I figure the PV cost at the total installed cost per watt (module, rack, labor)
R. Walters r...@solarray.com Solar Engineer On Apr 9, 2010, at 12:55 PM, toddc...@finestplanet.com wrote: > Has anyone included the extra racking costs to add additional modules used to > compensate for wire loss? > > Todd > > > > On Friday, April 9, 2010 10:46am, "R Ray Walters" <r...@solarray.com> said: > > All our economic analysis is based on a 20 to 25 year life. > Safety first, but then good design is to spend the customer's money where it > does the most good. > No matter how big the wire, you will always have losses. It is an exponential > curve that never reaches zero. > It just costs more and more for each extra watt saved. > Nobody would install a 4/0 cable for a 50 watt panel, even though the losses > would be lower. > As soon as the design wire starts getting big, I start looking at > alternatives: raise the array voltage, relocate the array closer, etc. > Also, this discussion concerns the DC losses, we've all agreed that AC losses > can cause shutdowns that greatly exceed the wire loss itself. > > R. Walters > r...@solarray.com > Solar Engineer > > > > > On Apr 9, 2010, at 11:31 AM, Bill Hoffer wrote: > >> Ray >> >> I think that the point is not the cost, but what is good electrical design! >> >> Voltage Drop in a wire is still undesirable and equates to an unneeded >> "heat" load on the wire. Are we advocating that if your water pipe is too >> small just increase the pressure so you get the same output you desired. >> Sure as long as you are well within the operational limits of what the pipe >> was designed to do (over the lifetime expectancy of the product). Maybe for >> a short period of time that is fine, but we are talking about a system that >> we want to perform for 25+ years. I am sure we have all seen 25+ year old >> wiring in a house that has become brittle due to operating right at the >> limit, not enough to pop the breaker, but enough over a long period of time >> to deteriorate the copper. Heat is not our friend. >> >> The worse use of solar electricity is for heating, and I really do not want >> to install extra PV just to heat my wire. Nobody said that good electrical >> design was cheap! I will continue to design my voltage drop at 1.5% and as >> always attempt to meet that goal as inexpensively as possible. NEC is a >> minimum we need to meet and is not necessarily the best electrical design >> practice! When we are talking about Mega-watt commercial installations, It >> would be pretty silly to have a system shut down (ie lost production = lost >> investment money) because of saving some money on wire. >> >> Bill Hoffer PE >> Sunergy Engineering Services PLLC >> >> On Thu, Apr 8, 2010 at 11:41 PM, R Ray Walters <r...@solarray.com> wrote: >> Over the same amount of time a similar investment in PV would save even more >> money. >> >> R. Walters >> r...@solarray.com >> Solar Engineer >> >> >> >> >> On Apr 8, 2010, at 4:28 PM, Bob-O Schultze wrote: >> >>> Guys, >>> Is it just me being dense or are none of you folks advocating for higher VD >>> looking at the savings over time? >>> If we assume that Kent's wire costs are correct (and even assuming a 33% >>> mark-up, he's paying WAY, WAY too much for wire) , the difference in >>> delivered watts between #10 and # 4 wire in this situation is 91W. If I >>> were installing this in Southern Oregon, which is pretty average as far as >>> peak sun hours/day go, we'd be looking at 91 x 4.5 (peak sun hours) x >>> 365days/yr x 25yrs = 3736 KW/H. Even at $0.10/KWH that's about $375 AT >>> TODAY'S POWER RATES. Anyone think those rates are going to stay the same or >>> go down over the next 25 years? Anybody think they won't go up by 5X? 10X? >>> 20X? >>> So... for what and for whom are we designing these systems? >>> Bob-O >>> >>> On Apr 8, 2010, at 12:40 PM, Kent Osterberg wrote: >>> >>> Nick, >>> >>> Advocating for an economic comparison between the cost of wire and the >>> energy saved by larger wire is not the same as advocating for high voltage >>> drops, or low ones either. Even with the present low prices for PV modules >>> and high prices for copper wire, a 100-ft long 350-volt dc input to a 3-kW >>> inverter should have around 1% voltage drop. Now consider a 350-volt >>> 10-amp PV circuit that's 500 feet long. Using 12 AWG copper the dc voltage >>> drop would be 5.5%. Sounds like that might be a poor wire choice, right? >>> Look what happens as the wire size is increased: >>> >>> Conductor Power $ per >>> AWG $/ft Cost ---- Loss ---- watt saved >>> 12 0.62 $620 193W (5.5%) -- >>> 10 0.95 $950 123W (3.5%) $4.71 >>> 8 1.54 $1540 77W (2.2%) $12.83 >>> 6 2.37 $2370 49W (1.4%) $29.64 >>> 4 3.73 $3730 32W (0.9%) $80.00 >>> >>> It would be reasonable to use 10 AWG copper, but before going up to 8 AWG, >>> I'd consider buying more PV instead. Why buy a watt of power at $12.83 >>> when it cost less to buy a watt of PV? The conductor price used here, just >>> for illustration, is from Southwire's price list for THHN/THWN wire dated 7 >>> April 2010. In the column of conductor costs I only considered the cost of >>> two current carrying wires. The cost of the equipment ground wire, >>> conduit, connectors, etc all go up too. That makes the dollars per watt >>> saved look even worse. >>> >>> Kent Osterberg >>> Blue Mountain Solar, Inc. >>> >>> >>> Nick Soleil wrote: >>>> >>>> I feel that it is best to maintain a 1.5% voltage drop on the AC and DC. >>>> However, I was just sizing conductors for a 400 KW project, with the array >>>> 1000' from the main service panel. With AC modules, I would have needed >>>> 5-Parallel runs of 700MCM at 208VAC (20 wires at 700MCM for 1.5%VD!) The >>>> cost would have been over 100K, which was cost prohibitive. However, by >>>> running DC wiring, and utilzing AL, we were able to maintain 1.5 VDC drop >>>> without being too expensive (yet still expensive.) >>>> >>>> Nick Soleil >>>> Project Manager >>>> Advanced Alternative Energy Solutions, LLC >>>> PO Box 657 >>>> Petaluma, CA 94953 >>>> Cell: 707-321-2937 >>>> Office: 707-789-9537 >>>> Fax: 707-769-9037 >>> _______________________________________________ >>> List sponsored by Home Power magazine >>> >>> List Address: RE-wrenches@lists.re-wrenches.org >>> >>> Options & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> >>> List-Archive: >>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >>> >>> List rules & etiquette: >>> www.re-wrenches.org/etiquette.htm >>> >>> Check out participant bios: >>> www.members.re-wrenches.org >>> >> >> >> _______________________________________________ >> List sponsored by Home Power magazine >> >> List Address: RE-wrenches@lists.re-wrenches.org >> >> Options & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> List-Archive: >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> www.re-wrenches.org/etiquette.htm >> >> Check out participant bios: >> www.members.re-wrenches.org >> >> >> >> _______________________________________________ >> List sponsored by Home Power magazine >> >> List Address: RE-wrenches@lists.re-wrenches.org >> >> Options & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> List-Archive: >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> www.re-wrenches.org/etiquette.htm >> >> Check out participant bios: >> www.members.re-wrenches.org >> > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org >
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