Hello Eric,
Actually, I think I have a lot of useful information to give you regarding your questions. I am in the middle of the West Bank in Palestine and cant go into a lot of details right now, but just as a quick note, I would definitely follow US guidelines on the combiner boxes (on anything over two strings), AND I would definitely use the LA302DC surge protection – on the combiners as well. Maybe we can get together off line, when I complete this work in the West Bank. I should be home in Washington State on Tuesday or Wednesday and maybe we can get together on the phone then. Thanks, Walt Walt Ratterman SunEnergy Power International 11 Laurel Lane South Washougal, WA 98671 (360)-837-3680 ▪ fax (360)-837-1315 ▪ Skype Walt-Mobile [email protected] ▪ www.SunEPI.org <http://www.sunepi.org/> From: [email protected] [mailto:[email protected]] On Behalf Of Eric Youngren Sent: Tuesday, December 15, 2009 4:02 PM To: RE-wrenches Subject: [RE-wrenches] quality off-grid PV for Africa Howdy Wrenches, First off, thanks for all of the nuggets of wisdom I have gleaned from this list over the years. You guys are great and I've learned important things from you. I am building what I hope will become a value-adding distribution company to export off-grid PV systems and equipment to Africa and other places in the developing world. I want to help take the best practices and experiences of the US off-grid industry to the people in the world that really need it. The quality of most PV installations I have seen in Africa is pretty bad. I have two 'whitepapers' on my website <http://solarnexusinternational.com> that explain in more detail what I mean. What I've seen is that the PV dealers and installers over there have access to good quality modules, controllers and batteries but they have to go to the local markets for their wire and BOS materials and most of that is poor quality and/or not appropriate for DC current and voltages. So our plan is to send complete system packages that will include all the BOS the local installers will need to install high quality systems that will be efficient, safe and durable. We will also travel to give installer training workshops and possibly develop a 'certified installer' type program for our Solar Nexus Systems that would enable dealers to purchase materials 'a la carte' and do the system design and integration themselves. I'm working out the design right now for an order of 30 small (by US standards) systems (roughly 400 W of PV, 300 W inverter, 12V PWM charge/load control, our SolarNexus power center, 400 AH VRLA battery) that will be installed on schools in rural Tanzania to run lighting, fans and one or two computers. I have some questions about best design, low cost high quality materials and where to toe the NEC line and where its okay to ignore the US code requirements in the name of cost efficiency and realistic risk assessment. Specifically, here are some of my questions: 1. PV combiners - for 12V systems using 3 to 6 modules in parallel -- I'm planning to use Midnite short TBB insulated busbars for parallel combiner blocks, similar in application to the old-school PDB terminal blocks but cheaper. I know the NEC would require individual string fusing, but is that a concern AT ALL on 12V or 24V systems? I have never seen a module short out and feed current into a parallel string, but I think that's why the code requires individual string fusing. Has anybody seen unfused PV combiners become a problem for 12 and 24 Volt systems? What is the practical limit at which it does make sense to require string circuit protection? Is this a case where the NEC could be optional in Africa? (trust me, any kind of PV combiner hardware is going to be better than the 'twist and tape' methods they're using now) 2. Meters - right now I'm planning to put Trimetrics on all of these systems. Obviously this will require user education for the meter to be helpful at all. But I feel that educated users can learn how to understand an amp-hour meter and they need more than red, yellow and green dummy lights to fully understand what is happening with their system. Thoughts or comments on that one? 3. Lightning protection - my kits will include ground rods and #6 bare stranded copper wire for solid array/rack grounding and bonding for the entire system. To me that seems like the best defence against lightning, but what about additional protection? Are Delta lighting arrestors worth the money? Do they work? Put it at the PV combiner or at the controller? Sorry for the long-winded post. I'd appreciate any thoughts y'all might have on anything I've mentioned here, or anything else that comes to mind. Thanks! best energy, Eric -- Eric Youngren NABCEP Certified Solar PV Installer Island Energy Systems, LLC dba Solar Nexus International PO Box 894 1016 Discovery Way Eastsound, WA 98245 (360) 376-6842 www.solarnexusinternational.com www.islandenergysystems.wordpress.com www.solarempowerment.net
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