Inverter Selection for: 8.8KW Array

cpetkucpetku Registered Users Posts: 22
Looking at various posts and tools such as NREL's SAM, there seems to be disparity on sizing inverters:cry:.

I've seen posts stating that the inverter should be oversized to ensure it doesn't run 100% of it's AC rating and miss out on bonus watts in low temperature months such as March/April. These would lead me to believe a 8.8K array can produce 10K STC in the spring and thus an 8K inverter (SMA is really 7.7K) is undersized for maximizing my harvest.

After applying derating factors, NREL predicts that a 7.7KW inverter (Fronius or SMA) is just barely undersized for an 8.8KW array in my location (2 - 32 hours/year of unharvested excess peak power from the array). The next choice in inverters is a 10K Fronius (and yes my panel can handle this per NEC).

My derating factors based upon name plate ratings and a shading work out to about 0.77 (PV watts and a solmetric study).

Q1) It just doen't seem to make sense to spend another $3000 to upgrade from a SB8000US to a Fronius IG+ 10K, am I missing something?

Q2) Any direct comparisons for current IG PLus 7.5 and SB8000US? I like the Fronius designs but posts seem to imply tracking issues (FW updates may have fixed this in the last year). I'm debating if the servicability of the 7.5 is worth the price premium.
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Comments

  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    I've seen several posts stating that the inverter should be oversized to ensure it doesn't run 100% of it's AC rating and miss out on bonus watts in low temperature months such as March/April.

    I've never heard this, or seen any professional installers recommending it. AFAIK (and I am not an installer), standard practice is to undersize the inverter slightly.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Inverter Selection for: 8.8KW Array

    You will rarely see the nameplate stc rating of 8.8kW from this array. It is generally regarded as not worth the extra inverter money for those few times. On the other hand, Inverters achieve their maximum efficiency at somewhat less than their max power so is a good reason for using one bigger than necessary.

    However, your real problem is that the NEC backfeed rule allows no more than 20% of the panel rating to be backfed. This mean your typical 200A panel is limited to a dual 40A breaker for the solar. Then the 125% overcurrent rule limits the inverter size to 80% of 40A which is 32A or 7.68kW at 240V. You can't do an 8kW inverter without either decreasing the size of the panel's main breakers (good luck finding that) or adding on another 200A service ($$$). The best I've been able to do is put in dual inverters - one 4kW and one 3.3kW. Costs a little more as an AC combiner panel is needed, but has the advantage of allowing two arrays at different roof orientations as is often desirable with larger systems.
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    FWIW:

    Main load center has 225A bus (QO142L225G) and 200A main breaker (QOM2200VH)
    http://images.tradeservice.com/Attachments/DIR100019/SQAREDE01297_1_5.pdf

    Allowable backfeed per NEC: 120% * 225 -200 = 70A

    Fronius indicates their 10K is really three 3.3K inverters (power stages) that switch in the various stages depending on array output (the 7.5K is 2 stages). Their claim is this keeps the power modules running in their peak areas, but simulations and data from NREL & Sandia don't show that this strategy is any more efficient than the SMA design over the course of a year.

    So far the only advatages I see from the 10K Fronius are:

    - Ease of replacing the failed unit (wiring box remains connected on the wall)

    -Redundant power stages in the event of a failure (it can run on two stages as a 6.6K inverter until a replacement arrives)

    - MTBF may be better on the Fronius due to typically only using two of the three power stages and rotating the master stage between all three (but it would be cheaper to budget replacing the SMA after 10 Years).

    - Ability to easily add a fourth string in the future by tapping into the combiner box (no additional AC panels would be required)

    In general, the first two are nicities and only the last of these options seems to justify the increased cost assuming all wiring is planned for four strings (i.e., 6ga from the combiner to the inverter) . Then again, this only makes sense if I can get the ITC, CBI and PBI payments on the future upgrade. Without these, the LCOE becomes excessive.


