IMHO it seems like we're all really on the same page here...... trying to make the the most out of the the resources we have available to work with......sun hours, pv, copper, labor, dollars, etc. Job specifics come into play. There are definitely times when a detailed cost/ benefit analysis is called for. Many other times, let's not miss the forest for the trees, an increase in wire size to avoid waste of other aforementioned resources, is low hanging fruit. As a percentage of the overall system cost, the decision is a no -brainer.
Dick Ratico Solarwind Electic --- You 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 > _____________ --- end of quote --- _______________________________________________ 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
