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  • High capacity grid tie single phase inverter

    I found a supply of panels that were excess from a solar power plant. I want to do somewhere in the 14kw range for our house. However I noticed single phase inverters seem to top out around 8kw. Anyone know why? Should I plan to use two inverters?

    Thank you littleharbor, could NOT for the life of me figure out why I was being truncated.

    Side note: I could not resist buying more panels that I need, so If you are in the ft worth tx area and want some 310-325w Jinko panels for $145 let me know.

    Last edited by Fourthbean; 07-10-2018, 04:42 PM.

  • #2
    Very odd, I can

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    • #3
      You can't use apostrophes' when a new poster, odd but look at where you were cut off.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #4
        When you say "single phase" do you mean normal USA 240V split phase? Aka two 120V legs 180 degrees out of phase?

        Solar Edge has a 11.4kVA 240V inverter (I have one). You can put up to 15,350W DC (STC) on it in theory. Of course I wouldn't necessarily do that unless you have a fair amount of shade, difference orientations, etc. our else you're liable to get a fair amount of clipping.

        https://www.solaredge.com/sites/defa...-datasheet.pdf

        What service is your main panel? 200amps or larger? You'll need to do a line side tap.

        -Jonathan

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        • #5
          You can also do two smaller (e.g. 7600W) inverters as well. I'll defer to others as to which may be the better approach.

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          • #6
            Yes, the inverters tend to top out around 7.6kW. There's a good reason for this. Most residential main panels in the US tend to be at most 200A (most new builds will be 200A and most upgrades go to 200A service and panel.) And they have a 200A main breaker by default. And the 200A panel bus rating is 1.20% of that 200A (i.e. it's 240A), leaving only 40A more that could be fed into it safely (you can mix and match to provide 240A total from grid + solar if you wanted - so you could go a 180A main and 60A for the solar (if you can find a 180A main breaker.) But for code, they're going to limit you to 1.20% of feed, even if you know darn well you'll never pull more than 10-15kW at any giving time. They don't care if you're never going to meet those numbers, they want to make sure that if something does happen and you're driving both ends to the max you're not going to overheat the bus bar.

            So why is 7.6kW the magic number? Well at 240V -> 32A, you size your breakers at 125% of the max current -> 40A breaker.

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            • #7
              Originally posted by Fourthbean View Post
              I want to do somewhere in the 14kw range for our house. However I noticed single phase inverters seem to top out around 8kw. Anyone know why? Should I plan to use two inverters?


              There are larger inverters for residential as noted SolarEdge has an 11.4kw inverter.

              You will need to do a lineside tap or derated your MSP.

              14kW for a residential install is pretty larger. Is your MSP 200A or more?
              What is your annual average usage? You will want to check with your power company on net metering regulations.
              Often there are limits to how much you can install in different regions as well as hard limits, there are often limits to a small percentage of overproduction (often 110% of annual usage).
              OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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              • #8
                How much is a 14 kW array likely to generate per year in your area ? What's your annual usage ?

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                • #9
                  So many quick and helpful replies, thank you!

                  I do have 320A service, but I can see why no one would sell an inverter for that since most are 200A max.

                  Yes by single phase I meant 240v as you described.

                  I amable to feed back to the grid any power I do not use, then choose my retail provider on how that is handled. Should be able to find one where I can pull the energy back in kw for kw. Pretty sweet deal, batter bank I do not have to maintain! I did not see any regulation on how much I could feed back in, just that I would lose any extra after a year.

                  I do not have a good baseline for power as we moved here in December. Last month we were cooling half the house and used over 1500kwh.

                  According to pvwatts with a 14% loss rate I get about 21k kWh a year. Right now I think it will be about right for our 4600sqft house. I do have plans for being more efficient in the future however so it could be overkill in the future.

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                  • #10
                    The PVWatts loss numbers are a bit conservative, most would say drop that 14% down to at least 10%. I'd say you can likely go lower than that even.

                    If you've got a Dec - Most of July history, you likely can get a pretty good estimation of your bills for the other part of the year. Your big changes are likely to be heat and air needs, and you can take a look at what you've used in winter months and summer months, and typical climate values for the other months (and find comparable months that you've already got numbers from) and get a decent ballpark estimate. May want to look to see what the baseline electricity is (i.e. everything off, fridge unplugged and see what the draw rate is on the house) as this is 24/7/365 consumption. There's likely some things you can reduce there, and by doing so reduce the overall PV Size needs.

