Who here has the best dump load management system going on?

[timselectric]

Google seems to have a wide range of answers, how long will a sand battery store useful heat?

Several months.
It's seasonal storage.

 

[kmin]

I'm using my excess power to heat water boiler, every single watt available, not more. But I'm on grid tied AC. Microcontroller reads consumption and adjust voltage regulator connected to heating elements every 5 second.
There are many ways of getting information needed from inverter or separated meter, varies according to hardware.
Anyway, if you need to know if you have excess or not, it's simple: Every solar string has it's MPP Voltage which is always the same within few volts (temperature effect). When you have excess, your string voltage is going up above MPP voltage. More it is, more you have excess, going up towards open circuit voltage.
For example, my string has Vmpp 118-121V dipending on temperature and VOC 140V. If I observe voltage of 125V I know I have little bit of excess but if voltage is 135V there is a lot of excess. So you just switch on/off or regulate your heating elements trying to keep string voltage at Vmpp.
This is valid only without shading which can change Vmpp.

 

[kmin]

Forgot to mention, you have to observe what is your real string Vmpp, not to take it from data sheets which are done in laboratory conditions.
Also, if you are pulling too much power your string voltage is dropping noticeably below Vmpp.

 

[efficientPV]

I have three dump controllers all connected to water heaters. The first water heater is small and has priority getting any excess first to heat a small amount of water to serve most needs. The second is a slightly larger preheat tank for water. It has a lower priority and heats next or takes any extra power which the first tank can't use. The heating elements are small and it is possible to both on. The third 40 gallon tank heats water for the clothes washer and all cycles are done with hot water. The control is located a distance away from the others. No wire or wifi communication is needed. It is the dump of last resort and the array can never fully heat the tank. All controllers are proportional sending from 5 to 600W to each tank. No power is ever wasted. No batteries, charge controller or inverter capability is needed. The controller looks at array voltage and when it goes over Vmpp it starts to divert power till the voltage drops back to Vmpp. Here is just one of the controllers and the diversion for a half hour of the laundry tank.

 

[wpns]

When you have excess, your string voltage is going up above MPP voltage.

Oh, clever, thanks for that! I was thinking I’d have to derive something from battery SOC.

The controller looks at array voltage and when it goes over Vmpp it starts to divert power till the voltage drops back to Vmpp

Ditto!

 

[Zwy]

I run 2 mini splits and heat pump water heater as dump loads now. All can be controlled on my phone. I had been using 1 mini split and a few radiant heaters plugged into Shelley smart plugs that could also be controlled by the app on my phone. Come next winter, I will use both mini splits and use the radiant on very cold sunny days if there is excess.

Even with those in place, I still get excess solar production I am not able to use. I'm currently switching my shop to solar power and will run power thru a Chargeverter to the shop from the house and vice versa. Put it where it can be used.

If today is cloudy but good sun in the forecast tomorrow, I will run the battery bank down so the next day I can capture more. The battery bank doesn't need to reach full SOC, we might do laundry or run the dishwasher the sunny day. Plan ahead and you can capture more. Having options on loads that can be switched on/off will help maximize the yield. Some wonder how I can get by with 8.4Kw of PV for the house. It isn't hard if you do loads management and plan ahead.

The best dump load was adding the hybrid heat pump water heater ahead of the propane water heater. I can turn it on/off with the phone, set temp and with the extra hot water storage it extends how long we can go with limited sun.

 

[efficientPV]

Oh, clever, thanks for that! I was thinking I’d have to derive something from battery SOC.

Ditto!

It has to be a proportional design or it won't work well. The nice thing is that this is very inexpensive to implement. Even have one on my dishwasher heating element. Even the clothes washer runs off array power. I have 3,000W of panels, a 500W charge controller and a single battery for a very minimal system. I live better than others who spend five times more.

 

[kmin]

One can implement also @efficientPV:s system simplified. Lets say, you have one big boiler. Put three 1kW heating elements, only one with power controller and few relays. And voila' you have 3kW fully regulated dump load.
Like mentioned before, I run everything on AC. You with DC, remember to use correct type of relays to prevent arching.

 

[kmin]

I run 2 mini splits and heat pump water heater as dump loads now. All can be controlled on my phone. I had been using 1 mini split and a few radiant heaters plugged into Shelley smart plugs that could also be controlled by the app on my phone. Come next winter, I will use both mini splits and use the radiant on very cold sunny days if there is excess.

