Solar production. Panel ratings/claim vs reality

[LD1]

Long story short....My local coop/electric company have made some favorable changes to their residential net metering policies that now has me re-evaluating going solar.

Basically I currently pay $51 as "meter" charge. Thats simply the pleasure of being hooked to their grid.
Beyond that, I pay 12.5 cents per kwh.

IF I install solar....they will truly credit 1:1 net metering. Going solar though increases the "meter" charge to $57.

So if I install a system that makes EXACTLY the same as I use in a given month....my usage would be $0....and I'd only owe $57.

If I make 100kwh less than I use, my bill will be for $57 + (100kwh x $0.125) = $69.50

If I make 100kwh MORE than I use I get "credited" at the cost avoidance rate which is 7.5 cents per kwh. So bill would be $57 - (100kwh x $0.075)....or $49.50

So in a nutshell I "save" 12.5 cents for every kwh I can make but ONLY up to the point I start producing more than using.....then my savings drops to only 7.5 cents per kwh

So there is not much incentive to have a system capable of producing more than I use in a given month. Because the diminishing returns and it will lengthen the ROI

My problem is my usage here in Ohio. Spring and fall months like April-May and Sept-Oct I I dont use much HVAC...which is my biggest usage. I only use 1100-1200kwh in those months. Summer months seem to cap around 1800kwh and winter months can be as high as 2200-2300kwh. Which is opposite of what one would want with solar.....because I will be making the least in the winter when I use the most.

I am inclined to want a system just large enough to make 1100kwh in the months of april/may and sept-oct. Which should make even less in the winter....but slightly more in the summer. By doing this....I can be sure that I am getting 12.5 cents per kwh for every kwh I can produce.....and not worry about making too much and only getting 7.5 cents. Not that it would be a bad thing to over-produce.....just not as cost effective in the long run when I could have purchased a few less panels and inverters. Basically.....if I can get a 9-10 year ROI at 12.5 cents credit.....that would go to ~16 year ROI for every panel that I oversize by.

Which leads to the point of this post. What size system? I have played with all the various calculators online, read what panels are "estimated" to produce in a give month, etc etc. But nothing trumps real world data. Those of you that have solar.....central ohio a plus....or at least the 40th parallel....whats some real world data from your system? What is your array size or # of panels and how many watts? And what is your actual production annually and for varying times of the year?
In a rolling 12 months I use 18,000kwh. So it would be easy to simply do the average of 1500kwh/mo and target that like so many online resources tell you to do.

And if my electric company net-metered on an annual basis that would be good. But since its a month-month.....I feel that would be too large of a system as I would produce more than I use for about 4-months out of the year. Leading to a diminishing return.

I know nothing is guaranteed and weather, etc etc. But basically.....what size system is ideal in the real world to give me 1100kwh in april and may in ohio. Cause various "formulas" and calculators and math.....I am getting anywhere between an 8kw and 14kw system. Which is a pretty big spread

 

[ponytug]

Go use PVWatts at NREL. It is very very accurate.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

You need to measure the slope of your roof and double check the orientation, and with that information it will give you detailed analysis of when and what your production should be.

I would also suggest that with the PVWatts numbers, you map out a spreadsheet to get your expected bills so you can see what the cost / benefits are to larger or smaller systems.

I would plan on a degradation of the solar output over time, so I would suggest oversizing the system by 10-20% at least.

In my experience very very few people look back on a solar installation and say "gosh, I should not have put in so many panels". (I've never met one.) It is almost always, "Darn! I should have put in more!" and putting in more later is usually more expensive because the team has to come out a second time, more permits, etc.

I have microinverters, which I highly recommend, as a micro inverter failure only takes out a small percentage of your production, whereas a single inverter failure will take out 40-100% of your solar for days to weeks to months, depending on your vendors.

We have batteries as well, but that is more of a "ride through the not so infrequent outages" thing, though it does save us some on our time of use electricity costs. Batteries often don't pencil out on a straight economic analysis, but after we had them, my wife went to 100% work from home, at which point the batteries became an essential item for her work.

All the best,

Peter

 

[workinonit]

I would never attach solar panels to my roof. I've heard so many horror stories about roof damage and leakage from those panels.

 

[LD1]

Go use PVWatts at NREL. It is very very accurate.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

You need to measure the slope of your roof and double check the orientation, and with that information it will give you detailed analysis of when and what your production should be.

I would also suggest that with the PVWatts numbers, you map out a spreadsheet to get your expected bills so you can see what the cost / benefits are to larger or smaller systems.

