diy solar

diy solar

automate power on/off of water heater

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zeeman

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I have an off grid system and I do not wish to use the energy from the battery banks for big appliances like water heater, I prefer to use the energy from solar array when there is enough of solar energy to run the water heater.

Is there is some kind of sensor/meter that can measure solar radiance and then turn on a relay that can control an appliance like a water heater? My growatt SPF 5000 Inverter does not seem to have that option, at low or no loads it simply float-charges the battery with a small current/wattage and unless you put the load on it you do not know how much energy it actually receives from the solar array or to put it in other terms how much energy "reserve" is available from the solar array. The only way to see how much energy this solar array produces at given time is to put the load on it and then you can see if it has enough energy to run the big appliance or it has to dip for additional energy from the battery bank.

Here is an example how I think this solution should work; if my solar array produces over 1.4KW at any given time then solar sensor/relay turns on the water heater that draws 1.2KW. In such scenario solar panel array produces enough energy to run the water heater without taking some of the power from the battery array. Conversely, if solar array output drops below 1.4KW at any given time then solar sensor/relay turns off the heater until solar conditions improve enough so that water heater can run purely off the solar array.

if anyone has any suggestions how to make this happen it will be very appreciated.
 
I really wish these were a thing.
Best i can come up with would be using a small solar panel(10w or less) to turn a solid state relay on, which controls the water heater. Sun comes out and it turns the dc side of the relay on. sun disappears and the thing closes. Might need to be a smaller panel than 10w, maybe a single cell I don't know.

here is something you could try. https://www.ebay.com.au/itm/263523458861

our charge controller turns our water heater on. Currently its set to come on at a float, however i also have set it for voltage based. Weather has been inconsistent so its set to float based currently. Charge contoller turns a solid state relay on.
 
Welcome to the forum! Found your way here from Serbia, pretty cool!

One simple set up would be to put the water heater on a timer from 2PM to 3PM. I bet your batteries are in float by then, most peoples are. Not perfect but with a little bit of intervention now I bet you could manage it.
 
Sorry but I don't know anything about Growatt All in One units but just in case, have you checked the Growatt manual under the Solar Charge Controller settings to see if there is a "relay" and settings, so that the Charge Controller (not the inverter) can turn on an external relay switch, when the charge controller reaches Float Voltage and then it turns the relay off when the charge controller requires going back into Bulk Mode / Voltage.

However, some Victron Solar Charge Controller models have such a relay built in and they mention it, but they do not provide nor does virtually anyone that I've read of, mention what relay to use for a 12-24-48V system and a120v or 240v hot water tank. It too isn't a perfect solution, but a charge controller relay would be helpful.
 
E. Cho said:
Sorry but I don't know anything about Growatt All in One units but just in case, have you checked the Growatt manual under the Solar Charge Controller settings to see if there is a "relay" and settings, so that the Charge Controller (not the inverter) can turn on an external relay switch, when the charge controller reaches Float Voltage and then it turns the relay off when the charge controller requires going back into Bulk Mode / Voltage.

However, some Victron Solar Charge Controller models have such a relay built in and they mention it, but they do not provide nor does virtually anyone that I've read of, mention what relay to use for a 12-24-48V system and a120v or 240v hot water tank. It too isn't a perfect solution, but a charge controller relay would be helpful.
Click to expand...
this is the relay i use with our system.....

Solid State Relays with AC or DC Control Inputs | Omega

The solid state relays used to control large resistance heaters with temperature controllers, up to 100 Amps, Control ac Lines to 660 Vac.
www.omega.ca www.omega.ca
 
Unfortunately, these are not a thing. I do it by looking at PV array voltage and proportionately diverting enough power directly from the array just enough to drop array voltage back to power point. Array voltage is the best predictor of excess power if you don't have a goofy location. Pretty simple and cheap to do if you have the technical know how. Just not an amazon click to buy thing.
 
You could do this with a UV sensor (a lot of weather stations have them, or standalone sensor), a beefy relay (to handle whatever load needs to be switched), and Home Assistant (Free home automation software). You could make an automation in Home Assistant that when UV reaches X, turn it on. If it goes below X, turn it off. Or you could use a combination of UV and time based, or even SOC of your batteries.
 
If this is a resistance heat water heater... consider moving to a heat pump style water heater. Uses 1/3 power for same BTU.
 
yodamota said:
this is the relay i use with our system.....

