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

[Roil]

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

Let's see then

[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.

[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.

[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.

[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)

[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

[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

[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

[inetdog]

Hi Olberg

What is an "arduino"?

Anders

Anders:

An arduino is a small computer which is designed by some folks in the open software community. It is very inexpensive and easy to program compared to industrial process controllers and there are a wide variety of input and output adapter boards for it to allow you input almost anything that can be measured and control almost anything that can be controlled by a logic signal, a relay, or an analog voltage.
You can get assembled arduinos in a variety of price ranges and capabilities, or build you own.

Check the internet and these forums and you will see, for example, people who are giving away software written for the arduino which can interact with Modbus, Canbus and other inverter/charger control protocols.
It does help to know at least the C programming language if you are going to set it up on your own.

Olberg:

One obvious choice would be to drive a solid-state relay that has optically isolated control inputs. You could also drive a standard relay for on-off control of the opportunity load.
If you want to do proportional control, you could use a solid state relay or SCR/Triac circuit that is controlled by a pulsed waveform.
If you want to switch DC to the load, you will have a harder time, since you need to find DC rated switches that can interrupt the current on their own instead of AC rated switches and relays which count on the current passing through zero 120 times per second.

[Roil]

Now we are talking - yes please one of those.

By pulling the details from your controller, you case CANBUS, my case MODBUS (Tristar), and wright a software capable on computing how much power we can pass on to the opportunity load.

Sounds great.

I struggle to understand your last part, but it sounds likt it is better to let the load be AC thus making it possible to be fully variable? Did I get it?

[inetdog]

I struggle to understand your last part, but it sounds likt it is better to let the load be AC thus making it possible to be fully variable? Did I get it?

You have found the essence of what I said.

[Stu]

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

I really haven't looked into the other controllers so have no idea if they also support this. The outback is specifically designed to interface to a solid state relay this way.

I went with one of the recommended relays in the post I read, it is the HDD-1V50E-HS1.0
For my setup I have 600w panels, but only about 500w of "free" energy max at float so the 50amp rating was good for my 12 volt 600w heating element. Using higher voltages for the heating element would probably allow you to get away with less amperage required of the relay.

You can see/purchase it here:

http://www.power-io.com/products/hdd.htm

I know there are cheaper versions on ebay etc. but with all that current I decided to go with what looks like a pretty solid unit.

I got the one with the heat sink already attached. improper heatsinking of these things seems to be the greatest source of failure. The one it comes with is huge! I notice though when operating at max output it does start to get a little warm so sure wouldn't recommend doing without it.

Even though the relay goes directly to the Outback AUX jack, I have placed a low voltage mechanical relay between them so that the arduino can control whether the heater is on or not even if the outback is putting out the signal. This lets me turn it off if the water gets too hot.

[Stu]

The Arduino is a pretty handy unit for controlling a system if you like to write software and dabble in electronics.

Mine has a wifi board attached and sends sensor data to the internet through Cosm which I interface to a web page. Fun to be able to monitor the system anytime/anywhere. My system is pretty small and just intended for learning so I like to watch it work. It just powers my one room home entertainment center. You can see the data in real time here if interested:

http://www.4sightinc.com/stu/Solar.htm

Note the water temp reading from the heater is down lower on the page, we have had two cloudy days in a row now so water is getting a little cold!

[Roil]

Anders:

Olberg:

One obvious choice would be to drive a solid-state relay that has optically isolated control inputs. You could also drive a standard relay for on-off control of the opportunity load.
If you want to do proportional control, you could use a solid state relay or SCR/Triac circuit that is controlled by a pulsed waveform.
If you want to switch DC to the load, you will have a harder time, since you need to find DC rated switches that can interrupt the current on their own instead of AC rated switches and relays which count on the current passing through zero 120 times per second.

I have done some search for a proportional control unit. The all seem to have a cyclic time from around a minute up to half an hour. If load is set to 50% it sounds like the full load is connected half the time, so 30 sec full load, 30 sec no load. Am I lost?

[Olberg]

pwm.gifStu: Fantastic with web monitoring like that. Something I certainly will look into after I’ve installed my system.

Stu, Inetdog and Roli:

I´m still a bit in the dark here but perhaps you guys could help shine some light and fill in the gaps:

Am I thinking totaly bonkers or could perhaps the solid state relay Stu’s using (lika a HDD-06V75) be controlled directly with PWM (analog pin) from the arduino?


Arduino: 5V max 40mA
SSR: Min turn-on voltage/current 4.25 VDC / 10 mA


When it comes to controlling the load:

Arduino:
Arduino's PWM frequency at about 500Hz, the green lines would measure 2 milliseconds each. A call to analogWrite() is on a scale of 0 - 255, such that analogWrite(255) requests a 100% duty cycle (always on), and analogWrite(127) is a 50% duty cycle (on half the time) for example.

SSR:
“High frequency switching test: 100% of relays are tested at 15 kHz, @ 50% duty cycle, @ 10V or greater control input, at >10mA, and a 10 volt or greater dc load. This generates a PWM switching speed of 33 microseconds "on" and 33 microseconds "off" or 15,000 ons and offs per second. With a strong control input signal, this provides: 15kHz PWM speed in the HDD-06V75 to HDD-6V15 models”

Is the 15kHz rating a maximum frequency and if I send a PWM @ 500Hz it will work?
Can a immersion heater be a PWM load?
Will the SSR work like a proportional control when used it in this way?

All the best
/O