                    As for the Net Metering - the devil's in the details and little things can add up quickly. I'd make sure you fully understand them before ever pulling the trigger. That said, it sounds in general to be somewhat standard (if there is such a thing) net metering practice of a kWh in a kWh out, you get to carry over excess credit to the next month (check to see if there's charges on this - I effectively get credited about $0.028 less than the pay rate for any excess credit at the end of the month), and then at the end of the year, if the balance is positive (negative is a credit) you owe the balance, if it's negative, you typically don't get the full credit amount that you would have added up, but you typically get paid at distribution rates, which for me would be about $0.03/kWh (meanwhile my rates on TOU vary from $0.21-$0.23 in the 'Winter - Oct 1 - April 30' and $0.27-$0.37 - 'May 1 - Sept 30' That is to say, it's not a financial incentive to overproduce on an Annual scale, it doesn't hurt too much (that cost of having installed a larger system) but it also doesn't really help too much either.

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                    • #11
                      Originally posted by Fourthbean View Post
                      So many quick and helpful replies, thank you!

                      I do have 320A service, but I can see why no one would sell an inverter for that since most are 200A max.

                      Yes by single phase I meant 240v as you described.

                      I amable to feed back to the grid any power I do not use, then choose my retail provider on how that is handled. Should be able to find one where I can pull the energy back in kw for kw. Pretty sweet deal, batter bank I do not have to maintain! I did not see any regulation on how much I could feed back in, just that I would lose any extra after a year.

                      I do not have a good baseline for power as we moved here in December. Last month we were cooling half the house and used over 1500kwh.

                      According to pvwatts with a 14% loss rate I get about 21k kWh a year. Right now I think it will be about right for our 4600sqft house. I do have plans for being more efficient in the future however so it could be overkill in the future.
                      Buy a book: " Solar Power Your Home for Dummies". You need more basic information. 20 bucks well spent.

                      As mentioned, doubling a Dec. - June usage may be a decent 1st approx. for annual usage. But know that conservation and use reduction before PV will pay back 2X - once in bill reduction that's more cost effective than throwing PV at a high electric bill, and 2d, when the PV system can be smaller (less $$) as a result of the smaller, conservation reduced electric usage.

                      Getting PV before conservation and use reduction is doing it exactly backwards.

                      Get familiar with the net metering options and rules your POCO (POwer COmpany) offers, and be aware that such options are probably changing and probably becoming less favorable than in the past. Don't believe much of what you read and hear from the peddlers and the media, or do so at your own risk. This is probably the biggest PITA of the whole exercise, but necessary if you expect any hope of a cost effective system.

                      Use 10 % system losses as suggested, get your own estimates of system output, and don't pay much attention to low production estimates from peddlers who make money putting product on your property, not putting cost effective systems in place or saving you money. No peddler ever got fired for oversizing systems.

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                      • #12
                        Originally posted by Fourthbean View Post
                        I found a supply of panels that were excess from a solar power plant. I want to do somewhere in the 14kw range for our house. However I noticed single phase inverters seem to top out around 8kw. Anyone know why? Should I plan to use two inverters?

                        Thank you littleharbor, could NOT for the life of me figure out why I was being truncated.

                        Side note: I could not resist buying more panels that I need, so If you are in the ft worth tx area and want some 310-325w Jinko panels for $145 let me know.

                        325W Jinko panels are probably 72-cell - make sure you are properly accounting for the voltage on them.

                        There are plenty of 10kW+ inverters.
                        Fronius has a 15kW inverter.
                        Solaredge has a 11.4kW - and you also have possible choice of doing multiple inverters (ex. a 7.6kW and a 5kW or a pair of 7.6kW)

                        Many places have simpler rules for 10kW and smaller installations - so you probably want to look into that. (And there are rules for the permit dept (AHJ) and for the POCO - so make sure you understand both before you buy more stuff.

