Utilizing excess energy from solar panlel - not a dumpload question ;-)

[Roil]

Interesting thread!

I can send this to an arduino and write a algorithm for when and how much energy use.
But then what?
What kind of controller should I look for to divert the energy to my “opportunity load"?

Hi Olberg

What is an "arduino"?

Anders

[Roil]

It is very rewarding to see the panels generating their full output while the battery is only taking a fraction of it! Happy to share more details if anyone is interested.
Stuart

Hi Stuart

Nice solution - Outback got it then!

I am looking for the same reward

Should I swap controller then? - hmm

How about some pics and specs of the solid state?

Anders

[Stu]

If you have an Outback FlexMax controller it is pretty easy to do. I have mine set up heating hot water whenever controller is in Absorb or Float. The cool thing is that the controller sends out a PWM signal in proportion to how much extra power you are generating and insures the proper charge voltages are maintained to the battery. For example, when Absorb just begins the heating element only gets a very small load, then it gradually increases as battery reduces its draw from the charger. I have had this set up for about 2 weeks now (in a large bucket of water!) and am now in the process of hooking up a second water heater as a preheater to my gas unit. I have a 12v heating element and am just replacing the 110 volt element that the water heater came with.

There is a great writeup on the details below and I basically followed it exactly. You just connect the PWM signal to a solid state relay (with serious heat sink!) and the controller takes care of the rest. Maybe other CC can do the same?

http://www.outbackpower.com/forum/viewtopic.php?f=29&t=2865&start=25

It is very rewarding to see the panels generating their full output while the battery is only taking a fraction of it! Happy to share more details if anyone is interested.
Stuart

[Olberg]

Interesting thread!
I’m also interested in using the overhead energy (opportunity load) which otherwise would be wasted.
I would like to do something similar to Roil, also in the winter months when my inverter is switched off.

My Victron MPPT Blue Solar 150/70 regulator sends these messages through its Canbus:

Battery voltage
Battery current
Battery temperature
Charger on/off will
Charge state (Bulk, absorption, float etcetera)
PV voltage
PV current
Equalization pending
Equal. time remaining
Relay and alarms

I can send this to an arduino and write a algorithm for when and how much energy use.
But then what?
What kind of controller should I look for to divert the energy to my “opportunity load"?



__________________________________________________ _____
8x 190W panels (Jinko JKM190M) 1520W at 72V
Solarcharger Victron Blue Solar 150/70
640Ah of Battery power (16x L6V160 Marathon AGM)
Inverter Charger (Victron Multiplus 24V 3000W 70A)
Old military genset 15kW (VW beetle motor from the 60s)

[Roil]

A small progress report.

Spring is in the air, night temp is minus 5-10 Celsius and I am trying to use excess energy to keep the bath room above freezing temp.

It's partly manually for now, but it looks like I would be possible to automate it with the help of a PLC and the use of MODBUS/TCP

Set-up is as follows:

- Victron 220V 3000W
- X-300 Controlbyweb - control unit
- Tristar 60 MPPT
- 550W panel capasity

The X-300 can start and stop the inverter manually or based on a temp sensor in the bathroom, On the 220V side the only consumer is a 220V heater set to 200W (max 500W).

When the temperature drops during night the X-300 switch on the inverter and the heater heats the bathroom. When the room temp has increased approx 5 deg, the inverter switch off. As the sun "wake up" the batteries are charged by the panels and approx 1000 Watt hours is consumed for this purpose. As the Tristar charger leaves the bulk charge and switch into absorption I pay attention from my remote location (using the Tristar web interface) and when absorption watt (A x V) is reduced with 250W I turn on the X-300 relay manually - still remotely. This secure that the batteries has priority and get as much charge as they can take, and the 200ish Watt of the excess energy is used to heat the bathroom. This daytime heating of the bathroom above the minimum temp works like an extension of the battery and "stores" energy in the form of heat. Approx 1000-1500Watt hours goes into heating of the room. Because the heater consume 200w static I miss around another 500-1000 Watt hours that could have been utilized.

So.........

this is not much you say, and in addition it's manually!

Well - next step is to do this automatically, and I believe it can be done. Both the Tristar and the X-300 can be controlled using the MODBUS/TCP standard and a PLC can be programmed to do exactly what I do manually. Any inexpensive PLC suggestions is highly appreciated. I might start by using my Iphone and a free PLC Modbus app

The only missing element is that my heater can not be remotely adjusted to different heat level. 100W, 200W, 300W, 400W and 500W. A variable MODBUS controlled unit would have been nice.

[inetdog]

This is a bit beyond me, but I know the Midnite 150 charge controller (and its siblings) has settings to divert excess energy (essentially by having a third-party gizmo, such as a solid-state relay [etc]control some device, such as a load, be it AC or DC).

So folks have thought of your issue.

A simple on-off signal to control a relay will not do what is needed to exactly match the available power. But if the output is instead a relatively high frequency pulse-width modulated signal, then that could be used in conjunction with a solid state control to continuously regulate the power delivered to that opportunity load.

