Solar diverter for hot water

[mauz81b]

Hi all,

I have a 5.3kW solar PV array and an electric battery (10kWh). I would like to further optimize the system by diverting PV electricity to a thermal storage with a 2.8kW resistance heating element in it. Ideally, I would be able to prioritize this over the electrical battery i.e. charge this first and then the electrical battery once the thermal storage is fully charged. Also, it would be great if it could vary the electricity (AC) to the heating element depending on the genreation of the solar panels. So, if the panels are generating 1kW, it will pass 1kW to the heating element, if it is then increasing to 1.5kW, the diverter is tracking it and increasing the electricity passed to the heating element. It should be capped to 2.8kW, the max wattage that the heating element can take. In the UK, this product would do it (I am not affiliated with them): https://myenergi.com/product/eddi/ , but it is not available in the US. Any suggestion?

thanks and regards

 

[acdoctor]

So you would prefer to have plenty of hot water and maybe run out of lights and refrigeration?
Normally people want to first keep the lights on next recharge batteries then if their is anything left try to figure out how to utilize it without dipping into the batteries that were just charged.

 

[再生可能 エネルギー]

>> I would be able to prioritize this over the electrical battery
>> In the UK, this product would do it: MyEnergy - Eddi

@mauz81b I looked at the Eddi User Manual but I noticed that there is no batteries in the provided diagram.

This could have been omited to simplify the diagram, but for your use case there should be some logic
for providing solar energy to the Eddi system only when the batteries are charged and then if some surplus is available.

Note: If you look at the page 10 of the manual, the Eddi system will redirect Solar energy, when available,
to the water heater (until the maximum temperature is reached) instead of sending the solar energy to the Grid.
Also The Eddi system can be programmed to always energize the water heater, using solar energy when available or the Grid otherwise.

 

[efficientPV]

The Eddi is a grid tie system which tries to prevent export. You want a simple power point water heater controller. These are available commercially, but presently expensive. When up to temperature, you just turn in battery charging. How many volts is your array? Technically this is a fairly simple problem but far out of the realm of most in solar.

 

[onokai]

I am doing this with a sol-ar hybrid inverter. Any extra power is diverted to whats called the smart load in my case it's a 3,000 watt water heater element in my solar preheat 80 gallon tank. I have run this for one year now with no issues
Sounds like a few inverters may do this as I'm not familiar with your brand
The other thing is I'm not grid tied

 

[wattmatters]

I have a 5.3kW solar PV array and an electric battery (10kWh). I would like to further optimize the system by diverting PV electricity to a thermal storage with a 2.8kW resistance heating element in it.

Is your system grid-tied or off-grid? Solutions would be a bit different in each case.

I recently installed a smart hot water solar PV diverter to my grid-tied set up. That's a whole story in itself I won't bore people here with.

If grid tied, then while it's nice to have something "optimal" sometimes the last 20% of optimisation is where all the costs are and it's not worth it. You can get most of the way by using a simple and reliable timer controller (to operate during peak solar production hours) and a contactor for switching the load on, and just accept a small proportion of heating energy will still come from the grid.

Some strategies which can help reduce grid power consumption are to use a lower power heating element, e.g. 1.8 kW, as that way you are more likely to have sufficient solar PV when conditions are not so solar perfect.

A lot depends on location and how much hot water (and hot water energy) you typically consume each day.

 

[Chris Kirk]

I found this thread because I was considering starting my own on a related topic..... We have lived entirely off grid for 40 years now. Power is solar + a little wind. I recently upgraded my Pb/acid battery bank to LiFePO (EVE cells and Overkill Solar BMS). Living in Wales, we have a huge excess capacity in Summer just so that we can generate sufficient electricity in Winter. We also use a solid fuel boiler for hot water that I'd rather not run in Summer if possible. I knew that these diverters are available off the shelf for grid-tie systems, but could find nothing for off-grid users like us.
I have now succeeded in cobbling together a controller that diverts power to our (1kw, may increase to 1.5kw) immersion heater once the batteries are full but turns the heater off when they fall to ~ 75%. These parameters are variable and I'm still experimenting with them, but the system certainly works.
The (Chinese) board that I've used is very cheap. I'm happy to share details if anyone is interested? The Solar side of our system is currently about 2.5kW (shortly to increase to 4kW) and the battery bank is 1120Ah at 24v. Current inverter is Victron 5000, but I've used many. The wind generator contributes a modest 0.5kW in a gale!

