I'm looking for advice on how to properly install/wire these 2 panel arrays.

MO-NH · March 2013

I'm looking for advice on how to properly install/wire these panels.

Ten 100w 12v panels located 40 feet from the 24v grid tie inverter and battery bank. Want to hook these up in series at 24 volts.

Six 235w 24v panels located 40 feet to the 24v grid tie inverter.

Both arrays will be on separate rooftops – the 100w array on the garage roof and the 235w array on the house roof. I'd like to put them all on the garage roof, but realize that the 10/2 wire on its own 20amp breaker that feeds the garage cannot handle it all if I were to grid tie them all. My calculation on what the garage can handle on that line is 1,440 watts (80% of max). That would mean I'd be fine with the 1kw array of 100w panels. Is this correct?

Looking for details on what size wire, how to wire them, where any necessary fuses go, what I need for simple/easy combiner box, etc. for both arrays.

I have two small AC breaker boxes that I could use as combiner boxes - I had thoughts of linking both bus bars for the positive and using the grounding bus for the negative. Is this reasonable or would you recommend against it?

I was thinking that I'd hook 100w array up to one of these (http://www.bluesea.com/productspecs/9001E) to manually switch between charging the battery banks and sending the power to the grid tie inverter. Any cheaper/easier/safer method for accomplishing this? I'd also be interested to hear if there were an automatic way of doing this that wasn't outrageously expensive.

On hand I have 200 feet of 10ga black PV cable that I'd like to utilize as well as eight 2-way branch MC4 connectors and three 4-way branch MC4 connectors all 12ga.

I have eight 6" roof mount standoffs that I'll bolt to the roof after sealing with Lexal and was planning on buying the gold colored superstrut lengths from Home Depot or Lowes to use as the rails and either fender washers or other brackets to hold the panels down.

Also looking for recommendations on a grid tie inverter for each array and a charge controller for the 100w array that will do the job but won't break the bank.

This is in the beginning stages, so now is the time to make changes - so what would you change about this plan and what else do I need to buy to make this happen? Keeping in mind that where I live there is no building inspector or code to meet, but I do want it to be safe.

Also looking for recommendations on a grid tie inverter and charge controller for each that won't break the bank.

Thanks for your input.

Cariboocoot · March 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

We're going to need the actual specifications for both panel types: Vmp & Imp specifically.
Also the specs on this "grid tie inverter". As a rule, and approved GTI will not operate at the same sort of Voltage as a charge controller for a battery system.
You haven't mentioned what the battery bank's Voltage/capacity is either.
Nor what, if any, charge controller(s) you have.

It sort of sounds like you're trying to do something that is either inadvisable or bound to be very expensive.

MO-NH · March 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

The 100w panels are: Voc 20.6V
Vop 17.3V
Short circuit current (Isc) 6.82A
Working current (Iop) 5.78A

The 235w panels are: Voltage: 29.3
Max Circuit: 7.8A
Open Circuit: 37V
Short Circuit: 8.6A
IPM: 8.02A

Only the array of 100w panels will be connected to batteries. The array of 235w will be grid tie only. The battery bank for the 100w panel array will be six or eight 6v golf cart batteries which I haven't yet purchased and am open to suggestions on reliable brand/type. The charge controller has yet to be purchased also - was looking at the Outback Flexmax 60 or 80 or one of the similar Midnite Solar controllers. What has been purchases is all the panels, wire and accessories that I mentioned.

Cariboocoot · March 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

Okay, so we have two separate systems here: one off-grid, one grid-tie.

Off-grid has ten 100 Watt panels 17.5 Vmp 5.7 Imp. What will the system Voltage be? You mention "six or eight" 6 Volt batteries, which implies 12 Volt with too many parallel strings. What your 1kW array could do is max out a 60 Amp controller on 12 Volt (about 64 Amps) which would be 600 Amp hours +/-, or three parallel strings of 220 Amp hours (six GC2 batteries) at most.

Your Grid-tie has six 235 Watt panels for a total of 1410 Watts. What GT inverter were you planning on using? One central like an SMA 2000? A bit short on panel for one of those. Usually you'd want a GT array to be slightly higher Watts than the inverter's output.

No offense, but you're kind of designing both systems backwards. Normally you'd pick the major components first (batteries & inverter for off-grid, inverter for grid-tie) and then plan the panels, controller, and wiring to suit. Maybe we should examine what it is you hope to achieve with either or both of these systems. It may be the right solution is to put them together in a hybrid set-up (GT with battery back-up).

Vic · March 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

Hi MO-

In addition to the other comments, Any GT system in the US will really need to be Permitted, Engineered (At least Structrually), and Inspected by the AHJ and Utility.

Using Strut material may work for racking, but may not pass muster for snow loads etc, and there can be galvanic corrosion caused by dissimilar metals twix the PV module frames and the strut.

The 235 W PVs are not really 24 V PVs, and as Coot metnioned may be short on the voltage requirements of most GT Invereters. And trying to switch the 100 watt PV string to the GT would probably be difficult -- string V would probably be incorrect for running a CC and/or the GT inverter ... and so on.

