Inverter Monitoring via the Internet, and other questions...

System

I'm going to be pulling the trigger on a PV system for my home here in the Bay Area (CA), and. Please correct me if I'm wrong, but it seems that the packaged systems are a bit less expensive than buying the component separately. Any thoughts on this? The package I want to buy comes with a PV Powered inverter. Does anyone use one of these and if so, what's your take on it?

1. Being able to remotely monitor my system via the internet is very important to me. I know it might be overkill and that the computer will use electricity if I leave it on, but I don't care...I want to be able to remotely monitor it. Which of the inverter manufacturers do this best?

2. It's my understanding that PG&E (in CA) no longer requires a AC Disconnect. So, the wiring comes from the panels, into a DC Disconnect, into the invererter, and then directly from the inverter to the main electrical panel? Or am I missing anything?

3. I'm confused about the "blocking diodes" or whatever they're called. Can someone explain what these are, how they work, how they're installed, etc?

4. For those of you that use Unirac mounts on a composition shingle roof, do you just use the angled brackets or did you use the standoffs with roof jacks on every one? My roof is a 5 year old 30-year composition roof. So, my system will be installed on an existing roof...(obviously I guess)

5. I will have some shading, but throughout the middle of the day I'll have strong sun exposure. It was suggested that I use two inverters...one on each string...so that the shade will only drag down one array as opposed to 2.

6. Anyone use a Solmetric?

I'm sure I'll have many more questions...but this is it for now. :-D

BB.

Re: Inverter Monitoring via the Internet, and other questions...

1. www.solar-guppy.com for support with the Xantrex GT software (RS 232 from Inverter). Others out there too--but please use a small/low power computer... 300 watts big desktop system w/ monitor * 24 hours = 7.2 kWhrs per day--that is about 1/3 to 1/2 the daily production of a 3.5 kWh array.

2. Some GT inverters include the AC/DC disconnect as part of the inverter (Xantrex GT).

3. Blocking diodes are (typically) used for installations where you just connect a 12 vdc solar panel (really ~17-21 vdc) directly to a battery without a charge controller. Prevents the battery from back feeding (small current) into the solar array at night. Not needed for your installation.

4. Don't remember my brand but it is just mounted flat to my ~35 degree pitched composition roof--no standoffs or manual/auto tilt.

5. What time is the shading--how long is the shading? Will you use two smaller inverters (say two 1.5 kW instead of one 3 kW)? What brand of inverter and what voltage are you planning on wiring your array for (as an example, the Xantrex GT will operate from ~200 vdc to ~550 vdc. If you wire your panels for 200 Vmp on a warm day, get shading, your inverter will hit low voltage cutout. If you wire your inverter for say 400 vdc, then if panel is shaded by -200 vdc, the inverter will still be able to output 1/2 power at 200 vdc input). (caution, made up numbers coming up here) If two inverter get you 20% more power--a 3.5 kWhr array may generate around 1,000kWhr extra power--or about $115 per year at E-1 rates. If that inverter cost you $1,150--it will take 10 years for you to break even (plus, the inverters are probably 10-20 year life--at best--products--you may be buying your replacement inverters about when you break even). There is at least one inverter out there that supports at least two independent strings--don't remember the name but you can find it with google.

6. Not me.

My two cents--dump the computer interface and use one (cheap/good quality) inverter unless you have something strange like an East/West installation (1/2 the panels on the East, and 1/2 panels on West facing roof). The computer/internet interface will probably eat up more power than you would generate with a second inverter (splitting arrays).

I too think computer access to the data is nice--but I am cheap (cheap means not buying a small data logging computer and not spending the extra couple kWhrs per day to operate it) and therefore just log the daily kWhr, Total kWhr and time to paper from my installation (about every night). There are so many variables out there (shading, growth of trees, dust, clouds, humidity, temperature, wind, aging, etc.) that can effect the array/inverter output that I could never justify (or even figure out what to do with) the fine grained amount of data. I type the daily log into a spread sheet (when I get my PG&E bill) and with the TOU meter readings from my bill, keep track of how much energy my home uses and my net power dollars to ensure that I am still not wasting energy.

