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

[AlaskanNoob]

I've searched and found some discussions, but it seems like this is a mostly untapped thing. Which is strange given all that extra energy that isn't getting used as a result. Down south I'm sure it's no big deal to let all that energy just vanish, but here in Alaska I can definitely use it to help season shift and lengthen our small growing window. Right now I'm sitting here in my cabin with only 2 of our planned 7 arrays up (we'll put the other five up this summer), and I still have feet of snow on the ground and the soil isn't anywhere near planting. At the same time, I can't use all the power that is being produced even on overcast days. I'm using two space heaters (heat pump gets connected here soon) and boiling water in the microwave just to try to see how much PV is coming in but I can't put enough load on to see it and I don't yet have an irradiance sensor.

I have a Victron Quattro and SmartSolar MPPT and make a ton of extra power in the shoulder seasons and summer, and I want to use that power. All of it. Somewhere around 100KWh+ a day worth of extra power. I'll use it to heat sand batteries or water tanks which I can use to extend growing seasons in Alaska or to melt snow along trails or something. I could certainly be growing food with this power being used to melt snow and heat soil.

It seems that the Victron system doesn't know how much PV is available unless there is a load at least as big as the available PV. So if the batteries are full and you have a small household load, the system won't know how much PV is being wasted. So it seems I will need one of those irradiance sensors.

Then I need to make it so that the system uses any power not being used to charge the batteries (so when it's near full and starts throttling the current to top them off or when the batteries are full) or to power household loads, and somehow turn on a DC dump load such that only the extra power is provided to that dump load. I'm not sure how this would be possible, because a load is a load and it would take whatever it could take. But what I desire is taking 25KWh of extra power potentially, and supplying that to a DC bus bar that will have multiple fat cables going to many resistance heating elements to heat sand or water. But if I only have 5KW of extra power, I only want 5KW sent to the DC dump load (all the resistance heaters can split the 5KW). I don't want any time the dump load is turned on, all the resistance heaters trying to take their maximum and thus depleting the batteries.

Is such granular control of the dump load possible? Somebody has to have done it. I'm guessing it will involve Node Red, an irradiance sensor, but I'm not sure what else beyond that.

 

[yodamota]

watching with interests. this is something id like as well.

 

[timselectric]

My setup, when completed. Will divert excess power to heat a sand battery.
When my battery voltage reaches 55v stage one turns on. At 56v stage two turns on. Each stage turns off when battery voltage drops 1v below its turn on voltage.
I'm setting up two stages because maximum production is a moving target.
The reason I chose the sand battery is because it will allow me to move excess summer production into winter home heating. When production is at its worst.

 

[ScrotusGobbleBottom]

it will allow me to move excess summer production into winter home heating

Please explain this. I am certain a lot of people here are interested in just a brief understanding of your idea.

 

[Hedges]

SMA Sunny Island uses frequency shift to curtail production from Sunny Boy AC coupled PV inverters.
At one time, SMA sold Smart Load 6000, which was a PF corrected AC to DC converter, able to take the requested amount of power and divert it to heating elements.

https://files.sma.de/downloads/SL6000-DEN102310.pdf

SI also has a relay control "surplus available", but simply switching a load on and off would cause cycling.

Server power supplies like used in ChargeVerter are PF corrected. If they had analog or digital controllable current limit, could operate CV/CC with controllable current, those could be commanded based on battery voltage or other.

 

[timselectric]

Please explain this. I am certain a lot of people here are interested in just a brief understanding of your idea.

It's been discussed several times in the forum.
Just search for "sand battery".

 

[ScrotusGobbleBottom]

Just search for "sand battery".

Thanks! I should have guessed that.

 

[DIYrich]

Maybe use Solar Assistant to control Load Controllers. Turn on one at a time until export or import is +/- 1kWh. A 5Kw, two 2Kw, and a 1kW load would allow controlling within 1-10kW.

 

[AlaskanNoob]

Maybe use Solar Assistant to control Load Controllers. Turn on one at a time until export or import is +/- 1kWh. A 5Kw, two 2Kw, and a 1kW load would allow controlling within 1-10kW.

I'm unfamiliar with Solar Assistant, but yeah it seems like since the load will take all it can take and destroy my plan (I'm guessing), that the best bet would be to have 5 relays each sending 5KW of power to a heating elements, and then program Node Red or whatever to turn them on in steps, so when there is 5KW extra power, turn on one, 10KW extra, turn on two, etc. I wish there was a more elegant solution but I'm guessing there isn't.

 

[AlaskanNoob]

My setup, when completed. Will divert excess power to heat a sand battery.
When my battery voltage reaches 55v stage one turns on. At 56v stage two turns on. Each stage turns off when battery voltage drops 1v below its turn on voltage.
I'm setting up two stages because maximum production is a moving target.
The reason I chose the sand battery is because it will allow me to move excess summer production into winter home heating. When production is at its worst.

In your setup, if you're at 55v and stage one turns on, how big will the load be for stage one? Are you anticipating much stage one on, stage one off, rinse and repeat if you're only getting a little bit of extra PV?