I would plan on a degradation of the solar output over time, so I would suggest oversizing the system by 10-20% at least.

In my experience very very few people look back on a solar installation and say "gosh, I should not have put in so many panels". (I've never met one.) It is almost always, "Darn! I should have put in more!" and putting in more later is usually more expensive because the team has to come out a second time, more permits, etc.

I have microinverters, which I highly recommend, as a micro inverter failure only takes out a small percentage of your production, whereas a single inverter failure will take out 40-100% of your solar for days to weeks to months, depending on your vendors.

We have batteries as well, but that is more of a "ride through the not so infrequent outages" thing, though it does save us some on our time of use electricity costs. Batteries often don't pencil out on a straight economic analysis, but after we had them, my wife went to 100% work from home, at which point the batteries became an essential item for her work.

All the best,

Peter

I have used that calculator....but still lots of variables....like premium, thin film, or standard modules. And system losses? How do I estimate?

No roof or roof angle to be concerned with. Not going on roof. Also no permits/zoning or labor/installer if I ever decide to add a few panels as this will be self install.

Ideally....I want simplicity, havent researched much racking....but plan to have it where I can change the tilt a few times a year to optimize it between winter when the sun is low in the sky vs summer when it gets much higher.

Which is why I am basically looking for similar monthly data like that site you linked....but from real world systems. people that actually have a system. # of panels and how many.....what is your monthly production

 

[ericm979]

Are you sure they true up monthly? Every net metering scheme I have seem true up annually because of the season effect you noted. If they do true up monthly that's a sneaky way of not really doing net metering.

 

[LD1]

Are you sure they true up monthly? Every net metering scheme I have seem true up annually because of the season effect you noted. If they do true up monthly that's a sneaky way of not really doing net metering.

Since I dont have solar and dont know anyone with my coop that has solar....all I can go off of is what they have told me. So can I be 100% sure its trued up monthly....no. But I can be 100% sure that they told me it is trued up monthly.

 

[ponytug]

I have used that calculator....but still lots of variables....like premium, thin film, or standard modules. And system losses? How do I estimate?

No roof or roof angle to be concerned with. Not going on roof. Also no permits/zoning or labor/installer if I ever decide to add a few panels as this will be self install.

Ideally....I want simplicity, havent researched much racking....but plan to have it where I can change the tilt a few times a year to optimize it between winter when the sun is low in the sky vs summer when it gets much higher.

Which is why I am basically looking for similar monthly data like that site you linked....but from real world systems. people that actually have a system. # of panels and how many.....what is your monthly production

PVWatts is based on extensive real world experience, so I would believe the outputs. The people I know who have used it say that it was within 1-2% for them, and that matches my experience.

Well ground mounts simplify things; I would play with the angles and see what you like. There is a new version out that are basically plastic tubs that you fill with rock/concrete, so the site prep is removing grass, leveling, adding base rock, compacting the gravel, putting the tubs down and filling them. The downside is a fixed angle. I like the center pole systems for changing the angle through the year. If you have access to an auger, either drilling the holes to make concrete supports for metal, or augering in ground anchors are alternatives, but make sure that your auger has a deep enough depth of cut.

As far as modules, go price a few and see what you want to spend, and then use those premium /thin film/standard settings. Generally, unless you are constrained by space the extra dollars/Watt for premium doesn't pencil out.

All the best,

Peter

 

[Mtsoxfan]

I was net metered in CT, the end of the year balance was a fraction of what they charge per kwh. I knew that going in, and was ok with it. My system over produced, or we under used, just enough to cover a few months service charge, at $20 or so a month. After 8+ years, output remained constant. Not like the internet "stories" you heard about decreasing and not working because the warrantee ran out. Sheesh, some people just like being negative and spreading falsehoods because they can...
Never have I heard of leaking roofs from installation, although I've only talked with 20 some odd people who actually owned, not internet stories. Can it happen? I guess, but why would someone do crappy work, unless they didn't guarantee against them like my installer.
The only reason we didn't get solar when we moved to VT is because the amount of sunshine average was less, and ROI didn't make sense to a retired couple.

 

[ning]

Consider also that while a panel may be, for example, a 350W panel, you may or may not spec the inverters (microinverters these days) to the same maximum.

I have 10kW of DC (panel maximum output) but my microinverters will put out a maximum of 7.68kW AC. The microinverters will unlikely degrade at the same rate as the panels, and the panels will only put out their rated maxima at very specific conditions (angle of incidence of the rays, temperature) and it was explained to me that while I could potentially end up with a few more AC watts in the first few years of operation, the extra cost for higher output microinverters would never come close to being paid off.

