12.2kw solar barn

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JP11

JP11

Minister of Fire
May 15, 2011
1,452
Central Maine
Day one of install was today.

Unfortunately.. I have to go back to work tomorrow and won't be here for the rest.

Good news.. Internet 'bridge' was able to work across my wires (install guys were unsure. about 500feet underground wire, and two panels to go through), and I now have wired internet in the barn, which will let me view solar array in real time via web.

A couple pics. Just boxes and racking.

JP


PS.. barn looks odd because my wife is a professional photographer. Different backgrounds for her to work with . The couple green ones are going to be a graffiti wall and a stucco wall. IMGA0112.jpg
 

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Are you using Enphase microinverters??...what is your configuration....roof orientation etc?
 
Roof is 205 with a 4/12 pitch.
No microinverters.
48 Panels that are 255W
2 SMA transformerless inverters.

It should be making power Thursday. I don't get home till Tuesday. Power company came by this monday and put in my dual meters. I'm all set to go once they finish.

JP
 
Congratulations, very exciting. What are the net metering rules in Maine with your utility? 4/12 pitch is about the equivalent of what my ground mount is. Good compromise summer vs winter. Did you do a PVWatts analysis for your system? If so, what did it show? Keep the info coming.
 
Time to buy out the local hardware store for roof rake extensions!
 
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No raking up there. walls are 16' high. I did the PVwatts calcs. In maine they won't cut you a check for excess production. Credits roll for 12 months. Over a year old.. you've given them away.

If it becomes an issue.. I own the house my parents are in. I can put that house in my name.. and send extra credits to that account.

Eventually, the wife's next car will likely be a plug in.

Here's the info I got.

PVWatts: Monthly PV Performance Data
Requested Location:
City: AUBURN-LEWISTON
State: ME
Lat (deg N): 44.05
Long (deg W): 70.28
Elev (m): 88
Array Type: Fixed (roof mount)
Array Tilt (deg): 33.3
Array Azimuth (deg): 205
DC Rating (kW): 12.24
DC to AC Derate Factor: 0.77
Average Cost of Electricity Purchased from Utility ($/kWh): 0.14
Cost of Electricity Generated by System ($/kWh): 0.15

Month AC System Output(kWh) Solar Radiation (kWh/m^2/day) Plane of Array Irradiance (W/m^2) DC array Output (kWh) Value ($)
1 580.762085 2.077308655 64.3965683 663.0841064 83.97
2 970.4955444 3.610863209 101.1041718 1073.975098 140.31
3 1278.183716 4.564380169 141.4957886 1417.144287 184.8
4 1355.656128 5.01350832 150.4052429 1503.063232 196
5 1625.287109 6.051045418 187.5824127 1787.557861 234.98
6 1442.623169 5.72269392 171.6808167 1599.946533 208.57
7 1485.337036 5.926843166 183.732132 1640.805298 214.75
8 1352.230469 5.228490353 162.0832062 1496.544556 195.51
9 1273.668701 5.048354149 151.4506226 1406.806152 184.15
10 1052.330444 3.823254824 118.5208969 1169.723511 152.15
11 705.9881592 2.622964621 78.68894196 794.2578735 102.07
12 733.9880371 2.522422552 78.19509888 817.9729004 106.12
 
Wait, they don't buy back the excess power you make and only give you a credit which is thrown away if not used? Damn, that's a shame.

About this system - are you installing it yourself or are you having it put in by some contractors? Buy a kit? I've been doing tons of reading and research on this and I'm curious about all you've done. How much for the total install, if you don't mind my asking?
 
You would be surprised with raking. I rake the bottom edge of my panels on the second floor roof of my house which is about 20 feet from the ground. Just getting the bottom edge cleaned off after a snow dump make a big difference in how quickly the rest of the snow will melt and slide off. Unfortunately, like a metal roof, the snow sometimes decides to come down in one big sheet and you really need to hope you aren't under it as it can cause serious injury. Folks use snow clips on metal roofs to stop the avalanche but with solar panels you really want them to clear.

Bummer on the net metering, I am spoiled with the NH system where they never expire. They even will buy them back but at a fairly low rate once a year but I prefer to just run my heat pump to burn it up.

Since you went with central inverters it will be interesting to see how them wire them. I would suggest in horizontal rows as I find that on occasion I will still have snow on the top rows and the bottom ones will be clear.
 
