Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Don Y 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: References: 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: 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.