Dump all excess PV to air heater?

rhino

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I have a Victron system and was wondering if there is any example of how I can make sure the solar charge controllers are always running at 100% and any excess the battery does not need gets diverted to some sort of electric heater to heat air. I used to have a system that used relay when the batteries were full but that would cause some power to be pulled from the batteries and it was always either fully on or off. If I have a 2kW heater for example, it would turn the full 2kW heater, wait for the voltage to drop on battery, then turn off when the battery voltage was below a setpoint. so you'd get wild fluctuations... I want the battery to stay 100% full and dump in this case everything else to the heater. Does someone know how you'd set up such a system?
 
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rhino

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Meaning I don't want the SCC to be reducing PV output because the battery is full.
 

JeepDaddy

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You don't need to worry about that, the controller will only accept what it needs. Think of it as the SCC switches the panels off when the batteries are full.
 

rhino

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Sorry if I am not making myself clear. I want alll available PV output to either go to the battery, loads, or the heater so there is no wasted PV output. Like a grid tied system except all excess going to heater instead of the grid. My point is I want heat in winter and don't want my SCC to be limiting the PV output when it could have been dumping it to a heater.
 

chrisski

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If you don't find anything here, you can see what the hydro and wind guys do.

Unlike solar which only provides what is needed up to as much as the panels can pull, hydro and wind can't limit the power that is pushed. They have a system of voltage dumps that dump the extra power that is not used on something. I have "A Wind Turbine Recipe Book," and the windmills use a load controller to dump the excess energy as heat.
 

Thor

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If you don't find anything here, you can see what the hydro and wind guys do.

Unlike solar which only provides what is needed up to as much as the panels can pull, hydro and wind can't limit the power that is pushed. They have a system of voltage dumps that dump the extra power that is not used on something. I have "A Wind Turbine Recipe Book," and the windmills use a load controller to dump the excess energy as heat.

try searching for diversion on victron community forums

Link
 

wattmatters

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Sounds a bit like a solar power diverter for resistive element tank hot water systems, like a Catch Power diverter. Problem is these monitor grid exports (i.e. excess production) to adjust how much power to divert to the HW element.

Without the grid export how can a system know if the PV array can output more power unless a load is first applied to find out?
 

Rider

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A few years back, there was a regular poster, Justin Laureltec, a tech rep for Victron. I offered a suggestion for Victron to add logic to their SCC to divert excess panel power to a different port. He liked the idea and said he would pass it up the line. Never heard anything further.
 

JeepDaddy

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Which Victron SCC do you have? Some of them have a load output that can be switched based on battery voltage. I'm planning to use that to dump excess power to a water heater.
 

740GLE

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Water heating seems like a best energy dump seeing the water will hold energy better than air if in a proper insulated vessel.


We use one of the 800 gallon of these to heat and hot water for our 2700 sqft house with our indoor wood boiler, it holds enough thermal mass so we only run the wood boiler once a day even in the dead of winter in NH.

in the shoulder season we can run the boiler once a week for enough hot water for all our needs.

upfront cost is a bit high but is a great setup once all the quirks are worked out.

but wont you run into more issues in the summer months when PV output will be greater? Why generate heat in the summer?
 

Leon

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If you don't find anything here, you can see what the hydro and wind guys do.

Unlike solar which only provides what is needed up to as much as the panels can pull, hydro and wind can't limit the power that is pushed. They have a system of voltage dumps that dump the extra power that is not used on something. I have "A Wind Turbine Recipe Book," and the windmills use a load controller to dump the excess energy as heat.

This series of videos covers a low budget arrangement.
 

FilterGuy

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Does someone know how you'd set up such a system?
The biggest challenge is getting a signal to indicate the battery is full that you can use to turn on the alternate load. I don't know a good way to get that from the Victron MPPT controllers. (There may be a way to do it with the Victron Venus or the Cerbo.... but I am not aware of it)

The previous post from @Leon shows a way of doing it using the Battery Voltage as a proxy for state of charge. It is a nice solution that manages the various corner cases and allows the load to be on the AC side of the system.

I have heard of people using a voltage sense on the battery that turns on a relay that diverts the solar output. If the resistance of the diverted load is close to the optimal resistance for the panels, you don't necissarily need another controller. However, if there is not a good match between the load and the solar, the panels will be opperating at a sub-optimal power point so you may need to put a 2nd SCC in the diversion path.
 

Hedges

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You could sense PV voltage. When it is above Vmp, less than 100% is being harvested. Varies a bit with temperature, but could be reasonably accurate.

