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From: KevinJ93 <kevin_es@whitedigs.com>
Newsgroups: sci.electronics.design
Subject: Re: Solar panels
Date: Fri, 31 May 2024 12:56:32 -0700
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On 5/30/24 10:00 PM, Don Y wrote:
> My understanding is that solar panels are typically series wired
> as many as 10 high -- 500VDC into inverter.

The maximum voltage is usually limited by inverters available and 
various electrical codes. As you say around 500V is common.

Note that the voltage increases as the temperature reduces so strong 
sunlight in the winter can give much higher voltages than on a hot 
summer day.

> But, the individual wafers (on a panel) are probably wired in a
> series-parallel configuration with a nominal 48VDC output.

Not usually true - I don't know of any panels where there is a 
series-parallel configuration. As wafer sizes increase the panel current 
increases.

It is common for the panel to be divided electrically into three series 
sections with a reverse diode across each so that if one section is 
shaded or damaged the panel will still give output at reduced voltage 
and the MPPT controller will adapt.

> To increase the ampacity from an array of such panels, I assume
> simply wiring in parallel would not be as effective as installing
> an MPPT controller on each and then combining to a 48VDC output?

Wiring panels in parallel would require heavier gauge wiring - it is 
usually more cost effective to go with a higher voltage.

> I.e., absorbing the cost of the conversion inefficiency in return
> for being able to eek a bit of extra power out of an underperforming
> panel?

Residential installations commonly use micro-inverters with one per 
panel. This minimizes issues with individual panels being shaded or 
being placed on different facets of a roof.

Having each panel dealt with separately also avoids a problem with 
having high voltages on the roof where it could endanger emergency 
personnel in the case of fire.

Electrical code in the US requires that where panels are placed on a 
residence that there be no more than 80V DC present when disabled.

Micro-inverters usually have a anti-islanding protection so that when 
the grid is not-present they stop producing leaving the roof safe.

In the case of DC systems this may require rapid-shutdown mid-circuit 
interrupters to meet these requirement.

Commercial solar farms don't have to meet these rules so they can go to 
higher voltages and avoid the expense of additional interrupters.
> 
> And, that this would be preferable to stacking them and then
> down-regulating to 48VDC?
> 

Why the conversion to 48V? Residential applications usually convert to 
direct to 240V AC.

Even batteries for residential are commonly AC-in/AC-out with their own 
bidirectional inverters. (eg Tesla Powerwall and Enphase)

kw