Amateur doing a 10kw system, can someone tell me if I missed anything

WhittakerJ

All,

I'm looking to build a 10kw setup using in my backyard. I'm going through a steel company to have them build a "solar carport" basically just to hold the panels. The panels I have found for a good price are the Trina TSM-275PA14. I'm actually getting ready to purchase 36 of these today. I'm going to use it in combination with the Fronius IG Plus V 10.0-1 UNI. Given that I have to install this in my backyard, given that my roof faces east and west, the run to the electric box in the front of the house is going to be roughly 110'. My first question is it better to get the panels into the inverter and shoot a 220v line 110' or to combine the DC voltage from the inverters and run this DC line 110'? I'm thinking the AC line will be better from other posts I've read. Given the panels and inverter can someone tell me if these will work good together? Are they good panels and is the inverter good? I've weighted going micro-inverter but the cost just does not seem justifiable. Any feedback would be great.

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Got your permit yet?

This is not something you'll be allowed to do without contacting the utility and the AHJ. At which point they should have requirements that must be met, including on the wiring runs.

In case they don't, you want the longest wire run to be at the highest Voltage. In a central GTI installation this is usually the PV array, which tend to run in the 400 Volt neighbourhood. Check Fronius's specs on the inverter for DC input Voltage. It will have at least a minimum and maximum, and possibly a 'best' range.

If you were to use micro-inverters it would be no choice, as there is only the 240 VAC output from the individual inverters ganged together.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot wrote: »

Got your permit yet?

This is not something you'll be allowed to do without contacting the utility and the AHJ. At which point they should have requirements that must be met, including on the wiring runs.

In case they don't, you want the longest wire run to be at the highest Voltage. In a central GTI installation this is usually the PV array, which tend to run in the 400 Volt neighbourhood. Check Fronius's specs on the inverter for DC input Voltage. It will have at least a minimum and maximum, and possibly a 'best' range.

If you were to use micro-inverters it would be no choice, as there is only the 240 VAC output from the individual inverters ganged together.

Cariboocoot,

I have not go the permit yet. I found a good deal on the solar panels so at this point I just really wanted to confirm that these are good panels with that specific Fronius inverter. Can you offer any insight on this? Is it worth spending more money on a different inverter? The guy that I'm buying the panels from indicated they are left over or extras from a large commercial install. I looked them up and their specs are 72-cell and they are the utility grade ones. I'm not sure if this matters or not? I live in Mesa, AZ. Any advice on getting the permit for the install?

Photowhit

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

They appear to be UL listed panels, Be sure the extra or left overs, isn't just a ploy to sell you something. I've seen Trina panels as low as 65 cents a watt FOB California.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Photowhit wrote: »

They appear to be UL listed panels, Be sure the extra or left overs, isn't just a ploy to sell you something. I've seen Trina panels as low as 65 cents a watt FOB California.

For that specific model it is a "utility grade" according to Trina's website. From which I understand just means they were built with higher quality from what I can find. I have scoured the internet and I have not been able to find them cheaper than $.79c/watt for that model and that is if you order them in a very large quantity. I'm paying $.74c/watt delivered which seems like a pretty good deal.

Here are the specs - http://www.posharp.com/photovoltaic/solarpanel.aspx?pid=3830bf22-0b77-4f6d-a505-edc95967be98

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

WhittakerJ wrote: »

Cariboocoot,

I have not go the permit yet. I found a good deal on the solar panels so at this point I just really wanted to confirm that these are good panels with that specific Fronius inverter. Can you offer any insight on this? Is it worth spending more money on a different inverter? The guy that I'm buying the panels from indicated they are left over or extras from a large commercial install. I looked them up and their specs are 72-cell and they are the utility grade ones. I'm not sure if this matters or not? I live in Mesa, AZ. Any advice on getting the permit for the install?

Trina panels are known to be good quality. Our host NAWS carries some. I see the 240's listed @ $0.99 per Watt.