Back calculating the usage by my home (and watching for any abnormal panel/system degradation) is why I still continue to collect data.

-Bill

mike95490

Re: Inverter Monitoring via the Internet, and other questions...

the link under my avatar goes to my monitor page. I usew a GT series inverter & I use an old laptop, it has a 70W power brick, and when it's monitor is off, I'll make a wild guess, that it only pulls about 30 watts.
30wx24hrs=720wh /day x30days = 21,600 month Gack !!!! is that right ?

BB.

Re: Inverter Monitoring via the Internet, and other questions...

Yep, my old laptop on 12+hours per day draws about 0.5 kWhrs per day.

And by the way blackmountain--I am not a Xantrex employee--it is just the unit that I ended up getting installed in my installation (and from what I have read and my own use--I am very happy with it).

-Bill

mike95490

Re: Inverter Monitoring via the Internet, and other questions...

BB wrote:

What brand of inverter and what voltage are you planning on wiring your array for (as an example, the Xantrex GT will operate from ~200 vdc to ~550 vdc. If you wire your panels for 200 Vmp on a warm day, get shading, your inverter will hit low voltage cutout.

I thought that the temperature was the Voltage influence, and the brightness was the Amperage influence, and that if using a MPPT inverter, that the inverter will hunt around to find the best wattage configuration.

Roderick

Re: Inverter Monitoring via the Internet, and other questions...

blackmountain wrote:

I'm going to be pulling the trigger on a PV system for my home here in the Bay Area (CA), and. Please correct me if I'm wrong, but it seems that the packaged systems are a bit less expensive than buying the component separately. Any thoughts on this? The package I want to buy comes with a PV Powered inverter. Does anyone use one of these and if so, what's your take on it?

I have a PV Powered PVP2800-XV. Probably from the same place you're thinking of. If I had to do it again, I would have asked the place that sold me the kit how much it would be for various options, such as discount for no inverter, or different inverter. And I might have been able to get a better deal on the inverter, elsewhere. On the other hand, the lion's share of the cost is the panels, themselves, so once you know what kind you want, then shop for best price. The PV Powered inverter has a few quirks, such as not starting up for a long time when perfectly good sun is shining on the panels, and putting itself to sleep for the night before the sun is completely down. This doesn't happen all the time, but I think their algorithm for determining whether the sun is up can use some work. I'm able to force the inverter on by disconnecting and reconnecting the AC, so I'm glad I put in that disconnect switch. I don't want to scare you - I don't think the inverter has cheated me out of large amounts of power, just bits at the start and end of the day.

Oh, also - in getting the kit, I'd tell them not to include wire, unless I knew it was THWN-2 or USE-2, individual conductor, and at a good price. The kit included this TC-2 wire, which was sunlight resistant, but only rated for 75 C when wet. I put it in conduit, and the inspector flagged it. Plain old #8 THWN-2 from Home Depot was the solution.

blackmountain wrote:

1. Being able to remotely monitor my system via the internet is very important to me. I know it might be overkill and that the computer will use electricity if I leave it on, but I don't care...I want to be able to remotely monitor it. Which of the inverter manufacturers do this best?

The PVP-2800XV is supposed to have a "Starlink" module available, that brings out 802.11 connectivity. However, that's not standard. If that's your interest, I would inquire as to its availability, first. The standard monitoring method for this inverter is RS-232. The monitoring program seems to be capable of supporting multiple inverters, but is only that - a monitoring program. I'm not aware of it being able to send any commands to the inverter.

blackmountain wrote:

3. I'm confused about the "blocking diodes" or whatever they're called. Can someone explain what these are, how they work, how they're installed, etc?

