Utility Intertie
From the beginning of the project, I planned to bring the solar panel home over my 30 day winter break. Initially I planned to disassemble the setup, bring it home or mail it back and reassemble it when I got home but I later came upon a related business opportunity: small scale utility intertie inverters. As it turns out, Trace Engineering produced a small scale utility intertie inverter known as the MS100 that could handle 100W of power at 24v DC. For those who are unaware, a utility intertie inverter takes DC energy, such as that produced by a solar panel and outputs 120v 60 Hz AC energy that is synced to the electric grid, so that it can offset household usage. If enough energy is produced, one can actually spin their electric meter backwards if their state has a net metering law. Utility intertie inverters are a popular alternative to off the grid, battery based systems and I tend to prefer them simply due to their much lower maintenance. The problem is, utility intertie inverters are only produced for large scale systems (the Sunnyboy 700 is the smallest system on the market) - Trace discontinued their Microsine line several years ago. However, with a tremendous amount of searching, I found a store that had 8 Microsines left in stock from years ago - I bought them out. Having control of the only Microsine inverters I could find online, I listed them on eBay, where I made about 55% profit on each sale. I put the money towards a much needed upgrade: a new solar panel. While my first weeks with the original system had been incredibly pristine, I quickly found out that Burlington was cloudy more often than it was sunny. I initially ordered a 72W GE panel from the Alternative Energy Store, however, I was informed that the GE panels would not be in till Spring of '06. I was offered a 102W Evergreen panel instead and accepted - it was actually a better deal, I received an extra 30W for another $50.
The 102W panel would do more than provide me with more energy - it would allow me to produce the 24v necessary to run a Microsine inverter, by wiring it with my existing panel. Intertie at UVM made no sense, but it would allow me to keep my infrastructure and all my wiring in place at UVM and only need to bring home the panels. At home, I could use the energy from the panels to directly offset our utility bills for the month. Additionally, it would allow me to gain experience with both grid connected and grid independent systems.
Wiring the Intertie
On Monday, November 24, 2005, I took the panel, which I had disconnected and repackaged the night before and attempted to carry it around 3/4 of a mile to the nearest FedEx Kinkos. I made it about 300 feet from my room when I decided that there was no way I was going to be able to carry a 65x25x8, 42 pound box that distance and still make it to class an hour and a half later. I moved the panel off the sidewalk, leaning it against a unused picnic bench near by, and ran to UVM Rescue, whose hand truck I borrowed. Wheeling the panel the distance wasn't too big a deal and I returned the hand truck with plenty of time to spare.
Another worry was whether the 12/24v pump controller would arrive on time. Early in the planning process of setting up an intertie I realized I had a 12v panel and the Microsine required a 24v input. I was thinking about wiring my old 20W panel with the 102W until I was told that would cap the output of the 102W at 20W. There had to be another way, as I couldn't afford a second 102W panel. The answer came by way of an e-mail I sent to Solar Converters, Inc, asking if they had a solution to the problem. They replied and stated that they had set up a similar application involving a wind turbine for another group, and that I should use their 12/24v constant voltage pump driver. Since I couldn't buy the product directly from them, I contacted Altenergystore and it seemed that most Solar Converters products where in short supply and were being shipped direct from Canada, with a 3-4 week lead time. I didn't have that kind of time, with less than two weeks till I would be home to wire the panel. However, an Altenergystore rep told me that they had one last pump driver in stock. At the cost of $50, they shipped it via UPS 3 Day Select from Canada.
I returned home on Wednesday, but by the time I was home, it was too late to wire the solar panel. However, all the parts (including the panel) had arrived safely, which was greatly comforting. I figured I'd jump start my progress on the wiring, and wired the plug head on to the Microsine, so it could be plugged directly into a household outlet. I simply cut one of my many spare computer power cords I had lying around in half and wired the end with the male plug to the Microsine and the ground to the grounding screw on the inverter itself.
Reading the directions before I do anything else.
My makeshift work area at the dining room table
The end removed from a computer power cord
The Microsine, wired with a plug
The next morning, which happened to be Thanksgiving, I set about wiring the panel to the roof of the house. The night before was the first snowfall in Connecticut for the year, and after many debates with my parents on how to get the panel on the roof, I decided it would simply be easier to wire it on the ground. We have a barn on the property that has a fairly decent view of the southern sky and had an electrical outlet that would allow me to plug the Microsine into. My largest concern was whether or not the Microsine would work with the pump controller.
I set up all my equipment on the hood of my dad's truck, which is kept in the barn, then removed the panel from its packaging, wired the panel to the pump controller, then wired the pump controller to the wire that would run back into the barn. I connected that wire to the Microsine and the Microsine into an outlet.
I waited to hear the buzzing of the Microsine to know it was working. I waited - nothing. All of a sudden, after about five seconds, the inverter kicked on and started making noise. I ran out to the utility meter and watched as it spun forward - but much more slowly. I went back to the barn, cleaned up my tools and temporarily sat the Microsine on a bucket, as I could find no other place to put it within the range of my wiring.
I made several trips during the day back to the meter, planning to shut off all the household loads to watch it spin backwards the next day, once Thanksgiving day meal preparation was finished. The in the meantime, I could take pride that I was offsetting the household's usage with clean, renewable solar power.
All my equipment on the hood of the truck
The panel, wired outside the barn
The solar panel connected to the constant voltage pump driver
The Microsine in the barn, feeding power back onto the grid
The point of interconnection
Last modified November 24 2005 08:43 PM
