Micro-inverter undersizing?

[Crapmaster]

My original plan was to do a DIY grid-tied system install, but I did obtain some quotes from the local (Seattle area) solar turnkey companies. I have a rather large, over 5,000sq. ft home, and I want some future headroom for an electric vehicle, which leads to a rather large, about 20kW system. One of the quotes I received was surprisingly attractive, $1.81/Watt. I'm still researching DIY options, I've mostly looked at Wholesale Solar (company) as the provider of the equipment. Would be open to other suggestions, if there is a known good provider of DIY solar gear.

Anyway, on that proposal I mentioned above, they propose 380W Silfab panels with Enphase IQ7+ microinverters. Any thouths, comments or concerns on these? My question is, the IQ7+ have max output power capacity of 295W, which is almost 25% less than the panel max output power. I asked about this, they referred to an Enphase white paper (attached), which states that the inverter max output can be up to 25% less than the panel output, and still only lose less than 1% of the efficiency. The white paper seems to back this up, the reasoning being that very rarely (less than 1%) of the time, the 380W panel actually produces more than 295W.

Does this make sense and do people agree with this? Their main argument is the cost saving on the lower output and therefore cheaper inverter. Any thoughts would be appreciated.

 

[kernel]

If someone quoted you $1.80 for an enphase system with decent modules, i would take it and skip the diy unless you are a torturer of yourself!

The parts are likely $1.5/W and more plus labor, design, permitting, etc. About 5k$ labor. Not bad. Thats 3 or 4 people onsite plus whatever sales/design office for 2-3 days or more depending.

 

[kernel]

You can overdrive the inverters to 125% absolutely and without fear of much loss.
Be wary of the 380 only does 295 bit though....... my dual 1200W arrays of solarworld 300s consistantly output 1200W -1320W when seperated with the combiner breaker (two days ago.... 1320 non ideal tilt.).

Its why i bought every last one i could get my hands on last season for myself and our installs. Know your equipment, but dont fret over the details.

Silfab.... yeah 125% overdrive will not hurt you especially if you are in a warmer climate.

 

[svetz]

You might like the Clipping wiki entry.

 

[Crapmaster]

If someone quoted you $1.80 for an enphase system with decent modules, i would take it and skip the diy unless you are a torturer of yourself!

The parts are likely $1.5/W and more plus labor, design, permitting, etc. About 5k$ labor. Not bad. Thats 3 or 4 people onsite plus whatever sales/design office for 2-3 days or more depending.

Thank you. It looks that I could get a DIY system for about ~$1.25-1.30/W depending on the panels, the difference is roughly $11k to turnkey system. But then I need to pay for the permits and at minimum hire an electrician to do the grid-tie portion, I'm not quite sure yet, how much those would cost. But you're right, it is borderline whether it makes sense compared to the amount of work it would by for myself. Decisions...

 

[Crapmaster]

You can overdrive the inverters to 125% absolutely and without fear of much loss.
Be wary of the 380 only does 295 bit though....... my dual 1200W arrays of solarworld 300s consistantly output 1200W -1320W when seperated with the combiner breaker (two days ago.... 1320 non ideal tilt.).

Its why i bought every last one i could get my hands on last season for myself and our installs. Know your equipment, but dont fret over the details.

Silfab.... yeah 125% overdrive will not hurt you especially if you are in a warmer climate.

Thank you. I'm in the Seattle area so it's not exactly a warmer climate, although we do get plenty of 85F+ days during the summer, but hardly ever break 100F. With Enphase IQ7+, the max output is 295W, compared to the nominal max of 380W from the panel, so the inverter overdrive is ~129%, which is a bit more than I'd like to see. I would have 56 micro-inverters in the system, I believe the cost difference between IQ7+ and IQ7A seems to be $25 or so, so this is is $1,400 question in my system.

Given my scenario, would you recommend IQ7+ or IQ7A?

 

[kernel]

Im the wrong person to ask. I typically build a grid tie machine to take all watts..... to a point. With off grid machines sometimes 225% over what the battery could take anx let it clip away till october.

You would really need to break down the performance in a simulation calculator to compare. At the total cost of the system, id not balk too heavily either way. It could be a couple hundred kilowatt hours/year..... never know.

Then its the question of whether itl support what your goal is. Some people want the best ROI, some cannot stand no matter what white paper that the machine will clip 30% of peak production.

Somewhere in here is the answer and its your 1400$ id run the simulation on pv watts or another one someone can suggest. The weather data and pitch is going to matter. If you have ideal pitch for all year production (edit:not so big a deal if) the pitch is non ideal in the best solar season, then inverters eating all watts is a good thing.

The consideration is mainly for large systems, 20kW is about there, but the focus is on industrial amd commercial for those papers.

I do pair 300-watt pv to the iq7+ and dont worry about the 5W

For my money and 1400$ spread out on 20kW over 45 years..... supply the slightly larger invrrters...... after being confident in the math.

 

[Mountainsolarev]

I have both Enphase IQ7+ and IQ7A paired with 345W Solarworld and 385W Axitec panels respectively with same tilt/azimuth and similar shading. Over the last 7 days, mix of sunny and cloudy days, the IQ7+/345W panels produced an average of 7.7 KwH ea and the IQ7A/385W produced 8.6 KwH ea. or about 12% more. Another way to look at it is how many panels to install to achieve your desired output. For my location in NC in late April, 20KW would take (68) IQ7+ equipped panels vs (57) IQ7A equipped panels. BTW, my 2 year old IQ7+ are rated at 290W and I see that they definitely clip at 290-291W absolute max whereas the IQ7A with often shoot up to 362W for extended periods on max solar days.

