72 Free 100 Watt Panels - off grid (mostly) would like comments

[Mark H.]

My friend and I obtained 72 used 100 watt solar panels and roof mounting brackets for free, and they are in good shape. We would like to put them on the roof of his home shop (which is huge) and while he is already the grid he does not wish to feed power to the utility, he just wants to transfer to the utility when his batteries get low and need grid power to recharge batts and power his shop and home (which are connected).

While we have some experience with making a 12 volt van system, this is new to us (although he has a lot of experience as a shade tree electrician). Would like some comments on our/my general idea.

Buy and install EG4 6000 XP (or two of them)
Use blocks of 4 panels in series to provide 48 volts and run to combiner box, then to XP|
Buy sufficient batteries to power home.

Our goal is too a) Run off grid normally b) auto switch to grid if power demands exceed capacity c) provide recharging via grid if needed.

He seems to think a microinverter system might work better but as there is no shade, to me an XP would be simpler and cheaper.

Thoughts anyone{?

 

[MisterB1959]

ditch/sell the panels, use the mounting rails and fit less but more capacity panels. for instance if one panel goes faulty, its a lot to trace and replace. new panels are more efficient and dropping in price all the time, so i would def consider buying new.
nothing wrong with buying or using s/h panels in general, but 100w panels ??? ...... you might be able to pass them on for RV projects - 100w panels are quite popular in the UK, not sure how they are viewed in other countries.

 

[Mattb4]

Likely you can run more than 4 panels in series. You will need to look up the max Voc specs for the 6000xp. For example if they are typical 100w panels they will have around 22Voc. In series that adds while amperage remains the same.

Microinverters are grid tie. They only work when they can parallel with a grid.

Yes you can set a 6000xp to run from PV and battery and switch to grid as needed. When running from grid it will charge battery if desired.

 

[Q-Dog]

Free solar is free solar. BUT, I would want to know how old the panels are and how far they may have degraded. You need to get the secifications from the inverter and the back of the panels to figure out how many you can install in a string. It should be a lot more than 4 per string.

I started with 100 watt panels and still have 16 of them working every day. They work fine, but they do not perform well when they get really hot. I will keep using them until I get my 300 watt panels mounted, then they may get installed on my shed for a small system out there.

 

[Mark H.]

Thanks all, I see we are going to have to give this a second thought. The panels seem to still have some life left but 72 points of failure may not be worth the trouble.

 

[Brett V]

It’s going to be a drag but you need to test each one for voltage at the least. You could get a panel load tester if you want to be sure, but it’s even a bigger drag if you go through all the trouble of putting them up only to find they’re shot.

 

[Mark H.]

Free solar is free solar. BUT, I would want to know how old the panels are and how far they may have degraded. You need to get the secifications from the inverter and the back of the panels to figure out how many you can install in a string. It should be a lot more than 4 per string.

I started with 100 watt panels and still have 16 of them working every day. They work fine, but they do not perform well when they get really hot. I will keep using them until I get my 300 watt panels mounted, then they may get installed on my shed for a small system out there.

By the way, one thing that bothers me is what appears to be very high voltage on a string of panels. Suppose it is 540 volts from a string of panels. I read that AC voltage is more dangerous because of its cycling and that DC isn't nearly as deadly. True?

 

[timselectric]

By the way, one thing that bothers me is what appears to be very high voltage on a string of panels. Suppose it is 540 volts from a string of panels. I read that AC voltage is more dangerous because of its cycling and that DC isn't nearly as deadly. True?

That's actually backwards.
AC is easier to disconnect, because of the cycling. Since the voltage drops to zero 60 times a sec. (50 on the other side of the pond)

 

[timselectric]

Just realized that you have asked about dangerous and deadly.
With the same voltage on both.
DC is more likely to cause damage or fire.
AC is more deadly to humans.

 

[Mark H.]

Just realized that you have asked about dangerous and deadly.
With the same voltage on both.
DC is more likely to cause damage or fire.
AC is more deadly to humans.

I guess what I am trying to determine is if microinverters on panels create 120v AC, then the AC lines strung to a combiner box are safer than strings of DC pushig voltage to 300v and then strung to a combiner box.

 

[timselectric]

I guess what I am trying to determine is if microinverters on panels create 120v AC, then the AC lines strung to a combiner box are safer than strings of DC pushig voltage to 300v and then strung to a combiner box.

Micro inverters output 240v. I have not seen any for 120v. (Maybe they exist) And they are for grid-tied systems. (Require a grid source to operate) I thought that you said this was an off grid setup.
Anything over 50v can kill you.
Higher voltage is more efficient and requires smaller (less expensive) wiring.
All electricity is dangerous and should be installed properly and safely.

 

[Mark H.]

It is off grid, save for use of the grids for recharging when needed, now I get it. Thx to all,