    Previous comment deleted based on new information


    The SB8000US is only conditionally recommended by their configuration program due to low Vmpp at 70c (high panel temps on roof in summer). It looks like when they changed from the 7000 to the 8000 the min peak power tracking voltage and start voltages increased by about 50V making my configuration marginal as it ages.: :cry: Since I'm out of usable roof space and using a SB7000US with 8.8KW array seems to be going the wrong direction, I guess I'm limited to one of the Fronius units...
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Inverter Selection for: 8.8KW Array

    The efficiency argument is true, inverters are more efficient at less than their max rating, but I don't think that's a reason to oversize.

    Looking at the efficiency curves inverters are most efficient at about 30% their max rating so a 7kW inverter is most efficient at around 2.5kW - and then we're only talking about a 1% gain. But the difference in efficiency between 7kW and 6kW on a 7kW inverter looks to be about 0.05%. Not really worth chasing IMO.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »

    -Redundant power stages in the event of a failure (it can run on two stages as a 6.6K inverter until a replacement arrives)

    - MTBF may be better on the Fronius due to typically only using two of the three power stages and rotating the master stage between all three (but it would be cheaper to budget replacing the SMA after 10 Years).

    Do you have in print, that it cycles the master stage between the 3 modules ? or that it can "limp" on only 2 ?? Or is that salesman blather ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    From their documents

    http://www.fronius.com/cps/rde/xbcr/SID-081F2885-BC2332F6/fronius_usa/40_0006_2850_110_USA_low.pdf

    "Failsafe. You can rely onFronius inverters. In the rare event that a power stage fails, the others will continue to operate. Once the replacement power stage is delivered, it can be quickly and easily replaced by a service technician, without having to dismantle the entire inverter. The wiring box, including all cabling, configurations and data (such as kWh production) remains on the wall, while your service technician removes two screws, exchanges the power module, and within five minutes the inverter is repaired."

    http://www.fronius.com/cps/rde/xbcr/SID-081F2885-BC2332F6/fronius_usa/In_the_MIX_1-09.pdf (applies to the 10K as well)

    "the Fronius inverter can scale back and run a single power stage. The three stage 12kW inverter can now perform as a 4kW or 8kW inverter. Hence, we keep the loading on the power stages higher than would otherwise be possible with a single-stage inverter. The central processor evaluates and determines which power stage has the least amount of operation hours, then selects that power stage as the Master. This is the first power stage to be turned on and will run until the end of the day. The other power stages are the slaves that will turn on
    and off as needed. This keeps an equal balance on component wear and extends the overall life of the inverter."
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    From their documents


    Awesome. very impressive, thanks for setting that straight.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • solarvicsolarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    From their documents

    http://www.fronius.com/cps/rde/xbcr/SID-081F2885-BC2332F6/fronius_usa/40_0006_2850_110_USA_low.pdf

    "Failsafe. You can rely onFronius inverters. In the rare event that a power stage fails, the others will continue to operate. Once the replacement power stage is delivered, it can be quickly and easily replaced by a service technician, without having to dismantle the entire inverter. The wiring box, including all cabling, configurations and data (such as kWh production) remains on the wall, while your service technician removes two screws, exchanges the power module, and within five minutes the inverter is repaired."

    http://www.fronius.com/cps/rde/xbcr/SID-081F2885-BC2332F6/fronius_usa/In_the_MIX_1-09.pdf (applies to the 10K as well)

    "the Fronius inverter can scale back and run a single power stage. The three stage 12kW inverter can now perform as a 4kW or 8kW inverter. Hence, we keep the loading on the power stages higher than would otherwise be possible with a single-stage inverter. The central processor evaluates and determines which power stage has the least amount of operation hours, then selects that power stage as the Master. This is the first power stage to be turned on and will run until the end of the day. The other power stages are the slaves that will turn on
    and off as needed. This keeps an equal balance on component wear and extends the overall life of the inverter."
    Another good reason for the IG-plus not mentioned. One person can install the inverter since it comes in two sectons. Also thier tech. assistance is great. I just self installed my 30.1-IG Plus today and got it set at 208 v. instead of 240 v. Called Fronius and they called me back in less than 10 minutes and got the voltage set right. Only took a couple minutes. Told me this happens a lot. Update= Just received personal message from person thinking my new Frounius 30.1-IG plus makes 30,000watts Actually rated 3000 watts. :Dsolarvic:D
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    Q1) It just doen't seem to make sense to spend another $3000 to upgrade from a SB8000US to a Fronius IG+ 10K, am I missing something?

