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Thread: Solar power inverter sizing.

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    Default Solar power inverter sizing.

    I am about to get a 1 KW solar system. Normally this would come with a 1 KW grid connect inverter. I am thinking of ordering a larger inverter say 2 KW so I can add more panels latter on without having to also buy a new inverter.

    From what I understand the panels are connected in a combination of series panels and parallel groups of series panels so as to not exceed the inverters maximum input voltage and to provide an optimum input voltage.

    Someone mentioned there would be efficiency losses using a larger inverter i.e. 1 KW of panels and a 2 KW inverter. Is that correct I would have thought bigger would simply mean the ability to supply more power and providing the panels feed the inverter with the connect voltage it would not matter.

    I thought it might be related to the minimum start voltage of the inverter but I can’t find any info on that being an issue. I am looking at using Sunnyboy inverters.



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    Wink A small price to pay.

    G'Day Cobber,
    My thoughts would be that the idle current (power) would be higher due to the higher rating of the active components. My opinion would be that this is a small price to pay in efficiency, for the benefit of later expansion, without the cost of upgrading the unit.
    Kindest Regards, " The Druid ".......

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    Well I've found the answer.

    SMA the makers of the inverter have some nice design software you can download.



    It's 161 MB in size when you install you must tell it to load the Australian data or it will default to Germany.

    Anyway the results of my what if's

    These assume 1 KW of panels located in Melbourne.

    SB1100 inverter = 915 kw per year performance ratio 77%

    SB1700 inverter = 899 kw per year performance ratio 76%

    SB2500 inverter = 488 kw per year performance ratio 41%

    I cant say I know when I would be adding extra panels so based on the above I will go with the 1700 watt inverter as the 2500 would create too much of a performance hit until I added more panels which at there current prices wont be anytime soon.

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    Was looking at RFI site for Variable in another thread and I noticed that they are selling SMA stuff now. Good choice, nice inverters.


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    I am getting in before the grant changes are doing the whole 1 KW system for free i.e. for the cost of the $8000.00 grant with the only extra in my case being a $120.00 charge for the tiled roof install.

    They take a $2500.00 deposit which is refunded on install. I paid that via credit card so if anything goes wrong I can claim a refund. They have been hammering the airwaves here and itís near impossible to phone them and their site has now exceeded its bandwidth so I think a lot of people are jumping on the offer.

    There competition Clear solar was running similar adís but they had a lot of add on charges including you had a $400.00 charge if you did not put a sign on the front fence for 12 months.

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    Senior Member Ramjet's Avatar
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    So you can choose the inverter & panels?

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    Standard is 6 x 175 watt panels and a Sunny Boy 1100 watt inverter grid connected.

    If you want a bigger inverter its extra plus if you have a flat or tiled roof its extra for the mounting hardware. In my case $120.00 for a tiled roof.

    The panels are CEEG and have a 25 year warrenty.

    The new power meter that can read back flow is extra. A friend had one installed for $220.00 it pays to shop around for that as some charge a lot more.

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    NU Energy
    Suite 11, 10 Lakewood Boulevard,
    Carrum Downs, Victoria 3201
    Australia

    Telephone: 1300 768 225

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    Thats a cracker of a deal really. I didnt know SMA stuff was part of the deal.

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    Quote Originally Posted by SystemRat View Post
    1 KW system for free i.e. for the cost of the $8000.00
    WOW... Im going to have to check that out.... I cant get the grant bc I rent. But I'll convince my parents too.

    As for the whole solar and renewable energy, my dream is to farm it. I live on acreage that is goin to watse bc I'm no farmer Joe. But electricty is a passion so renewable energy and I mix.

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    I should hit them for a commission although they have been flogging this pretty hard on 3AW.

    I went to their office as I could not get through on the phone but email works ok too. I was thinking of adding some more panels now but I am not sure on the return on investment of spending $7000 extra. The 1 KW system is free plus the $120 for tile mount, the extra for the bigger inverter and the new power meter so I will see what happens with the bill.

    I work from home so during the day I have the PC going and a radio above the normal fridge and standby crap. If I see a marked change in the power bill I might lean to buying more panels.

    I am trying to get my head around grid connect. The inverter produces power in phase with the mains power. So if I have a new power meter it will record what I pump back into the grid and so that will be worth 60 cent per kw to me. So without that meter does the excess generation to my needs simply flow out to the grid and stop or reverse the existing meter. It does not matter as I will be getting new meter anyway.

