Grid Tie Solar Power

I installed TIGO panel optimizers on 5 panels nearest my house in my ground mount array. Day one and the data is already enlightening. You can see the early sunrise reflecting off the second story of my home. The top panels, A1-A2 and some of A3 are getting a slight headstart in energy production. The A4 and A5 panels are not getting the reflection and it shows. I’m looking forward to additional data that will be gathered in the coming weeks. I purchased this system as a test and so far, I’m impressed. For the price, simplicity, and flexibility it cannot be beaten. Let’s hope it proves to be reliable.

In the second screen capture, you will see the shade that starts to hit my panels from the top of my second story. With the TIGO Optimizers, A4 drops to almost nothing, followed by A5. I do not have enough shade to warrant the cost of micro-inverters or SolarEdge HD Wave inverters. In fact, the cost of the TIGOs for the 5 panels was more than I will ever recover. However, I do get an additional 1Kw every 4 days which was much better than I expected. I love being able to see panel-level data and if you need Rapid Shutdown and optimization on all panels or just a few in your string, TIGO is an impressive product.

This chart shows daily production of the 25 x 325-watt panels where there are minimal clouds and less than ideal conditions for the array later in a summer evening. At around 4:15 pm (1), the first string of 5 panels begins a significant reduction in power. At 5:41 the second string of 10 panels begins to shade and quickly drops production of that string. Finally, at 6:47 pm, the last string of 10 panels begins to shade.

During a typical Florida summer day, the evening hours sometimes produce heavy clouds and thunderstorms. This reduces the impact of the second story shading the solar panels. The design of the ground mount with a 15′ back height also helps to continue producing as late into the day as possible in the current configuration. Based on my calculations, on a cloudless summer day, I’m losing about 4% of the possible energy production for the day. I can calculate loss fairly accurately as I have a smaller, second array that is not affected by the shade of the 2nd story. I’ve considered optimizers, however, I like the simplicity of the strings and I’m not convinced it will provide much of an improvement over the current configuration. 

With Duke Energy providing a credit bank of unused kilowatts, it may have been better to reduce the panel angle to 5-10 degrees. This would likely improve summer production and reduce the shade to the lower edge of the ground mount which is currently 8′ in height. I could then use the kw credits later in the year. Duke will zero out the credits and pay me .06 for them a the end of the calendar year so maybe it’s best at 21 deg. 

Over the course of a couple of years, we have added 21 SEER mini-split heat pumps, home automation to control every outlet, light and thermostat, a 3 hp variable speed pool pump, heavy insulation, inverter refrigerators, convection oven, and instant hot water heaters to reduce our energy consumption. We still have more we can do. New windows, more insulation, and better sealing would do a lot for our air conditioning costs. I’ve included a spreadsheet and chart with a couple of days in a hot month showing the kW we use vs. the kW we produce. We are charging our electric cars but with Covid-19, we only have to charge every couple of days due to not driving every day.

The fuel charge for Duke Energy is currently low but increases in kW cost have compensated for some of the drops in fuel costs. Currently $.13-.15 per kW. As fuel costs return to normal, we will likely be in the $.17 to .18 per kilowatt rate for over 1,000 kW and a couple of cents cheaper on < 1,000 kW. These rates include all costs billed. Duke will buy our extra power at .06 per kW at the end of each calendar year.

Considering we had a high of $500 and an average of $300 a month in electric costs prior to the changes and solar, we are very happy with the results and considering the jumps in kW costs over the last several years, our average costs would have been even higher. 

Sun Edison F325 BMD Monocrystaline solar panels have arrived. This was the biggest investment in my goal of installing a grid tied solar system for under $1.00 per watt. The delivery company could not figure out how to get the 1,390 pounds of silicone, glass and aluminum off the truck. I tried for almost an hour and finally decided to cut the box open and pull them out one at a time. We had to carry them up an incline, into the garage, in the heat, rain and humidity. Two and a half hours later we were done. That’s my youngest son in the video and he was a great help. When you crunch the timeline on the video to a little over a minute, it is kind of depressing. It does not represent the difficulty of the task. Despite that, my confidence that I might actually be able to pull off a DIY solar grid tie installation is building. I will be applying for the permit tomorrow. I’ve often fought with hubris, let us hope this is not one of those fights.