This past week, I turned in my proposal for my solar electric system to the local power utility. Here’s the equipment I’ll be using and why. Please keep in mind that there’s more than one way to design a solar electric system. What is right for me may not be right for you, but I hope that explaining it gives you some greater insight on designing YOUR system!
In a Nutshell:
The solar system will be 24 solar panels, each with a micro-inverter on it. Those will connect to a combiner/disconnect box on the exterior of the garage. From there the power will feed in to the garage and connect to the main breaker through a 30A fuse. The garage panel is connected by buried cables to the house and from there, out to the electric grid.
The solar panels are Helios brand, 60 cell panels rated at 260 watts. The panels were made in Milwaukee, Wisconsin, 30-35 miles from my house. That’s right, buy local!
Enphase M250. Micro-inverters simplify wiring. There’s no need for a DC disconnect. The inverters mount to the racking under the solar panels. They then plug in to a quick-connect “trunk cable”. All power is 240V AC, which is what regular residential electricians are used to. Wire lengths and gauges are all standard at that point. Also, the micro-inverters are isolated from the DC power and the EGC grounding is done through the trunk cable. That means that I won’t have to install a thick bare copper wire between the inverters, panels, and racking. That saves costs and labor on the installation. (For details on grounding this system, please see Enphases technical paper on the subject at LINK.)
Iron Ridge XR-100 racking. This racking looks nice. Iron Ridge has a great wizard on their web page for calculating snow loads, wind loads, total weight of system, etc. That’s great information to have to show the building inspector and power utility. It shows that I know that the roof won’t collapse from too much weight, nor will the solar panels come off in a wind-storm and damage my neighbor’s property. The Iron Ridge system also uses fasteners designed to electrically BOND the solar panel frames, the equipment rack, and the micro-inverters. Using this racking with the Enphase system together bonds everything and provides all grounding necessary through the Enphase trunk cable.
To connect the Iron Ridge Racking to the roof, I’ll use S-5! brand clamps. The “Mini” are still very powerful and completely appropriate for solar applications. I did a test set-up of a sample piece of my roofing with an S-5! clamp on it. The holding power is pretty amazing! It’s all done by just the shape of the clamp pinching on to the roofing with a set-screw. No holes are made in the roofing. It’s a great way to provide a solid connection to the roof with no risk of leaks. I’ll be using the “N” style to match my roofing profile.
Because 24 micro-inverters is too many to have on a single 20-amp circuit, I’ll need TWO circuits to handle the power. That also means that I need a way to combine both circuits. That could be done with something as simple as a breaker sub panel on the outside of the building. I also need a dedicated AC Disconnect with a red handle that can be locked in the off position. That’s both common sense and required by the power utility. To do BOTH at the same time, I’ve ordered a MidNite Solar MNPV-6 Disco Micro AC Combiner/Disconnect. In a single box, it provides up to three circuit breakers for combining the roof-top power. On the cover of the box is a red lever, which physically flips the breakers to OFF, and can be locked in place.
Power Utility Requirements:
I had to turn in paperwork to the power utility. The main form was the PSC 6027 – “Standard Distributed Generation Application Form”. That includes the basics, such as customer name and address, up to a very complete listing of the equipment to be used and how it will all be connected. It also requires a Single-Line Electrical Diagram and a Site Map. I generated the Single-Line Diagram by using the trial version of the software at http://get.solardesigntool.com The software acts as a wizard – you just enter what equipment you will use and a little other information, and it will generate a very professional looking electrical diagram. The only problem I had with it was that the MidNite Solar disconnect was not listed in their database of disconnects. So, I ended up editing the exported diagram in Photoshop to correct for it. Still, a pretty good deal for some free software!
For the Site Map, I made a new document in Photoshop, keeping the fancy looking edging from my generated Single-Line Diagram. I put in an aerial view of my property, cut and pasted from Google Maps. I also traced an old copy of a property line map that I had, making clean new lines for the house and garage, and then labeled them where the existing utility meter is and where the disconnect box will go.
I turned in the PSC 6027, The Single-Line, and Site Map, and PDF spec sheets of all the equipment I would use to the power utility. At this point, I’m just waiting to hear back from them, hopefully with approval and no changes needing to be done to the proposal.
At this point, the U.S. Federal government offers a nice 30% tax credit for installed renewable energy systems. It’s just a one-page form filled out when you do your taxes. It’s a great way for the government to encourage installation of renewable energy.
Unfortunately, the State of Wisconsin has NO incentives. Fortunately, there IS an incentive through the power utilities through a program called Focus on Energy. This program is funded by a mandate on utility company profits to be directed towards energy conservation and renewable energy. In my area, people are most familiar with it for discounts on energy-efficient light bulbs at the home improvement store. Last year, the Focus on Energy incentive for solar was a set rate per kilowatt, maxing out at $2,400 – and my installation would max out that number. This year, the incentive is instead changed to a COST of installing the solar. The incentive is 12%. In my case, the solar should cost about $10,000, so the rebate would be only $1,200 – HALF of what I could have earned last year. Even worse than that, it seems likely that there will be NO money next year for installing solar through this program. Still, the cost of solar has dropped dramatically over recent years, and I hope people keep installing even more, not matter what the state of local incentives is.
Economic Return on Investment:
Adding up the cost of all the system components, I expect my system to cost nearly $10,000. I’ll earn 30% back on my taxes ($3,000) and up to $1,200 on the local incentive, which should bring my total out of pocket cost down to just under $6,000. Also, it’s a 6kW system, so when I’m done, I’ll have built a solar system for about a dollar per watt (after incentives.) The PVWatts and other predictions that I’ve run show that I should produce electricity to save right around $1,000 per year. So, after 6 years the system will have paid for itself.
I’ve also run numbers on creating my own electricity and using it to run an electric car. Just using averaged numbers for fuel economy and cost, this could bring the return on investment down to as little as 3.5 years! I can’t think of any other investment that can double my money in that little time! The other thing to keep in mind is that it’s a SURE THING. I KNOW what my electric costs will be (capitol investment divided over time…) whereas I DON’T know what the cost of gasoline, natural gas, and other fossil fuels will be OR if my power company DID want to hike the cost of electricity.
That’s it for now! I’m waiting to hear back from the power utility. I hope this overview of the solar system helps you learn a little bit more about solar and maybe help you to install your own!
Until next time, stay charged up!