The way I might do it is sample PV+ and PV- with resistor dividers. Compare that voltage to a setpoint from a potentiometer. Use it as input to a servo (PID, etc) circuit controlling a heavy duty light dimmer. That controls power delivered from inverter AC output to heater.
 

rhino

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The biggest challenge is getting a signal to indicate the battery is full that you can use to turn on the alternate load
I have the Victron BMV which is returning the SOC of the battery so would at least have that.

Use it as input to a servo (PID, etc) circuit controlling a heavy duty light dimmer. That controls power delivered from inverter AC output to heater.
This looks like interesting idea.. I'll look into this. I can keep it simpler by using large DC resistor(s) so no inverter would be involved.

I agree with others that heating water would be good use but I really need it to be able to heat my basement since there is no heat source there.
 

Tecnodave

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This has been done for many years, its called load diversion. I have been doing this for years, when my large format flooded lead acid batteries are nearing full charge i use a diversion controller that diverts excess power from the batteries to a dump load. Everything is direct DC as resistive loads will use either DC or AC but DC diversion is much simpler. The input of the diversion controller is the battery bank and the output are resistive water heating elements. The diversion controllers sense the batteries only, they do not connect to the panels. This is far more commonly used for hydro power as a method of controlling the system voltage.

I have two rather large systems with MidNite Classic 150 controllers with about 2.4 kw. solar on each system charging two sets of L-16 batteries at 28.8 volts, 426 amp hour. The diversion controllers are Trace C-40 controllers that can be configured as a PWM controller or as a Diversion controller, it works in PWM mode doing either function. It can divert up to 40 amps to a resistive load. These controllers feed low voltage DC water heating elements, which are commonly available.

There are 4 total controllers, 2 each MPPT controllers that charge the batteries from the solar and 2ea. PWM diversion controllers that shunt the excess battery power to heat water. The diversion controllers do not communicate with the battery charging controllers other than using the output of the MPPT controllers at the battery.

The water heating elements that i use are 12/24/48 volt elements that are universal pipe thread same as standard water heating elements, I bought them from Northern Arizona Wind Sun....NAWS...solar-electric.com, they are also used in cattle farming to keep cattle water troughs from freezing..
It was not plug and play, it takes a bit of work to get the systems to balance out.

I beleive the Trace C-40 line of controllers are still available, Trace was bought by Zantrex which was bought by Schneider Electric. In any case there are many used C-12, C-20 and C-40 controllers out there. They were the mainstay for many years until MPPT was developed.

Most chinese PWM controllers will not be capable of diversion mode, it must be designed in. Unlike MPPT and PWM battery charging controllers which regulate the OUTPUT voltage the diversion controller regulates the INPUT voltage.

Like i have mentioned this is widely used in micro hydro and small scale wind power as a means of regulation system voltage.

Much more on this topic can be found on forum.midnite.com and on solar-electric forum
 
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Leon

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I have the Victron BMV which is returning the SOC of the battery so would at least have that.


This looks like interesting idea.. I'll look into this. I can keep it simpler by using large DC resistor(s) so no inverter would be involved.

I agree with others that heating water would be good use but I really need it to be able to heat my basement since there is no heat source there.
So water heater + radiator?
 

Tecnodave

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I use a standard water heater tank meant for domestic hot water with two 1600 watt low voltage elements for domestic hot water and at one location used a small circulating pump connected to a automotive heater core custom configured as a space heater. Currently i use only domestic hot water. Im right on the edge of a very big pond...the Pacific Ocean and as such have very soupy weather at times thus the rather large solar system that can withstand 10 days of pea soup air. This time of year we get “June Gloom” where we will have days on end of fog/clouds, etc. Obviously the hot water will not happen when i have days of in-climate weather, the electricity is more important, I use a propane gas “flash boiler” heater to boost the sometimes luke warm sometimes frigid cold solar heated water.
 

efficientPV

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I do it. Sense the PV voltage and when it goes above power point it proportionately diverts power to a heating element enough to bring the voltage to juat above the power point voltage of the panels. No charge controller of batteries are involved, just direct power from the panels to the heater. You always have full battery and not unnecessarily heating up CC. DIVERSION FROM BATTERIES IS NUTS. I can divert as little as 5W. The ACTii AC7391 can do it in fixed mode but it is limited to about 8A. I use my own design for 12A diversion up to 200V (120V array). Two wires in, two wires out and set the voltage.
New_HW_Garage.jpg
 
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