    It seems in some states youíre paid for gross generation not just what you put back if that made it to Victoria I would be impressed


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    Quote Originally Posted by SystemRat View Post
    I am trying to get my head around grid connect. The inverter produces power in phase with the mains power. So if I have a new power meter it will record what I pump back into the grid and so that will be worth 60 cent per kw to me. So without that meter does the excess generation to my needs simply flow out to the grid and stop or reverse the existing meter. It does not matter as I will be getting new meter anyway.

    It seems in some states youíre paid for gross generation not just what you put back if that made it to Victoria I would be impressed
    60 cent is excelent.... In NSW they give you 16 cents. Our metres work in revers if you "put back" to the grid.

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    16 cents here too at the moment but it changes to 60 cents shortly

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    I thought there was a cap on how much you could feed back into the grid...not sure if its still the go or not.

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    Quote Originally Posted by SystemRat View Post
    I should hit them for a commission although they have been flogging this pretty hard on 3AW.

    I went to their office as I could not get through on the phone but email works ok too. I was thinking of adding some more panels now but I am not sure on the return on investment of spending $7000 extra. The 1 KW system is free plus the $120 for tile mount, the extra for the bigger inverter and the new power meter so I will see what happens with the bill.

    I work from home so during the day I have the PC going and a radio above the normal fridge and standby crap. If I see a marked change in the power bill I might lean to buying more panels.

    I am trying to get my head around grid connect. The inverter produces power in phase with the mains power. So if I have a new power meter it will record what I pump back into the grid and so that will be worth 60 cent per kw to me. So without that meter does the excess generation to my needs simply flow out to the grid and stop or reverse the existing meter. It does not matter as I will be getting new meter anyway.

    It seems in some states youíre paid for gross generation not just what you put back if that made it to Victoria I would be impressed

    I can add quite a bit before you sign on the dotted line.

    Firstly so you understand how they are able to supply this system at the price they are , I will save you some research.
    Before I even explain this is a super deal BTW !

    You will notice on the inverter page ( SMA are the leaders and the best by far ) there models with "TL" on the model number , this is the new just release 2009 Transformerless Models of the Sunny Boy , they are lighter , more efficient , they have graphical display and blue tooth enabled , These will become the industry standard.

    The SB series SB1100 , 1700 , 2500 etc without the "TL" are the normal transformer models , Less efficient , Run very hot , no network connection by default , but available with a RS485 board from SMA for $285
    These older type units are being sold off to make room for the new TL models, they are still better than anything currently available beside the TL versions.

    There is also an over supply worldwide of PV modules due to large scale projects being put on hold in other countries , this has reduced the price to slightly that before the financial crisis hit , so again helpful in bringing the system price down.

    You will also notice in the Term and Conditions that by accepting this contract you have to sign over all of your REC's "renewable energy certificates" for a 1kw system this is about 22 REC's worth about an average of $45.00 , safe to say about $500 you are signing over to them.
    This is the clever part of this deal and part most people just glance straight over.
    Once the $8000 rebate is finished ( very soon ) it will be replaced with much higher values for REC's , enough in fact that is will almost make up for their being no $8000 rebate anymore.
    Great deal for these guys selling you the system , they get paid for the system and have your REC's ( now theirs btw ) that can be traded for a fortune in a few months time when they become the new rebate exchange system.

    Another way of look at this is if you paid another company $3000 more for the same system but kept your REC's you will walk away with a profit next year , Take my word while the stock market crashes REC's are hot property atm and it is all hush hush

    Anyway back to where I said this is still a great deal because you get your first KW for very little outlay , the equipment is first class so you win anyway but with a bit extra outlay at the start , the extra money you will gain might just pay for some extra Watts in panels down the track .


    Apart from the financial side of things the technical side is far more interesting.
    You question about how the power is metered , Basically if you are drawing 500W in your house and your panel are making 500W the in / out meters remain static , if you keep drawing the same and the panels pump out 900W the 400W extra is fed into the grid and recorded on the "Sell" or Export part of your new meter.
    Once your loads increase to more than you are producing the difference it measure on the "Buy"or import side of the meter.

    The Import and export readings are separate and calculated on your bill.
    If you are using smart power , there are different rates for different times and days , Peak periods cost more but you also sell at the same price less GST.
    The best part about Peak periods is that this is always when your PV system is producing , so here in WA it's 22 cents per KWH , If you save all your usage for off peak times when it only cost 7 cents a KWH you can with some careful management reverse your power bill.
    EG: My last power bill was $19.00 for 60 days , Same time last year it was $363.16 , Although I have a 2.8KW system the reduction has come with a lot of family retraining as far as usage ( Wastage ) habbits.

