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diy solar

Adding a second system to my detached garage?

gunningopher

New Member
Joined
Jun 16, 2021
Messages
7
A year ago, right before the pandemic, I added a 4500w system with a Tesla Powerwall. I'm happy with the system but I wasn't happy with the contractor. They did some pretty shoddy electrical work and the communication was horrible. I'm also a pretty handy person and am a DIY'er by nature. Naturally, once the pandemic hit our energy use went up quite a bit and I'm considering expanding our system, but I don't want to void the warrantee on the one I have, so I'd rather just add another system somewhere else. I'd be comfortable doing the work myself if the wife would let me!!

I have a detached garage with a 1/2 south facing roof and 2 40 amp circuits in the house main panel feeding the garage sub-panel. Could I add a second complete system to the garage and tie it into the subpanel? All I run off the garage are the tools, smaller compressor, small welder and a 30A receptacle I installed for the motorhome (which has a LiFePo4 battery and 2500w inverter). I have a feeling we'll end up with an electric car in a few years, so I'll definitely be looking to expand the system at that point. While I like the idea of having a battery, this 1 backs up the circuits I need to keep on, so I'm not rushing to add any more right now.

Does it even make sense to add a system on the roof of this? What are the limitations I'm facing? I could probably add another 4500w on the south facing side of the garage. I know my subpanel amperage may be a little low but I don't exactly understand how that could restrict it, since the biggest system I could install wouldn't exceed 40 amps. I could replace the subpanel easily, but I can't replace the feed wire coming from the main panel to it since it is direct buried.

I'm wide open for enlightenment!!
 
use an all in one... feed the power from the panel to it then feed the sub with the all in one. you see it once the batteries reach X voltage it passed grid power to sub panel
 
I replaced the pitifully small subpanel in the garage with a 12 position, 100A one. I wanted to split some of the circuits up a little and add some receptacles on the outside, so it needed to be done. I'm a year or two from doing any enhancements to the service, but I definitely want to start thinking about the plan. I have 8 gage wire coming from the main service panel. When my panel was upgraded a couple years ago to 225A, the electrician said that the wire could handle 50A, so that is the breaker he put on it. I don't know what was on the old panel. I can't find the temperature rating on the wire to confirm it myself. I am not too comfortable with a 50A breaker on an 8 gage wire, so I might cut it to 40A. That being said, this might make me want to add solar and battery to the garage sooner than I was thinking. I can manage 40 amps easily enough but I don't really like having that little amount of power there. Also, If I ever get a new motorhome, I'll want to add a 50A plug for it. I think I understand correctly that the solar inverter will add power to the panel, but I'd like to have an battery inverter smoothing it out and being available at at night, too.

Are there solar inverter/charger/mppt combos that are programmable to smartly add power to a grid tied system? For instance, lets say I want to run 70A (2 leg) service on this panel, could I take 40A from the main panel, and use the solar or battery/inverter to boost the service on the subpanel as needed? 30 (x2) amps might be a little much, but hopefully I make the point. Providing the added power would take precedence over charging the battery. The one in my motorhome is either grid or inverter, it doesn't combine them. I think I've seen some that will do that but I can't find that right now.

I would also love to be able to partially discharge the batteries to the grid during the peak rate period when the sun starts to set. I know my local utility doesn't want us doing that for some reason, but I think I'd be able to keep it off their radar. This would be a very low priority for me.
 
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