What this comparison doesn't tell you is how the same 385W panels would perform with the two microinverters. I think the improvement of the 385W over the 345W on the IQ7+ would be very marginal. Likewise I'm not sure my 345W panels offer much benefit over 300W panels

Looking at the Solaris website (where I bought my DIY panels):
IQ7+ $149.50 + Axitec 310W panels $180 = $329.50/295W = $1.12/W
IQ7A $173.50 + Axitec 385W panels $215 = $388.50/349W = $1.11/W
Very little difference but I would expect that the labor for (68) panels would be more than for (57). For your (56) panel system, you might expect 12% less total power from the IQ7+ equipped system, although that is only a rough guess based on one week of data.

If you bought (56) ea sets, the IQ7+ would save you $3,304 in materials.

As far as DIY vs professional install, I found that I paid about $1,000/panel for professional including engineering analysis of the roof structure, permits and Duke Energy rebate filings. For my DIY addition, I paid about $500/panel but I did wiring myself and permits myself. Of course both are dramatically reduced by the Federal tax credits and in my case a Duke Energy rebate.

The ROI depends on your state's net metering rules. In NC, we get 100% credit per KwH however all excess is erased at the end of May. Also, any system over 12KW requires special approvals by Duke Energy.

 

[Crapmaster]

Thank you Mountainsolarev, excellent analysis! Currently i'm trying to decide between two systems, the original 56 Silfab 380W panels with IQ7+ inverters and an alternative 57 either Hyundai or Heilene 365W panels with IQ7+ inverters. While I would lose 475W in theoretical system output if going with the smaller panels, the turnkey installation cost would $1,000 less with Hyundai panels, at $1.76/W before the tax incentive. The Heliene would be a DIY option, but I don't have that price quote yet.

I'm leaning towards the 57 x 365W panel option because of the cost saving and less potential for system loss due to lower imparity between the panel max output and inverter max output, but it does lead to another question, which is the differences between Silfab and Hyundai panels. Aside Silfab being American made, which I like, the specs look quite similar for efficiency and 25 years output warranty. Any opinion between these two panel makers, anybody?

Here in Washington state we get 100% credit via net metering, and the "solar bank" resets at the end of March. We also pay no sales tax for solar system, which is a big one, because otherwise it would be 9.6% on top of the system cost. The no sales tax incentive applies both for equipment and installation/services.

 

[Danny]

My original plan was to do a DIY grid-tied system install, but I did obtain some quotes from the local (Seattle area) solar turnkey companies. I have a rather large, over 5,000sq. ft home, and I want some future headroom for an electric vehicle, which leads to a rather large, about 20kW system. One of the quotes I received was surprisingly attractive, $1.81/Watt. I'm still researching DIY options, I've mostly looked at Wholesale Solar (company) as the provider of the equipment. Would be open to other suggestions, if there is a known good provider of DIY solar gear.

Anyway, on that proposal I mentioned above, they propose 380W Silfab panels with Enphase IQ7+ microinverters. Any thouths, comments or concerns on these? My question is, the IQ7+ have max output power capacity of 295W, which is almost 25% less than the panel max output power. I asked about this, they referred to an Enphase white paper (attached), which states that the inverter max output can be up to 25% less than the panel output, and still only lose less than 1% of the efficiency. The white paper seems to back this up, the reasoning being that very rarely (less than 1%) of the time, the 380W panel actually produces more than 295W.

Does this make sense and do people agree with this? Their main argument is the cost saving on the lower output and therefore cheaper inverter. Any thoughts would be appreciated.

I have 385w panels with iq7+. Large panels make sense in many designs like mine where I wanted to minimize my racking expense. I discuss is in the following video about minute mark 7:30 of this video. The short answer in my case was that the racking costs was large and the extra cost per watt "lost" was not a big deal. I'm glad I have the 385w with the iq7a+. In fact I would consider larger panels and I would also consider the iq7a for $30 extra but I"m not sure the $30 extra / panel would pay for itself with the 385 panels.. The goal for me was to have less racks and the associated labor.

 

[Crapmaster]

Great video, and good angle on the racking! In my case, I don't really have much options, I need about a 20kW system, which takes pretty much all my roof space. Good info on the inverter overdriving!

 

[Mountainsolarev]

Thank you Mountainsolarev, excellent analysis! Currently i'm trying to decide between two systems, the original 56 Silfab 380W panels with IQ7+ inverters and an alternative 57 either Hyundai or Heilene 365W panels with IQ7+ inverters. While I would lose 475W in theoretical system output if going with the smaller panels, the turnkey installation cost would $1,000 less with Hyundai panels, at $1.76/W before the tax incentive. The Heliene would be a DIY option, but I don't have that price quote yet.

I'm leaning towards the 57 x 365W panel option because of the cost saving and less potential for system loss due to lower imparity between the panel max output and inverter max output, but it does lead to another question, which is the differences between Silfab and Hyundai panels. Aside Silfab being American made, which I like, the specs look quite similar for efficiency and 25 years output warranty. Any opinion between these two panel makers, anybody?

Here in Washington state we get 100% credit via net metering, and the "solar bank" resets at the end of March. We also pay no sales tax for solar system, which is a big one, because otherwise it would be 9.6% on top of the system cost. The no sales tax incentive applies both for equipment and installation/services.

You are welcome! You might want to consider asking your installers to quote you the IQ7A inverters vs the IQ7+. Retail price looks to be around $24 more each but will get you much closer to your 20KW output than the 365W with IQ7+ since they will clip at 295W. I would think the 365W panels would be a perfect match to the IQ7A because I have seen actual outputs of up to 362W with mine. Good luck!