    Q2) Any direct comparisons for current IG PLus 7.5 and SB8000US? I like the Fronius designs but posts seem to imply tracking issues (FW updates may have fixed this in the last year). I'm debating if the servicability of the 7.5 is worth the price premium.

    Just curious...your array is on the larger size, have you
    thought about installing two mid-size inverters instead
    of one large one?

    Two vs one has a slight disadvantage in cost, i.e., one
    would cost less than two, assuming equal total
    capacity.

    Two would have these advantages:

    1. If one inverter failed, you only lose half your array.
    2. If you have any shading issues or not all the panels
    share the same azimuth or tilt angle, you could group
    the panels such that lower performing panels do not
    affect the output of higher performing panels.
    3. The smaller-capacity inverter also has a smaller
    low efficiency (<30% input) realm, which means you
    might get a smidge more harvest during low light times
    (early morning/evening).

    --

    A relative just installed a 10kw system, and his contractor
    went with two.

    John
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    Right now I'm planning one array of three strings of 12 each (SW245's) on a single roof plane (45 tilt) with southern exposure. Breaking this into two arrays would require reducing the total size due to Voc and Vmpp tracking limits on most inverters.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    Right now I'm planning for three strings of 12 each (SW245's) on a single roof plane (45 tilt). with southern exposure. Breaking this into two strings would require reducing the array size due to Voc and Vmpp tracking limits on most inverters.

    Just to clarify on the terminology...

    There are two ways to speak of "strings":

    1. A physical grouping, for example, one set of PV
    modules on one roof and one set on another;
    2. A logical grouping, i.e., all panels that are connected to
    one inverter make up one string. The panels could be
    located on different facets of your roof, or have
    different angles, etc...they would still be considered part
    of "one string."

    I sense you are referring to definition #1, whereas I
    am referring to definition #2 in my prior post.

    For the purposes of discussing inverter count, your
    originally planned 36 panels connected to one inverter
    is therefore be "one string" in my mind.

    --

    With regard to the Voc and Vmpp limits you allude to,
    I'm not personally familiar with such limits, so I can't
    comment on your hypothesis. That being said, many
    models of mid-size inverters support 18 PV panels
    and more. My relative is running 22 235w panels off of
    each of his two inverters. In his case, where all his
    panels are in a single uniform plane of panels, he
    has half wired to one inverter and half wired to the
    other.

    John
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    jcgee88 wrote: »
    Just to clarify on the terminology...

    There are two ways to speak of "strings":

    1. A physical grouping, for example, one set of PV
    modules on one roof and one set on another;
    2. A logical grouping, i.e., all panels that are connected to
    one inverter make up one string. The panels could be
    located on different facets of your roof, or have
    different angles, etc...they would still be considered part
    of "one string."

    I sense you are referring to definition #1, whereas I
    am referring to definition #2 in my prior post.

    For the purposes of discussing inverter count, your
    originally planned 36 panels connected to one inverter
    is therefore be "one string" in my mind.


    I think definition 2 would more properly be referred to as an "array".
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array
    jcgee88 wrote: »
    With regard to the Voc and Vmpp limits you allude to, I'm not personally familiar with such limits, so I can't comment on your hypothesis. That being said, many models of mid-size inverters support 18 PV panels and more. My relative is running 22 235w panels off of each of his two inverters. In his case, where all his panels are in a single uniform plane of panels, he has half wired to one inverter and half wired to the other.


    Glad to hear that your relative is happy with his system. In his case, his series strings are probably 11 each which does result in a functional solution. However when I worked through the numbers Vmpp just doesn't work great when I make four even strings of 9 modules each (maybe two Fronius IG4000's). Also, Voc on two strings limits me to a max of 26 modules. due to NEC regulations (600v).