[Vern Faulkner]

This is a bit beyond me, but I know the Midnite 150 charge controller (and its siblings) has settings to divert excess energy (essentially by having a third-party gizmo, such as a solid-state relay [etc]control some device, such as a load, be it AC or DC).

So folks have thought of your issue.

[Roil]

Some of the designers visit this forum, so you may get some feedback from them.

Let's see then

[inetdog]

My wish would still be that all of this was built into the MPPT

Some of the designers visit this forum, so you may get some feedback from them.

[Roil]

If you do a google search for power management systems, you will eventually find a company that sells something to the UK market that regulates the opportunity load to exactly null out any power returned to the grid in a grid tie system. The only reason this makes sense it that the UK tarifs pay the user more for each KwH generated and used on the premises than for the same amount of power generated and returned to the grid. So the concept is around, just not apparently in the context of off-grid.
At some point the extra complexity and risk of failure is not justified by the energy saved. Also, it requires the CC and the inverter to be closely coordinated.

And that coordination is the challenge of course, thats why I believe what it takes is a MPPT controller with a built in Regulator capable of diverting the computed excess energy to a DC load, it would be impossible ofcourse to run an inverter on this energy.

The problem with a resistive load, of course, is that it has a fixed rather than a variable resistance. So you have to either control the voltage applied to it or switch the load on and off in multiple segments. The best way to deliver a variable power to a resistive load is via a DC-to-DC converter or an inverter combined with an SCR type current regulator.

This is what the Tristar PWM is capable of doing isn't it?

And, no a simple diode network cannot do this since the CC needs to be able to draw power back from the battery at all times and sense the battery voltage, while the inverter needs to see constant power or trip out from low battery voltage or overload on its output.

Kind of knew this, but the Tristar does have a separate voltage sense kabel, and if the controller would have drawn it's needed power from that connection instead of the main connection, the diode idea could have worked? The load would still have to be DC and regulated.

My wish would still be that all of this was built into the MPPT

[inetdog]

Perhaps, I have not read the entire manual. I believe these can be used in conjunction with a Morningstar tristar MPPT but read the manual and check with Morningstar to be certain.

When an MPPT controller is set up to work with a wind or water turbine, it is no longer in classic MPPT operation, and the dump load required by the turbine is usually provided separately for when the MPPT controller is not drawing enough. Maybe there is a config somewhere in the manual though.

[Naptown]

Yes but can it be done in the combination with a MPPT controller?

Perhaps, I have not read the entire manual. I believe these can be used in conjunction with a Morningstar tristar MPPT but read the manual and check with Morningstar to be certain.

[Roil]

Take a look at the Morningstar tristar charge controllers. Not the MPPT but the PWM type.
these can be used as a load controller, charge controller and diversion control.

http://www.morningstarcorp.com/en/support/library/TriStar%20Datasheet%20English.pdf

This may do what you want it to do. In an unoccupied cabin however the possibilities for an opportunity load other than perhaps running a heater of some sort is limited.

Yes but can it be done in the combination with a MPPT controller?

[Naptown]

Take a look at the Morningstar tristar charge controllers. Not the MPPT but the PWM type.
these can be used as a load controller, charge controller and diversion control.

http://www.morningstarcorp.com/en/support/library/TriStar%20Datasheet%20English.pdf

This may do what you want it to do. In an unoccupied cabin however the possibilities for an opportunity load other than perhaps running a heater of some sort is limited.

[inetdog]

Now we are talking



Using the inverter is not a bad idea but typically in an off grid solution it's not turned on, that can be acomplished ofcourse.



But still there is a problem to be able to regulate the load to match the available PV power since this is not nessesary stable.

I must admit that I am about to conclude that the Solar Industry has missed this opportunity. As fare as I can understand the only proper way to achieve this is an advanced MPPT controller with to different output's
One charging the batteries, and another being able to supply the excess power to any load we want. The load will of course have to be able to accept whatever voltage and current avalable. I guess a heater element is fine, a fan might be more difficult.

Doesn't anyone know sommeone in the industri who can have a look at this?

If you do a google search for power management systems, you will eventually find a company that sells something to the UK market that regulates the opportunity load to exactly null out any power returned to the grid in a grid tie system. The only reason this makes sense it that the UK tarifs pay the user more for each KwH generated and used on the premises than for the same amount of power generated and returned to the grid. So the concept is around, just not apparently in the context of off-grid.
At some point the extra complexity and risk of failure is not justified by the energy saved. Also, it requires the CC and the inverter to be closely coordinated.

The problem with a resistive load, of course, is that it has a fixed rather than a variable resistance. So you have to either control the voltage applied to it or switch the load on and off in multiple segments. The best way to deliver a variable power to a resistive load is via a DC-to-DC converter or an inverter combined with an SCR type current regulator.

And, no a simple diode network cannot do this since the CC needs to be able to draw power back from the battery at all times and sense the battery voltage, while the inverter needs to see constant power or trip out from low battery voltage or overload on its output.