Solid State Relays with AC or DC Control Inputs | Omega

The solid state relays used to control large resistance heaters with temperature controllers, up to 100 Amps, Control ac Lines to 660 Vac.
www.omega.ca www.omega.ca
Click to expand...
Wow, thanks and a Canadian source too! I'll try it with my Victron 150/85 charge controller.

Too bad it may not help the OP if the Growatt charge controller doesn't have a relay trigger or dump load function.

Here is the Victron Charge Controller video I mentioned that talks about controlling a hot water heater with a dump load. No actual how to, but this video, unlike a previous one, suggests that more info is available in a how to video or maybe manual. But searching the Victron Community website did not find specifics such as what you provided.

Victron Charge Controller Dump Load Control

Hopefully this gives the OP food for thought if nothing else.
 
Last edited:
time2roll said:
If this is a resistance heat water heater... consider moving to a heat pump style water heater. Uses 1/3 power for same BTU.
Click to expand...
Yes a heat pump water heater could be nice but not yet on my poverty level pension. It will take many many months to save for and I'm not sure that for my needs at least, it would be worth it vs another solar panel or 2?

Lots of previous threads on hot water heating methods to read through, but many are about DC modifications.
 
I do this, but my method is probably a bit involved. I make decision based on weather forecast etc. as well...

In essence, I use something like a Shelly (https://www.shelly.com/ - depending on how much power to switch) controlled by a central computer (a WYSE 3040 in my case, or something like an R-pi). This system knows the state of the battery, temperature in the water tank, weather forecast, power generation history, usage history, etc. and can made power diversion decisions based on that.

For example, if tomorrow is going to be sunny, and the battery is pretty much full but the water temp is low: kick in the heat pump x amount of hours before sun comes up, drain the battery for x%. This way, once the sun comes up, it will power the heat pump, and the battery will get back to 100% as well - maximizing both the power stored and generated.
 
Not to drift the thread from the OP's Growatt need, but here are some videos on what some other people do. Reading the comments of videos offers even more methods.

YouTube - Hot Water Heating with Solar Power

IF, one has a Victron MPPT Charge Controller or other charge controller with a Relay function, plus getting a solid state relay swtich to turn on / off the heater, this could be a pretty simple solution, at least for me. I just have to figure it out and get the appropriate solid state relay switch as linked above. Otherwise, I presently just switch on my hot water heater manually when sunny and hot water is desired. Fortunately we don't need hot water 24/7 and only use a small 50L tank, but even that was $500 and took me a year to save up for. I sometimes even forget to use the heated water until the next day, by which time it's just warm enough.

Hopefully the OP can figure out a Growatt dump load method using different sensors tied in as others have mentioned.
 
yodamota said:
I really wish these were a thing.
Best i can come up with would be using a small solar panel(10w or less) to turn a solid state relay on, which controls the water heater. Sun comes out and it turns the dc side of the relay on. sun disappears and the thing closes. Might need to be a smaller panel than 10w, maybe a single cell I don't know.

here is something you could try. https://www.ebay.com.au/itm/263523458861

our charge controller turns our water heater on. Currently its set to come on at a float, however i also have set it for voltage based. Weather has been inconsistent so its set to float based currently. Charge contoller turns a solid state relay on.
Click to expand...
that (on ebay) is a very interesting product! something like that may be used in my setup.
BTW, I was also thinking of using a small solar panel as a "sensor" that in turn would turn relay when a certain power level is reached. I probably would have to use a dummy load on that small solar cell and a tunable current sensor that in turn would activate the relay when conditions are met.
 
E. Cho said:
Not to drift the thread from the OP's Growatt need, but here are some videos on what some other people do. Reading the comments of videos offers even more methods.

YouTube - Hot Water Heating with Solar Power

IF, one has a Victron MPPT Charge Controller or other charge controller with a Relay function, plus getting a solid state relay swtich to turn on / off the heater, this could be a pretty simple solution, at least for me. I just have to figure it out and get the appropriate solid state relay switch as linked above. Otherwise, I presently just switch on my hot water heater manually when sunny and hot water is desired. Fortunately we don't need hot water 24/7 and only use a small 50L tank, but even that was $500 and took me a year to save up for. I sometimes even forget to use the heated water until the next day, by which time it's just warm enough.

Hopefully the OP can figure out a Growatt dump load method using different sensors tied in as others have mentioned.
Click to expand...
I watched your video clip, it is very informative. Thanks for the tip on growatt inverter, I will look into it.
 