I was thinking one big power rectifier per string to prevent one shaded string from dragging down a sunny one. This is all theoretical for me; I didn't actually do it. It seems that the only time there is a big differential in lighting between the two strings is early morning and almost sunset, so I said never mind.

blackmountain wrote:

4. For those of you that use Unirac mounts on a composition shingle roof, do you just use the angled brackets or did you use the standoffs with roof jacks on every one? My roof is a 5 year old 30-year composition roof. So, my system will be installed on an existing roof...(obviously I guess)

I expressly asked the vendor to substitute Unirac standoffs for the L-feet that would be supplied by default. I'm glad I did - the higher the array can sit off the roof, the better it gets cooled by the afternoon wind. If I had to do it over again, I'd go with 12" standoffs, or at least 6", and would pay more to get them. 6" is about the minimum you or a roofer would need to flash the standoff with conventional flashing. If you choose a 3" standoff, then you'll be forced to go with something like an Oatey no-calk flashing, which is still ok.

The bad thing about standoffs is they are more work to put in. With the L-feet, you simply lag screw them into the rafters right through the composition shingles and felt, trying to seal up as best you can with roof caulk. The difference is work is the difference between 3 hours and 3 days.

blackmountain wrote:

5. I will have some shading, but throughout the middle of the day I'll have strong sun exposure. It was suggested that I use two inverters...one on each string...so that the shade will only drag down one array as opposed to 2.

Two inverters sounds expensive. I think the Magnatek inverters used to have two independent MPPT inputs. I could be wrong.

Small inverters might be easier to mount, though. With PV-powered, it seems that the more one of their inverters is rated for, the heavier it is.

BB.

Re: Inverter Monitoring via the Internet, and other questions...

Mike,

Temperature does affect, mostly, voltage. Light intensity mostly affects current. You have that right.

However, I was talking about shading of panels by trees/power lines/etc.--so, for example, shade one panel will stop producing voltage, but the bypass diode(s) will let the current pass through from the other panels--thereby, in theory, the current will remain the same but the output voltage of the string will be reduced by the Vmp of the panel + ~1 volt drop of the bypass diode.

Panels are wired differently between models and vendors (for example a 200 watt 12 vdc panel may have two strings in parallel, but the 24 vdc version may have all cells in series) and will react to shadows differently. So, if yo have specific obstructions (say a vent pipe), you may find panel orientation may affect its output when shaded. Also will be dependent on how many and were the bypass diodes are installed in the panel (I think that silicon PV cells go "high resistance" when dark--so you need a bypass diode to pass current and prevent damage from over voltaging a dark cell/panel when connected to a high voltage (typically) Grid Tie type inverter).

Also, we can bring up at this point that not all MPPT algorithms are created equal. On solar controllers that charge batteries, the algorithms seem to be a bit weak. One very good vendor only recalculates the V-Impp only every 5-15 minutes (IIRC). Another controller simply takes the open circuit value and sets the voltage to xx% of the open circuit voltage--neither of these algorithms will really track changing MPP's very well for short term disruptions (clouds, moving shadows, etc.).

Solar Guppy--one of the Xantrex GT designers--says that the Xantrex GT ajusts MPPT on a cycle by cycle basis (60 Hz AC Output).

You can go over to his site at www.solar-guppy.com and talk with him more about his experiences with MPPT functions on different controllers (he tested many of the leading products before).

-Bill "so much to type, so little time" B.

System2

Re: Inverter Monitoring via the Internet, and other questions...

To answer some questions, I haven't decided on those levels of details. I'm shooting for somewhere around 20-22 panels, probably Mitsubishi 165w panels, which I'm sort of under the impression are good panels and decently priced? I was planning on dividing the up into 2 parallel strings...well, let's say 10 panels wired in series, paralleled with the other string. Most likely one inverter, unless someone can convince me that it would really be worth having two.

As for my shade, my winter sun is a little weak. I've accepted it and it's fine. I don't have a perfectly ideal location, but that's OK.

I don't know. The problem with doing this myself (I'm a contractor so of couse I'm installing them myself), is that there are so many options and choices to make, that I don't really even know where to begin!