setup help combining voltages

[alangarvey]

I was wondering if anyone could tell me about combining voltages with my grid tie inverter.
I have a 60v 350watt solar panel and a 36.8v 230watt solar panel.
My grid tie inverter is 50-100v 1200watts.
The question is can I connect both panels to the same inverter?

[inetdog]

I was wondering if anyone could tell me about combining voltages with my grid tie inverter.
I have a 60v 350watt solar panel and a 36.8v 230watt solar panel.
My grid tie inverter is 50-100v 1200watts.
The question is can I connect both panels to the same inverter?

Simple answer: Yes, but there would not be enough power gain over just the 350 watt panel to make it worthwhile.

The two panels have wildly different Vmp values, so you will not get full power from either of them if you put them in parallel.
If you try to put them in series, the Voc of the string will be more than the input rating of your inverter and it will either shut down or fry.
(If it were not for that, the Imp values of 5.8 amps and 6.25 amps are close enough that you would probably get a useful power boost from putting them in series.)

[alangarvey]

Hi, thanks for replying so quickly.
It might be worth mentioning that the voltage ratings I gave for the panels are voc. I don't know if this makes a difference or what.

[inetdog]

Hi, thanks for replying so quickly.
It might be worth mentioning that the voltage ratings I gave for the panels are voc. I don't know if this makes a difference or what.

It would make a big difference under some circumstances, but you are still out of luck.

With those Voc voltages at nominal temperature (typically 77 Fahrenheit), you would be at 96.8 volts, right at the edge of the inverter limit.
But when you allow for the increased Voc at lower temperatures, you are way outside the safety range. Unless the 100 volt rating on the inverter is an operating voltage rather than a safety limit voltage.

For example, if you live in the American North, a quick approximation for coldest Winter morning as the sun comes up would be a factor of 1.25. So figure on 120 volts or more hitting the inverter.

Also, with those as Voc voltages, there is good chance that inverter would never draw enough current from the combination to get the voltage below that, and the second panel would not contribute at all. Now if the two panels were facing in different directions so that they were at peak power at different times of the day, there is a chance that you would get some good power from the second panel. But there is also the chance that the inverter would just keep watching the first panel and not try to pull from the second panel even then. It depends on the way that particular inverter does its MPP tracking.

[alangarvey]

Thanks once again, I am humble as to your knowledge.
All is not lost though as I have 2 more inverters and I was just exploring possibilities:

At present I have the 60v 350w panel with the afore mentioned 50-100v inverter.
The 36.8v 230w panel is with a 28-52v 300w inverter (the fan comes on when sunny).

And I have a 3rd 48v 300v inverter which is currently idle.

I was thinking maybe I could share the lower voltage panel between the 2 lower inverters in parallel, what do you think?

[inetdog]

Thanks once again, I am humble as to your knowledge.
All is not lost though as I have 2 more inverters and I was just exploring possibilities:

At present I have the 60v 350w panel with the afore mentioned 50-100v inverter.
The 36.8v 230w panel is with a 28-52v 300w inverter (the fan comes on when sunny).

And I have a 3rd 48v 300v inverter which is currently idle.

I was thinking maybe I could share the lower voltage panel between the 2 lower inverters in parallel, what do you think?

Never try to drive two different inverters from one panel or set of panels. It will not work well! As long as the rated power of the panel is not above the rated input power of the inverter, the fan coming on is just fine.

[alangarvey]

That's great, I will leave my setup as it is then. Another question I have though is about my actual output.
The 2 inverters go through a single cable from my shed into an amp meter, then a circuit breaker into the socket.
The amp meter has so far only read max 150 watts and this seems a bit low to me since the combined wattage of both panels DC is 530w. This is on a relatively sunny day in England which is not so sunny this time of year (but at least cloudless). I was putting it down to a loss in DC to AC conversion and also the stepup to 240v which is our system here.
Is this normal or is something amiss?

[inetdog]

That's great, I will leave my setup as it is then. Another question I have though is about my actual output.
The 2 inverters go through a single cable from my shed into an amp meter, then a circuit breaker into the socket.
The amp meter has so far only read max 150 watts and this seems a bit low to me since the combined wattage of both panels DC is 530w. This is on a relatively sunny day in England which is not so sunny this time of year (but at least cloudless). I was putting it down to a loss in DC to AC conversion and also the stepup to 240v which is our system here.
Is this normal or is something amiss?

Well, first now that it is clear that these are "plug-and-play" inverters designed to be attached via a cord to the house electrical system, my first advice to you must be not to use them at all, as their safety is questionable and their use is probably illegal wherever you are.

There have been reports that the efficiencies of some of these inverters are a lot lower than advertised.
You may have a significant voltage drop in the wiring from the panels to the inverters and from the inverter shed to the house.
A "relatively" sunny day is not going to produce the rated output from your panels even if they are pointed directly at the sun. In fact, for most panels the STC rating is an amount which they will never produce under ideal normal conditions.

Adding all of this up (actually, multiplying it out) I do not find 150 watts particularly surprising.

[alangarvey]

Well, first now that it is clear that these are "plug-and-play" inverters designed to be attached via a cord to the house electrical system, my first advice to you must be not to use them at all, as their safety is questionable and their use is probably illegal wherever you are.

There have been reports that the efficiencies of some of these inverters are a lot lower than advertised.
You may have a significant voltage drop in the wiring from the panels to the inverters and from the inverter shed to the house.
A "relatively" sunny day is not going to produce the rated output from your panels even if they are pointed directly at the sun. In fact, for most panels the STC rating is an amount which they will never produce under ideal normal conditions.

Adding all of this up (actually, multiplying it out) I do not find 150 watts particularly surprising.

Wow! I guess its because the power goes into the socket instead of out of it. Would connecting the units via a fused spur make it legal? What are my options with these 2 panels if I decide to sell my inverters on Ebay?

[inetdog]

Wow! I guess its because the power goes into the socket instead of out of it. Would connecting the units via a fused spur make it legal?

That is a large part of it, yes.
Connecting via a fused spur (or in US terms, connecting as the only device plugged into a dedicated circuit) would certainly make it safer, although it would not meet all of the electrical code requirements, nor remove all safety objections about the unapproved and uninspected nature of the device itself.

In particular, if your inverter could generate 1000 watts and the circuit into which it is plugged is fused at 6 amps/240 volts, then in the event of a fault condition in other equipment plugged into the same circuit, that fault current could be driven by the combination of the mains and the inverter, doubling the fault current without either fuse activating.