Even with those in place, I still get excess solar production I am not able to use. I'm currently switching my shop to solar power and will run power thru a Chargeverter to the shop from the house and vice versa. Put it where it can be used.

If today is cloudy but good sun in the forecast tomorrow, I will run the battery bank down so the next day I can capture more. The battery bank doesn't need to reach full SOC, we might do laundry or run the dishwasher the sunny day. Plan ahead and you can capture more. Having options on loads that can be switched on/off will help maximize the yield. Some wonder how I can get by with 8.4Kw of PV for the house. It isn't hard if you do loads management and plan ahead.

The best dump load was adding the hybrid heat pump water heater ahead of the propane water heater. I can turn it on/off with the phone, set temp and with the extra hot water storage it extends how long we can go with limited sun.

If you are using Shelly plus, you could write a script to check forecast and automate your logic

 

[fmeili1]

Until now, I'm using a smart home rule to ramp up the RV garage minisplit's if batteries reached 100% SOC to the lowest possible temperature with turbo mode to cool the garage as low as possible. The inverters and batteries are mounted in this garage and this helps to keep the equipment cool and also helps the house central heat pump (attached garage) to keep the house cool.

But I think about how to make this more smart in future, but it's not easy at all. If the dump device itself has no smart control mechanisms you can only control the voltage to drive this load from "outside" the device. Depending on the type of these dump loads there are different options and not all of these options are usable for each type:

1. burst mode, just turn it on and off - with or without zero crossing control (it could be very fast or very slow and everything in between)
2. phase angle control (like classic RPM regulation of an AC motor)
3. PWM control
4. Integral Cycle (burst firing)

For all load types which usually could not be controlled at all, only option burst mode with low frequency may be used like switch it on and 1h later switch it off again, etc. Some types of motors may be able to use PWM control or phase angle control, others don't like it. This may be used to control the RPM of a water pump where the volume/speed doesn't matter. For resistive loads all options would be possible, for example to drive a typical water heater like @efficientPV implemented it. Option 2 and 3 has their own challenges regarding harmonics/noises if used for non-resistive loads, etc.

This dump load thing highly depends on everything

 

[kmin]

You are not clear, what are you trying to control. With your four options, your minisplit not for sure. For resistive load all your options are possible. Options 1 and 4 is the same thing. You want to control AC or DC?

 

[Zwy]

If you are using Shelly plus, you could write a script to check forecast and automate your logic

If only the forecast was accurate.

I'm here just about everyday, not need for automation. I can look out the window, look at SOC and pretty well know what/when to turn on/off.

 

[kmin]

If only the forecast was accurate.

I'm here just about everyday, not need for automation. I can look out the window, look at SOC and pretty well know what/when to turn on/off.

Totally agree!!

 

[wpns]

I have three dump controllers all connected to water heaters. The first water heater is small and has priority getting any excess first to heat a small amount of water to serve most needs. The second is a slightly larger preheat tank for water. It has a lower priority and heats next or takes any extra power which the first tank can't use. The heating elements are small and it is possible to both on. The third 40 gallon tank heats water for the clothes washer and all cycles are done with hot water. The control is located a distance away from the others. No wire or wifi communication is needed. It is the dump of last resort and the array can never fully heat the tank. All controllers are proportional sending from 5 to 600W to each tank. No power is ever wasted. No batteries, charge controller or inverter capability is needed. The controller looks at array voltage and when it goes over Vmpp it starts to divert power till the voltage drops back to Vmpp. Here is just one of the controllers and the diversion for a half hour of the laundry tankView attachment 211760View attachment 211761.

Nice, please tell us more about those dump controllers!

 

[AlaskanNoob]

I have three dump controllers all connected to water heaters. The first water heater is small and has priority getting any excess first to heat a small amount of water to serve most needs. The second is a slightly larger preheat tank for water. It has a lower priority and heats next or takes any extra power which the first tank can't use. The heating elements are small and it is possible to both on. The third 40 gallon tank heats water for the clothes washer and all cycles are done with hot water. The control is located a distance away from the others. No wire or wifi communication is needed. It is the dump of last resort and the array can never fully heat the tank. All controllers are proportional sending from 5 to 600W to each tank. No power is ever wasted. No batteries, charge controller or inverter capability is needed. The controller looks at array voltage and when it goes over Vmpp it starts to divert power till the voltage drops back to Vmpp. Here is just one of the controllers and the diversion for a half hour of the laundry tankView attachment 211760View attachment 211761.

How can I learn more about your dump controllers? Are these off the shelf components?