There are many aspects that appear to need more thinking, consideration, and design time, IMHO, not to be too hard on you or your system design. Vic

MO-NH · April 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

Vic, could you please clarify what "would really need to be" means? I'm not big on asking permission and we've got one of the older style dial meters on the house so from what I understand I won't run into issues like I would if we had one of the smart meters.

The 235 watt Sharp panels were sold as specifically being for grid tie systems, so I assume that the lower voltage won't be a grid tie issue. If it is Sharp has some 'splaining to do.

Perhaps it would be easier to handle one system at a time, so let's go with the 235w panel grid tie only array. Thanks for the heads up on the possible dissimilar metal issue. I imagine that a plastic spacer or rubber washer of sorts between the aluminum z brackets and the 1-5/8" galvanized superstrut would rectify that. There cannot possibly be a load issue with this stuff - it's way more rugged than any of the aluminum commercial rooftop stuff like Unistrut that I've seen. This is the link: http://www.homedepot.com/p/Superstrut-1-5-8-in-x-10-ft-Metal-Framing-Channel-ZA1200HS-10/100125003#header

And the 6" steel standoff mounts are seen here: http://www.ebay.com/itm/181079743086

I could add a few more panels if that would be wise to get better grid tie inverter performance. How many would you recommend?

The inverter that I'm looking at is the Fronius IG Plus-V 3.0-1 UNI 3000 Watt. It seems to be one of the better bangs for the buck at a bit over 50 cents per watt of capacity. And it includes a 6 string combiner so I was thinking that adding to it later would be a possibility.

Do you think I have a reasonable handle on beginning the project or do I appear over confident and likely doomed for trouble?

Thanks for any wisdom that may help.

Vic · April 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

OK MO,

Thanks for some more data.

The neat thing about Grid-Tied systems, is that they are part of a grid. The power Utility will want to make certain that EVERYTHING is on the up-and-up. This of coure almost always means that Building Permits will need to be pulled, and, often at least some of the work done by licensed Electricians. Any Inverter needs to meet certain UL standards, and be wired in a certain way. This helps to protect Line workers from electrocution and other pesky things like SHOCKS etc.

Most mechanical electric meters have a provision that they will only spin one way, and if someone tries to back-feed the Grid, the meter spins as if you are really consuming that amount of power as is being fed into the Grid (this is what I read, have not seen this with my own eyes). It IS possible that when the amount of power your system produces is exactly equal to the amount that your address is consuming, that the meter would simply stop turning ...

Have used very similar UniRac stand-offs as lilnked. They work fine, particularly as a part of a system supplied by that manufacturer.

Many Building Authorities require stamped, Engineered drawings, showing calculations of physical loads of the PV array as applied to the structural members of the roof, if the racking is not a part of an Engineered system. This can seem like overkill, but helps protect the structure, and Electrical Permits help protect against FIRE and ELECTROCUTION hazards, and so on.

As Coot mentioned, GT Inverters have specific requirements for String V. Although battery-based Hybrid inverters behave more like off-grid inverters.
Some here do use Fronius GT inverters, will look at that one ... did not know that it supported a battery bank.

AND, you are correct about using insulating washers and Stainless hardware probably elinimating Galvanic corrosion twix the PVs and Strut-type rails.

There IS quite a lot to designing systems like the one that you are probably proposing. Looks like you have spent quite a bit of time thinking about this. There are many here that have experience with GT systems, and know far more than I. Good Luck, Vic

vtmaps · April 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

MO-NH wrote: »

Vic, could you please clarify what "would really need to be" means? I'm not big on asking permission and we've got one of the older style dial meters on the house so from what I understand I won't run into issues like I would if we had one of the smart meters.

Another consideration is that your insurance company (fire, liability) may deny a claim if you have an illegal, unpermitted system.

MO-NH wrote:

I have two small AC breaker boxes that I could use as combiner boxes - I had thoughts of linking both bus bars for the positive and using the grounding bus for the negative. Is this reasonable or would you recommend against it?

Are these breaker boxes weatherproof for use on the roof? It's also good to have a lightning arrester at the combiner... you don't want to bring lightning into the house. What will you use for the circuit breakers that each string of panels must have?

--vtMaps

ggunn · April 2013

Re: I'm looking for advice on how to properly install/wire these 2 panel arrays.

MO-NH wrote: »

Vic, could you please clarify what "would really need to be" means? I'm not big on asking permission and we've got one of the older style dial meters on the house so from what I understand I won't run into issues like I would if we had one of the smart meters.

If you want to install a grid-tied system, then you must get permission from the utility and at the very least allow them to inspect it. When you tie an inverter to the grid it becomes part of the grid and therefore comes under their jurisdiction. You will need to fill out an interconnection agreement with them and install it the way they tell you (in some jurisdictions that means using the services of a master electrician), and if there are any incentives from the utility that you want to take advantage of there may be other hoops to jump through. If you ignore this and connect illegally, they may disconnect you from their service and/or fine you, and they will sue you if anything goes wrong with the installation that damages their equipment.

I'm looking for advice on how to properly install/wire these 2 panel arrays.

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