 

[timselectric]

In your setup, if you're at 55v and stage one turns on, how big will the load be for stage one? Are you anticipating much stage one on, stage one off, rinse and repeat if you're only getting a little bit of extra PV?

The size of the load hasn't been determined, yet.
I haven't picked out the heating units, yet.
But I'm guessing 2 or 3 kw each stage.
And I don't expect any short cycling, as it would take a lot to drop a 200kwh battery bank a full volt..

 

[Michelle Konzack]

I've searched and found some discussions, but it seems like this is a mostly untapped thing. Which is strange given all that extra energy that isn't getting used as a result. Down south I'm sure it's no big deal to let all that energy just vanish, but here in Alaska I can definitely use it to help season shift and lengthen our small growing window. Right now I'm sitting here in my cabin with only 2 of our planned 7 arrays up (we'll put the other five up this summer), and I still have feet of snow on the ground and the soil isn't anywhere near planting. At the same time, I can't use all the power that is being produced even on overcast days. I'm using two space heaters (heat pump gets connected here soon) and boiling water in the microwave just to try to see how much PV is coming in but I can't put enough load on to see it and I don't yet have an irradiance sensor.

I have a Victron Quattro and SmartSolar MPPT and make a ton of extra power in the shoulder seasons and summer, and I want to use that power. All of it. Somewhere around 100KWh+ a day worth of extra power. I'll use it to heat sand batteries or water tanks which I can use to extend growing seasons in Alaska or to melt snow along trails or something. I could certainly be growing food with this power being used to melt snow and heat soil.

It seems that the Victron system doesn't know how much PV is available unless there is a load at least as big as the available PV. So if the batteries are full and you have a small household load, the system won't know how much PV is being wasted. So it seems I will need one of those irradiance sensors.
an
Then I need to make it so that the system uses any power not being used to charge the batteries (so when it's near full and starts throttling the current to top them off or when the batteries are full) or to power household loads, and somehow turn on a DC dump load such that only the extra power is provided to that dump load. I'm not sure how this would be possible, because a load is a load and it would take whatever it could take. But what I desire is taking 25KWh of extra power potentially, and supplying that to a DC bus bar that will have multiple fat cables going to many resistance heating elements to heat sand or water. But if I only have 5KW of extra power, I only want 5KW sent to the DC dump load (all the resistance heaters can split the 5KW). I don't want any time the dump load is turned on, all the resistance heaters trying to take their maximum and thus depleting the batteries.

Is such granular control of the dump load possible? Somebody has to have done it. I'm guessing it will involve Node Red, an irradiance sensor, but I'm not sure what else beyond that.

Hi,

I have recently started a Device which try to communicate with the Victron SmartSolar MPPT 250/100-Tr VE.Can and will have probably the same size of not even the same housing.

It is connected directly to the Power Bus and the Output is a Heating element of up to 100A Load which is PWM controlled

Hence it will get the state of charge, tail current and voltage (it will start the PWM, if the SmartSolar enter the Absorbtion phase) and then try to output power trough the PWM.

The biggest challange is to get the total load which goes off the Battery and all charging currents, and then use so much excessive power, that it does not disturb the absorbtion, equalizing or float phase...

Believe me, my brain is smoking.

Since I have a Farm to care about, I can not work fulltime on this project, hence I do not know, when it get ready for testing.

 

[Michelle Konzack]

My setup, when completed. Will divert excess power to heat a sand battery.
When my battery voltage reaches 55v stage one turns on. At 56v stage two turns on. Each stage turns off when battery voltage drops 1v below its turn on voltage.
I'm setting up two stages because maximum production is a moving target.
The reason I chose the sand battery is because it will allow me to move excess summer production into winter home heating. When production is at its worst.

Yeah, this was my first Idea, but I would use an ADC to get the Voltage and output it as 16 digits (4bit in and 16bit out).
It should then work for example in a 24V System with an ABSORBION VOLTAGE of 29,6V, beginning with 28,0V every 0,1V the bits increase and ramp up a PWM controller for the output. It should decrease the same way but with a hysteresis if around 0,2V.

I have build this electronic in 2011, but it got lost with my stolen transporter van.

 

[timselectric]

That's over my head. I'm just a simple man, who prefers to keep my projects simple. I avoid electronics whenever possible. I can do anything I need with simple relay logic.

 

[offgrid-curious]

If you're using Victron Venus OS and a software dev, I can imagine that you could build something quite elegant with the amount of data available. Basically any data that is displayed on the console UI is available to a custom application. You could have some simple logic that just enables a relay based on the reported battery SoC. You could get even fancier by hooking up an irradiance meter and using that as an input to determine if power is "available" but not currently being used by comparing it to the output current of the SCC. You could then use that to drive even more complex logic, e.g. prioritized dump loads, time of day scheduling, etc.

 

[kommando]

I monitor my SI's grid frequency which is increases to throttle the PV output via MQTT on a Pi. The Pi then activate extra loads using Node-red to soak up the extra and de-throttle the PV automatically. I use Wemo switches which are on Wifi and the UK version will switch a load up to 230V at 16 amps on or off as required. Wemo's are no longer made but someone will have a Node to activate other Wifi or networked switches.

