Author Topic: Diverting excess power from Solar PV to a heater - immersion controller  (Read 345 times)

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Offline RFburns

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As I am on grid and only get about 8 cents per Kwh for feed in ;I have been looking at using my excess to heat my hot water (instead of the tariff 31) and came across this

http://www.mk2pvrouter.co.uk/33001.html

.Thought it interesting enough that someone else maybe interested . Yes there are various commercial product's available for this Iboost +, Watterson Optimmersion controller, WATTrouterEco (appears to be a programmed PLC unit), Solax, Gem, Immerson, Solic are a few that I have come across before finding a real  DIY unit.

 for a monitor  have a look at this https://github.com/openenergymonitor/emontx3
Get With It ,Get Over It , Get On With It ...Or Leave

Cheap and reliable wont be fast.
Cheap and fast wont be reliable.
Reliable and fast wont be cheap.

Offline fourtytwo

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Interesting products. I am also on-grid but coming at it the other way around having installed PV for water heating I am now in the process of adding a GTI to burn the surplus in the house! I was thinking of monitoring the grid export also to control my GTI to minimize export as I wont get paid for it and it will add to wear and tear on the system. There are so many possibilities for the fertile mind :)

Offline eidolon

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The HotShot program was undertaken by several utilities to monitor the effectiveness of heat pump water heaters at reducing peak KW demand on the grid.  It found the major demand from water heaters was 6-8an and 7-10pm.  The lowest use was around noon when solar output is peak.  Timers have been used to lock out tank heating at these times and encourage heating mid day.  From my own experience with heating 30 gallons of water, 3KWH is not a lot of energy that can heat water. A greatly oversized tank and elevating water temps gives a little more margin.  Use of a tempering valve to control temperatures of course is necessary. Adaptive systems that learn your usage will be key in evening out demand. Just monitoring back feed won't be enough if the dump isn't sufficient.

Offline RFburns

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Hi Eidolon timer/contactor are certainly the cheapest option ;peak demand is regulated by the energy company for tariff 31 - from supplier

"The Economy Plan can be applied to suitably sized electric storage water heaters, solar-electric water heaters and heat pump water heaters. You can also use this tariff for other domestic loads such as swimming pool filters, water bed heaters and some freezers, provided they are permanently connected. Electricity supply is available for at least 18 hours per day and is switched via load control equipment supplied and maintained by ENERGEX. The times of supply are at ENERGEX's discretion. On some days electricity supply may not be turned off at all."
All usage - cents per kWh  21.956    

My initial idea is to install some sort of efficient diverter, monitor the result and if this work's O.K move to traiff 31 ;as the GTI already supplies the house and I only get 7 cents per kWh for export. This looks like a good/efficient way of maximizing my solar usage without behavior/system modification .
  Not sure what your reference to 3kWh is (maybe thats all you are allowed?) here we are allowed to export 5kWh maximum; but the system can be any size (10Kw systems retail for $6k here 40 x Tier 1* 265 Watt ET brand panels,A Zever brand inverter A 25-year warranty on the panels and a 5-year warranty on the inverter) and most of my excess is when no one is home to use it which would be the same for most working people I guess.

"This is the cheapest tariff available for water heating. This is because the electricity supply is available only at low electricity-demand periods, such as at night when generators would otherwise be idle. Electricity supply is made available for a minimum of eight hours per day at times set by the network owner (ENERGEX) at their discretion, generally between the hours of 10pm and 7am. On some days electricity supply may not be turned off at all".
All usage - cents per kWh  15.865
Get With It ,Get Over It , Get On With It ...Or Leave

Cheap and reliable wont be fast.
Cheap and fast wont be reliable.
Reliable and fast wont be cheap.

Offline DJ

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Very interested to do the same sort of thing only with a prebuilt unit. For what they are these things seem very expensive. 

I'm wondering if something could not be tied together with prebuilt Chinese boards or something SIMPLE with an arduino that didn't require a circuit board of it's own to be constructed but rather relied on pre built boards wired together or the built in features of the arduino itself.

While everyone says it's inefficient, I'm also thinking about actually trying to direct wire a couple of arrays to a HWS going a little over voltage on the array and using 2 in parallel to keep the amps up without over shooting the voltage too much on the bright sunny days. I believe for something like an element, thee is a fair bit of tolerance for over driving anyway so if one did set it up to be somewhat over voltage on the brightest days it should still fall back to producing good output on the not so bright days.

Once the heater was up to temp, I believe the local units here have a thermostat available for twin element heaters that first run the top then the bottom element. Using one of these on a single element setup would give an automatic " Changeover"  to divert the current elsewhere when the heater was up to temp.

Offline RFburns

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I think that IF you have the programming skills that the PLC avenue would provide everything either already assembled or available as din modules -simple and reliable but as these are industrial units not necessarily cheap .This however is well beyond me  :'( (still wrestling with arduino  ::) )   
 My hot water unit is a single element with a thermostat
Get With It ,Get Over It , Get On With It ...Or Leave

Cheap and reliable wont be fast.
Cheap and fast wont be reliable.
Reliable and fast wont be cheap.

