heating hot water with pv panels

[Ampster]

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Put a power meter on that ECOsmart and you will see that 700WH a day meets all your needs. That is low enough for a small solar array.

It is on a switch so the Ecosmart is only turned on when hot water is needed. It gets to a warm temperature for washing hands in a few minutes. It doesn't furnish water for bathing. It also wasn't a good location for a flash water heater.

[PNPmacnab]

This was an actual daily measurement for the months of November and December. That would be 1,100HWH a year and I don't live there for 5 months a year. Not everyone is a family of four. If I actually had a decent place to put 500W of panels, It would be lowered more than enough to pay for the panels in 5 years even with reduced occupancy.

Put a power meter on that ECOsmart and you will see that 700WH a day meets all your needs. That is low enough for a small solar array.

[Ampster]

........ I had been wanting to test the practicality of a 6 gallon point of use and went for an ECOsmart with a 1500W 120V element that would be a common solution for camps. ......

Makes sense. I put one of those 6 gal Ecosmarts in an outlying building in the same complex where I had installed a HPWH in the main building. The Ecosmart isn't used much but I agree in that low use situation it consumes less energy than trying to heat a 50 gallon tank.

[nwdiver]

My heat pump at home saves me 47 cents a day. That is a hard way to make money. It is natural for you to think your situation is the same as others.

How did you calculate that? I'm not going with my personal situation but the average. On average a family of 4 will use ~4000kWh/yr. A HPWH will on average save 70% or ~2800kWh/yr. On average that's $336/yr a ~3.5yr payback.

But even with your situation of $0.47/day that's a ~7 year pay back which is better than most installed PV systems.

[PNPmacnab]

My heat pump at home saves me 47 cents a day. That is a hard way to make money. It is natural for you to think your situation is the same as others. At my vacation home I have two hot water tanks, a 6 gallon and a 10 gallon tank in series. I initially had a 10 and a 20 given to me. The 20 was near end of life when I got it and it started leaking three years later. I had been wanting to test the practicality of a 6 gallon point of use and went for an ECOsmart with a 1500W 120V element that would be a common solution for camps. The other tank is 2,000W 120V and both work at 60V DC. This isn't heating a teapot. It is certainly practical for a segment that visits here.

Without adding any extra panels to my system I have sufficient hot water for showers and the dishwasher. The control expense was about $40. It was shocking to me just how much energy isn't utilized in a typical PV system. It demonstrates how many of those just wanting a minimal camp system can have hot water on demand for not much more than the price of a tank. I typically feed less than 300W and sometimes just 20-50W. It all adds up and at least compensates for heat loss. I am about to add another 30 gallon tank for the clothes washer because the current system turns off so early in the day.

Supplemental heating is having 500-800W of panels feeding into the lower element of the tank. Tanks stratify and there are companies that have control systems just to prevent lower elements from coming on at night and low demand. Daytime only heating usually isn't a big problem. A low number of panels is ideal. It insures that 100% of available energy is utilized. Extra energy is banked as higher temp water that maintains temperature thru the night. It is low cost, uses existing tank and everyone has room for two panels. I've seen thermal siphon heaters added externally.

The technology works and is practical. It is worth talking about and maybe demand will make these system more common in the market. It is discouraging seeing how people heat water with PV. You could PV heat water with a dead chicken as a control system and that is about what people are doing. I just find that people are just so happy if anything works at all in solar.

[Ampster]

Heat pumps get rebates so it is cost effective.

I got no rebates and mine still paid back in less than 5 years.

Supplemental water heating with PV resistance heating has an equally impressive payback. It is not really a discussion.

Give us an example. I am not sure what you mean by "supplemental water heating"? Perhaps the details are worth discussing if it has such an impressive payback. I can turn on my resistive element but I know it will take 3 times the energy to heat the water in my tank than the heat pump mode. Are you talking about boiing a pot of water on a hot plate?

No need for the expense of storing that electrical power and extra hot water can be stored.
I heat two residences, one with each. They have their individual advantages. I see no clear winner. In low use situations HPWH is a clear looooooser.

Low use situations? I agree. When I need a cup of hot water, I use an induction teapot. I wouldn't hook up a solar panel to do that.

[nwdiver]

Heat pumps get rebates so it is cost effective. Supplemental water heating with PV resistance heating has an equally impressive payback. It is not really a discussion. No need for the expense of storing that electrical power and extra hot water can be stored. I heat two residences, one with each. They have their individual advantages. I see no clear winner. In low use situations HPWH is a clear looooooser.

What do you use for PV resistance heating? Apologies if you've already posted up thread.

[PNPmacnab]

Heat pumps get rebates so it is cost effective. Supplemental water heating with PV resistance heating has an equally impressive payback. It is not really a discussion. No need for the expense of storing that electrical power and extra hot water can be stored. I heat two residences, one with each. They have their individual advantages. I see no clear winner. In low use situations HPWH is a clear looooooser.

[Ampster]

I just find it interesting that every discussion about PV water heating turns into heat pumps.

I guess you could say the same thing about charge controller discussions. They often turn on MPPT vs PWM. Even though we treat the sun as a free resource, I always prefer to utilize that resource as efficiently as I can. Especially since the infrastructure to utilize that free resource has costs associated with it.
Like heat pump discussions there are circumstances where MPPT controllers may not be the best fit.

[nwdiver]

I just find it interesting that every discussion about PV water heating turns into heat pumps.

It's the best way to use PV to heat water... what's not to love about turning 1w from PV into ~3w of heat?

[PNPmacnab]

I just find it interesting that every discussion about PV water heating turns into heat pumps.

[nwdiver]

It still puzzles me why there is so much negativity about HPWH.

More puzzling still is so much negativity about electrification. If there's so much solar that some is being curtailed.... doesn't it make sense to use solar do to more things that were once done with natural gas? Like... like heating water?

[Ampster]

I'm not sure thinking winter lasts 12 months counts as an opinion

Haha. Most of us are ignorant so we would probably not know that.

It still puzzles me why there is so much negativity about HPWH. It doesn't take rocket science to know that it is more efficient to move heat than generate it. That is relevant to the title of this thread which is, "heating hot water with pv panels". It does seem that the sidetracks to the original topic are often made in order to demonstrate superior knowledge about a subject that is NOT relevant to the original posters question.

[nwdiver]

No worries @J.P,M. A few different opinions are what make these kind of forums worthwhile.

I'm not sure thinking winter lasts 12 months counts as an opinion

[Ampster]

.......
From where I sit and type, you seem full of anecdotal and what seems to be casual observational information with little background or explanatory information to back up what you write. I believe you believe what you write. I don't believe what you write adds much that's meaningful to the conversations or the body of knowledge.
.......

No worries @J.P,M. A few different opinions are what make these kind of forums worthwhile. Everyone has a different learning style and each reader is going to chose to do what makes sense to them. If many are indeed as ignorant as you continually believe them to be, then many are not going to understand your very complete and detailed explanations anyway, The one or two thank yous I do get give me enough feedback that I am going to continue doing what I believe is of some value to a few.