Thirty-six of the 275's would be 9900 Watts, just under the Fronius's 10 kW rating. Is this the inverter? http://www.solar-electric.com/frigpl10uni1.html Usually you want a bit more panel than the GTI is rated for in order to keep production at its maximum. Fronius has an array configuration tool here: http://www.fronius.com/froniusdownload/tool.html
Usually can't beat the company's own calculations.

If the panels do not have the UL listing (or similar qualification) on them the AHJ isn't going allow them. Not sure what "utility grade" means in that respect.

Unfortunately I don't live in Mesa - or even in the US - so I can't really help you there. I know there are people on the forum who do live near there so I hope they'll chime in.

Photowhit

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

It does sound like a good deal, I would be sure that they are considered new panels with full warranty, so you can receive the 30% tax credit.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot wrote: »

Trina panels are known to be good quality. Our host NAWS carries some. I see the 240's listed @ $0.99 per Watt.

Thirty-six of the 275's would be 9900 Watts, just under the Fronius's 10 kW rating. Is this the inverter? http://www.solar-electric.com/frigpl10uni1.html Usually you want a bit more panel than the GTI is rated for in order to keep production at its maximum. Fronius has an array configuration tool here: http://www.fronius.com/froniusdownload/tool.html
Usually can't beat the company's own calculations.

If the panels do not have the UL listing (or similar qualification) on them the AHJ isn't going allow them. Not sure what "utility grade" means in that respect.

Unfortunately I don't live in Mesa - or even in the US - so I can't really help you there. I know there are people on the forum who do live near there so I hope they'll chime in.

I ran the utility, thanks by the way. It looks like I can do 4 strings with 9 panels each totaling 9912. According to the utility it says this is optimal. Can you confirm I'm reading this correctly?

Attachment not found.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Photowhit wrote: »

It does sound like a good deal, I would be sure that they are considered new panels with full warranty, so you can receive the 30% tax credit.

How would I know if they are not considered new with full warranty? According to the guy, private seller, he said they were. He said he would write up a receipt and everything with attached drivers license. He is arriving from Nevada in about an hour to deliver them. I hope they qualify!

Photowhit

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

I think he would need to be a retailer for Trina, but I honestly don't know what the standard of compliance is for Trina. I would suspect if they haven't been installed someone else hasn't taken the tax credit, but I don't know what Trina's standard is for a warranty, or if perhaps they sold them to a utility with the understanding that the utility would self insure, some large projects/companies will do this when negotiating, but I don't know if this is common in the solar industry.

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Could someone with a bigger screen/better eyesight confirm the OP is reading that sizing tool results right?

The 9x4 9912 Watt array looks right to me.
10x4 11012 Watt array looks a bit better.

If you're buying from a private seller they will probably be classified as "used" and miss on the incentives. I don't know; we have no such incentives up here. We have the opposite of incentives: high prices and 12% sales tax.

Photowhit

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot wrote: »

The 9x4 9912 Watt array looks right to me.
10x4 11012 Watt array looks a bit better.
We have the opposite of incentives: high prices and 12% sales tax.

Yes it looks like 4 strings of 10 would be optimal on the inverter, but that 4 of 9 would work and is one of the recommended setups.

You don't even have solar as a tax free item? I was surprised how many states(US) have solar as tax free and often not an additional tax burden (added value) in considering a homes tax value.
under page
Ever try 'blowing up' the image on your screen? In IE you can set a zoom %, mine lives at 125% since I switched to a 12" screen portable. Most browsers have this feature, and most web pages will scale to fit.

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Uh, mine is already enlarged. If I poke it up any further it just gets blurry.

No, the government here isn't very helpful on solar. They say they want people to be efficient and save energy, so they discontinue incandescent bulbs. Used to have a tax break on insulation and panels and such ... not any more.

Photowhit

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot wrote: »

...They say they want people to be efficient and save energy,....

Careful, the only sure way to get "people to be more efficient and save energy" is to raise the cost of energy... new tax revenue for the government! and more efficient populous! ...a win-win! ...just a bunch of poorer, stressed voters!

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Photowhit wrote: »

Careful, the only sure way to get "people to be more efficient and save energy" is to raise the cost of energy... new tax revenue for the government! and more efficient populous! ...a win-win! ...just a bunch of poorer, stressed voters!