 

[namtr0]

I found this thread because I was considering starting my own on a related topic..... We have lived entirely off grid for 40 years now. Power is solar + a little wind. I recently upgraded my Pb/acid battery bank to LiFePO (EVE cells and Overkill Solar BMS). Living in Wales, we have a huge excess capacity in Summer just so that we can generate sufficient electricity in Winter. We also use a solid fuel boiler for hot water that I'd rather not run in Summer if possible. I knew that these diverters are available off the shelf for grid-tie systems, but could find nothing for off-grid users like us.
I have now succeeded in cobbling together a controller that diverts power to our (1kw, may increase to 1.5kw) immersion heater once the batteries are full but turns the heater off when they fall to ~ 75%. These parameters are variable and I'm still experimenting with them, but the system certainly works.
The (Chinese) board that I've used is very cheap. I'm happy to share details if anyone is interested? The Solar side of our system is currently about 2.5kW (shortly to increase to 4kW) and the battery bank is 1120Ah at 24v. Current inverter is Victron 5000, but I've used many. The wind generator contributes a modest 0.5kW in a gale!

I'm interested as I need an off-grid solution. Want to divert when possible right now I seem to waste power I could be using after batteries are topped off

 

[SolarForU2]

Here is a copy of a post I made on another forum, may be a solution.


Full circuit and PCB here PV Diverter

The device is designed to seamlessly add a load (Hot Water Element) to the PV array whilst connected to existing PV controllers.

Mike

 

[HighDesertOffgrid]

Here is a copy of a post I made on another forum, may be a solution.


Full circuit and PCB here PV Diverter

The device is designed to seamlessly add a load (Hot Water Element) to the PV array whilst connected to existing PV controllers.

Mike

I like this. Having a similar thought, I designed a load optimization system some time ago that works on the a/c side of things. When my system reaches a preset voltage, the microcontroller can energize circuits in the ac panel. I have had the electric water heater connected this way for about 18 months without issue.

 

[Cheap 4-life]

My outback fm80 charge controller has many settings to power a relay when certain battery voltages are reached. It has times for diverting, delaying etc.. it can shut off diverting at a voltage of your choosing..
when my batteries are fully charged I let the charge controller close a relay that the water heater is on.. if my battery voltage begins to drop to much due to clouds (not much extra pv available) then the diversion stops..
I’m not actually diverting but rather turning on the water heater when there’s excess pv power available and letting the inverters supply the water heater..

 

[Chris Kirk]

I'm interested as I need an off-grid solution. Want to divert when possible right now I seem to waste power I could be using after batteries are topped off

I posted more details here: Thread 'Working diverter for off-grid LiFePO. Powering immersion heater when solar power is plentiful.' https://diysolarforum.com/threads/w...n-heater-when-solar-power-is-plentiful.47143/
Basically I use a cheap circuit board off eBay or Ali to switch on my 1kw immersion heater when the LiPOs reach 27v and cut out again at 26.3 v.
Although LiPOs have a very shallow discharge curve, this seems to work. I estimate that this arrangement cycles about the top 20% of battery capacity, but I am now making more complex measurements to confirm this. I'll post some data when I have it.

 

[efficientPV]

Or DC right off the solar panels like this. it is not rocket science. This is proportional, whatever is excess goes to heat water. No need for bigger battery, interfere with charge cycles or leave battery in a lower charge stare. Works with all existing thermostats.

 

[Cheap 4-life]

Or DC right off the solar panels like this. it is not rocket science. This is proportional, whatever is excess goes to heat water. No need for bigger battery, interfere with charge cycles or leave battery in a lower charge stare. Works with all existing thermostats.

View attachment 113732

So all your pv runs thru this and only the excess not used by loads goes to the water heater?

 

[efficientPV]

No thru, parallel. This is a full featured board with many options that can also do some interesting stuff. I run three off the same array with priority. It can also drive two heating elements on a priority basis. One output can have priority, like early morning low power levels. At mid day when there is maximum power it will power both heating elements in parallel. Afternoon when power has dropped primary and heater has turned off, the single secondary heater gets the power. All this is far too much for people to think about. You have to be really into hot water theory.

 

[daklein]

I'm looking for a way to modulate or variably control my 240VAC WH element, from my raspberry pi nodered / mqtt system controls.

