Over the same amount of time a similar investment in PV would save even more money.
R. Walters [email protected] 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: [email protected] > > 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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