Different information from installers

WatchdogWatchdog Registered Users Posts: 1
Hello from Texas,

The more I read, the more I learn that I don't know a lot about solar setups. The installers I am shopping around here in San Antonio are like car salesmen (and I used to be one too)

I just want an efficient grid tied system for my home.

I like the Sunny Boy inverters from what I've read. And I have been offered two types of panels.

In the States, the best exposure is on the South side of a roof. The array I want (6 - 6.5 kW) would have panels on the South and East side of my roof. Now comes the tricky part...

The panels I have narrowed it down to are similar I believe. They are the Canadian Solar CS6P-250P and the Phono Solar - PS250P-20/U (Black/Black). In both systems, there will be 24 panels for a 6kW system or 26 for a 6.5kW system.

I am trying to decide what are the choices I have in an SMA inverter. My home will have an South and East array system. One set on the a South slope and the other on an East slope of the home. The West side is too small.

I have heard that if there are two different orientation of panels (South and East), that the panels have to be the same amount on each side (12 on the South and 12 on the East - total of 24 panels). If they are uneven, the inverter will be "unbalanced". Is this true? Again, I am getting two different answers from the companies I am talking to. One company says it's okay to put 11 panels on the South and 13 on the East side with the SMA SB6000TL-US-12 (240v) inverter. The other company says it has to be even set of panels on each side.

The SMA inverters they suggested were the SMA SB6000TL-US-22 and the SMA SB6000TL-US-12 (240v). I was leaning toward the SMA SB6000TL-US-12 (240v) but there is so much I don't understand which can affect production like...

how two arrays tie in and if they need to be "balanced",

if MPPT has anything to do it; does series or parallel have anything to do with my type of grid tied system

if I should take into account the start up voltage difference

I did a comparison of the inverters on a web page that gave me this...

http://http://www.solardesigntool.com/compare-inverters.html?submit=Compare+Inverters&inverters=453&inverters=492&_inverters=on&compare=true

I would appreciate any help you solar wizards can give me ;)

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,190 admin
    Re: Different information from installers

    A couple of recent threads similar to your installation:

    Looking to go solar...everything looking good, am I missing

    Finally chose a system and starting the process!
    The more I read, the more I learn that I don't know a lot about solar setups. The installers I am shopping around here in San Antonio are like car salesmen (and I used to be one too)

    Even if you are not goin gto install the system yourself--Learning as much as you can about "best practices" can help save you against the (hopefully) rare installer without scruples:

    Panel Fire Question

    I like the Sunny Boy inverters from what I've read. And I have been offered two types of panels.

    Probably one of the best mfg of inverter/systems out there for smaller installs. Out of Germany, so not cheap in the US.
    In the States, the best exposure is on the South side of a roof. The array I want (6 - 6.5 kW) would have panels on the South and East side of my roof. Now comes the tricky part...

    The panels I have narrowed it down to are similar I believe. They are the Canadian Solar CS6P-250P and the Phono Solar - PS250P-20/U (Black/Black). In both systems, there will be 24 panels for a 6kW system or 26 for a 6.5kW system.

    Canadian Solar seem to have a good reputation--Have not heard of the other (does not mean much, I am not in the business).

    In general, the solar panel market is very turbulent and warranties are of questionable value when companies keep starting/going out of business. As the various installers their panel experiences (they should be able to tell you which vendors have a high failure rate in the field).

    As always, this is not an "investment"--It is a hedge against future power hikes for the next XX years. Panels are pretty cheap these days--So you may end up paying for replacements (if that is every needed). Also, watch the political environment around your state's public utility commission. There is a shift away from rebates and rate plans that give "subsidies" to people who install Grid Tied solar power systems. In California, there appears to be a hard 20 year limit for GT systems with "good" tariff plans. In my case, my system is already 10+ years old, and I may lose my rates in 10- years--At that point, GT solar may not make any sense/save me much money.
    I am trying to decide what are the choices I have in an SMA inverter. My home will have an South and East array system. One set on the a South slope and the other on an East slope of the home. The West side is too small.

    I have heard that if there are two different orientation of panels (South and East), that the panels have to be the same amount on each side (12 on the South and 12 on the East - total of 24 panels). If they are uneven, the inverter will be "unbalanced". Is this true? Again, I am getting two different answers from the companies I am talking to. One company says it's okay to put 11 panels on the South and 13 on the East side with the SMA SB6000TL-US-12 (240v) inverter. The other company says it has to be even set of panels on each side.