I replaced my nat gas boiler with a 85 gal plastic Marathon electric WH tank, 3800w elements, running the previously set up baseboard hydronic heating system. It's mostly backup and keep the ends of the house warm, with a wood stove in middle of the house. Just hooked it up this last few weeks. Future long term plan is to use it as the buffer tank for an ASHP, instead of resistance heating.

I wired the top element through a mechanical 24hr timer, to the grid panel, to heat only with off peak grid power. I have a primarily AC coupled solar and battery system, with excess off-grid solar, and solar during off-peak weekend days that I don't want to export.

I plan to run the lower element from the off-grid system, but a simple relay banging on/off 3800w is much too big a step. I need it to be a variable load, so it can be controlled to keep the main battery near zero current (once that's full enough). I replaced the lower element thermostat assembly with a typical top element thermostat and thermal cutoff assy, so the top and bottom will be completely separate circuits (grid and off-grid are not typically in phase..)

Something like one of these should work, if I make a microcontroller to replace the pot or button panel? https://smile.amazon.com/dp/B08W2XYLNB

https://smile.amazon.com/dp/B075QZ9GZT

The op mentioned the Eddi diverter. It would likely work, if their wifi interface is open, but it's $100s more that I'm likely to pay....

Has anyone done this? Am I missing a reasonably priced 'smart' AC load controller with wifi/zigbee already available? Or a dumb device that can be controlled by a low voltage DC signal,etc.

 

[wattmatters]

If commercially available PV diverters for resistive elements loads are not your bag, perhaps this is an option:

Mk2PVRouter - Introduction

A DIY Constructor’s project to build a Mk2 PV Router system for surplus energy diversion.

mk2pvrouter.co.uk

Although I think it's mainly designed for avoiding grid imports for grid-tied PV.

 

[daklein]

Thanks, I do recall seeing the mk2pvrouter project. I'm not looking for a export limiter w/ AC current sensor. My controls are in the garage with the main SMA battery inverters, which provide the target close to zero current for the main FLA battery bank.

So I'm looking for a (triac or SCR) device that will control split phase 240 (two 120v legs, in case a device is designed for single phase 230V EU where one leg is neutral or roughly ground potential and the other leg is +-230V). I want to be able to give it something simple like a pwm or analog DC control voltage, and have it modulate the load resistance on/off per AC cycle. Ideally in a way that won't confuse or disrupt my pair of SMA 120v inverters, power factor wise.

 

[HighDesertOffgrid]

I want to be able to give it something simple like a pwm or analog DC control voltage, and have it modulate the load resistance on/off per AC cycle. Ideally in a way that won't confuse or disrupt my pair of SMA 120v inverters, power factor wise.

Something like this?

//Map average voltages of 13.2-14.2 to SSR1
if (average < 890){
analogWrite(SSR1, 0);
display.print ("0%");
Serial.println ("0%");
}
else if (average > 930){
analogWrite(SSR1, 255);
display.print ("100%");
Serial.println ("100%");
}
else if(average >=890 && average <=930){
outPut = map(average,890,930,1,254);
analogWrite(SSR1,outPut);
display.print (outPut / 2.56);
Serial.println (outPut / 2.56);

}
}
//display.println (" % ");
delay(10);

 

[daklein]

Something like this?

//Map average voltages of 13.2-14.2 to SSR1
if (average < 890){
analogWrite(SSR1, 0);
display.print ("0%");
Serial.println ("0%");
}
else if (average > 930){
analogWrite(SSR1, 255);
display.print ("100%");
Serial.println ("100%");
}
else if(average >=890 && average <=930){
outPut = map(average,890,930,1,254);
analogWrite(SSR1,outPut);
display.print (outPut / 2.56);
Serial.println (outPut / 2.56);

}
}
//display.println (" % ");
delay(10);

What SSR or device would you be using, and what's between the (arduino?) analog output and the SSR input.

I have started with putting a small box on the wall, on the conduit going to the water heater, and in the box is going a cheap SCR dimmer (claimed to be good for 10kw, I'll try the water heater 3.8kw element and see). It looks about like the output control of the Mk2PvRouter, but this is an SCR instead of a triac. I'll get that hooked up and see. If it's an SCR like it says, it may only do 0-50% load?

I could replace the pot that controls it with 16 resistance steps from a 4 channel wifi relay board that I have several of in my controls. 16 power levels would be 240w steps if made evenly spaced, and that could work fine.