Sun Tie

At the time I was designing the system, Trace was about to introduce the Sun Tie (ST) series of inverters, which promised to lower the cost and ease the installation of a grid-tied system. Normally, I would be wary of buying a brand new product, but I figured that Trace had been in the inverter business long enough that a new product might not be a big risk.

As things turned out, the display on the unit I received was dead out of the box. It took about six weeks between my first contact with Trace and the replacement of the inverter. The second inverter's display only worked for the first few hours of each day. Eventually, I did some troubleshooting and found the problem. The display was in close proximity to the inverter's power components, and electrical noise was causing the display to fail. Wrapping it in a grounded copper envelope solved the problem.

This was more involvement than I wanted with a product, but I did know that I was buying an early release, and the process was kind of fun, anyway. Other than the problem with the display, the Sun Tie is a wonderful product. Getting it working consisted of nothing more than bolting it to the wall, and attaching the DC wires from the panels and the AC wires to the house electrical panel. All breakers and fuses are factory installed. There is nothing to set up or configure-it just works.

In order to get my cost per installed watt down as much as possible, I went with an ST2500 inverter and twenty-four Kyocera 120 watt panels. The cost per watt of the ST inverter goes down as the capacity goes up. An ST2500 does not cost 2.5 times the price of an ST1000. I figured that once I got the lowest dollars per watt inverter I could find, the best value would be to load it up as fully as possible with PVs. That meant I wasn't paying for any inverter capacity that I wasn't using.

For the California buydown rebate, the calculations look like this: twenty-four 120 watt PV modules have a PVUSA Test Conditions (PTC) value of 105.7 watts each, for a total of 2,537 watts. The 94 percent efficient inverter makes a system output of 2,385 watts total.

I was ready to order the equipment from out of state to save the sales tax. But when I heard that I'd have to pay it anyway to get the buydown, I figured that I'd keep my money in state. I wound up making my purchase from Solar on Sale, who beat the out-of-state price anyway. The people there have been very knowledgeable and helpful. In all, the system cost me about US$6 per watt. I'll get half of that back from the buydown program.

I did all of the installation with the help of my friends . Since I have a pretty complete metal shop in the basement, I made my own mounts using aluminum angle and stainless steel hardware.Next: Net metering