5.12kW Solar Refresh Project on My Garage Roof

4 August 2022

We decided to DIY refresh the old system! My brother Mike and I did most of the work in one day, including all the hard labor of removing the old panels, cleaning the roof, and installing the new panels.

But first an update on the old system. As part of the new project I replaced the inverter with a 5kW SMA first, still hooked up to the old panels. The new inverter has 3 MPPTs (the old one had only one), plus wifi monitoring, and this revealed a discrepancy. It turns out that one of the old SHARP panels had failed and was in bypass. The other 17 panels were fine. Since the old inverter had only one MPPT, though, this meant that both strings were running non-optimally. The new inverter, now running the two strings independently, instantly added another 100W or so in peak production.

The new project replaces the 2 x 9 x 165W SHARP panels with 2 x 8 x 320W Renogy panels. Since we are DIYing it and using the same rails, the total cost wound up being around $8K or around $1.56/kW, including the new ($2K) inverter. Total nameplate capacity is 5120W. As of the switch-over in August, the old system was producing around 16kWh/day and the new one 32kWh/day.

So almost double the production in essentially the same roof area. The Renogy panels were chosen as a trade-off between cost and wanting to fit them in the same space using the same rails. In actual area, including spacing, the old system was (32.52 + 0.5) x (62.1 + 0.5) x 18 panels equals 37207 in^2 and the new one is (39.5 + 0.5) x (65.6 + 0.5) x 16 panels equals 42304 in^2.

I decided to stick with a string inverter. We are using the latest 5kW SMA inverter with three MPPTs and wifi/portal access. Generally speaking, microinverters or optimizers just don't make any sense unless there is a lot of variable shading... which there is not in this particular location. Its a lot of expense for very little (or no) gain, and it is usually better to simply spend that money on adding more panels even when some shading may occur.

In the original project way back in 2003 I asked the installers to intentionally over-size the wiring, so we were able to reuse the existing 10-gauge copper wire runs without modification. The new system pushes 10A per string on the DC side and 20A on the AC-side, about double what the old system was pushing. For power-carrying the 10-gauge is perfect for the long DC runs. The AC run is only 6 feet long so it works there as well. All with minimal losses.

The SHARP panels were a premium brand 20 years ago. They were 14% efficient and had good (for 20 years ago) indirect light gathering capabilities. The new panels are 21% efficient and have significantly better off-light and low-light capabilities. The grand result is about double the production. I don't have full-year data yet but we were getting 32kWh/day in early August so my expectation is around 25kWh/day in Winter to 36kWh/day at the solar peak in June. Even cloudy days in August are clocking in excess of 20kWh/day. So this is looking to be a great upgrade!

Renogy 320W panels on pallet Pile of old 165W SHARP panels
Old panels taken off - dirty roof
Begin installing the new panels (Compressed air cleaned the roof up nicely)
Cargo-pants butt-shot
Grounding Strap Installation
2 lugs per panel / 4 on the corner panels