    It's possible to verify my comments with the various inverter manufacurers online configuration tools. Yellow warnings appear when these (and other) specs are violated. However, don't assume all green is good to go unless additional analysis have been run on the total system and any design tradeoffs that have been made are well understood. (my reason for starting this thread)

    I briefly considered installing 18/36 enphase units, but I haven't bought into their reliability numbers and dislike the idea of paying someone to replace a few defective units over the next twenty years on a 12:12 pitch roof. If I had a ground mount system, I might consider it if they offered a cost advantage. But again, with 36 modules I would need to add an AC combiner box and design this as two enphase feeds.


    MOD: Let's give this thread 48 hours then close it for new posts. Tech support at one the inverter manufacturers has confirmed the first response to this thread was correct. As predicted by SAM (https://www.nrel.gov/analysis/sam/download.html), there is no ecconomical advantage to oversizing the inverter. Thanks for letting me explore this in the community durring off hours untill I could get ahold of the manufacturer.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    MOD: Let's give this thread 48 hours then close it for new posts.

    Why close it?

    Around here old threads are often brought back to life when someone new comes along and has additional questions or thoughts on the subject.
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    My assumption is that since this started out as a question of what the best practice was and it has been properly answered, leaving it open could confuse future searchers/readers if it gets hi-jacked. However I am open to whatever the standard practice is for this site.
  • System2System2 Posts: 6,290 admin
    Re: Inverter Selection for: 8.8KW Array
    cpetku wrote: »
    From their documents

    http://www.fronius.com/cps/rde/xbcr/SID-081F2885-BC2332F6/fronius_usa/40_0006_2850_110_USA_low.pdf

    "Failsafe. You can rely onFronius inverters. In the rare event that a power stage fails, the others will continue to operate. Once the replacement power stage is delivered, it can be quickly and easily replaced by a service technician, without having to dismantle the entire inverter. The wiring box, including all cabling, configurations and data (such as kWh production) remains on the wall, while your service technician removes two screws, exchanges the power module, and within five minutes the inverter is repaired."

    http://www.fronius.com/cps/rde/xbcr/SID-081F2885-BC2332F6/fronius_usa/In_the_MIX_1-09.pdf (applies to the 10K as well)

    "the Fronius inverter can scale back and run a single power stage. The three stage 12kW inverter can now perform as a 4kW or 8kW inverter. Hence, we keep the loading on the power stages higher than would otherwise be possible with a single-stage inverter. The central processor evaluates and determines which power stage has the least amount of operation hours, then selects that power stage as the Master. This is the first power stage to be turned on and will run until the end of the day. The other power stages are the slaves that will turn on
    and off as needed. This keeps an equal balance on component wear and extends the overall life of the inverter."

    Thanks for info, I just started using Fronius.
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    The comment about a rare event should be read as when it fails in 10 to 12 years... Most Inverter execs state that a 10 year life is about all that can be expected using todays technologies.

    http://www.nrel.gov/pv/pdfs/38771.pdf

    Started the process to get the 8.8K unit installled this year and hopefully I can document the install for those who are interested. Just hope it doesn't look butt ugly.
  • Energy EfficienciesEnergy Efficiencies Registered Users Posts: 11
    Re: Inverter Selection for: 8.8KW Array
    jcgee88 wrote: »
    Just to clarify on the terminology...

    There are two ways to speak of "strings":

    1. A physical grouping, for example, one set of PV
    modules on one roof and one set on another;
    2. A logical grouping, i.e., all panels that are connected to
    one inverter make up one string. The panels could be
    located on different facets of your roof, or have
    different angles, etc...they would still be considered part
    of "one string."

    I sense you are referring to definition #1, whereas I
    am referring to definition #2 in my prior post.

    For the purposes of discussing inverter count, your
    originally planned 36 panels connected to one inverter
    is therefore be "one string" in my mind.

    --

    With regard to the Voc and Vmpp limits you allude to,
    I'm not personally familiar with such limits, so I can't
    comment on your hypothesis. That being said, many
    models of mid-size inverters support 18 PV panels
    and more. My relative is running 22 235w panels off of
    each of his two inverters. In his case, where all his
    panels are in a single uniform plane of panels, he
    has half wired to one inverter and half wired to the
    other.

