Blending Grid and Solar power to my Hot Water Heater

DrDog

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Jul 17, 2020
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Im researching solutions and cant figure out how grid power and Solar are blended. I have been looking a MPP solar off grid solutions, but want to be sure how it works. I am hoping that any power from the solar panel will be combined with grid to meet the requirements to drive my hot water heater element (just the bottom). If the solar is not used until there is enough to meet the requirements, then I need a bigger array.

I was hoping to start small to offset the power requirements of the water heater.
 

mopat

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Jun 22, 2020
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Your first sentence refers to grid-tied solar systems. Your second sentence refers to off-grid systems.
how grid power and Solar are blended? solar direct current DC is inverted to grid alternating current AC, then either used locally "off-grid" or sold to utility company "grid-tied".

Water heater electric elements run from 2000- 5000 watts. Generally you cannot direct where your solar power is consumed.

Are you in USA?

Have you considered a tank less water heater?

I am trying to read your mind on what you are asking. Possibly to use an MPP off-grid unit to just power your (lower) electric water heater element?
 

efficientPV

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Sep 24, 2019
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I have a heat pump water heater and power the spare resistive heating element with solar. I think it is a great way to get into solar because it will at least pay for itself as my cost was little over the cost of the panels themselves. Powering sheds, garages, home office tend to be super loooooosers economically. The problem is there is just not hardware to buy which is cheap. A great experimenter project for people who build electronics.
 

melkier

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This is also something that interests me (blending)

Check this out:


1596913626687.png


Also, there is a standalone unit that does it (kinda pricey imo) and the example is for pumps:


1596913779149.png

IMO we need more tech like this ... I really don't want to grid tie and I don't want to completely off-grid (even with an ATS to fall back on the grid). It would be nice to have something that pulls from the PV/Bats and anything extra is pulled from the grid (blending). There may be something out there like that, I'm still learning.
 

Rider

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Sep 20, 2019
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Southern Maryland
I've been thinking about something like this:
Many tanks have two coils on independent thermostats, probably 240VAC. Break them apart electrically. One goes to the grid power. The other, replace the coil with a 120VAC and connect that to the solar side. Replacing the coil reduces the overall power needed, and has been documented somewhere on this forum a while back.

The coil on the bottom of the tank might be the grid, and set to say... 90 or 100*. The coil on the top goes to solar and is set to 120*. That way the grid quickly pre-heats the tank, and then solar takes it to full temp over a longer period of time, not unlike using a heat pump tank.
 
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Rider

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replace the coil with a 120VAC and connect that to the solar side. Replacing the coil reduces the overall power needed, and has been documented somewhere on this forum a while back.
Maybe I got that backwards..... a 240VAC coil fed by 120VAC.
 

efficientPV

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Any 240V heating element will be one quarter of the rated power on 120V. This reduction in power will work better with most inverter installations by not hogging all the inverters power. In solar the excess is a typically a smaller wattage. I run my 120V elements on 60V and have no problem supplying my hot water needs. Just takes a little longer.
 

Rider

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Location
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Any 240V heating element will be one quarter of the rated power on 120V. This reduction in power will work better with most inverter installations by not hogging all the inverters power. In solar the excess is a typically a smaller wattage. I run my 120V elements on 60V and have no problem supplying my hot water needs. Just takes a little longer.
Right. It was your posts a bunch of months ago that I remember. Never got around to trying it out...
 
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