[RE-wrenches] PV-direct electric water heating

[Bill Hoffer]

Luke

I know that this is different than your off grid situation, but I have a
grid connected home with 2.4KW array AC coupled with an 1.8kw Exeltech
system to an Outback that has been powering my all electric house to
include an electric instant hot water heater ( 2 x 55amp 240 circuits!), I
even have baseboard heat.  I am selling excess to the grid and banking it
for half the year during the summer and I use grid power to make up the
difference in the winter.  I have the cheapest power rate in the US
($00.0178/Kw), so that is why I am connected to the grid and also it is a
very small efficient passive solar straw-bale house here in central
Washington.  I plumbed in solar hot water, but never got around to hooking
it up......seems like it is not worth the hassle at this point the PV meets
about 1/3 my power needs during the year and the Grid is a pretty cheap
battery for me in the winter!  I mention it just to illustrate that the
cost of PV electric is getting to the point where it could in some
instances make solar hot water not worth dealing with!  I will proabably
spend the money to increase the PV in the future.  The made in Washington
incentive payment of $.54/Kwhr PV produced until 2020 will easily finance
that addition!

Bill


On Tue, May 14, 2013 at 8:22 AM, David Katz <dkatz at aeesolar.com> wrote:

> 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" <sgsrenewables at gmail.com>
> 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
> SGSRenewables at Gmail.com
> 719.588.3044
> www.sgsrenewables.com
>
>
>
>
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>
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>
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-- 
Bill Hoffer
P.O. Box 1823
White Salmon, WA 98672
sunengser at gmail.com <bhoffer at sunergyengineeringservices.com>
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