Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Solar panels
Date: Fri, 31 May 2024 13:43:12 -0700
Organization: A noiseless patient Spider
Lines: 92
Message-ID: <v3dcpl$2cp7v$2@dont-email.me>
References: <v3blhq$23g3e$1@dont-email.me> <v3da1h$2c9ha$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Fri, 31 May 2024 22:43:34 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="7e46410b07efc6aee5b3a9962861ea77";
	logging-data="2516223"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+w42u18kZThoCwheTpZv2j"
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.2.2
Cancel-Lock: sha1:g2uUDHdcYMplCg6ZaChv+rUH+qI=
Content-Language: en-US
In-Reply-To: <v3da1h$2c9ha$1@dont-email.me>
Bytes: 4853

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.