In other words - don't think your 10kW of panels all added up together will give you 10kW.

I was also concerned about putting panels on my roof: 1, my roof wasn't exactly new, but it wasn't old enough to require a re-roof yet; 2, my roof hip is aligned N-S and I couldn't easily tilt panels at all toward the south; 3, some shading of the roof.

Due to setbacks here, my 8ac of land had a 50'x50' region that allowed new "structures" to be placed on it (we have to be 100' away from water, 30' from property lines, and other places have bad shade in the mid to later afternoon). I'd imagine I could've gotten a variance because a solar ground mount isn't particularly polluting to water features (meanwhile I can plow and run cattle right next to the pond and irrigation canal but I can't put concrete into the ground?) but I went with the easy spot because it really had the best sun. Still, it was a 550' cable run from the panel mount to my service entrance; the trench and the cable added to the mount itself weren't particularly cheap, but I can also clean my panels from the ground; I'm still a proponent of the ground mount (plus I intend to add 50% more on another ground mount next to it if I need to).

 

[Mtsoxfan]

Yeah, that 550' will run up some cash. I would have preferred a ground mount, specifically a "follow the sun" style to increase output, but being in CT, with ledge everywhere including my yard, they couldn't nail down installation costs if the ledge interferred. I didn't like the unknown, as we were stretching finacially to get the system as it was.

 

[ericm979]

I think one advantage to roof mount panels in the summer anyhow is that the panels shade part of the roof.

 

[LD1]

Did lots of research today. Lots of options. Enphase micros seem about the best....but there are other micro inverters too. Some do two panels per.

Looking at kits....but don't know if the "kits" are more expensive for convenience or cheaper because it's a package.

I have seen panels asl low as 25-30 cents per watt.

10kw system would be about $3000 worth of panels.

Ive seen the micro inverters for $150-$200. I guess since one per panel is needed....I should pay attention to getting higher wattage panels to reduce the number of those needed. But about 26 390w panels puts me close to 10kw

So about $5k for the inverters.

That's $8k right there. But a lot of the 10kw "kits" I'm seeing are $15k with no racking. And ground racking adds $3k but I still need structure pipes sourced locally.

Is there really another $7k worth for the cables and combiner box and other odds and ends to connect all the panels together? I'd still have to buy the service wire to go from there to house too.

Looking like "kit" options are gonna push the final product to ~$2 per Kw. Bout $20k for a 10kw system.

Don't seem to be many good options for sourcing stuff. Not sure how much I trust the places selling the kits online cause there aren't many. And I'm sure they are making quite the markup.

 

[LD1]

Consider also that while a panel may be, for example, a 350W panel, you may or may not spec the inverters (microinverters these days) to the same maximum.

I have 10kW of DC (panel maximum output) but my microinverters will put out a maximum of 7.68kW AC. The microinverters will unlikely degrade at the same rate as the panels, and the panels will only put out their rated maxima at very specific conditions (angle of incidence of the rays, temperature) and it was explained to me that while I could potentially end up with a few more AC watts in the first few years of operation, the extra cost for higher output microinverters would never come close to being paid off.

In other words - don't think your 10kW of panels all added up together will give you 10kW.

I was also concerned about putting panels on my roof: 1, my roof wasn't exactly new, but it wasn't old enough to require a re-roof yet; 2, my roof hip is aligned N-S and I couldn't easily tilt panels at all toward the south; 3, some shading of the roof.

Due to setbacks here, my 8ac of land had a 50'x50' region that allowed new "structures" to be placed on it (we have to be 100' away from water, 30' from property lines, and other places have bad shade in the mid to later afternoon). I'd imagine I could've gotten a variance because a solar ground mount isn't particularly polluting to water features (meanwhile I can plow and run cattle right next to the pond and irrigation canal but I can't put concrete into the ground?) but I went with the easy spot because it really had the best sun. Still, it was a 550' cable run from the panel mount to my service entrance; the trench and the cable added to the mount itself weren't particularly cheap, but I can also clean my panels from the ground; I'm still a proponent of the ground mount (plus I intend to add 50% more on another ground mount next to it if I need to).

What does your 10kw system produce through out the year? What's January production? May? And maybe July to give me an idea

What latitude?

 

[ponytug]

What does your 10kw system produce through out the year? What's January production? May? And maybe July to give me an idea

What latitude?

