Questions on DIY small off grid solar system. Grounding, fusing and panel combining

**Sunking** · 11-15-2012, 12:35 AM

Originally posted by DarkPassenger

1. When I connect the two panels should there be a fuse on the + lead between the two panels? If so, what amp fuse? the panels produce a max of 4.8a each. Morningstar recommends a 25a inline fuse between the battery and the controller within 6 in of battery on the + cable so I am assuming it would be wise to fuse most of the + wires wherever they run between components.

2. I intend to connect + to +, then - to - on the panels, and then run wire from the (+) of Panel #1 and (-) of Panel +2 into the controller. Is there a better method such as a junction box or similar that I would combine the two panels together instead? also, should I have another fuse between the panel and controller? and that fuse should be rated higher due to the higher amperage from the two panels I would assume.

3. Is there something I can wire between the panels and the controller so that I can see the panel output prior to it reaching the controller due to there being no display on this controller? Also, is there something I can wire between the controller and the battery so that I can monitor the output of the controller. I am assuming my battery monitor will not provide any info on input to the battery but rather the necessary readings coming from the batteries themselves.

4. Is there any reason to have a dc disconnect between the panel and the controller/ battery bank since it is not grid tied? Would it be needed to shut off the array during times I might charge the battery with the generator or will the controller take care of that?

5. What should be earth grounded? Panel frame, panel negative lead, controller, battery, Ac breaker panel? Also, is it safe to have just one earth ground copper wire and rod that all grounds connect to? The location of the panels on the roof is approx 30 feet to the ground. Is it okay to have the ground wire in some type of pvc conduit along the wall of the building? What is the necessity of the earth ground and what risks are associated with not grounding anything to an earth ground?

I understand that there is much involved in proper wiring, solar installation, etc.. and do not claim to have anything beyond a less than basic understanding of any of it.... so please I am only asking for advice and realize I have asked a lot of questions. I look forward to learning as much as I can before beginning my installation and appreciate anyone taking time to respond.

Thanks to anyone that replies

A1. Wire your panels in series and there is no requirement to use an over current protection device.

A2. Refer to A1

A3. You can install a voltmeter and/or amp meter.

A4. You need an over current protection device like a fuse which will act as a disconnect

A5. Sorry I am not going to answer this.

**Beanyboy57** · 11-15-2012, 03:14 AM

When installing my own off-grid system I was not advised by anyone (manufacturer or expert on this site) that I had to earth my PV array or charge controller. My inverter had a connection for earth but in the install manual it said there was no real need to earth the inverter. I do have fuses between my panels because I was advised by a moderator on this site that I should protect the panels from each other in case one of them fails. My off-grid setup has been operating for around 9 months without any problems but maybe I am missing some information.

**Naptown** · 11-15-2012, 10:25 AM

You could leave it as a floating system meaning no ground. you will however need to fuse both sides of the battery.
Depending on the size of the cables from collectors to the CC you might get slightly more watts from putting the panels in series. Your charge controller will accept up to 75V. To determine if your panels will put out more than this take the VOC of each panel and add together. Multiply that by 125% if the result is less than 75V put them in series.

**DarkPassenger** · 11-15-2012, 01:41 PM

Originally posted by Naptown

You could leave it as a floating system meaning no ground. you will however need to fuse both sides of the battery.
Depending on the size of the cables from collectors to the CC you might get slightly more watts from putting the panels in series. Your charge controller will accept up to 75V. To determine if your panels will put out more than this take the VOC of each panel and add together. Multiply that by 125% if the result is less than 75V put them in series.

Thank you. By leaving it as a floating system I assume fusing both sides of the battery means fuse the positive coming from the cc to the battery and fuse the positive coming from the battery to the inverter?

Also in regards to wiring in series vs parallel, my thoughts on putting the panels in parallel was to increase the amp output. Would my battery receive a better charge with more watts and voltage in series vs. more amps in parallel?

I had heard that a good rule of thumb was to have at least 10% amp output of the total AH of the battery bank

**Naptown** · 11-15-2012, 01:47 PM

Originally posted by DarkPassenger

Thank you. By leaving it as a floating system I assume fusing both sides of the battery means fuse the positive coming from the cc to the battery and fuse the positive coming from the battery to the inverter?

Also in regards to wiring in series vs parallel, my thoughts on putting the panels in parallel was to increase the amp output. Would my battery receive a better charge with more watts and voltage in series vs. more amps in parallel?

I had heard that a good rule of thumb was to have at least 10% amp output of the total AH of the battery bank

That is a MPPT charge controller. Generally higher voltage and lower amps will mean less wiring losses between panels and CC.
Your runs at approx 10' are not long at all. So losses or gains will be minimal.