E. Cho said:
Wow, thanks and a Canadian source too! I'll try it with my Victron 150/85 charge controller.

Too bad it may not help the OP if the Growatt charge controller doesn't have a relay trigger or dump load function.

Here is the Victron Charge Controller video I mentioned that talks about controlling a hot water heater with a dump load. No actual how to, but this video, unlike a previous one, suggests that more info is available in a how to video or maybe manual. But searching the Victron Community website did not find specifics such as what you provided.

Victron Charge Controller Dump Load Control

Hopefully this gives the OP food for thought if nothing else.
Click to expand...
That is very informative! thanks for this tip!
This gives me an idea; When batteries are fully charged or at float charge (in my system that is 54V) a dump load (water heater) can be triggered. I can probably tie a voltage probe to my battery bank so when a certain voltage level has been reached (54v, first condition) next step is activation of dump load relay (second condition) and water heater is powered by the sun energy. And, if voltage of the battery drops below float charge (<54v) that would indicate that there is not enough solar energy to solely power the dummy load and relay disconnects the load. Of course, relay could be programmed with a small delay so that there is not too frequent of cycling of dummy load. And, maybe there is an even easier option - if there is a way to measure volts and amps that go to/from the battery?
 
Yes you do it indirectly by using the battery/mppt V. I don't understand all the confusion. You dump load with a relay at float or a bit below. If it can float from solar, you dump. If not, you dip, relay opens, and no dump. What am I missing?
 
zeeman said:
I have an off grid system and I do not wish to use the energy from the battery banks for big appliances like water heater, I prefer to use the energy from solar array when there is enough of solar energy to run the water heater.

Is there is some kind of sensor/meter that can measure solar radiance and then turn on a relay that can control an appliance like a water heater? My growatt SPF 5000 Inverter does not seem to have that option, at low or no loads it simply float-charges the battery with a small current/wattage and unless you put the load on it you do not know how much energy it actually receives from the solar array or to put it in other terms how much energy "reserve" is available from the solar array. The only way to see how much energy this solar array produces at given time is to put the load on it and then you can see if it has enough energy to run the big appliance or it has to dip for additional energy from the battery bank.

Here is an example how I think this solution should work; if my solar array produces over 1.4KW at any given time then solar sensor/relay turns on the water heater that draws 1.2KW. In such scenario solar panel array produces enough energy to run the water heater without taking some of the power from the battery array. Conversely, if solar array output drops below 1.4KW at any given time then solar sensor/relay turns off the heater until solar conditions improve enough so that water heater can run purely off the solar array.

if anyone has any suggestions how to make this happen it will be very appreciated.
Click to expand...
Very easily and cheaply done with any type of smart home power switching socket adapter. I would use the Tuya range such as this

EU Standard Wi-Fi Smart Plug Timer Energy Monitor Intelligent Socket Outlets Alexa Google Home echo Smart Plugs | Smart Plugs | Tuya Expo

The EU Standard Wi-Fi Smart Plug Timer Energy Monitor Intelligent Socket Outlets Alexa Google Home echo Smart Plugs - Smart plug-1 supplied by Corunsmart. Designed to connected with Wi-Fi,Bluetooth. One of the best Smart Plugs offered by Tuya Expo. Get value-added services with Tuya, helping...
expo.tuya.com expo.tuya.com

Together with a Tuya lux sensor can be programmed via Smart Life app to switch on only when full sun hits your solar array if you position the sensor right, then either on a timer configured in Smart Life so it runs for a set duration, or more usefully set to switch off below a certain lux level. You might possibly need a zigbee gateway too if your wifi coverage doesn’t extend as needed, but all three items I mentioned are available on AliExpress shipped from China around $5 each, so very cheap!
 
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Not IT savy at all, so I use a 2P relay controlled by a 1P smart plug with my phone to switch on/off HWT for the shop as a dump load - pretty low tech but it works for me from anywhere my phone has connectivity.
 
As @Cronix mentioned, many weather stations have a solar meter built in. I use an Ecowitt weather station that has this built into the anemometer (wind sensor). I also have a Hubitat home automation device that can read values from the Ecowitt station and control a relay device. With similar equipment, you could turn on a relay controlling the hot water hearer only when the solar value has been over a certain level for a certain amount of time. Another idea...
 
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