverter and cutting the other set in half and crimping new ends on to use them for the battery interconnect cables, but since I can't find #3 AWG ring terminals anywhere I wasn't sure if 2 AWG ring terminals would work in its place.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions

    Yes, crimping your own can be an adventure in loose wiring. #3 is kind of an odd size. Might be worthwhile to just get some pre-made #4 cable for the interconnections. It's not like there will be a lot of them, right?
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Re: Small Off-Grid Solar Setup Questions

    Lugs are pretty maleable, so long as you use the right size die. But thing is, short lengths of cable of any size is cheap. So why compromise? Work out the correct size cable using your voltdrop calculator, then buy it! And matching lugs. I know 2,1,0 guage cable isnt laying around on every street corner, but if you go to an electrical supplier, you can shop to your hearts content all the way up to 4/0 and beyond. An inverter draws lots of amps, and to get nice surge support, proper sized cables are just what you want.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Yes, crimping your own can be an adventure in loose wiring. #3 is kind of an odd size. Might be worthwhile to just get some pre-made #4 cable for the interconnections. It's not like there will be a lot of them, right?

    Just 4 interconnects. Looks like I can order a set of (5) 14" 4-gauge golf cart battery cables for $19 shipped. Sound like the way to go?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small Off-Grid Solar Setup Questions
    Just 4 interconnects. Looks like I can order a set of (5) 14" 4-gauge golf cart battery cables for $19 shipped. Sound like the way to go?

    I live in Canada. One of those cables would be $7. Looks like a deal to me. :p
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    No.
    Connecting two panels in parallel with no fuse and then connecting the third with a fuse offers no protection: you still have three panels in parallel. EACH panel must have a fuse or breaker when connecting more than two in parallel. There's no shortcut for this.

    Revisiting this. Regarding the fusing with MC4 connectors, what is the best approach for installing the fuses? Using MC4 in-line fuses (like this: http://www.amazon.com/Vktech-Photovoltaic-Protective-Connector-Waterproof/dp/B00LVG5B1A/) and then using branch connectors to connect panels in parallel? I can't just clip off the MC4 connector of the solar panel itself and install a regular in-line fuse due to it voiding the warranty.


    If you're using a 30 Amp controller and running current under 30 Amps using at least 10 AWG wire that will work fine.

    With BB's input regarding perhaps needing a 40 Amp breaker, would this work as an all-inclusive surface-mount solution?
    http://www.amazon.com/Blue-Sea-Systems-285-Series-Surface/dp/B005168AOG/
  • PhotowhitPhotowhit Solar Expert Posts: 4,861 ✭✭✭✭
    Re: Small Off-Grid Solar Setup Questions

    Probable be almost as cheap, just to get a Baby box or a Big Baby box and 4 breakers in the amperage you need and a short busbar and make a mini breaker box.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • westbranchwestbranch Solar Expert Posts: 5,135 ✭✭✭✭
    Re: Small Off-Grid Solar Setup Questions

    And you can order those boxes with MC4 connectors installed... end of MC4 issues
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • SolarShed2014SolarShed2014 Registered Users Posts: 16
    Re: Small Off-Grid Solar Setup Questions
    Revisiting this. Regarding the fusing with MC4 connectors, what is the best approach for installing the fuses? Using MC4 in-line fuses (like this: http://www.amazon.com/Vktech-Photovoltaic-Protective-Connector-Waterproof/dp/B00LVG5B1A/) and then using branch connectors to connect panels in parallel? I can't just clip off the MC4 connector of the solar panel itself and install a regular in-line fuse due to it voiding the warranty.

    I did find these Y branch cables that combine 4 panels to 1 output with pigtails that I could splice 10amp fuses into:
    www.amazon.com/Signstek-Branch-Female-solar-Connectors/dp/B00FWO54RI/

    Does that look like it would work?
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