Adding dissimilar panel string to existing install

[Mike90250]

Here is what to consider in solar installation. There are basically 2 types of Inverters used in Grid Tied Installation. One is the String Inverter and the other one is the Microinverter. A panel when exposed to light will produce a DC voltage and develop a DC current ( Photo Voltaic Effect ). A 250 watt panel will produce 30 volts DC and develop 8.3 Amperes DC current ( 30 X 8.3 = 249 watts which is Power ) when exposed to good sunlight. The String Inverter is used when the panels are connected in series. When panels are connected in series, it is important that all panels receive the same light exposure so that the developed current of each panel will be the same and the individual panel voltage will Add up. If they develop different currents, the least current will prevail ( that is why same light exposure is important ). This is where the String Inverter is used and the AC side of the String Inverter is connected to the Utility Grid ( 240 volts ) via an AC disconnect switch.

The Microinverter is used when the panels cannot be installed to receive the same amount of light exposure, therefore will all develop different amount of current. Each panel will have a microinverter installed in the back of the individual panels and will be independent of each other. The output of the microinverter is already AC, 240 volts and the current will depend on the amount of light exposure the panel receives. In this case the 240 volt AC output will be connected in parallel and the currents will ADD up. This will be tied to the Utility Grid ( 240 volts ) via an AC disconnect switch.

I hope this theory helps in understanding the principle of the difference between Series connected panels and Parallel connected panels. You are welcome to ask questions for clarity.



I teach Home Solar Installation and this is one of the lessons that I teach. If anybody has questions, I will try and answer them.

Wow. Just wow. You teach this ?? Seriously ?
You get one chance to carefully read your posts, and correct them before you get flamed to ash. I was going to let this slide, until I saw your post that you teach lessons about solar.

[Island mon]

I'm off the grid with a separate battery bank and one large split phase inverter.
so there are no individual inverters on the panels.

The fuse holders and fuses I was thinking about are marine(made for the elements) DIRECT CURRENT fuses for now. Since they are made for DC applications, it should address the arching gap brought up in a overloaded "blown" state.

I'm not opposed to ordering DC breaker boxes for long term.

I have understand current, but like the explanation of water pipes bottlenecking the flow of current.

[Mike90250]

I'm off the grid with a separate battery bank and one large split phase inverter.
so there are no individual inverters on the panels.

Good, it's much simpler with fewer parts.

The fuse holders and fuses I was thinking about are marine(made for the elements) DIRECT CURRENT fuses for now. Since they are made for DC applications, it should address the arching gap brought up in a overloaded "blown" state.

it's not the fuses that arc, but it's the holder, you can't open them to check the fuses , with daylight on the panels

I'm not opposed to ordering DC breaker boxes for long term.
I have understand current, but like the explanation of water pipes bottlenecking the flow of current.

getting good gear works out better than getting wrong gear in the long run