Mark, You haven't provided enough information for the questions you're asking. You have said nothing about the customer's load profile.
Did you install a Tri-Metric in the system? CAH will allow you to estimate daily consumption. Otherwise, get the customer to provide a load analysis, and compare it to the you did with him/her when you designed the system. Part of the likely problem is that neither gennie or array will charge sufficiently. You didn't say what the charge amps is with the gennie, but I suspect it's surprisingly low, meaning a small degradation in charge efficiency substantially increases charging time. The combination of a cheap portable generator and DR inverter(s) is particularly prone to poor charging, as the DRs grab the peak of the gennie's waveform, and cheaper gennies provide adequate RMS voltage but poor peak voltage. Check you peak voltage on the gennie under load - it needs to be 164V for full DC output. Low peak voltage often results in very low DC charging current. This is covered in more detail in the sidebar on page 100 of the June/July 09 HP article on generators. There are no cheap solutions for your customer. For a no-cost solution, take 4 L16s out of the system, run one string. The cheapest charging solution is a good-sized 5,000-6,500 W) 120/240V inverter-generator, such as Honda or Yamaha. Don't run the inverters at max charge rate (70A on a DR2424 X 2 inverters is a C/5 rate, too hot for those L16s). Otherwise add lots of array. We set C40s to 1.600 bulk, .900 float. The C40 only absorbs for two hours; this could also contribute. Allan Sindelar al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.PositiveEnergySolar.com <http://www.positiveenergysolar.com/> From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Mark Frye Sent: Thursday, December 03, 2009 10:23 AM To: 'RE-wrenches' Subject: [RE-wrenches] Off-Grid Sizing Case Folks, I have a customer with a 3 year old system in northern CA: 8 - Deka 370AH, 6V, 2x4 banks - 740Ah @ 24V 2 - DR2424 120/240V series 4 - EC-120-GL 1 - C40 CC 1 - 5000W, old portable gas gen The problem is increased gen runtime probally due to chronic undercharging. Based on estimated consumption in the home, I think he needs about 2X the PV to meet the energy production needs in the summer (5 kWH/day)(30% DOD/day). But in order to get C10 charging during the summer he would need 5X the PV? Money is and issue. So what should I recommend: 1 - Increase PV 4X to 5X, add MPPT controller to get to a PV based system with gen support 2 - Get a 3K to 5K propane gen and and run as a gen based system with PV support 3 -? Mark Frye Berkeley Solar Electric Systems 303 Redbud Way Nevada City, CA 95959 (530) 401-8024 <http://www.berkeleysolar.com> www.berkeleysolar.com
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