[RE-wrenches] PV-direct electric water heating

[Steven Lawrence]

Luke,

Most tankless hot water heaters can't accept pre-heated water.  Some of
them can, but even still these have a minimum heat input into the water.
You may run into a situation where you have 105F water into the tankless
and the thing won't fire up due to safety reasons (can't put out 130F or
something similar like that).  And the issue with 105F is you start
exposing yourself to the potential of getting Legionnaires' disease.

-Steven

>
>
> 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
>
>
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