    Solar panels are sometimes thought as "solar batteries"--In reality, they are not at all like batteries. Their output current is proportional to the amount of sunlight hitting the panel and their output voltage (Vmp, voltage maximum power) falls as the panels get hot (which happens to most folks--summer weather under full sun--panels/solar cells get really hot and voltage can fall by upwards of 20%)...

    So--With String or Central GT inverters--You are putting something like 10+/- panels in series... If some get less sun than others, that limits the current through the entire string. Also, if the the panels get different wind/cooling/heating--You can have voltage suppression issues... Sort of like mixing old+new batteries in series for your flashlight--The output of the string is really limited to the weakest cell.

    Home style Central type GT inverters generally have "one MPPT" input. MPPT means Maximum Power Point Tracking... Basically, the MPPT input circuitry of the GT inverter allows the inverter to figure out the "optimum Vmp-array" that you put on the front of the inverter without having to configure the system... I.e., it may take from 8-12 panels in series (just an example). This allows for easy configuration. And, it also allows for the +/- 20% or so voltage variations between cold (winter) and hot (summer) panel temperatures (think of a variable AC transformer that allows you to adjust from poor AC input voltage regulation and "automatically" adjust for running your home appliances).

    With panel "strings"... More or less, if the Vmp-array voltage is matched to 10% or better--The solar panels are forgiving enough that you will not lose very much power due to the miss-match of voltages.

    However, 11 on one string and 13 panels on another--That is getting pretty questionable. Basically you have two Vmp-string peaks--One at (for example) ~330 volts and a second at ~390 volts... What should the GT inverter "choose" as its operating voltage--330 volts or 390 volts, or something in-between.

    I would be very concerned about this sort of installation. Would you lose 5%, 10%, 20%, or sometimes even 50% of your system output--I really do not know. MPPT systems are not usually designed to resolve 2-3 peak "optimal" Vmp-array voltage.

    if you have multiple "angles"--You are many times better off using either one inverter per "facet", or using "micro inverters" (one small GT inverter per panel). There are pluses and minuses to any of these decisions.

    There are also string balancers which can "adjust" different string outputs to a common central inverter input (I do not know much about them, but they are becoming more popular--it seems).
    The SMA inverters they suggested were the SMA SB6000TL-US-22 and the SMA SB6000TL-US-12 (240v). I was leaning toward the SMA SB6000TL-US-12 (240v) but there is so much I don't understand which can affect production like...

    how two arrays tie in and if they need to be "balanced",

    if MPPT has anything to do it; does series or parallel have anything to do with my type of grid tied system

    if I should take into account the start up voltage difference

    I did a comparison of the inverters on a web page that gave me this...

    http://http://www.solardesigntool.com/compare-inverters.html?submit=Compare+Inverters&inverters=453&invert ers=492&_inverters=on&compare=true

    The "-22" has two MPPT inputs and would be a good match for your two arrays vs the single (if this is the inverter the vendor wanted to use--then mixing 11+13 strings is fine--Each MPPT input will match the different string Vmp-array voltages).

    Note that the range of Vmp-array where it "tracks" is different between the two units:

    345V - 480V (240V) vs 125V - 500V

    The narrower range will work "optimally" with a narrower range of input panels (like 12-14 panels vs a wider range for the second -22 inverter).

    Matching the strings to the inverters, picking vendors and installers, making sure the building permits are pulled, do you get the rebates, etc. are all very important.

    Another is your utility's rate plan and how they interact with your GT solar system. Also, do you have Time of Use billing (pay more for noon-6pm, less from 6pm to 11:59am, etc.). This can be helpful for you (if you have a west facing array, you get more "offset" from generated power in the afternoons, if you have an east facing array, you get less credit for power generated--For me, summer peak is $0.30 per kWH, off peak is ~$0.09 per kWH--So afternoon power generation gives me a 3x larger credit).

    For me, I do not use much power in the afternoons (no A/C, no electric heating/hot water, etc.). For others with heavy afternoon A/C loads--Time of Use plans can be "expensive". When I installed my system, I could pick flat rate or TOU. Later folks had to pick TOU--And those plans changed over time (with grandfathering of older installs).

    How your utility bills are affected by GT solar will make or break installs for many people. Some utility's have very good plans (for the customer), others may not allow GT solar at all... It all depends.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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