I find myself repeating many aspects of the solar-panel saga, so I thought that I would write them down here, so that you might benefit.
I will revise these notes as I go along.
Notes on installing the solar panelsLove the folks at Solar Electric Supply. From them, I bought a kit including:
- Solar panels (x14)
- aluminum rails to mount them on
- Fronius inverter
- DC Disconnect
- DC Collector
- AC Disconnect
- wire to get the electricity off the roof
- Fast-Jacs to mount the panels on the roof
- schematics and instructions
We picked them up from the local Roadway trucking distributor in two trips. (That's one of the reasons Charlotte is popular with trucking companies: I-85 and I-77 intersect here.)
We oriented the house so that the long dimension was facing south. The roof angle was close enough to our Longitude of 34 degrees that we could mount the panels parallel to the roof. We used Fast-Jacs to get them off the roof because cooler panels produce more electricity. Daniel and Mark Jakubisin mounted them directly into the trusses before the roof shingles went on. (The roofers had more work, but they're better at putting on the flashing than we would have been.)
The panels have DC power cords built in. They snap together like Lego (tm) pieces. I hooked up 7 in series for the left array and 7 in series for the right array, and measured around 265 VDC for both. The two positives go into a fuse and get combined for the same voltage and the combined amperage.
About the Fronius: it senses the sine wave of the Duke Energy line in order to figure out if it should sent out power.
Of course it has to be in phase with that incoming power to work right. Also, if it senses that there is no incoming power, then it will cut off AC output (because otherwise there could be a Duke lineman working on an energized line). If there is an interruption of Duke power, it will not deliver AC power until the power has been re-established for ten minutes.
Our
electrical inspector had us move the DC disconnect to the attic, and an "accessible" place. This meant placing it above the attic access. He also had us put a galvanized "hard pipe" through the roof, and a weatherhead on top of it. These were readily available at Lowes. We used flexible ("smurf") conduit to get it from a junction box next to the combiner over to the DC disconnect.
Make sure that the inspector indicates that he inspected the solar system on the form that you get from Duke.
Notes on NC GreenpowerI dealt with Sunny (what a great name for someone working in renewable energy!). I signed contracts saying that I would sell my RECs to them and them only. She sent me a sheet of return addresses and I will send her my Duke Energy bills once I start producing. I can also fax it in.
Notes on Duke EnergyI went with a dual meter can, at Dave Cook's suggestion (more on Dave in a minute) because it looks a lot better on the outside and the schematic would not need to be overhauled. See my other post for why I went with dual metering. I had to get John to put a second wire out to the second meter, because the Fronius is putting out +120 VAC and -120 VAC in phase (to make it +/- 240 VAC).
They have a
checklist which describes the $100 application fee and the documents they need. They also wanted a copy of my homeowner's insurance declarations page.
Strange as it may seem, I had to register with the North Carolina Utilities Commission and also with Federal Energy Regulatory Commission. They take their power seriously. (These sites were also on the checklist.) If you don't have an electrical engineer handy to answer these questions, you are not a co-generational facility
I had some extended conversations with Beth H. and Steve Smith at Duke. They really helped me think about the options (dual metering versus bi-directional, and Option A versus Option B). I created a spreadsheet to estimate how much each of the four options would reap, and went with dual metering, option B. Steve confirmed that this was the combination that most people used at my size of array (3.1 kW). (I believe that they are not allowed to advise and recommend.) They were very patient in correct my spreadsheet errors, some of which were typos (like .000239 instead of .00239) and some of which were misconceptions. For example, they explained that Capacity credits have on-peak and off-peak
months, while energy credits follow Time-of-Use and have on-peak and off-peak
hours.
The spreadsheet used an estimate of the solar day of 4.7 hours. (This means taking the average number of sunshine hours and reducing by factors such as clouds, haze, pollution, and bird poop.) It also took into account the length of the days at 35 degrees 14 minutes and used that as a proxy for how the 5318 kWH would be distributed over the year, by month. It also made a really rough guess as to how many Energy hours would be on-peak and off peak: 26% on peak in the winter and 37% on peak in the summer. Here's my reasoning: the average length of day in June through September is 13.5 hours. About 7 of those hours are during on-peak hours. But two of those days each week are on the weekend. So I'm thinking 35 hours / (7 * 13.5) = 37%. Average days in the winter are 11.24 hours long. On peak is from 8 AM to 1 PM, so that would be about 5 hours a day.
An engineer, Dave Cook, dropped by today to take some pictures of the solar panels and to get a picture of the boiler plate of the Fronius. There still is some question as to whether we will need to add an AC disconnect on the outside, between his meter and the Fronius. NC Utilities thinks it is unnecessary, but Duke Energy wants to protect its employees. My take on it is that the Fronius will disconnect itself if there is no power. However, Dave's point is that if I shorted the wire in the house, there would be no cutoff between the short and the transformer. Great for my Fronius, but bad for the Duke equipment. He put a cutoff sign outside the house near the utility access point.
Financial considerationsNorth Carolina will give you a tax credit for 35%, up to $10,400.
I waited until after January 1, 2009 to put the solar panel into service, because the federal tax credit is no longer capped at $2000 for the 30%.
Charlotte Mecklenburg is offering up to 25% off on houses that get LEED certified. I may have waited too long for this, because I needed to have applied BEFORE I got my CO. As of today, the web site does not show anyone claiming this money, although there are a number of corporate applications pending.
Time to break evenThis is assuming that the RECs will hold steady, which many consider doubtful.
Cost of the array: $18,000. Delivery and Installation: $1000. State tax credits: $6650. Federal tax credits: $5700. Breakeven will be in about 7 years.
The breakeven time for a solar water heater may be even shorter. I have heard that it is 7 years, without taking any tax credits into account.