 

[Mattb4]

I've searched and found some discussions, but it seems like this is a mostly untapped thing. Which is strange given all that extra energy that isn't getting used as a result. Down south I'm sure it's no big deal to let all that energy just vanish, but here in Alaska I can definitely use it to help season shift and lengthen our small growing window. Right now I'm sitting here in my cabin with only 2 of our planned 7 arrays up (we'll put the other five up this summer), and I still have feet of snow on the ground and the soil isn't anywhere near planting. At the same time, I can't use all the power that is being produced even on overcast days. I'm using two space heaters (heat pump gets connected here soon) and boiling water in the microwave just to try to see how much PV is coming in but I can't put enough load on to see it and I don't yet have an irradiance sensor.

I have a Victron Quattro and SmartSolar MPPT and make a ton of extra power in the shoulder seasons and summer, and I want to use that power. All of it. Somewhere around 100KWh+ a day worth of extra power. I'll use it to heat sand batteries or water tanks which I can use to extend growing seasons in Alaska or to melt snow along trails or something. I could certainly be growing food with this power being used to melt snow and heat soil.

It seems that the Victron system doesn't know how much PV is available unless there is a load at least as big as the available PV. So if the batteries are full and you have a small household load, the system won't know how much PV is being wasted. So it seems I will need one of those irradiance sensors.

Then I need to make it so that the system uses any power not being used to charge the batteries (so when it's near full and starts throttling the current to top them off or when the batteries are full) or to power household loads, and somehow turn on a DC dump load such that only the extra power is provided to that dump load. I'm not sure how this would be possible, because a load is a load and it would take whatever it could take. But what I desire is taking 25KWh of extra power potentially, and supplying that to a DC bus bar that will have multiple fat cables going to many resistance heating elements to heat sand or water. But if I only have 5KW of extra power, I only want 5KW sent to the DC dump load (all the resistance heaters can split the 5KW). I don't want any time the dump load is turned on, all the resistance heaters trying to take their maximum and thus depleting the batteries.

Is such granular control of the dump load possible? Somebody has to have done it. I'm guessing it will involve Node Red, an irradiance sensor, but I'm not sure what else beyond that.

Part of the problem here is understanding that potential PV power is not the same as actual PV loading. As you notice you can load your panels up and see what they will do. Without load they just sit in the sun producing nothing but voltage. Any methods that try to take advantage of the potential power from the panels can only do so by matching a load to the actual power capability.

Panel potential power is not a constant though. It rises as the sun rises and falls as the sun sets. It drops if panel is shaded or a cloud passes over the sun. Loads on the other hand tend to be more of a constant during operation. Matching a dump load to the panels potential is always going to be a bit of a guessing game. This is where being grid tie shines for those that have it. There is always load from the grid to maximize panel output.

I tried touching on this subject in my Thread on bottling or canning excess PV. I understand the desire of fellow Off grid PV folks about wanting to maximize all they can get.

It sounds like in your situation with the massive PV over potential that some operator controlled additional loads would be a good idea. Automating it would take a AI.

 

[rogerdw]

I'm going through the same thought processes myself of maximising the use of power generated.

We're heading into winter here in Oz so I've been manually turning on a couple of 3kW underfloor heating circuits whenever I see there is unused power available ... to try and heat soak the house as much as possible.

I can see when there is excess available because the four mppts display the wattage, and the current being pumped into the battery ... and a quick mental calculation tells me whether to turn on more loads or not.

I've been researching various aliexpress WIFI Smart Circuit Breakers ... like these ... but of course they still have to be switched manually ... and the idea is to be able to automate the process. I've also been looking at Home Assistant to see if that could be used for the automation part.

 

[justinm001]

With a Victron inverter you can easily have AC2 turn on when SOC is above a percentage like 80%. Use AC2 to power heaters.

If DC you can do the same but use the relay on the inverter to trigger at 80% SOC and then have that relay connected to 1 or more DC relays or thermostat to turn on the heaters.

Set the assistants to turn off at like 70%. Then your batteries are always charged 70-80% and MPPTs are always in bulk.

RV and vanlifers do this with hot water. I do this on my RV when at home on shore so solar is powering the RV but if not enough then itll pull from shore.

 

[wpns]

With a Victron inverter you can easily have AC2 turn on when SOC is above a percentage like 80%. Use AC2 to power heaters.

If DC you can do the same but use the relay on the inverter to trigger at 80% SOC and then have that relay connected to 1 or more DC relays or thermostat to turn on the heaters.

Set the assistants to turn off at like 70%. Then your batteries are always charged 70-80% and MPPTs are always in bulk.

RV and vanlifers do this with hot water. I do this on my RV when at home on shore so solar is powering the RV but if not enough then itll pull from shore.

Indeed, SOC is a better indicator of ‘wasted’ (potential) power though IMHO you are chasing a chimera if your goal is to use every Joule.

Either you are throwing it away on something frivolous or something useful. If useful you need to supply that load (eventually) and then you need more panels. #IfYouGiveAMouseACookie.

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