How do most people heat water with solar panels and batteries?

[wpns]

We have solar thermal with ground mount panels and electric boost. It made sense 18 years ago but with the cost of solar electric so low it probably would be better to do more solar electric and standard electric water heaters these days.

Of course when there’s no sun for a few days there’s also no spare solar power for the electric boost.

There’s probably an overly complex and expensive solution involving a combination of solar thermal, solar electric, and heat-pump (would be nice to dehumidify and cool the laundry room) technologies but space is limited, we just replaced the solar thermal system proactively, life’s too short, and my heirs will probably have to rip it all out if (when) it has an issue.

 

[Zwy]

@Zwy
so you use a hybrid water heater like this RHEEM XE50T10HS45U1 ?
why not just an electric water heater but a hybrid ?

Mine is the Richmond version, same water heater. Hybrid heat pump is the way to go, you have the option to use the heat pump for efficiency and the element if demand is high. Original plan was to use the element in winter if my basement temps did get too low as the heat pump will draw heat from the area it is located. I have found the uninsulated basement temp never gets below 52°F. The inverters, charge controllers and batteries are located in the basement. In summer, the heat pump water heater will help with keeping the basement cool.

I installed the heat pump water heater 1 year ago on March 1st. Great unit, I am very satisfied with it.

 

[CaySol]

So you dont use hot water when you are charging your car?

I do. The inverters have been able to cover all our loads so far, but I have the car charger on a smart port so potentially could load shed if need be.

 

[time2roll]

80 Gallon Heat Pump Water Heater.. with two kids and the wife it does switch to heating elements and yeah it pulls around 5400 watts if it needs to recover/recharge quicker than normal. When running in heat pump mode you are good to go for a long time on battery power. I am going to need to add more battery capacity to keep up when it kicks into what it calls high demand mode and turns the elements on.

Has the WH run in heat pump only mode and actually run out of hot water? I think I would press a bit for conservation.

 

[trdstarlet]

So on a not so hot spring day I am wasting 10KW/H of sun with my batteries at 100%. if I could only.....

View attachment 281351

I've thought of this too LOL! I need more batteries SMH!

 

[BarracudaBob]

I've thought of this too LOL! I need more batteries SMH!

I hooked it up this morning. I have home automation switch setup that I can remotely turn on or it'll turn on between 12:30 p.m. to 3:00 p.m.

It turns on one immersion heater at 1500 watt AV off the inverter.

Today is a wonderfully cool sunny day in South Florida so I don't even need to turn on the air conditioning so I'm going to be loaded with power.

It might only do a little bit at a time at 2.45 Watts per gallon per degree but at least I know I'm sucking down those photons!

 

[trdstarlet]

@BarracudaBob That's awesome! Yeah, I need to set up something like that...

I'm away from home during the week, so I just run a space heater near the air circulator to use up excess energy when the batteries are topped off. I'd like to pick up six more batteries to populate a second server I just picked up, creating a larger buffer for cloudy days and allowing me to run the HVAC on hot days.

 

[chamilun]

lady I get my panels from just purchased a hybrid heat pump water heater as well. the difference is massive

 

[quantum`]

A resistive element makes no sense to me. A monobloc AtW heat pump heats water for space heating, chills water for space cooling, and dynamically heats domestic hot water. (The above linked models are made for Arctic, a US brand)

 

[wattmatters]

A resistive element makes no sense to me.

It really depends on the individual circumstances in play for each home.

We have an 85 gallon stainless steel hot water storage tank with a resistive element.

It is powered with solar PV via a variable power PV diverter which adjusts the power delivered to the resistive element based on available excess solar PV (IOW it avoids importing any grid energy). If I choose, I can also have it boosted with super off-peak grid power (free between 12-2PM every day).

We get ample solar PV throughout the year from our 11 kW grid-tied system. Our average water hearing demand is a little over 5 kWh/day.

We forego less than US1c/kWh in excess solar export credit, so our water heating costs ~US$20 per year to run. The technology is simple, very reliable, quiet, inexpensive to install and can be maintained with cheap off-the shelf parts always available and not requiring electronics or refrigeration technicians. Our last tank was 30 years old when I replaced it. The current one will outlive me.

In our case an expensive heat pump makes no sense for water heating.

Space cooling/dehumidification for our long summer (and a bit of heating for our short winter) definitely, we have air source heat pumps for that.

 

[Brucey]

A resistive element makes no sense to me. A monobloc AtW heat pump heats water for space heating, chills water for space cooling, and dynamically heats domestic hot water. (The above linked models are made for Arctic, a US brand)

How much does the smallest version of that cost?

 

[WorldwideDave]

80 Gallon Heat Pump Water Heater.. with two kids and the wife it does switch to heating elements and yeah it pulls around 5400 watts if it needs to recover/recharge quicker than normal. When running in heat pump mode you are good to go for a long time on battery power. I am going to need to add more battery capacity to keep up when it kicks into what it calls high demand mode and turns the elements on.

Do they make a 120V heat pump hot water heater?

 

[WorldwideDave]

Also @BarracudaBob You said, "I hooked it up this morning. I have home automation switch setup that I can remotely turn on or it'll turn on between 12:30 p.m. to 3:00 p.m."
Can you tell me about that? Presume you have a 120V or 240V solenoid of some sort you can remotely program, or is this an Intermatic mechanical timer (which has wicked high idle consumption)?