 

[1234enough]

I have Victron MP 2 GX AC2 supplying small DB ( AC2 on /off at given voltage ) this supplies socket running convector heater directly and immersion heater on a contactor switched by aux relay from MP2 on/ off at slightly higher voltage than AC2. Then in summer the socket running convector heater has a changeover switch to supply socket in garage which runs a pool heater. Works a treat and keeps battery voltage between set voltages.
Also have a small AC unit to use further excess power, this is manual on / off, as this defaults to off if power is interrupted.
Next upgrade is arduino based relays - currently in R&D stage ( if anyone has any info on this would be good ) .
Also In R&D ( custom software ) is a MK3 PV router, this used to be brilliant with non victron/battery PV system, sensing export power with CT on main incomer & diverting to immersion/ heater, once victron / battery was installed it kept going into a loop of diverting more power with victron supplying more power until both where flat out with battery draining.

 

[kmin]

I have Victron MP 2 GX AC2 supplying small DB ( AC2 on /off at given voltage ) this supplies socket running convector heater directly and immersion heater on a contactor switched by aux relay from MP2 on/ off at slightly higher voltage than AC2. Then in summer the socket running convector heater has a changeover switch to supply socket in garage which runs a pool heater. Works a treat and keeps battery voltage between set voltages.
Also have a small AC unit to use further excess power, this is manual on / off, as this defaults to off if power is interrupted.
Next upgrade is arduino based relays - currently in R&D stage ( if anyone has any info on this would be good ) .
Also In R&D ( custom software ) is a MK3 PV router, this used to be brilliant with non victron/battery PV system, sensing export power with CT on main incomer & diverting to immersion/ heater, once victron / battery was installed it kept going into a loop of diverting more power with victron supplying more power until both where flat out with battery draining.

Maybe you could program your MK PV router to switch of your load, then sense export power with CT, and finally power your load regulated to match your measured export. Repeat every xx seconds. This way you divert only your excess.

 

[1234enough]

That is one way, but generally export only occurs( and thus diverted power in that scenario) if battery near 100%, which is not ideal and as standard as I said it got into a loop of sensing export then diverting power, then MP would sense more power required until both flat out.
Plus when near 100% SOC MPPT's / MP start to throttle any DC charging ( MP set not to export due to grid tie restrictions).
I'm after a gradual ramp up of diverted / dump loads, basic example is - battery is at 60% and 30% of PV production is diverted, battery at 80% and 50% is diverted, battery at 95% and 95% diverted.
If MK3 PV router can be controlled from data from Victron MP the amount / wattage of diverted power is near on infinitely variable ( up to 3kw total ) to 2no. Separate loads.
I'm not the software guru, that is my sons department, but as any parent will tell you they do want they want when they want, so R&D is sometimes Lacking LOL.

 

[kmin]

That is one way, but generally export only occurs( and thus diverted power in that scenario) if battery near 100%, which is not ideal and as standard as I said it got into a loop of sensing export then diverting power, then MP would sense more power required until both flat out.
Plus when near 100% SOC MPPT's / MP start to throttle any DC charging ( MP set not to export due to grid tie restrictions).
I'm after a gradual ramp up of diverted / dump loads, basic example is - battery is at 60% and 30% of PV production is diverted, battery at 80% and 50% is diverted, battery at 95% and 95% diverted.
If MK3 PV router can be controlled from data from Victron MP the amount / wattage of diverted power is near on infinitely variable ( up to 3kw total ) to 2no. Separate loads.
I'm not the software guru, that is my sons department, but as any parent will tell you they do want they want when they want, so R&D is sometimes Lacking LOL.

Method that I wrote above WOULD work, you just didn't mention about zero export restriction. So of course it doesn't work.
In this case it's much easier to pull all the info from your inverter. I don't know Victron, but I'm 100% sure you can get what you need from it either with modbus wired connection or wirelessly through inverters web server or MQTT server. Even the cheapest cinese crap inverters offer this.
By the way, my setup is also with export restriction, one way to handle that is setting no export from battery but allowing tiny export from inverter. So you can ramp up your diverted load as long as there is that tiny export.

 

[efficientPV]

Nice, please tell us more about those dump controllers!

There are dozens of ways to do this, none off the shelf. It costs more to do Rube Goldberg designs and they don't work as well.

This is a Lithuanian video of someone who built one of my designs. He had no prior experience in electronics and even managed to make his own circuit board, I mean he etched it himself. Used a few more components than I did due to limited availability. All it takes is motivation. And as the video says, this is for the adults in the room.