Funny you should mention that, as BC Hydro rates are going up next Spring and then again until they reach their 50% over-all rate increase in a few years (they keep changing the scheduling on us so I can't pin it down).

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

First I just want to say thanks for answering my questions yesterday.

I received the panels and I'm measuring the wattage to make sure they are putting out the amount they should be. They are registering 8.71 amps and 40 volts. It is my understanding that you multiply the volts and the amps to get the wattage. Which in my case it comes out to 348.4 watts. How is this the case if the solar panels are only rated at 275 watts? Are they really producing 26% more power than they should be?

BB.

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Because most people measure Isc (short circuit current) with their meter and not Imp (current maximum power).

Isc is roughly 10%-35% higher than Imp (which is measured with voltage held at Vmp). And panels are around +/- 5% (some are tighter) tolerance.

Also, you are assuming Vmp which is measured/spec'ed at STC (standard test conditions with cell at ~25C). The "real" operating temperature is around ~45C at the cell (and upwards of 55C+ on hot summer days).

Assuming a typical -0.43% per degree C derating:

(45C-20C) * -0.0045 per C derating = 0.0645 = ~-6.5% derating in panel power in a "real" installation) [should have been -25C, not -20C]

Multiply all of your deratings together, and you will really be at ~81-85% of panel name plate rating on a clear/cool day.

-Bill

Plus it sounds like you may have used Voc (voltage open circuit) times Isc -- Which is not a "real" number. Voc is only "true" when there is no current flow.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

BB. wrote: »

Because most people measure Isc (short circuit current) with their meter and not Imp (current maximum power).

Isc is roughly 10%-35% higher than Imp (which is measured with voltage held at Vmp). And panels are around +/- 5% (some are tighter) tolerance.

Also, you are assuming Vmp which is measured/spec'ed at STC (standard test conditions with cell at ~25C). The "real" operating temperature is around ~45C at the cell (and upwards of 55C+ on hot summer days).

Assuming a typical -0.43% per degree C derating:

(45C-20C) * -0.0045 per C derating = 0.0645 = ~-6.5% derating in panel power in a "real" installation)

Multiply all of your deratings together, and you will really be at ~81-85% of panel name plate rating on a clear/cool day.

-Bill

Plus it sounds like you may have used Voc (voltage open circuit) times Isc -- Which is not a "real" number. Voc is only "true" when there is no current flow.

BB,

Thanks for the reply. I'm not an electrician so I'm honestly not sure how to I switch my multimeter to measure current maximum power and not ISC? I only see one option on it for measuring voltage other than changing it to a lower voltage setting.

If I understand your math right regarding the temperature and it's 39c here currently in Mesa, AZ then (30c-25c) * -.0045 = 2.5% (You also quoted 25c and 20c in your calculation so I'm not sure which it is.

In regards to using VOC how do I do that with no current flow?

I guess my real question is this. How can I verify that these are putting out 275w given that I only have a $20 multimeter. Is it not possible?

BB.

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Sorry, it is supposed to be 25C.

Also, you forgot temperature rise from the sunlight... Remember that NOCT (normal operating cell temperature) is something like 45C @ 25C ambient temperatures. And you can get ~20-30C rise (lots of sun, not much wind/ventilation around panels) of cell temperature... So worst case:

Pderate = (30C rise + 39C ambient - 25C STC) * -0.0043 per C derating = -0.1892 = -18.9% power derating

Also remember that it is Voc/Vmp that fall with increasing temperatures (as well as copper trace/wire resistance). Imp/Ioc does actually increase, but only by 1/5 or 1/10 as much as Vmp falls.

Regarding measuring Imp--It is actually not that easy. A "close" method would be to connect your solar array to a 12 volt battery (if Vmp~18 volts). Then measure current from the panel.

Measuring/estimating Voc is easy--Just measure the panel voltage with a digital volt meter--They draw such little current that the voltage you measure will be very close to Voc (open circuit voltage). Note that Voc (and Vmp) need to be derated for "hot" panels.

