confused about micro vs string for ground array in empty field

[stuffnjunk]

Background: Doing my due diligence on a ground array grid tie in setup with battery backup (for emergency loads). This ground array would be about a meter off the ground using bifacial panels. I am in the northern U.S. on a hilltop, and we do get snow. I have several acres I can place these panels on that do not get any shading at all as I mainly have an empty field.

IF someone can answer this by providing a clear link I would appreciate it. I'm not sure I completely understand the difference between the two, as most articles I have read are only discussing one sided panels, or roof top mounts. Are micro inverters mainly for panels that get shade from trees, or are they talking about an array that gets partial shading from passing clouds, or is it all shading? With the half cut bifacial panels I don't understand what the benefit is to using them vs. a string. Other than making different panel layouts? I am only seeing it as more ways to block sunlight on the backside of the bifacial panel (more boxes). So if I use a string I have to use optimizers? This adds more boxes that could potentially block the backside of the panel. What doesn't make sense to me with the optimizer is that with bifacial panels, the front and the back should never be the same, and I don't think an array would have identical panels through the whole array as that array would partially block some of the Irradiance? throughout the entire array (depending on layout). I probably just don't understand this well enough to wrap my head around it.

I know there are a lot of other issues, but I am trying to work out an issue or two at a time then do more reading. To make matters worse I did read about sodium batteries and perovskite panels.

 

[tmprof]

I have 12 bi-facial panels on a ground type array without any micro inverters or optimizers (They work great BTW). I don't have any shade from trees, but obviously weather will affect all panels at the same time so micro/optimizers won't really help in my opinion.

 

[shadowmaker]

Sorry no link and no experience with micros. My vertical/bifacial setup is on open field so decided to use string inverters. To my understanding there is no gain with micros when you have no hard shadows (clouds are considered soft). With string you get no individual monitoring which would be nice, but maybe not worth the extra cost. My panels are shingled cell technology so instead of two (half cut) they have six independently working areas in them, so no micros for me.

Don't overthink bifacial panels. They are just your regular panels with the added potential to produce some extra from the backside. Up here we get over 19 hours of sun in mid summer, so here the backside actually works as frontside in evenings and the main production comes from there.

 

[shadowmaker]

With bifacials I'd avoid backside shadows if possible. Of course if you only get reflected (diffuse) light to the backside it's unlikely to get any hard shadows there, but in any case I see no reason to deliberately create obstacles for light. "Loose" installation and panels 1-1,5m above ground gets you more light for backside production. Also albedo of the surroundings plays a big role for the backside production. I seem to get 30-40% boost in production when there is snow in the ground, so white paint, gravel, etc can give nice boost for summer production. Bifacial panels some 5m front of super white wall + white gravel/plastic sheet on the ground should be interesting.

My DIY array is optimized for winter production (low sun angle and snow) and can't be adjusted in any way. Seasonal tilt adjustment could make more total production, but as panels are cheapest part of the system, I just bought ~14kWp more. Under 0,2c/W (24% VAT and delivery included) I just couldn't resist temptation.

 

[stuffnjunk]

I have 12 bi-facial panels on a ground type array without any micro inverters or optimizers (They work great BTW). I don't have any shade from trees, but obviously weather will affect all panels at the same time so micro/optimizers won't really help in my opinion.

Thank you, so you just use string? If you don't mind me asking, what is your array like?

 

[tmprof]

Thank you, so you just use string? If you don't mind me asking, what is your array like?

I'm running all 12 of my bifacials in series. On a sunny day, I pull about 5000W or 22kW per day

 

[stuffnjunk]

With bifacials I'd avoid backside shadows if possible. Of course if you only get reflected (diffuse) light to the backside it's unlikely to get any hard shadows there, but in any case I see no reason to deliberately create obstacles for light. "Loose" installation and panels 1-1,5m above ground gets you more light for backside production. Also albedo of the surroundings plays a big role for the backside production. I seem to get 30-40% boost in production when there is snow in the ground, so white paint, gravel, etc can give nice boost for summer production. Bifacial panels some 5m front of super white wall + white gravel/plastic sheet on the ground should be interesting.

My DIY array is optimized for winter production (low sun angle and snow) and can't be adjusted in any way. Seasonal tilt adjustment could make more total production, but as panels are cheapest part of the system, I just bought ~14kWp more. Under 0,2c/W (24% VAT and delivery included) I just couldn't resist temptation.

Thank you for posting. So your set up has no optimizers, nor any micros. I like to follow the KISS principle, which stands for Keep It Simple Stupid.

