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DC solar water heater viable?

Stephen E | Posted in General Questions on

I live in a state that makes it very hard to grid tie to utilities. On a duplex I own it has two 50 gallon electric water heaters. One for each side. My thought is to offset the over $1000 a year that it cost the renters. Its in a zone 6 so a normal solar water heater wouldn’t work. Gas and renters do not mix so gas solutions are out of the question. The heat pump water heaters don’t have enough space to operate, make noise and more likely to break down.

That leaves DC water heating with PV Panels. The thought is to place a 50 gallon water heater before the other two electric water heaters. A DC heating element 1kw at 144 volt range in that water heater. Run wire directly to around 1 kw solar panels. I figure that this set up would get around 8 degree rise at full power at 1kw per hour. Not exact science or figures. The cost per watt on the solar panels is less than a dollar. So a 1 kw setup should be around $1700 material cost.

Is this set up a dream or is it a possiblity? The cost of the controller, inverter, batteries are taken out of the equation. The heating element can take high voltage as long as the wattage isn’t exceeded. The DC wire would be under 9 amps because of the high voltage. Can increase to a 2kw system later on by just adding panels.

Just a thought as PV panels are becoming cheaper and gridtie isn’t an option.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Stephen,
    Your idea can work. If you are designing the system yourself, however, you need to pay attention to sizing issues -- you want to match the size of the tank to the expected electrical production -- and you need to decide whether the system needs any electronic controls.

    Another option is a commercial product called the "Liberty Box." Here is a link: Liberty Box from Premium Solar.

  2. D Dorsett | | #2

    It will probably take more than 1kw of panel to deliver sufficient hot water during the "dark season" in a zone 6 climate, and you'll need to have controls to prevent tank temperatures in excess of 100C or so to keep the pressures bounded.

    Occupant behavior will also make a difference- those who use a lot of hot water after dark but still want a hot shower in the AM may be out of luck.

  3. Stephen E | | #3

    It's good its viable. This set up would be connected to a preheating 50 gallon tank so cold water rise verses hot water rise. I'll have to put expansion tank and temperature monitor on it. The controller I might add as well, see if its needed. Looks like that controller works with 850 watt element in a 80 gallon WH. That system replaces one of the two elements on an existing Hot water heater. So using the controller verses not might be a wash since another water heater won't be needed. But two controllers needed then for two water heaters. Thanks for the advice.

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