Otherwise, we measure Isc and Voc and assume the panel has a 90%+ chance of being good. There are a few failure types where you would need to do the 12 volt battery measurement to find certain panel failures.

Measuring Vmp is easiest by simply attaching a MPPT type charge controller with a partially discharged battery bank (or heavy load on the battery) to insure the MPPT controller is in "Bulk" charging mode and using MPPT algorithms.

In general, our deratings work pretty well on a properly designed and configured system. Humidity, dust in air, altitude, etc.--It is easy to have a +/- 10% variation in solar radiation--So measurements that are within ~10% of expected values are perfectly OK.

On a running system, failures generally are only "obvious" when the system approaches 50% (or less) of typical rated output.

-Bill

NorthGuy

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

WhittakerJ wrote: »

If I understand your math right regarding the temperature and it's 39c here currently in Mesa, AZ then (30c-25c) * -.0045 = 2.5% (You also quoted 25c and 20c in your calculation so I'm not sure which it is?

When derating panels, you should use temperature of the panels, not the ambient air. Panelas are usually 25-30C warmer than the air around them.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

So given that all I have at this point are the panels and no other equipment except for my multimeter is there any type of test I can do that will simply give me the approximate range of the solar panels wattage? I just want to make sure that they are actually working since I did buy them from a private seller and not retail.

DanS26

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

WhittakerJ wrote: »

So given that all I have at this point are the panels and no other equipment except for my multimeter is there any type of test I can do that will simply give me the approximate range of the solar panels wattage? I just want to make sure that they are actually working since I did buy them from a private seller and not retail.

Just take your measurements with a good quality mutimeter measuring DC volts in the proper range. If it equals or exceeds the panel rating volts as indicated by the panel label then you are good to go.

Sounds like you got got a good deal. Many here are envious on this forum. Some old timers here have paid over $5 per watt. Good luck with your install and get that permit.

Check out the IronRidge mounting systems. Good quality stuff that will last.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

DanS26 wrote: »

Just take your measurements with a good quality mutimeter measuring DC volts in the proper range. If it equals or exceeds the panel rating volts as indicated by the panel label then you are good to go.

Sounds like you got got a good deal. Many here are envious on this forum. Some old timers here have paid over $5 per watt. Good luck with your install and get that permit.

Check out the IronRidge mounting systems. Good quality stuff that will last.

Thanks DanS26. The panels are measuring almost exactly 40 volts. But on the label there are two separate voltages the Vmp and the Voc. The Vmp is 35.85V and the Voc is 44.4V Hopefully it is the Vmp that I need to be higher than because I'm almost 10% lower than the Voc!

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

WhittakerJ wrote: »

Thanks DanS26. The panels are measuring almost exactly 40 volts. But on the label there are two separate voltages the Vmp and the Voc. The Vmp is 35.85V and the Voc is 44.4V Hopefully it is the Vmp that I need to be higher than because I'm almost 10% lower than the Voc!

With no load on the panel you will be measuring Voc - Voltage open circuit. This matters for calculating maximum input to a charge controller or grid tie inverter. It will vary somewhat with insolation.

Vmp is Voltage maximum power and is what matters for operation. You will not be able to measure this under normal circumstances. What is more, with MPPT operation (either controller or GTI) you may never see it as the Voltage will be "fixed" at what the input controller thinks is best, and will change with varying conditions.

inetdog

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot wrote: »

With no load on the panel you will be measuring Voc - Voltage open circuit. This matters for calculating maximum input to a charge controller or grid tie inverter. It will vary somewhat with insolation.

It will vary a lot more with the temperature produced by the combination of ambient and insolation than it will with insolation alone. In fact, as the insolation gets stronger the temperature will rise and the Voc will go down.

Cariboocoot wrote: »

Vmp is Voltage maximum power and is what matters for operation. You will not be able to measure this under normal circumstances. What is more, with MPPT operation (either controller or GTI) you may never see it as the Voltage will be "fixed" at what the input controller thinks is best, and will change with varying conditions.