                        And I'd definitely want to iron out the details on how the POCO billing will work.
                        I'd be surprised if you can bank kwh for over a year. I'm not saying it's impossible - just that such a thing would be unusual.
                        The typical (or typical for favorable-to-solar ) is that the kwh and $ billing is settled up once a year on the anniversary of the system being online (from POCO's perspective)
                        Sometimes the kwh are paid out at $0/kwh - sometimes at a small amount per kwh (like what the POCO pays for power, which may be like $.04/kwh
                        Every POCO is different though - so make sure you understand *your* POCO's rules.


                        BTW - if you do solaredge system make sure the optimizers are right for your panels - most people have 60-cell panels, and I *think* yours are 72-cell, which probably means a different optimizer.

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                        • #13
                          TAZ427, I appreciate the insight that the 14% number is conservative. I will dial it up to 10% as you suggest for my calculations.

                          As mentioned I should have a handle on cooling/heating costs with the months I have been here. I have likely gotten ahead of myself as my panel price is low enough I am considering "throwing panels at my utility bill" as it seems easier than air sealing, blowing insulation, replacing windows, sealing 16x8 holes in our floors, you know - the basic stuff . Looks like my panel cost is going to be about the same as my inverter cost.


                          J.P.M, I cannot stand peddlers. Can't trust a word they say . Do you know if that book is something I could digest in audio format or should I get a text version? Some times there is a lot of reference material that is hard to understand in audio format.

                          Thankfully here in Oncor territory it is regulated by the Public Utility Commission of Texas. The customer is looked out for pretty well in that sense. So one of the plans I looked at allowed me to store KWh in the grid for when I need it later.


                          foo1bar, I forgot Solaredge did the power optimizer deal. Sure hits my per panel price when I have to throw one of those on each. And good point with my 72 cell panels being higher voltage than most residential systems. I'll check out the other options you presented, appreciate it! I hadn't found Fronius in any of my previous searching.

                          Comment


                          • #14
                            Originally posted by Fourthbean View Post
                            TAZ427, I appreciate the insight that the 14% number is conservative. I will dial it up to 10% as you suggest for my calculations.

                            As mentioned I should have a handle on cooling/heating costs with the months I have been here. I have likely gotten ahead of myself as my panel price is low enough I am considering "throwing panels at my utility bill" as it seems easier than air sealing, blowing insulation, replacing windows, sealing 16x8 holes in our floors, you know - the basic stuff . Looks like my panel cost is going to be about the same as my inverter cost.


                            J.P.M, I cannot stand peddlers. Can't trust a word they say . Do you know if that book is something I could digest in audio format or should I get a text version? Some times there is a lot of reference material that is hard to understand in audio format.

                            Thankfully here in Oncor territory it is regulated by the Public Utility Commission of Texas. The customer is looked out for pretty well in that sense. So one of the plans I looked at allowed me to store KWh in the grid for when I need it later.


                            foo1bar, I forgot Solaredge did the power optimizer deal. Sure hits my per panel price when I have to throw one of those on each. And good point with my 72 cell panels being higher voltage than most residential systems. I'll check out the other options you presented, appreciate it! I hadn't found Fronius in any of my previous searching.
                            On the book: 20 bucks softcover. Don't know about other formats, but for the amt. of reference data, tables etc. contained, it doesn't seem to lend itself to an audio format. Good, basic stuff.

                            I think I understand about peddlers. Few who claim sales job titles are little more than order takers and clerks. I spent 10 yrs. as a sales rep/slug. Got bored and sick/tired of explaining simple principles to people claiming to be engineers, so I went back to school and became one (an engineer, that is). Took a pay cut to do it, but not bored afterward.

                            As for living in an energy sieve, suit yourself. Just sayin' it's cheaper and probably more comfortable to not use energy through conservation than to produce more of it, particularly where electricity costs are relatively low as in most of TX, and particularly now that net metering will be winding down. You'll understand why as you get more informed.

                            Good luck.

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                            • #15
                              IMHO go with a couple of smaller inverters and shoot for a model with two or more independent MPPT circuits. That way you end up with 4 independent MPTTs in case you have a shading issue with part of the array the other 3/4s keep chugging along unless they too are affected. Also if you smoke an inverter you still have 50% capacity while you replace the smoked one. Its also nice to be able to compare the two to each other for troubleshooting.

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