As far as fusing goes both the inverter and charge controller are fused on both terminals of the battery both + and -
This type of system however must be kept below 50V.

**DarkPassenger** · 11-15-2012, 02:36 PM

What are your thoughts on using a 100 watt panel wired to say a 70 watt panel in parallel with mppt cc. Any issues related to using unequal panels?

**Naptown** · 11-15-2012, 03:15 PM

Originally posted by DarkPassenger

What are your thoughts on using a 100 watt panel wired to say a 70 watt panel in parallel with mppt cc. Any issues related to using unequal panels?

Yes and no it depends on the characteristics of the two panels. You will not see 170 watts however but something less than that. How much less depends on the differences in the panels

**inetdog** · 11-15-2012, 03:16 PM

Originally posted by DarkPassenger

What are your thoughts on using a 100 watt panel wired to say a 70 watt panel in parallel with mppt cc. Any issues related to using unequal panels?

For MPPT inputs, the rule of thumb is that two panels in series should match Imp within 5%.
and two panels in parallel should match Vmp within 5%. Also for series, Voc of the lower voltage panel must be higher than Vmp of the higher voltage panel.
Beyond that rule of thumb, the relative wattages of the two panels and other factors may allow you to go outside the 5% and still get useful added power.

**thastinger** · 11-16-2012, 01:13 PM

For grounding, you need to know/check your local electrical codes which are often times more strict than the national codes.

I.E. my local code calls for 2 copper grounding rods spaced 6 feet apart and the resistance has a min spec as well...this is just for an outside electrical box, the panels have their own requirements. Call your area building inspector and discuss it assuming you pulled a "self" permit.

**Sunking** · 11-16-2012, 01:27 PM

Originally posted by thastinger

I.E. my local code calls for 2 copper grounding rods spaced 6 feet apart and the resistance has a min spec as well...this is just for an outside electrical box,

There is nothing special about that as it is standard NEC and does not have to meet any resistance specification. Just drive two rods and collect a check. Only time the code will specify a maximum resistance is if you drive only 1 electrode. Drive two rods and call it a done.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(4) through (A)(8). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.

**thastinger** · 11-16-2012, 01:40 PM

Originally posted by Sunking

There is nothing special about that as it is standard NEC and does not have to meet any resistance specification. Just drive two rods and collect a check. Only time the code will specify a maximum resistance is if you drive only 1 electrode. Drive two rods and call it a done.

250.56 Resistance of Rod, Pipe, and Plate Electrodes. A
single electrode consisting of a rod, pipe, or plate that does
not have a resistance to ground of 25 ohms or less shall be
augmented by one additional electrode of any of the types
specified by 250.52(A)(4) through (A)(8). Where multiple
rod, pipe, or plate electrodes are installed to meet the requirements
of this section, they shall not be less than 1.8 m
(6 ft) apart.

Was that really worth responding to just to say it wasn't a special requirement? I was simply trying to relate to the OP that his answers could be found in the code books/building inspectors/permit process. When I installed an outside panel, I had to leave both rods exposed and the inspector measured the resistance of both before signing off on my line item. Was that more than is required...guess so but the bottom line is that it is what he wanted to see before he signed the line item, which is another point of my reply...being that if you don't know what the inspector likes to see you should talk to him/her before you begin.

**Sunking** · 11-16-2012, 01:46 PM

Originally posted by thastinger

Was that really worth responding to just to say it wasn't a special requirement?

Yep that is why I do not give detailed answers to grounding and wiring questions. It is well beyond DIY capabilities. To many code requirements and hoops to jump through. If something were to happen and the OP followed your advice, you are liable.

**fernandonh** · 04-23-2013, 06:32 PM

Originally posted by Naptown

As far as fusing goes both the inverter and charge controller are fused on both terminals of the battery both + and -
This type of system however must be kept below 50V.

Hey Naptown, you have suggested this for my set up in a previous thread. My one 250w panel will be installed in a moving golf cart so there isn't really a way to ground it. I am just wondering, what is the logic behind fusing the - side as well?

Thank you!

**Naptown** · 04-23-2013, 09:40 PM

Originally posted by fernandonh

Hey Naptown, you have suggested this for my set up in a previous thread. My one 250w panel will be installed in a moving golf cart so there isn't really a way to ground it. I am just wondering, what is the logic behind fusing the - side as well?

Thank you!

Can't hurt may or may not help.
The NEC does not really apply to golf carts.

Questions on DIY small off grid solar system. Grounding, fusing and panel combining

Questions on DIY small off grid solar system. Grounding, fusing and panel combining

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