Not sure how the schematic goes. I know there are 8 conductive wires. So that means 6 panels per wire.

As for your questions.

Contractor
just a whisker under 35k.

Snow really didn't hang around on that roof last winter (my first with the building). I guess it's just we'll see. Panels don't go down to the part I could rake anyway. Wife sent me a pic of today's progress. I'll post

JP
 
JP11 said:
No raking up there. walls are 16' high. I did the PVwatts calcs. In maine they won't cut you a check for excess production. Credits roll for 12 months. Over a year old.. you've given them away.

If it becomes an issue.. I own the house my parents are in. I can put that house in my name.. and send extra credits to that account.
Click to expand...

Your program sounds like net metering to me. Only difference is at my house is I have one smart meter that tracks my Net and Delivered. Sounds like your power company installed a separate meter to track outgoing to subtract it from what you might buy. My credits (if I ever make any) don't roll past the end of the year. At the end of December I would get paid ~$0.03/kWh for any excess, and it just didn't seem right to generate excess for that little return.

In Florida, the power companies don't let you swap kWh between different accounts at different addresses. Some farmers who installed panels with multiple meters found that out the expensive way.

Thank you for the photos!
 
Yes.. it's as you describe. Net metering. I sell anything I don't use.. on a minute to minute basis. I get to let them have that KW.. and I get to use it until it gets to be a year old. Contractor said even though I'm oversized.. will take a LONG time for me to worry about credits going un used.

I SHOULD have web access to see production real time tomorrow... assuming they finish and set it up as promised.

Been very happy with the installers. I only met the 'roofing' guys, and not the electrician... but been very impressed with them thus far.

JP
 
Do I have this figured out right?

The most return you would get in a year would be what your power bill would have been in a year? If you generate more than you use, they resell it but they don't pay you for it?

I'd be looking at a 25 or 30 year payback if I understood right.
 
maple1 said:
Do I have this figured out right?

The most return you would get in a year would be what your power bill would have been in a year?
Click to expand...
^^^ Sounds about right. With my undersized system (4.4kW), I still had just under $500 in total electric bills for the last 12 months. That beats the heck out of the $1500 I had in total electric bills in 2012, in my all electric house with all the creature comforts. My co-workers spend anywhere from $1500-$2500/yr on their electric bills. I'm not planning on selling my house any time soon, so 12-15 year pay back does not discourage me. (my system is 4.4kW, because that was the max I could fit on my second story south facing roof). Even if I had a system that generated every kWh my house uses. I'd still have close to $100 in total bills for a year, since my base meter fee is close to $8/mo.
 
Maple.. I'm guessing your power is quite a bit cheaper than mine. I had calculated payback at around 11 years. The week after I sent in the deposit, PUC announced rates going up 4%.

I've got a spreadsheet going, and plan to put in production numbers, and let it extrapolate out and average to see where it crosses over. I'm only 40.. and plan to stay in my house a good long while.

There is a tax CREDIT of 30% of installed cost. You need to of course be paying that much in taxes to have it work out.

The numbers all scale rather well. I have power bills in the 2k per year range.. I should have zero usage with this setup. Bill should be around 12 dollars a month.

I think my install is about as simple as it gets. Flat, south facing roof. Didn't have attic insulation in. Other than the walls being insulated and sheathed, they couldn't have asked for it to be any easier. I even let them use my forklift.. so no lugging anything.

JP
 
Agreed you should end up with a near $0 bill. I added up your PVWatts estimated average AC Output = 13,855kwh @ $0.14/kwh = $1940 annual credits. I also sized my system for a near $0 bill (at current rates, annual usage about $978, value of estimated annual production is $1035).

MN net metering is somewhat different from yours in that if credits at the average retail rate ($0.108 currently with my utility) exceed usage, the utility pays us back the excess $ on request.

Since the utility pays us back the excess at the retail rate, my wife and I also are on a mission to further reduce our usage so that the payback also will cover some or all of our base charge of $14/mo.

What I'm having difficulty understanding is the DC to AC derate as applied to my system. My DC system is rated at 6.89kwh maximum output, the system microinverters are rated at system 6.5kwh DC nominal maximum input, and so far for year 1 the system is providing AC output at very close to 6.4kwh, which is a DC-AC derate of 0.93 based on the DC system or 0.98 based on the microinverter DC input.

I'm guessing that the new panels may be performing somewhat better than on average they will perform after being in service for awhile. I will be interested in seeing your data as to whether the 0.77 derate may be somewhat excessive and you will experience higher than estimated AC output.