    John

    There are a couple of issues I am unsure of in this post. First, a "string" in the profession in my area always refers to how many panels are wired in series regardless of where they are physically located. The series strings are then combined in parallel strings typically, unless it is a small system (2KW or so).

    Now I have been on this forun only recently, but I dont see yet where anyone explains that string sizing in grid tied applications is way different than off grid. What I mean is you have to take many temperature calculations into consideration. When a panel is cold and in the same percentage of sunlight, it will create more DC voltage. When it is hot, just the opposite. To keep a system within the MPPT range, you must know how to figure these voltages, as well as max potential amperage. Go too few panels in a string, the system doesnt stay in the MPPT. Too many panels in a string you will go above the MPPT and potentially go over 600V.....hence frying the inverter. Guess what, it isnt covered by warranty if it EVER goes over 600V.

    Thats my two cents. Please if there is a post that explains this, point this thread to it. This is a VERY important point to make to people that dont know. IT isnt as simple as looking at a wattage range for an inverter and buying that many panels to be in the range...
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Inverter Selection for: 8.8KW Array

    energy efficiencies,
    you are essentially correct in all of your assumptions except that strings are only in reference to series and not in parallel.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Inverter Selection for: 8.8KW Array
    ...in my area [string] always refers to how many panels are wired in series regardless of where they are physically located. The series strings are then combined in parallel strings typically, unless it is a small system (2KW or so).

    Your using that term as defined is perfectly acceptable.

    And, I sense that the OP used it in the same way.

    That being said, not everyone is in the profession, and
    in my case, I have heard the term "string" used a variety
    of ways. The most frequent use I've seen is to describe a
    physically associated set of panels, e.g., those that are situated
    contiguously on one roof facet. That's how I use the term
    for my own array...especially since with my micro-
    inverter implementation, the concept of "panels wired in
    series" has no meaning for me.

    With regard to the rest of your post, that's good insight!

    John
  • Energy EfficienciesEnergy Efficiencies Registered Users Posts: 11
    Re: Inverter Selection for: 8.8KW Array
    jcgee88 wrote: »
    since with my micro-
    inverter implementation, the concept of "panels wired in
    series" has no meaning for me.
    John

    Very good point! I overlooked mentioning that.
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    The definition I was using is an array is a group of parrallel strings

    A string is a group of modules in series.

    With any luck...

    - The re-roof starts on this Thursday
    - The 8.8K array goes up the following Monday
    - The oversized inverter (more on this later) goes in mid-week
    - Inspections the next week and commissioning before the end of the year.

    That is, if there is no bad weather in the next two to three weeks.

    The SB configuration tool is more conservative than some of my calcs as well, this is one of the reasons I specified a Fronius 7.5KW inverter.
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    Installation Update

    Delays

    Reroof of southern exposure starts next week 12/7? (+7D)
    Special order materials delayed in transit

    Panels and Inverter arrive Wednesday (12/8) (+2D)
    Module substitution required due to availability

    Design Changes
    Sharp 240W panels substituted for SW245's


    RFC

    Is there is a significant quality difference between Sharp and Solar World and if so what is it? Both companies have been in business for years and I planned on giving the buisness to SW, but they seem to have a bigger distribution issue than Sharp.

    My installer was able to get a commitment to ship the Sharp panels 24 hours after starting his hunt (his distributor sold the SW245's that were quoted while we waited on approval from the utility company. Right now SW's would require piecing the job together across multiple distributors or waiting for the next set of shipments to arrive (hopefully this year). A call to SW confirmed that they have a capacity problem and don't expect to ship any more stock until mid 1Q11. Only what is already in transit will be delivered this year.

    I have asked for flash data on the 240's that are being shipped, but have already committed to taking them to get the installation in this year. Any guesses if I made the right choice?
  • cpetkucpetku Registered Users Posts: 22
    Re: Installation Update

    Still trying to get this in in 2010...

    Installation of Unirac Rails using Quickmount PV's completed 12/17. Installers worked in sub 20F to get these installed. The rails highlighted deficiencies of the original builder (trusses were not properly aligned when the house was built. The adjustment capabilities of this system will hide the sins of the original builder.

