When Maryland passed their plug-in solar law, I started planning my own 1600W DC / 1200W AC system. My original plan was for a ground-mount array, however, county code setbacks for auxiliary structures would have pushed my array into the shadows. A coworker joked that I should put it on wheels, since vehicles, RVs, & trailers are not subject to these setbacks. Hmmmmm.
Solar System – (4) 400W Longhi panels connect directly to a Hoymiles inverter. This inverter is perfect for my system. It has four dedicated solar panel inputs and dual MPPT controllers. This grid-tied inverter meets the latest UL standard (UL1781 SB.) The Hoymiles Data Transfer Unit (DTU) is expensive, so I opted for a less expensive/less capable OpenLabs OpenDTU to monitor my system. A 12 AWG heavy duty extension cord delivers the output to a dedicated 20A branch circuit receptacle. An AC disconnect is mounted adjacent to this receptacle.
Racking – I settled on the IntegraRack IR-45. They were expensive, but I really wanted to be able to adjust the panel tilt angle each month (to maximize the output of such a small array.)
Trailer – I bought a small DIY trailer kit intended for small watercraft (jet skis?) and mounted a 4x4 pressure treated frame on it. The two main rails are 16’ long, so I had to replace the original trailer tongue with an optional (longer) version to accommodate the 16’ rails. The 4’ long 4x4 crossbeams provide the mounting surfaces for the IntegraRack frames. To keep this assembly stable in high winds, I set ground screw anchors at the four corners of the trailer and secured the trailer with ratcheting straps. I’m sure it won’t survive a tornado, but it’s fine for the occasional 40-60 mph winds. It's a fully functional trailer with lights, so I could tow it if needed. I would be puckered if I had to drive on the highway, but local roads would be fine.
Observation 1 – Best orientation is situational. I originally set my array to face due south (per standard practice.) However, my neighbor has some tall trees and I discovered that my system only delivers full rated output when the sun peeks thru three gaps in the tree line (at 11:30, 1:30, and 4:30pm.) So, I centered the array on the middle gap to maximize results when the sun peeks through. This was an unanticipated advantage of the trailer; I would not have been able to make this adjustment with a fixed ground mount!
Observation 2 – IntegraRacks are oddly not ideal for Maryland. According to AI, my optimal solar tilt angles for my location (by month) range from 21-68° (with respect to the ground). The IntegraRacks only adjust from 15-45°. This surprised me, since Maryland is sort of in the middle of the country, latitude-wise. It seems these racks are optimized for more southern locations. On the other hand, since the max tilt is only 45°, I can leave it at 45° from September thru March!
Observation 3 – Mounting is Expensive! The solar portion of this project was only 25% of the total cost! The solar components were a little over $1000. The mounting system (trailer, IntegraRacks, lumber, hardware, etc.) was closer to $3k.
Observation 4 - Performance. For the last 3 weeks of October (including 4 rainy/cloudy days), the system averaged about 4.5 kwhr/day (about $1/day.) It should be much better in the summer, when the sun stays over the trees all day. The solar portion should pay for itself in about 2 years. The mounting system? Payback should be shortly after I’m dead! Lol!
Observation 5 – Don’t give your watts away! When you sign up for plug-in solar, part of the deal is the utility will not pay you for any power you push back on the grid. Since I only generate power during the day, I don’t want to waste it. I have a Shelly Pro 3M installed on my main panel, so I can see if I’m pushing power out to the grid. It’s become a game for me. Our loads during the day are pretty low, so I looked for opportunities to load-shift. Now, we only run the dryer during peak generation times. I can’t really load-shift the HVAC, so no real options there. However, I installed a pool timer on my hot water heater so it only runs during peak generation times (10am-5pm). Even after being off all night, morning showers are fine.
Observation 6 – Tilt Matters! Based on a south-facing roof with a fixed 30° tilt in my town, AI predicts Oct average of 4.7kwhr. After 3 weeks of operation (w/ 4 rainy/cloudy days) with a 45° tilt, I’m getting peaks of 5.1 kwhr and an average of 4.4 kwhr (when my panels only see direct sun 3 times per day!)
Observation 7 - Mobile solar doesn't penalize the next owner. If/when I move from this property, the next owner can decide if he wants to keep the array or not. They won't be saddled with a fixed structure in their yard anchored in a ton of concrete. Plug-in solar was really intended for renters, so it's right that the system should be mobile/easily removed.
Observation 7 – It’s a fun hobby (that slowly pays you back!) Honestly, I get pretty jazzed when that spud is cranking out the full 1200W. Since it’s on a trailer, I can play with the orientation based on the season. It’s also really heightened my awareness of how much power we use in our home. I expect this system will cut our monthly electric bill by 10-15%.
