Hi: When deciding on voltage drops and otherwise working out the design of a solar system, one thing that needs careful attention is to make sure that the array voltage does not drop below a level at which the inverter cannot produce full power.
This voltage will occur when the inverter is working at full input current such as a hypothetical 3000 W inverter which can handle a maximum of 10 Amps of input current to produce its full rated 3000 Watts (10Amps @ 300 Vdc). At any voltage less than 300 Vdc, the power will be limited by the maximum 10 Amps. For example at 290 Vdc you get 2.9 kW, 280 Vdc you get 2.8kW, and so on. Even if the inverter can operate down to 100 Vdc, you don't want to be anywhere near there, especially not during the midday hours as that will hurt peak power production, a lot. In this case -0.3% loss for every volt below 300Vdc. Identifying this voltage for a particular inverter may not however be straightforward due to wide variety of wording used in specifying ratings. Wording such as, 1. operating voltage range 2. full power operating voltage range 3. MPPT operating voltage range 4. minimum operating voltage 5. minimum MPPT operating voltage 6. rated operating voltage range 7. Rated MPPT operating voltage range 8. starting voltage 9. nominal operating voltage range 10. maximum input current 11. minimum input voltage 12. minimum DC voltage 13. nominal DC input current 14. maximum operating DC input current 15. maximum continuous operating DC input current 17......... When looking for the voltage below which you don't want go, look for the following: 1. The maximum operating input current 2. The minimum MPPT operating voltage Then make sure the array can produce at least that much voltage and current when its really hot when the resistance of all the wires is more than at room temperature. JARMO _____________________________________________________________________________________ Jarmo Venalainen | Schneider Electric | Xantrex Brand | CANADA | Sales Application Engineer Phone: +604-422-2528 | Tech Support: 800-670-0707 | Mobile: +604-505-0291 Email: jarmo.venalai...@schneider-electric.com | Site: www.Xantrex.com | Address: 3700 Gilmore Way, Burnaby, BC V5G4M1 *** Please consider the environment before printing this e-mail From: Glenn Burt <glenn.b...@glbcc.com> To: RE-wrenches <re-wrenches@lists.re-wrenches.org>, Date: 07/25/2015 12:46 PM Subject: Re: [RE-wrenches] DC conductor line loss numbers Sent by: "RE-wrenches" <re-wrenches-boun...@lists.re-wrenches.org> You would want to confirm hot temp PV circuit values with chosen Vdrop to ensure the irrelevant value doesn't drop you out of the inverters' operational limit, however. Sincerely, Glenn Burt Sent from my 'smart' phone so please excuse grammar and typos. From: Chris Mason Sent: 7/25/2015 15:20 To: RE-wrenches Subject: Re: [RE-wrenches] DC conductor line loss numbers It should be noted that the NEC recommendations for feeder circuits are to do with acceptable voltages at the load, i.e., you do not want your 208V equipment running on 200V. PV circuits are not feeder circuits, voltage drop is irrelevant. Power loss may be relevant, but only in terms of economic value. If it is preferable to add more PV and lose 10% of the power, as long as there are no issues of heat and potential fire, why shouldn't you be able to make that decision? As PV gets cheaper, replacing cables costing $10,000 to save $10 a year does not make sense. The NEC rules on voltage drop were never designed for PV source circuits. On Fri, Jul 24, 2015 at 11:52 PM, Jerry Shafer <jerrysgarag...@gmail.com> wrote: Wrenches I have 3 engineering firms and one in-house engineer that only use 1% because in the NEC it is stated as a suggestion and not a requirement but they take this as a must not exceed instead, I cant change CC as it will be remotely monitored via the Outback connection, the Engineers refuse to make any changes to the 1% and still stamp the drawings. This is what I have found in my research it came from Mike Holt Contrary to common belief, the NEC generally doesn't require you to size conductors to accommodate voltage drop. It merely suggests in the Fine Print Notes to 210.19(A), 215.2(A)(4), 230.31(C), and 310.15(A)(1) that you adjust for voltage drop when sizing conductors. It's important for you to remember that Fine Print Notes are recommendations, not requirements [90.5(C)]. The NEC recommends that the maximum combined voltage drop for both the feeder and branch circuit shouldn't exceed 5%, and the maximum on the feeder or branch circuit shouldn't exceed 3%. This recommendation is a performance issue, not a safety issue. Jerry On Wed, Jul 22, 2015 at 11:28 AM, Starlight Solar Power Systems < la...@starlightsolar.com> wrote: Jerry, A long distance wire run is practical now days using a high voltage controller. Have a look at Schneider and Morningstar 600Vdc controllers. Not sure what you mean "by nothing can be changed but wire size” but you will have to rewire the strings into series and protect the wire run. Larry Crutcher Starlight Solar Power Systems On Jul 22, 2015, at 10:37 AM, Jerry Shafer <jerrysgarag...@gmail.com> wrote: Wrenches Some time back there was discussion on the conductor size and efficiency rating requirement for long DC runs. What I am looking at is this, 400 feet of MCM 400 to keep the line loss at or below 1% per NEC code for an off grid application, cost vs return is not acceptable. 2/0 is less than 2.5% and the cost is far less. Specs are 4 strings of 3, 250 watt modules feeding one Outback FM 80 charge controller. There are lots of things I can do like SMA instread, or 200 VDC charge controller but nothing can be changed except the wire gauge. Does anyone recall a thread with this topic. thoughts ?? Jerry ________________________ _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org -- Chris Mason NABCEP Certified Solar PV Installer™ Solar Design Engineer Generac Generators Industrial technician www.cometsolar.com [The entire original message is not included.] ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
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