Re: Solar panels

On 5/31/2024 12:56 PM, KevinJ93 wrote:

On 5/30/24 10:00 PM, Don Y wrote:

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.

I count ~72 wafers on a panel I have here.  How does *it* get to a 48V
nominal output?

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.

Yes.

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.

Yes.  But, if your goal is 48VDC, you then need to regulate that ~500VDC
back down to 48VDC.
It then boils down to where the various components are located (long,
high amperage runs suffering higher IR drops; conversion losses for
long high VOLTAGE runs)

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.

Yes.  Or "power optimizers" in lieu of inverters.

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.

Thus arguing against a high string voltage.

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.

Local electronics at the panel ensure that -- whether microinverter or power
optimizer.

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

I'm not looking for grid connection.  So, the grid is never present.

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

Yes.

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.

The straight forward approach is to AC then BACK to a lower voltage DC
that can then be used, as is, and directly backed up with a low voltage
(48) battery pack to carry over through periods of cloud cover.
When "dark", I expect nothing from the array, having *consumed* all
available power during the illuminated period.
I'm not trying to power AC loads.  So, going to AC means an inverter
followed by a BIG "power supply".

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

But, those try to back up the entire array's capability.  Give me 3-4KW
during daylight and I can get by on < 100W for the rest of the day (night).
So, a modest battery can carry the dark load and act to bridge small
variations in output during full illumination.  Adjusting the load
accomplishes the rest.