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.