In theory (famous last words) the Vmp will not change much at all with anything but temperature and partial shading of the panel.
If you have really high loop resistance in the DC leads from panels to MPPT device, Vmp as seen at the device may change with current because of that. The MPP combination as determined by the power reaching the controller will not necessarily correspond to the panel MPP alone either.

Skippy

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot wrote: »

Uh, mine is already enlarged. If I poke it up any further it just gets blurry.

No, the government here isn't very helpful on solar. They say they want people to be efficient and save energy, so they discontinue incandescent bulbs. Used to have a tax break on insulation and panels and such ... not any more.

Ya, I here ya. . . I am still working thru setting my panels up - AND - getting them running... 77 cents a watt - delivered - REALLY GOOD DEAL.

But then it's only a good deal if you can use em.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Ok, guys so I'm trying to move forward on this system and trying to figure out my options. I appreciate the feedback on the Fronius calculator. My question as it pertains to this calculator setup however is, can I only create the array in their given sizes? Or is it possible to create a different layout? I'm assuming they have this utility so that the inverter makes sure it's getting the right amount of inputs in volts and amps per string?

Attachment not found.

The reason I ask this is I'm trying to put 6 panels on my roof and the rest of them on a steel structure that I would create in my backyard. The problem I'm facing is I would have to mix and match the panels on my roof with a couple from the array in the backyard on the same string. According to the string calculator I would have to do 9 modules and 4 strings to get 36 total. It is the only way this would work from my calculation, correct? So would I have to take 3 panels out of my ground array and add them to the roof panel string?

Here is my proposed plan:

Attachment not found.

Is this method going to degrade the system given the panels on the roof face a different direction than the ones in the backyard? Should I purchase 6 Enphase micro-inverters for the roof mount panels? and then just do 3 strings of 10 modules for the backyard PV array?

Cariboocoot

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Panels facing in different directions and/or in different locations is going to have an effect of the total array output at any one time. You really do not want to break up the array on a central inverter, as it may not supply the full power possible ever. And if the strings themselves get divided then you could fall short on Voltage for the string so that it would not contribute to the production. If all the strings are broken up you may not even achieve the minimum Voltage to activate the array.

If you've got a situation where the panels have to be in various places and not all oriented the same micro-inverters will do better for maximizing the power from the total panels.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

Cariboocoot,

Thanks for the quick reply. Given the layout that I've drawn and my equipment. Would you suggest micro-inverters for the roof then?

In regards to my panels on the back structure. Would it be ok to run those 72' using DC voltage? If I were to break out my panels on the roof using microinverters I could then choose to mount my central inverter in the rear yard and run 240v AC. Which would make more sense? Or how would you run this given my setup?

solar_dave

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

WhittakerJ wrote: »

Cariboocoot,

Thanks for the quick reply. Given the layout that I've drawn and my equipment. Would you suggest micro-inverters for the roof then?

In regards to my panels on the back structure. Would it be ok to run those 72' using DC voltage? If I were to break out my panels on the roof using microinverters I could then choose to mount my central inverter in the rear yard and run 240v AC. Which would make more sense? Or how would you run this given my setup?

Central inverter in backyard and micro inverters on the roof, It may require a AC combiner to make a single connection the load center, it is a question for the AHJ as to what is acceptable.

WhittakerJ

Re: Amateur doing a 10kw system, can someone tell me if I missed anything

solar_dave wrote: »

Central inverter in backyard and micro inverters on the roof, It may require a AC combiner to make a single connection the load center, it is a question for the AHJ as to what is acceptable.

Thanks Dave, so then my AC run would be about 108' from the inverter to the AC box. That would not be a problem?
Lilkewise I would installer a combiner box on my air conditioner for the 6 micro-inverters and then run one 240v line down to a breaker/combiner box about 80 ft total to the electric box. Is this going to be ok?

Couple of other questions. I live in Mesa, AZ. I'm not sure who my AHJ is. Does anyone know what:
Breaker sizes would need to be for the two AC runs?
Cable gauge?
Length to bury 240v run from rear of house?
Acceptable conduit?