Keep the information coming!
 
jebatty said:
What I'm having difficulty understanding is the DC to AC derate as applied to my system. My DC system is rated at 6.89kwh maximum output, the system microinverters are rated at system 6.5kwh DC nominal maximum input, and so far for year 1 the system is providing AC output at very close to 6.4kwh, which is a DC-AC derate of 0.93 based on the DC system or 0.98 based on the microinverter DC input.

I'm guessing that the new panels may be performing somewhat better than on average they will perform after being in service for awhile. I will be interested in seeing your data as to whether the 0.77 derate may be somewhat excessive and you will experience higher than estimated AC output.

Keep the information coming!
Click to expand...

According to this link,

http://davebuemi.com/2011/03/21/pv-system-derates-explained/

apparently the magic '0.77' includes many factors you haven't considered, including losses due to 'soiling', less than spec performance, wiring losses and system downtime (for repairs). Seems intended more for a worse-case scenario over long periods of time, with unreliable inverters and underperforming panels.

It includes a 8% loss for the inverter. Does not include any downtime for snow.
 
I think the derate factor was set intentionally conservative, few folks complain if the model underreports but most would complain mightily if it overestimates.

Panels used to degrade differently. When I got my first set of Sharp poly panels, they were intentionally down rated from the test value to cover initial degradation. When first put on line they definitely appeared to generate over rating and then gradually dropped over the first few months.

PV WATTS1 had one location in my state and it its quite a distance away and a completely different regional climate. I expect the derate also factors in the potential for model error due to a course data set.

The snow factor is big unknown. My roof mounted panels without raking may sit covered for 5 to 10 days after a snow storm with zero output. If I rake the lower edge, they normally would be clear in two days.
 
Curious how it all shakes out. Guys doing install just said.. You're gonna be a BIG summer producer.

Inverter efficiency is pretty high with the transformer less design.

we'll see

like a kid at christmas... waiting for my login to see it working. Im in Alabama at the moment.. hot and sunny here!
 
JP11 said:
Maple.. I'm guessing your power is quite a bit cheaper than mine. I had calculated payback at around 11 years. The week after I sent in the deposit, PUC announced rates going up 4%.

I've got a spreadsheet going, and plan to put in production numbers, and let it extrapolate out and average to see where it crosses over. I'm only 40.. and plan to stay in my house a good long while.

There is a tax CREDIT of 30% of installed cost. You need to of course be paying that much in taxes to have it work out.

The numbers all scale rather well. I have power bills in the 2k per year range.. I should have zero usage with this setup. Bill should be around 12 dollars a month.

I think my install is about as simple as it gets. Flat, south facing roof. Didn't have attic insulation in. Other than the walls being insulated and sheathed, they couldn't have asked for it to be any easier. I even let them use my forklift.. so no lugging anything.

JP
Click to expand...

My bills are right around $200 every 2 months. If I run our electric hot water heater in the summer, it gets close to $250. So say $100-125/mo. All-in cost is around 0.18/kwh.
 
It [derate] includes a 8% loss for the inverter. Does not include any downtime for snow.
Click to expand...
The microinverters are rated at [correction] 96% efficiency. With my ground mount, snow clearing is easy, about 10 minutes of time with a long-handled broom, and I cleared snow regularly for the first winter, including at -30F outside temp. I have a little winter shading effective for about 5-6 weeks on each side of Dec 20, with my estimate being about a 4% derate (360 kwh) from annual production.

My panels are Suniva 265 watt and appear to be high performing compared to competitive panels used by others in my area. I also washed half my panels once this summer after the spring pollen season, and although there was a slight film on the panels not washed off by spring rains, I did not notice any change in per-panel output.

Time will tell as the years roll by.
 
Last edited:
When I asked the contractor about micro inverters instead.. he said I didn't have big shading issues, or really much of ANY shading issues.

He did say that 80% of their problems or service calls are micro inverter systems. Don't know.. have no frame of reference other than what he told me.

remains to be seen how it all works.

JP
 
It will be interesting to see how are two systems compare over time. You're right, remains to be seen how it all works out.

Correction: The Aurora micoinverters are rated at 96% efficiency, not 98%.
 
Up and running on a cloudy day. Real time monitoring every minute via internet or appScreen Shot 2014-08-21 at 5.20.38 PM.png
 
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