Water heating with solar

[martinwvogt]

Hello, I currently have excess solar capacity (3.2kw) and I am wondering if anyone has experience using a dedicated water heater powered directly by dedicated solar panels. My option would be to use a 24 or 48v heating element and connect directly to a single inverter. Maybe a bad idea, but I wanted to check ,.. I have the ability to use a propane on demand heater as a backup. Any thoughts are appreciated ... Thx

 

[MaikaiLife]

I've certainly not seen everything, but typically if you want to heat water with panels you use a Solar Panel which is different than a PV Panel which converts sunlight to electricity.

It's unlikely that a device that can consume your excess solar could run exclusively off the output from your PV panels. Electric water heaters have large inrush and running current needs that typically a PV panel and even a configuration of parallel PV panels cannot support without an inverter, even if you found a water heater like this, it would most likely have an integrated inverter.

What is it that you're trying to achieve, where does the extra capacity currently go, why do you want to heat water with only excess?

 

[martinwvogt]

Thanks, I have an extra array that's not needed (long story). I'm trying to make some use of that array to lower my dependance on propane. I have checked into water heaters which allow low-voltage heating elements ... so at least in the summer it should be doable.

 

[MaikaiLife]

How many panels are in your array and what are they currently hooked up to?

 

[Bluedog225]

Search here. There are many threads on this with good info.

I’ve seen them in passing but not dug in.

 

[martinwvogt]

thanks, I have close to 12kw ... more than enough,

 

[Jbird2000]

Some inverters have a feature ( or an add-on) allowing you to dump excess AC into a tank of water

 

[martinwvogt]

yes, that is correct. That’s definitely another option and would leave existing batteries and inverters out. In my case I’m assuming the charge controller would take the excess and feed a water heater when the battery is full

 

[OzSolar]

yes, that is correct. That’s definitely another option and would leave existing batteries and inverters out. In my case I’m assuming the charge controller would take the excess and feed a water heater when the battery is full

I'd tie it into my current system using using a standard AC water heater that is ran by your current inverter(s). Install it upstream so it acts a preheater to your current propane water heater. Not perfect but quite simple and reliable.

What is the AC voltage of your current system? 120 or 240?

There's many choices of water heating element wattages. I can suggest one based on your answer above for one that doesn't tax your inverters but still gives you a place to send extra energy.

Dedicating PV modules water heating takes them away from ever being able to charge your batteries. Even if you don't need them it still takes away from the flexibility of having redundancy.

The FlexMax charge controllers have a programmable "diversion load relay that you could use to to control a water heater via a standard relay.

Diversion (AUX Mode)
When external DC sources (wind, hydroelectric) are directly connected to a battery bank, any excess power should be sent to a diversion load, such as a heating element, using a mechanical relay or solid-state relay

https://www.outbackpower.com/downloads/documents/charge_controllers/flexmax_6080/owner_manual.pdf

 

[Daddy Tanuki]

I agree with OZ Solar, unless you are heavily retarded like I am you should follow his advice...

I on the other hand being mentally challenged, am building a dump load water heater with a 1600 liter tank that will heat in the spring-fall with excess solar.

it will also provide heat in the winter via a waste oil burner boiler that will heat the water in the tank if the tanks temperature gets to low.

solar water heater/waste oil boiler

Been talking about this for over a year now, its time to get started, So originally this idea was formulated as a way to use up excess production as my panels and batteries are all specc'd for winter time with low solar output, and then it morphed into why not heat the house, or at least the...

diysolarforum.com

 

[efficientPV]

It is no different than charging a battery. You can connect up a solar array directly to a battery if you are careful. Don't pay attention and disaster will soon follow. With 3200W of dedicated panels there is no need to be concerned about efficiency. 1KW is more than enough for domestic use when converter efficiently. Don't heat more than you need. Everybody wants to use 24 and 48V heating elements. That is their comfort level. Heating with low voltage is insane, the high currents and wire losses make a bad design. Higher voltage is your friend and it allows you to use standard heating elements. Element resistance has to be matched to the array and there are videos of how to calculate that. They are technically correct but in practice are very wrong. Use a resistance of twice that ideal for best overall performance. With just small drops in current, wattage drops dramatically and full current almost never happens. Power is a function of the square of the current. It is best to design for more typical currents like half the array rating.

The hard part of this is turning it on and off with temperature. Heating elements with a built in thermostats that can run on DC is just a lie. These really don't work for long and when connected to a solar array the open circuit voltage is far too high for them and the contacts burn. In electronics, switching currents and efficient matching of panel to the heating element is stupid simple. But that is far beyond most everyone in solar. I have no experience in low tech switching methods and will leave that to others. With that much power you shouldn't have much of a problem whatever you do.

 

[Daddy Tanuki]

It is no different than charging a battery. You can connect up a solar array directly to a battery if you are careful. Don't pay attention and disaster will soon follow. With 3200W of dedicated panels there is no need to be concerned about efficiency. 1KW is more than enough for domestic use when converter efficiently. Don't heat more than you need. Everybody wants to use 24 and 48V heating elements. That is their comfort level. Heating with low voltage is insane, the high currents and wire losses make a bad design. Higher voltage is your friend and it allows you to use standard heating elements. Element resistance has to be matched to the array and there are videos of how to calculate that. They are technically correct but in practice are very wrong. Use a resistance of twice that ideal for best overall performance. With just small drops in current, wattage drops dramatically and full current almost never happens. Power is a function of the square of the current. It is best to design for more typical currents like half the array rating.

The hard part of this is turning it on and off with temperature. Heating elements with a built in thermostats that can run on DC is just a lie. These really don't work for long and when connected to a solar array the open circuit voltage is far too high for them and the contacts burn. In electronics, switching currents and efficient matching of panel to the heating element is stupid simple. But that is far beyond most everyone in solar. I have no experience in low tech switching methods and will leave that to others. With that much power you shouldn't have much of a problem whatever you do.

much easier to buy a sigineer all in one and have it power the water heater. put it on a timer so that the inverter is only on from xx to xx time. or better yet use a voltage sensing relay to turn the inverter off and on. batteries full at 54.4? turn on the inverter. below xx.xx turn off.

no need for extra batteries, solar controllers and the wiring is for the most part 200-240 single phase so not overly expensive.

this is my plan anyway. here is a link to the EU standard inverter which is under 1k, but puts out 230 VAC single phase, so not useable for much of anything else in the US... but since it is 230 volts and does not sell well in the US its price is right. at 5000 watts it is just the right size to drive an electric water heater.

5000W Off Grid European Solar Inverter 100A Charger 48V 220V 230V

5000W European Solar Inverter 100A MPPT Solar Charger DC 48V to 1220V 230V 240V with 80A Utility Charger 50HZ 60HZ. High Frequency Stackable Batteryless operation. Wide PV input range. M5000H-48BP

sigineer.com

 

[SeaGal]

I am wondering if anyone has experience using a dedicated water heater powered directly by dedicated solar panels.

Check out @Steve T - IoW UK's Loadmaster Open source Arduino PV Hot Water Project.

See his posting here..

Direct PV water heater MPPT controller

Hi All This is my first post here, after I've spent countless hours of reading. I am the happy owner of 2 grid-tied systems, one 6.6 kWp the other 4.4 kWp. But now I've got hand on some second hand panels I would like to use for water heating as it's not possible to add them to the existing...

diysolarforum.com

and project here.

LoadMaster XP - A Smart PV MPPT Solar Hot Water Controller

A solid-state, low-cost, reliable solution for solar hot water from PV. Zero maintenance & CO2, connected, smart combi pre-heat control.

projecthub.arduino.cc