Replace, reuse, or ditch panels after roof replacement?

[HighVoltage]

We bought our house in 2019 with a roof-mounted 4.2kW system. The system is 13 years old now and we know we are less than a couple years away from a new roof (assessment of home inspector and some roofing contractors). We lived in the house for just 2 months before renting it out for the past 2 years while we are overseas so I don't know how efficient the panels are. The inverter (Sunny Boy SMA 7000) seemed pretty basic and wasn't connected to the network so I can't pull any stats except for what's on the small LED screen.

We plan to start a major remodel including an extension after we move back this summer. When that happens we will replace the roof.

We didn't buy the house because it has panels, but it seems a shame to just remove them and not do something with them. The panels are never shaded but they're not optimally facing the sun either. I don't want the panels back on the roof. We have over an acre and the panels face away from the neighbors towards a farm field. My thought if I am going to continue using the panels is to ground mount them, but how can I evaluate if it's worth the time and money? There are 24 175W Suntech panels up there. If I doubled the system capacity, is it a bad idea to mix old and new panels?

Thanks,
Paul

 

[robby]

Thirteen year old 175W panels IMHO are not worth the effort. I would just craigs list them after the roof contractor takes them down and see if someone wants them. If not see how you can get them recycled.

 

[Rednecktek]

IMO, as someone still learning and trying to scramble over the solar paywall...

Free Panels > Cheap Panels

4.2Kw worth of panel? Even if they're only putting out 80% that's still 3.3Kw of panel. A 100a SCC on a 48v system would cost you a couple hundred bucks, and whatever wire you needed to run.

I'm just sayin...

 

[timselectric]

If it ain't broke, don't fix it.

 

[HRTKD]

If you used brand new panels, they would be larger and may need a different ground mount structure. You would need fewer of the new panels, which translates to less mounting hardware and less work. The output of the new panels would be greater than your old panels, some of which may already be on their last diode.

Do it once and do it right.

 

[Hedges]

7kW Sunny Boy, 4.2kW of older panels.
The older panels might be 13% efficient (130W/m^2) and today you can get panels 20% to 22% efficient (200W+/m^2)
In same area you could fit enough panels to more fully utilize the inverter. Right at the moment, panels are hard to come by, but a batch of quality newer panels can usually be had for cheap. Recalculate string voltages (including increase in cold temperature) to remain within inverter specs.

When roof is replaced, make provisions for well sealed mounts. Some panels are just lag screwed through singles, others have flashing and standoffs for rails. You want the new installation well sealed for life of roof.

You can mix old and new panels if Vmp is similar, multiple strings in parallel. You can also mix orientations of strings. All within a given string should be same orientation.

 

[Ampster]

Free Panels > Cheap Panels

I agree, but twenty four 175 Watt panels are going to take as much effort to install as twenty four 400 Watt panels. For that much effort I would spend the money on new larger panels to get two and a half times the power. It all depends on where you are standing. The SMA inverter might be worth repurposing.

 

[schmism]

If I doubled the system capacity, is it a bad idea to mix old and new panels?

If I had this setup I would sell the sunnyboy and add 2 new all in one inverters. 48v 3kw growatt/mpp take 4kw PV. One inverter for the old panels and another 4kw of new pannels for the second inverter giving you either 6kw of 120v or 3kw of 240v. Perfect for installing a critical loads pannel and running a significant portion of the house on solar. (for how long is mostly dependant on how much battery you choose to buy)

 

[Hedges]

The inverter is young, and of quality. I would keep using it to the end of its natural life. I recently bought a bunch of this series.
If it is the 7000US (not TL-US), it can be configured either positive or negative ground. Prevents "PID", although newer panels are relatively immune.

 

[edcoopered]

I'd replace the panels but keep the inverter.

 

[fromport]

My thought if I am going to continue using the panels is to ground mount them, but how can I evaluate if it's worth the time and money? There are 24 175W Suntech panels up there. If I doubled the system capacity, is it a bad idea to mix old and new panels?

Re-use the panels and the inverter.
There are no moving parts in PV panels and the first years the lose the most in power production. After that it is 0.[1-3]% per year.
My main array panels are from 2002 and don't see any noticable degrading of my power year over year.

When you are going ground mount it is so easy to work on. Sunnyboy inverters are almost bullet proof and unless fans stop working (they will limit power production if they do) it will keep working. There are raspberry pi solutions with interface to read you SB.

If I were you keep the existing setup.
Get a second array with a second inverter if you need more power. If you can get a great deal I would even buy reputable used panels.

 

[ncowan]

We bought our house in 2019 with a roof-mounted 4.2kW system. The system is 13 years old now and we know we are less than a couple years away from a new roof (assessment of home inspector and some roofing contractors). We lived in the house for just 2 months before renting it out for the past 2 years while we are overseas so I don't know how efficient the panels are. The inverter (Sunny Boy SMA 7000) seemed pretty basic and wasn't connected to the network so I can't pull any stats except for what's on the small LED screen.

We plan to start a major remodel including an extension after we move back this summer. When that happens we will replace the roof.

We didn't buy the house because it has panels, but it seems a shame to just remove them and not do something with them. The panels are never shaded but they're not optimally facing the sun either. I don't want the panels back on the roof. We have over an acre and the panels face away from the neighbors towards a farm field. My thought if I am going to continue using the panels is to ground mount them, but how can I evaluate if it's worth the time and money? There are 24 175W Suntech panels up there. If I doubled the system capacity, is it a bad idea to mix old and new panels?
I highly recommend https://easternmelbourneroofing.com.au/services/flat-metal-roofing/
Thanks,
Paul

A few months ago, I had to replace my roof. I was dreading the process because I had never done it before and I didn't know how much it would cost. However, I found a great company that did an amazing job and now I don't have any issues. The process was actually not as bad as I thought it would be, and the results are perfect. If you're ever in need of roof repairs or replacement,

 

[Zwy]

We bought our house in 2019 with a roof-mounted 4.2kW system. The system is 13 years old now and we know we are less than a couple years away from a new roof (assessment of home inspector and some roofing contractors). We lived in the house for just 2 months before renting it out for the past 2 years while we are overseas so I don't know how efficient the panels are. The inverter (Sunny Boy SMA 7000) seemed pretty basic and wasn't connected to the network so I can't pull any stats except for what's on the small LED screen.

We plan to start a major remodel including an extension after we move back this summer. When that happens we will replace the roof.

We didn't buy the house because it has panels, but it seems a shame to just remove them and not do something with them. The panels are never shaded but they're not optimally facing the sun either. I don't want the panels back on the roof. We have over an acre and the panels face away from the neighbors towards a farm field. My thought if I am going to continue using the panels is to ground mount them, but how can I evaluate if it's worth the time and money? There are 24 175W Suntech panels up there. If I doubled the system capacity, is it a bad idea to mix old and new panels?

Thanks,
Paul

How are the panels mounted on the roof. If the mount can be utilized for larger panels, I'd opt for selling the old panels off and install new on a ground mount. If the mount will only work with those panels, then you have the choice to convert to a ground mount or sell it all complete.