 

[Zwy]

Do they make a 120V heat pump hot water heater?

They do but 240V is equal load on each inverter leg. Same with mini split heat pumps. Helps keep loads balanced.

 

[BarracudaBob]

Also @BarracudaBob You said, "I hooked it up this morning. I have home automation switch setup that I can remotely turn on or it'll turn on between 12:30 p.m. to 3:00 p.m."
Can you tell me about that? Presume you have a 120V or 240V solenoid of some sort you can remotely program, or is this an Intermatic mechanical timer (which has wicked high idle consumption)?

I don't have the solar panel to the water heaters direct yet but I am going through my inverter on 120 volts AC.

I have a home automation relay hooked up that when I see that my batteries are 100% and it's throttled back on the solar because there's nowhere for it to go with low loads and full batteries I turn on one of the immersion heaters.

Right now my panels will be putting out about 6 KW but it's only showing three so I'm wasting the other half
Because there's no where for it to go
So it's my load dump for my pool dip

In the future I'm going to rig something where I can turn the solar arrays DC go right to them.

So even though it might be a decimal point I'm putting 1.5 kWh for at least 3 hours a day into my pool to heat it up for the season.

 

[Zwy]

Also @BarracudaBob You said, "I hooked it up this morning. I have home automation switch setup that I can remotely turn on or it'll turn on between 12:30 p.m. to 3:00 p.m."
Can you tell me about that? Presume you have a 120V or 240V solenoid of some sort you can remotely program, or is this an Intermatic mechanical timer (which has wicked high idle consumption)?

My heat pump water heater is a smart water heater connected to house wifi. I can turn it on/off with the app from anywhere with cell service. I can program it to run only certain hours of the day. Plenty of options.

 

[BaylentheSky]

Do they make a 120V heat pump hot water heater?

Likely not. In the event that the house needs hot water quickly (several consecutive showers/washing machine loads), there's no way a 120V 15A continuous outlet plus the heat pump can supply hot water quick enough for such use.

 

[CaliSunHarvester]

Do they make a 120V heat pump hot water heater?

I have one. It's a RHEEM 20 Gallon resistance water heater. It pulls 20A, I believe, and runs for about an hour to heat it up.

Rheem 20 Gal. 120-Volt 1.5 kW 1-Phase Point of Use Commercial Electric Water Heater EGSP20 120 Volt 1.5kW POU - The Home Depot

Give a flawless look to your dwelling by selecting this amazing Rheem 1-Phase Commercial Point of Use Electric Tank Water Heater. Easy to handle.

www.homedepot.com

My model is from about 1985-1990, so I am not sure if it pulls 1.5kW or 2.0kW or even 2.4kW. Hooked up to a dedicated 20A breaker. It supplies a 1BR guest house, which is occupied by 1 or 2 people. And, it's been standing OUTSIDE unprotected from elements until last summer, when I finally built an enclosure with insulation around it.

 

[BarracudaBob]

2.45w per gal per degree F for resistive heater

120 volt heat pump water heater

Rheem Performance Platinum ProTerra 50 Gal. 120-Volt Plug-in Smart Heat Pump Water Heater with 10-Year Warranty XE50T10HM00U0 - The Home Depot

Introducing the Rheem ProTerra Plug-in Heat Pump Electric Water Heater. Like the Rheem Proterra models, this 50 gallon model is known for its high efficiency. The ProTerra Plug-in was created to make it easier to replace your natural gas tank with an electric model. Over 4.5X the efficiency of a...

www.homedepot.com

 

[WorldwideDave]

They do but 240V is equal load on each inverter leg. Same with mini split heat pumps. Helps keep loads balanced.

if you have a 240V inverter I could see that, thanks.

 

[WorldwideDave]

Likely not. In the event that the house needs hot water quickly (several consecutive showers/washing machine loads), there's no way a 120V 15A continuous outlet plus the heat pump can supply hot water quick enough for such use.

wondered if there was a 30A 120V option or something as well.

 

[BarracudaBob]

wondered if there was a 30A 120V option or something as well.

I mean at that point you could run an auto transformer would it be cheaper to do 240.

 

[wattmatters]

Likely not. In the event that the house needs hot water quickly (several consecutive showers/washing machine loads), there's no way a 120V 15A continuous outlet plus the heat pump can supply hot water quick enough for such use.

With sufficient hot water storage it doesn't need to.

Good heat pumps will deliver ~ 4 times the heat power as they draw in electricity. Here the CO2 models deliver 5-6 kW of heat and draw ~1-1.2 kW of electrical power.

 

[BarracudaBob]

With sufficient hot water storage it doesn't need to.

Good heat pumps will deliver ~ 4 times the heat power as they draw in electricity. Here the CO2 models deliver 5-6 kW of heat and draw ~1-1.2 kW of electrical power.

Heat pumps four to six times more efficient just takes longer so if you're running off solar all day it'll heat that water up so go for the bigger quantity.

And it'll cool the room off that he's got to come from somewhere You're just providing energy for it to transfer heat from the room to the water heater.

So here in South Florida that's not an issue but what happens when you're up north in the winter?

 

[Brucey]

In winter time up north a heat pump water heater in the basement is going to make it colder. Guess it depends if you have hvac down there to control the climate.