Hi Luke I am doing this with a 1200 watt array that is AC coupled to my off grid home inverter. I am using an SMA 1800 inverter because it is 120vac. I use a relay connected to the AC output that connects the 4500 watt water heating element to the AC breaker panel when battery voltage reaches the bulk setting. I use the auxiliary output of a Midnite charge controller to control the relay. Using a grid tie inverter is more efficient because the array is MPPTracked. Without the inverter an array connected to a water heating element, the array will spend a lot of time off of the. Maximum power point, especially n low light, and early and late in the day. Also the AC coupled array adds to battery charging when needed, before heating water. I see you point, that PV is so cheap, you could add an extra 1000 watts for the price of the inverter, but be careful what you used to disconnect 150+ volts DC. He temp switch on the water heater will arc and fail. David Katz
Sent from my iPhone On May 13, 2013, at 7:59 PM, "Luke Christy" <[email protected]<mailto:[email protected]>> wrote: Hi Wrenches, Now that the cost of modules has come down so much, has anyone out there experimented with solar electric water heating? As in: direct connecting a short series string of PV modules to a tank -style electric water heater with an element of an appropriate voltage and wattage rating…? A off-grid customer of mine who is also an electrical engineer has a situation that seems ideal for trying this idea out: he has a gas-fired tankless water heater and a water source that is very cold year-round. The idea is to take a 30 or 40 gal electric tank heater, switch out one of the the 240V elements to something like a 96VDC, 1000W element (difficult to find, but available), and direct connect 3 or 4 60-cell modules in series (with a disconnect and high-limit control of course). The tank would then serve to preheat the cold feed to the tankless heater. We think we can get a decent daily temperature rise with this setup. Probably not enough to heat the tank to a normal DHW temperature, but certainly enough to offset a good deal of propane consumption, and all for what I predict will be considerably less cost than a small solar thermal system. Has anyone tried this? I'd appreciate any insights or opinions. Thanks -Luke Christy NABCEP Certified PV Installation Professional™: Certification #031409-25 NABCEP Certified Solar Heating Installer™: Certification #ST032611-03 CoSEIA Certified PV Installer Solar Gain Services, LLC PO Box 531 Monte Vista, CO. 81144 [email protected]<mailto:[email protected]> 719.588.3044 www.sgsrenewables.com<http://www.sgsrenewables.com> _______________________________________________ List sponsored by Home Power magazine List Address: [email protected]<mailto:[email protected]> Change email address & 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<http://www.re-wrenches.org/etiquette.htm> Check out participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org>
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