    Installation of Sharp U240F1 panels started 12/20. We had a relatively nice sunny day and got 24 of the 36 panels installed. This should be completed tomorrow if weather permits (snow forcasted for tonight). The flash data on all of the panels was around 241W. While I had hoped for some +10% units, I was concerned with getting -5% panels based upon the spec and a general lack of respect I'm sensing for Sharp lately as cheaper panels start entering the market.

    Installation of electrical BOS started 12/17. I managed to get signed up as a beta site for a new (CEC approved) inverter. Hoping to have a live trial before XMAS with code approval between XMAS and new years.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Inverter Selection for: 8.8KW Array

    Thanks for the pictures! With that sharp of a roof angle, I
    hope your installers are wearing safety harnesses!

    By the way, you have two big trees right in front of your
    array. What are your plans for those trees? It looks
    like you will take a big hit during the summer.

    John
  • dreesdrees Solar Expert Posts: 482 ✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    jcgee88 wrote: »
    By the way, you have two big trees right in front of your array. What are your plans for those trees? It looks like you will take a big hit during the summer.
    I doubt summer will be an issue, but you can see that it will be shaded in the winter.
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Inverter Selection for: 8.8KW Array

    Is this 8.8kw figure STC or PTC of array? I don't get this oversized inverter thing....

    Why not use a SMA7000? I read through posts and prob missed something.

    Can I ask if a pole mount option was discussed...just outside the driveway area behind the trees?
  • stumpy40stumpy40 Solar Expert Posts: 35
    Re: Inverter Selection for: 8.8KW Array
    drees wrote: »
    I doubt summer will be an issue, but you can see that it will be shaded in the winter.

    Will be shaded more than just winter.....is this array facing west?
  • solarvicsolarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: Inverter Selection for: 8.8KW Array
    stumpy40 wrote: »
    Is this 8.8kw figure STC or PTC of array? I don't get this oversized inverter thing....

    Why not use a SMA7000? I read through posts and prob missed something.

    Can I ask if a pole mount option was discussed...just outside the driveway area behind the trees?
    Cpetku is using the oversized inverter so he can add 1 more string of panels if he decides to upgrade. Probably too late to get a different inverter before his install is done anyway. Everyone follows thier own personal direction to arrive at the same destination. I would have probably had a 7.5 fronius for the present install and added a smaller inverter if I added more panels later. :Dsolarvic:D
  • cpetkucpetku Registered Users Posts: 22
    Re: Inverter Selection for: 8.8KW Array

    Here's the deal on the inverter:

    A 7.5KW Fronius would have been a great choice for the installation. However I managed to get into a BETA program for a new 11KW Grid Tie inverter and the cost of this unit ended up about the same as the 7.5KW Fronius. Since I have extra roof space on another southern exposure, I now have the opportunity to easily upgrade the system with a fourth string when funds become available again (I combined on the roof and had 4Ga run from the roof to the inverter).

    Not sure if I'm allowed to state the inverter manufacturers name and model yet.

    With regard to the trees, I had a solmetric report run and shading was estimated to be an issue on the bottom string in the winter. The Photo's I took indicate this may have been too optomistic. I really don't want to cut these down so we'll be monitoring the situation over the next few months.

    Pole mount was not an option as the driveway area suffers from severe shading. The best ground mount location for no shading would have compromised the septic field and drainage.


    SMA7000 would have been another possible choice but would not harvest all of the energy from the array. The 8000 was not appropriate due to potential tracking issues durring summer months as the panels age.

    Todays test only generated 500W but that was with Snow on the panels, at 2:30 in the afternoon on a very overcast day.

    AHJ is coming out tomorrow to do the inspection then it's wait for the local utility to do the final commissioning of the system.

    I had permanent D-RINGS installed at the ridge when the shingles were replaced. The roofers mounting the panels chose to work without harnesses until the last day when they got stuck on an icy north face (opposite from the panels) after mounting the last panel. The electricians appreciated the rings while wiring up the Soladeck today.

    Flash Data came in for the Sharp panels yesterday. They were all about 0.5% above NamePlate.
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