I'm really glad you posted that vertical setup. I am so tempted to try it but with my wind ratings I'm not sure it would be optimal. I live on a hill top and our winter winds are pretty bad, summertime is more mellow. I've read so many articles about the benefits of that style (heat, degradation, etc). Optimal setup for me would be a solar/wind setup, with wind being the primary generator in winter. For cost reasons I am not contemplating that.

I think I read that you set up your array for winter with no way to adjust for summer. If that is true, in hindsight would you do it again? I'm the only person that goes into my field and cuts my field in the season, so I could zig zag fences all over if I had an unlimited budget and a desire to do that. I was contemplating an E-W setup for winter with the bifacials, but probably on a steep pitch and not vertical (just due to wind loads).

 

[stuffnjunk]

I'm running all 12 of my bifacials in series. On a sunny day, I pull about 5000W or 22kW per day

View attachment 179045

View attachment 179047

Nice, and you get a free pergola out of it. That is a lot of production. Here I was thinking I needed 20 panels at a min. Is that production at the peak during summer?

One suggestion, as I do this as part of my side hustle, get some oil based penetrating stain. It doesn't peel, flake or chip, just wears away. Semi transparent will last at least 2 years on horizontals and 4 years on verticals. With panels there and less degradation, you could get a longer lifespan. I can give you the names of some manufacturer's I have dealt with if you are interested. I don't get a kickback from them.

 

[tmprof]

No, I just finished installing them in late October! I am planning on adding another 12 panels on the roof of my house, but I wanted to make sure I knew what I was doing before I committed. I'd appreciate a link of course! I live in Houston Tx, and the humidity here is pretty high. I don't anticipate this living much longer than 15-20 years.

 

[zanydroid]

Optimizers and micros are pointless with no shading situation and actually waste money while also cause problems with future proofing. Lose lose. (And I operate a 100% microinverter system, because I have terrible shading)

Clouds are generally diffuse shading effects when looking at the scale of a residential array. Over a large land area, one can indeed have different insolation due to clouds. But over a 10kW array area? Rarely. Diffuse shading does not require MLPE to compensate, and I’ve never heard of anyone in this forum caring about it.

 

[Hedges]

If not rooftop, no need for RSD, no need for optimizers, no reason to use microinverters.
To avoid RSD, the inverter must not be mounted on the house itself.

String inverters like Sunny Boy or Fronius are higher efficiency than microinverters, and can have array sized to not clip.
Array can have multiple strings of different orientations, getting more hours of operation out of the electronics.

For Battery Backup, some microinverters (IQ8) may not work with other brand battery inverters.
Most Rule-21 inverters should AC couple well.
Some inverters accept HV strings of PV panels and optional batteries. SolArk, Sunny Boy Smart Energy, others. (SBSE will require extra hardware or full backup.)

 

[Brucey]

With bifacials I'd avoid backside shadows if possible. Of course if you only get reflected (diffuse) light to the backside it's unlikely to get any hard shadows there, but in any case I see no reason to deliberately create obstacles for light. "Loose" installation and panels 1-1,5m above ground gets you more light for backside production. Also albedo of the surroundings plays a big role for the backside production. I seem to get 30-40% boost in production when there is snow in the ground, so white paint, gravel, etc can give nice boost for summer production. Bifacial panels some 5m front of super white wall + white gravel/plastic sheet on the ground should be interesting.

My DIY array is optimized for winter production (low sun angle and snow) and can't be adjusted in any way. Seasonal tilt adjustment could make more total production, but as panels are cheapest part of the system, I just bought ~14kWp more. Under 0,2c/W (24% VAT and delivery included) I just couldn't resist temptation.

So your 700W bifacials are less than $140? Damn that's good pricing I'm throwing my self a party getting some Hyundai 300Ws for around $100 shipped here in the US. We do get a 30% tax credit on them but still...

 

[OPTIMALSOLAR]

The only advantage may be uptime. Lose a micro inverter you lose 8% of your production until it can be replaced. Lose a string inverter 100% until replacement. In the solar world replacement is rarely just a phone call away. Think weeks to months. I see all sorts of inverter issues on this forum, not much about Enphase failures. And Enphase may be the best company in the solar world.

If micros be sure to match their ability to invert watts to panels ability to produce watts. If string and uptime is critical on site inverter spare might be an option.

 

[stuffnjunk]

No, I just finished installing them in late October! I am planning on adding another 12 panels on the roof of my house, but I wanted to make sure I knew what I was doing before I committed. I'd appreciate a link of course! I live in Houston Tx, and the humidity here is pretty high. I don't anticipate this living much longer than 15-20 years.

