[RE-wrenches] PV-direct electric water heating

[Tom Elliot]

I suppose it would be an interesting exercise to do the math but my experience with very cold groundwater input to a gas on-demand heater (Aquastar) showed very efficient fuel usage even with the  cold water input.  It seems that trying to heat a tank of that cold water with PV, especially if they are using water during the day and thus always adding cold water to the tank, would be an exercise in futility and a waste of good PV.

Tom

From: Luke Christy 
Sent: Monday, May 13, 2013 4:59 PM
To: re-wrenches at lists.re-wrenches.org 
Subject: [RE-wrenches] PV-direct electric water heating

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
SGSRenewables at Gmail.com
719.588.3044
www.sgsrenewables.com

   










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