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Solar water heating is dead?


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Hi,

For my new place I'm trying to decide how to do the hot water.

Seems like I can do a traditional solar water panel - from which you can choose between various products (I'd be inclined to an EV tube panel; not sure about whether pumped or syphon).

Or I can try to heat my hot water with "excess" power from my proposed PV system.

Here's an article that claims its cheaper to do it with PV (though maybe this is a "temperate climate'" view?)

http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-really-really-dead

The "winning formula" seems to be a nice efficient heat pump powered by power from the PV system.

By the way - this article links to a nice site PVWatts which is a US Department of Energy predictor for generation.  US developed but it works for us too.

So - what say the gurus?

Thanks,
Elbow

 

 

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  • 2 weeks later...

I have looked into possibility of running a heat pump from PV for extra heat on the days that the sun shines (Give PV power) but not hot enough to heat the geyser through EV tubes to 55C.

Taking into account that a Heatpump cost R10k and upwards it almost seems more viable to spend the R10k on another 1KW of Panels, change the element to a 1.5kw one and run it directly from PV.  You can then use the PV power in summer (when EV is enough) to run other things like swimming pool pump/borehole pump.

 

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55 minutes ago, Louw said:

change the element to a 1.5kw one

If you do this, just remember it will take twice as long to heat up. It takes around 8kwh to heat a 150 liter tank from cold to hot (assuming a delta of 45 degrees), so with a 3kw element it takes 2 hours and 40 minutes. With a 1.5kw element it takes 5 hours and 20 minutes. Also keep in mind that you have a standing loss of 2kwh per day, the larger element will take 40 minutes to restore the heat, the smaller one an hour and 20 minutes. Since the standing loss is also happening while you're heating, one can roughly estimate that it will take over 6 hours to get up to temp with the small element, and just over 3 with the large one.

In other words, never turn off your geyser when going away for the long weekend. Your wife will not be happy when you come back.

:-)

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  • 3 weeks later...
On 9/8/2017 at 1:36 PM, Louw said:

I have looked into possibility of running a heat pump from PV for extra heat on the days that the sun shines (Give PV power) but not hot enough to heat the geyser through EV tubes to 55C.

Taking into account that a Heatpump cost R10k and upwards it almost seems more viable to spend the R10k on another 1KW of Panels, change the element to a 1.5kw one and run it directly from PV.  You can then use the PV power in summer (when EV is enough) to run other things like swimming pool pump/borehole pump.

 

I did this but opted to use a 2KW element instead of the 1.5KW element. It heats up a bit quicker and I have more space power in the mornings for the washing machine or dishwasher.

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