Ours is a smaller system, with less than perfect orientation.

Dec/Jan is about 20% of June. If we were to pull the angle of the panels from about 20 degrees up to about 30-35 degrees, the winter production rises to about 40% of the summer production, though the summer production would take a 10% or so hit, per PVWatts. That's the plan for the next array.

All the best,

Peter

 

[LD1]

Ours is a smaller system, with less than perfect orientation.
View attachment 878366
Dec/Jan is about 20% of June. If we were to pull the angle of the panels from about 20 degrees up to about 30-35 degrees, the winter production rises to about 40% of the summer production, though the summer production would take a 10% or so hit, per PVWatts. That's the plan for the next array.

All the best,

Peter

What is your system size? And what latitude?

Looking at your spring/fall months....I would like to make right about double that.

I need to do some research on racking.

I definitely want to optimize the angle....maybe once every month or two.

Playing with the pvwatts calculator it seems to make quite a difference.

 

[Roric]

Our array is 7500 watt (375X20) via Solaredge optimizers and inverter.
Production is just short of 9 mega-watt-hours per year, just under 25
kilowatt hours per day. Located near central Minnesota so it may be applicable to your location, (except for snow loads). Roof mounted, fixed south orientation.
Our utility uses two meters: one bi-directional for the service and another for PV production. Monthly bill shows both totals.
When installed, it produced enough to exceed our use in the summer and resulted in a credit on the bill and in the winter we had a bill due.
On average it was a "wash".
Since 2019 we have done some energy saving changes (but also some energy using ones: A PHEV for her, EV for me). This has resulted in having a bill most months although it is small compared to pre solar.
So install as much as you can is what I can say.
The Solaredge app says we are on track to be at 45 MWH when we hit the 5 year anniversary date.
My favorite thing is when I turn off a light switch and say "Do you think we get free electricity around here?" SWMBO say "Yes, yes I do..."
Good luck with your self-install.

regards,

R

 

[LD1]

The "install as much as I can" will extend the payback. According to PVwatts estimate for generation.....a 10kw system will exceed what I use in my home 6 months out of the year but fall well short for the other 6 months.

I did a quick spreadsheet as if I had a 10kw system
Month..........usage............Potental generation........difference
Jan..............2124.....................716........................1408
Feb..............1615.....................805........................810
Mar..............1645....................1034.......................611
Oct..............1355....................1139.......................216
Nov..............1710....................786.........................924
Dec..............2085....................638........................1447

Those are the 6 months I fall way short and have to purchase all those KWH at 12.5 cents per kwh from the electric company

Apr..............1153...................1180.....................+27
May.............1282...................1379.....................+97
Jun..............1220...................1406.....................+186
Jul...............1466...................1545.....................+79
Aug.............1348...................1404.....................+56
sep..............1135...................1278.....................+143

Those are the 6 months I'd make more than using and get credited at 7.5 cents per kwh from the electric company

So ~5416 kwh I have to buy at 12.5 cents = $677
The ~588 kwh I made surplus Id get 7.5 cents credit = $44.10

And I have a monthly meter fee of $57 x 12 = $684

$677-$44+$684 leaves me with a $1317 electric bill for those 12 months.

The ACTUAL cost of those 12 months without solar, my bill was $2655 for the year.

If I had a 10kw system....in the past 12 months I estimate my savings would have been ~$1338

Looking for no more than a 10 year payback means I need to find a 10kw system....ground mounted, all racking, etc and spend no more than $13,350.

OR....factoring 30% fed credit.....no more than $19,000 for EVERYTHING.

Thats a tall order and I need to do some more shopping. But we are certainly closer than I ever have been in the past to possibly hitting this 10 year target

 

[Roric]

If the utility allows you to "over-size" production it is to your advantage.
(We were limited to 120% of historical use).
Make hay while the sun shines is the old saying.

NAZ lists a 11,200 system with Enphase inverters for $14,000.
Depending on your utility rules and regulations it may prove a faster payback. There is a value in taking a bill off the table every month.

best of luck,

R

 

[Roric]

My all-in cost was $14,000 in 2019
Minus 30% federal incentive was about $9,800.
Purchased kit from Wholesale Solar for about 9k.
All the rest of costs were rented and purchased locally.

 

[ponytug]

What is your system size? And what latitude?

7.6kW DC, 6.9kW maximum typical production due to orientation, roof planes, etc.

37N, so quite a bit south of you.

All the best,

Peter