    As far as expanding at a later date is concerned , this is something less that 1% of people ever end up doing although 90% start out with expansion as a distinct possibility later on.
    People selling these system will often say no problem you can add extra panels any time , but reality it's not so simple.
    You need to remember before deciding on an inverter what is actually possible, for example all series strings should be of the same type , age , voltage ect , Panels cannot not mixed on a grid feed system.
    All parallel strings needs to be the same size , So in your example with an SB1700 you would need to install another string of 6 panels at a later time because Parallel string can be different ages. , but the problem is that is to big for this inverter.
    You can add 2 extra panels to make one series string of 8 but this needs to be done at the same time.
    Or you can have 2 strings of 5 panels , which would mean buying an extra 4 but this is no good either unless you do it within a couple of months because the panels will be different ages and you would need to take 1 old panel to add to the 4 new panel to get your 2 strings of 5 , not ideal .

    My recommendation , stay with the SB1100 , add an extra panel up front , they might hate you for asking because adding an extra panel to the standard mounting frame is a pain in butt this will yield optimum results for now.
    Later if you want to add on , the SB 1100 and other models will be selling cheap in the couple of years as people want to convert to the TL models , and hopefully panels will be even cheaper , so make the add on a new system .

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    What's the theory behind a transformerless inverter?

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    Quote Originally Posted by Joey View Post
    I can add quite a bit before you sign on the dotted line.

    Firstly so you understand how they are able to supply this system at the price they are , I will save you some research.
    Before I even explain this is a super deal BTW !

    You will notice on the inverter page ( SMA are the leaders and the best by far ) there models with "TL" on the model number , this is the new just release 2009 Transformerless Models of the Sunny Boy , they are lighter , more efficient , they have graphical display and blue tooth enabled , These will become the industry standard.
    Great info thanks.

    I realize they take the REC’s as part of the deal Clear Solar also do that and list what they see as the value of them plus the feed in tariff also has a clause about assigning REC’s to the energy company too but latter says if you don’t have them you can still sign up.

    Re the inverters that’s very interesting any idea what the price differential is between the new to old is I might try and get one.

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    Quote Originally Posted by Studio1 View Post
    What's the theory behind a transformerless inverter?
    It seems SMA are the first with this technology and for obvious reasons aren't revealing to much about it , They a lot lighter and definitely more efficient.

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    Quote Originally Posted by SystemRat View Post
    Great info thanks.

    I realize they take the RECís as part of the deal Clear Solar also do that and list what they see as the value of them plus the feed in tariff also has a clause about assigning RECís to the energy company too but latter says if you donít have them you can still sign up.

    Re the inverters thatís very interesting any idea what the price differential is between the new to old is I might try and get one.
    There is nothing is their Terms & Conditions contract PDF that says the offer is available if you dont sign over your Rec's , in fact it is boldly printed that assigning REC's over to them is a condition of sale.


    I have been trying to get firm pricing on the new TL series , in theory they should be less expensive to produce but like anything from SMA you pay top dollar for anything with their name on it . ( Quality is first class ) .
    They have been approved for grid connection in Australia for just over 3 months now but supplies haven't really started rolling through yet , then again it could be that suppliers are trying to dump the old models first.

    I have already put my name down for the 4000TL but delivery date and firm price is not available yet.

    Something else worth noting , the Pricing on Certain brands of Panels is coming down as new shipments arrive in Australia , the pricing being offered by suppliers here in Australia is less than when the Au $ was at 98cents.
    The new pricing is going to have a major impact on system pricing over the next few months.
    All exciting really

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    What is the quality of the CEEG panels. Do they have a significant manufacturing history.
    I can buy plastic clothes pegs in the supermarket with 5 year guarantee.
    How many people pay 52c to send a peg back?
    I rang the Nu-energy crowd who said they've been round for 20 years .... How can I find out if this claim is true?
    I was thinking of making a Credit card payment with credit protection - Good for most purchases but does have time limits to reverse transactions. I think around 75 to 90 days. The Nuenergy people were very evasive on giving an expected time frame, cited the government may take up to 8 weeks to approve rebate - if they could satisfy me the payment was going into a regulated trust account then that may ease the decision.
    Does anybody know if there are there any other companies in Vic or eastern Vic that compare in their offer?

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