Ok, now since you are in TX I would tell you to use Wood Defender, since they are in your neck of the woods so to speak. If you are shopping for prices, I would also tell you to look at Stain and Seals stuff (they are out of Tennessee). I have used both products and have talked to multiple people at both companies. Oil is pretty simple to apply and fairly simple to clean up. Just have to make sure the wood is good and dry first (which isn't really a problem in your climate). I don't get a kickback from them for mentioning it, only if I was your contractor and ordered it direct from them and marked it up. If you don't feel comfortable with applying it yourself you could call a contractor. From what the guys in TX tell me at the trainings, there is a stain guy on every corner down there. I wouldn't even really prep your pergola once it is dry, but that deck needs some prep. If you hire a contractor, make sure they don't spray near that array unless they mask it out first. You can get overspray off, but why bother if you don't have to.

If you have some questions on doing it yourself hit me up, not much to it, but there are a few things to make it easier. Most contractors bid on sq ft, but that deck is super easy with no balusters/spindles/top rail. There are other products out there, but those two are the ones I recommend to my customers and have applied. I paint decks too, but I think it is a waste of money.

 

[stuffnjunk]

If not rooftop, no need for RSD, no need for optimizers, no reason to use microinverters.
To avoid RSD, the inverter must not be mounted on the house itself.

String inverters like Sunny Boy or Fronius are higher efficiency than microinverters, and can have array sized to not clip.
Array can have multiple strings of different orientations, getting more hours of operation out of the electronics.

For Battery Backup, some microinverters (IQ8) may not work with other brand battery inverters.
Most Rule-21 inverters should AC couple well.
Some inverters accept HV strings of PV panels and optional batteries. SolArk, Sunny Boy Smart Energy, others. (SBSE will require extra hardware or full backup.)

chock full of info thanks.

 

[peakbagger]

A lot of commercial outfits buy in bulk and dont want to do the math to size a string. I have seen several commercial installed ground mounted arrays int he middle of south sloping field and still use microinverters.

Do note that many string inverters come with multiple MPPT circuits. If there ia snow concern it usually builds up down low so in this case the strings could be wired to have one sacrificial string on the lowest row of panels. One small benefit of micros is that at least Enphases have an LED on them that conveys basic operation of the inverter. Not visible on roof mount but to someone with ground mount they can walk behind the array and watch the LEDs flash when they are running and pulsing. No need to log on a website to check them.

 

[zanydroid]

But over a 10kW array area? Rarely

And to clarify. Yes the insolation will vary. But the gradient will typically be gradual at the scale of your array. And a sharp gradient will probably not persist that long.

 

[Hedges]

I have good history with SMA inverters, including up to 5 inverters running 17 years, 2 failures (one in warranty, one out) works out to about 32 years MTBF.
We rarely if ever encounter failed ones. Fronius I think is of comparable quality. Unlike some other brands.

Latest model SBSE has 10 year warranty standard, 25 year optional. SMA increasing warranties 5, 10, 20, 25 years over decades indicates confidence and experience.

If you are just using or net-metering, always have grid, I would have zero concerns about downtime.
If you need power offgrid or when grid down, then redundancy is advisable. I have that, with multiple Sunny Island battery inverters and Sunny Boy PV inverters.

 

[zanydroid]

A lot of commercial outfits buy in bulk and dont want to do the math to size a string. I have seen several commercial installed ground mounted arrays int he middle of south sloping field and still use microinverters.

Thanks for sharing that. I was somewhat confused by why Hoymiles targets utility scale with its pricing and advantaged control and management features.

 

[shadowmaker]

I think I read that you set up your array for winter with no way to adjust for summer. If that is true, in hindsight would you do it again? I'm the only person that goes into my field and cuts my field in the season, so I could zig zag fences all over if I had an unlimited budget and a desire to do that. I was contemplating an E-W setup for winter with the bifacials, but probably on a steep pitch and not vertical (just due to wind loads).

No regrets so far. I'm about 3000km north from you, so my winter consumption is 3-4x summer consumption for 5-5,5 months even with pretty nicely insulated buildings (old though). At the same time I'm only getting less than 10% of my summer production (Nov-Dec-Jan). Every winter kWh is welcomed. Saw sun today briefly. Last seen three weeks ago...

If you want winter production E/W setup might not be ideal. You probably would do much better with S/N orientation. My array has 138 azimuth, because I didn't want to interfere farming that field. It is quite ok for winter production, but suffers summer afternoons when sun is perpendicular to it. But in summer my current setup produces 2-3x what's needed.