Re: [RE-wrenches] PV-direct electric water heating

[Allan Sindelar]

Hilton, That sounds like a good idea at first glance but a bad one when you dig a bit deeper. In essence he is sacrificing proper absorption on the batteries and will pay the price in reduced battery capacity and life. As soon as the batteries reach the bulk voltage setpoint, which is typically about 85% SOC and would normally trigger the absorption stage, the charge current is diverted to the heating element. As soon as the controller switches it over, the battery voltage drops to the reconnect point - sort of like an old Trace C30A, which was never a good controller. In the best case, the energy cycles back and forth between absorption and diversion, or if the controller has PWM, I suppose a portion would go to each. Somehow I just can't see how it could be made to work without these inherent complications. Allan Allan Sindelar al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Founder and Chief Technology Officer Positive Energy, Inc. 3209 Richards Lane (note new address) Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com On 5/14/2013 6:22 PM, Hilton Dier III wrote: A friend of mine lives off grid with PV and wind. He added a shunt-type controller to his battery bank and connected it to a DC heating element in his hot water tank. Below a set voltage the element is dormant. When the battery bank hits a high voltage (at the end of a particularly sunny day or during a windy spell) the element comes on. That way, instead of just a PWM shutoff and wasted energy, he gets some benefit. I wouldn't deliberately install PV just for hot water, but in an off grid situation where the excess would go to waste, it makes sense. Hilton -- Hilton Dier III Renewable Energy Design Partner, Solar Gain LLC 453 East Hill Rd. Middlesex, VT 05602 _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org 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 Check out participant bios: www.members.re-wrenches.org

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