Hi Walt, Thanks for the reply. I hope you don't mind me posting it on the wrenches list.
Your experience matches mine. The genset were already installed before the owner contacted me about PV. If the owner has any money left after buying land and building a house with genset power, then buying PV or wind is a no-brainer. Even just adding batteries and an inverter to a lightly loaded genset reduces run-time and gives the homeowner some quiet power at night. I know some RE contractors who let the homeowner do the genset themselves to avoid having to deal with it. Still, they get a lot of calls because the owner has trouble synchronizing the inverter and battery charger with the genset. A real point of frustration for non-tech homeowners. Joel Davidson ----- Original Message ----- From: Walt Ratterman To: 'Joel Davidson' Sent: Tuesday, March 03, 2009 8:24 PM Subject: RE: [RE-wrenches] Backup generator labor (was How large is toolarge?) Hello Joel, Actually, the gen-sets are usually already installed. But in the case of the 2 to 4 kw systems, sometimes it amounts to a plug and a cord that can plug the system into a 4 kw portable generator. Something like a half hour, plus some testing time. On the larger systems…..like 20kw and above, the generators are almost never installed exclusively for the pv/hybrid systems, and connecting to them takes relatively little time. My point is that on larger systems that are primarily PV, generators are a real need – even if they only have to run a couple of hours a week, or even a month. Batteries need to be charged regularly, and pv cant always be depended on to do this. Thanks!! Walt From: Joel Davidson [mailto:joel.david...@sbcglobal.net] Sent: Tuesday, March 03, 2009 6:41 PM To: wratter...@sunenergypower.com; RE-wrenches Subject: Re: [RE-wrenches] Backup generator labor (was How large is toolarge?) Hi Walt, I'm not knocking PV/genset when they serve a real need. Is your installation time-spent 50% PV and 50% genset of what? Joel Davidson ----- Original Message ----- From: Walt Ratterman To: 'RE-wrenches' ; jry...@netscape.com Sent: Tuesday, March 03, 2009 6:14 PM Subject: Re: [RE-wrenches] Backup generator labor (was How large is toolarge?) Hello….Walt here. I think the real question, when dealing with an off-grid system of any size is: Do you want the system to work? If so, use a generator. Of course, there are, as always, variations to that theme (oversizing the solar 300%, and things like that), but in general – large grid = pv / diesel hybrid, at least in my book. Walt Ratterman SunEnergy Power International www.sunepi.org From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Joel Davidson Sent: Tuesday, March 03, 2009 6:07 PM To: jry...@netscape.com; RE-wrenches Subject: [RE-wrenches] Backup generator labor (was How large is too large?) Off-grid wrenches, Genset backup or PV and wind supplementing a genset is cost-effective (except for its environmental impact). But what about the time spent setting up the genset and fuel storage, and maintenance, and repairs. A 2 to 6 kW PV system goes in pretty quickly, even with batteries. If you add a 4 to 10 kW genset to the mix, what percent of the job time does the genset take? How many hours are spent synchronizing the PV or wind system to the genset? And how many hours a year is reasonable for maintenance and repair? How many call-backs can you expect in the first 2 years? Thank you very much for your insights. Joel Davidson ----- Original Message ----- From: Jeff Yago To: RE-wrenches Sent: Tuesday, March 03, 2009 4:13 PM Subject: Re: [RE-wrenches] How large is too large? I have designed and installed many off-grid systems and all but one included a backup generator. The generator allows using a much more realistic sized battery bank and the fast charging process reduces generator run time.
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