Offline eidolon

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The Arduino is a very powerful device for control.  If you can load the compiler into your computer and download a BLINK program, you got it made.  I have a real problem with most of the programs found on the internet.  The style of writing is far to complicated for most to understand for almost a one time application a user may have.  I've been writing demonstrator programs for beginners.  The use a boilerplate
setup.  Then the user only has to add or modify applicable code.  I refuse to include do loops, arrays, and other code that doesn't follow intuitive English. each line of code stands on its own.

read voltage
if voltage higher than setpoint turn on
if voltage lower than setpoint turn off
delay  (to prevent rapid cycling)
go back to beginning

There is a lot of power in just those few statements.

Forget displays.  I have a blinking LED for my entire house. From 20 feet away I know the state of battery, hot water and refrigerator. Most of the hard work is done for you with ready made routines.

In my water heater I have to heating elements. One turns on first.  When that gets to a set temp it switches to the other.  If available energy, both turn on till a very high limit is reached.

There really aren't modules that will work with a water heater on ebay, but building one only uses four parts.

Offline DJ

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I'm super advanced!
Not only have I downloaded the Blink routine, I modified it, coupled the nano it's on to a Voltage controller and the output to a relay which drives a pump and the thing now ( for several months) runs my aquaponic watering system with a small solar panel charging a battery!  Woo hoo! Worlds most over complicated electronic basic single stage cycle timer. The next step is to put in a light sensitive switch I bought to turn the pump off at night and wait till day to re activate. I'd also like to put in a soil moisture sensor but the loads of them I see on fleabay look fine for a dip in a glass of water for a demonstration but clearly aren't going to last a week in a hydro system or probably any other garden.

Also modified a program to give variable pulsing of an LED bar light to give my neighbors some of the hell they have caused me and to pulse a fuel injector to hopefully control an Oil burner.  That's about all I got so far.
Solar power control is something I really want to use these things for but keep coming up short on info I can use at my (low) level.
If I could find an AC voltage sensor like the 5V output 0-25V DC sensors I'd probably be able to hash a lot more together by myself. An AC voltage sensor seems a crazy omission from the range of accessory boards to my way of thinking!


I find the hardest thing ( and biggest piss off) is people share their code but not the schematic. I'm F.. buggered if I know how the hell I am supposed to figure out the components and wiring by looking at the code? Clearly If I'm too ignorant to figure it out, I'm not going to be able to learn it by NOT being able to build it. OK for those geniuses ( and people competent in electronics ARE geniuses in my esteem) that know what they are doing but for the rest of us enthusiastic plebs, it's pretty much a brick wall. I have looked a lot and can't find anything that says " How to figure out the components and wiring from Arduino code. "

I would certainly like to see how your heater controller works as far as the full thing, code and schematic.  I'm barely smart enough to work out a wiring diagram but can struggle through a schematic, not far enough along to backward engineer the code.

Offline eidolon

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I have a general problem with that. If someone just copies what I do, they don't have the ability to repair or tailor it to their exact needs, all advantage is lost. My camp system is quite complex operating a half dozen devices with multiple control loops. I can break parts of it out, without actually testing  I can never be sure they are fully functional. I am only in the development  phase when at camp about three weeks from now for the next couple of months.  I can tell you I'm working on a universal board right now that will support many of my core programs like refrigerator, MPPT controller, linear current booster for running a pump without a battery, and water heating. My system currently runs on multiple arrays the highest voltage string is 36V.  I am going to buy 3 grid type panels so I can test without interrupting my home system. I will make all these programs available as they are verified.

If you use the micro for only heating water you are wasting the power of this device.

Here is the basic concept of my water heating.  A capacitor bank is used to short term store energy from the solar panel. When I mean short, less than 1/100 sec.   This is the premise of every power supply, storing the peaks of every cycle to supply power in the valleys.  Multiple capacitors are used because general consumer capacitors are limited in ripple current to less than an amp. This current causes heating of the capacitor which shortens life.  More caps, the less current in each cap, less heating and longer life.  This is the same principle that the techluck works on.  They only have three caps and they will not last long.  If someone has this system add an external capacitor bank.  Solar panels are current sources.  That current will add to the capacitor current and you can have peak current at the MPPT voltage for the given resistance it is connected to.   That power is dumped with PWM for a duty cycle, 5% to 100% depending on how much current the panel produces.

This is where the arduino comes in.  It measures the voltage on the capacitor bank and a simple decision is made, is the voltage higher or lower than the setpoint. It has an analogWrite function to create PWM duty cycle 0-255.   So a simple counter is used that increases or decreases the count depending on voltage read each loop.  The loop is slowed down so the system has a chance to respond.  More than fast enough to respond to clouds.

I count up to 3 X 255.  The first 255 turn the first element on.  If the number gets larger the second heater is also turned on.  When top  heat is high enough the first heater is turned off and all energy goes to lower second heater.  If that turns fully on, the top heater begins coming on again until the high limit temp is reached.  Then a small PWM is enabled equal to tank heat loss.

The power electronics is quite simple.  I use opto isolators for voltage level shifting.  The micro is 5V and that drives the LED through a resistor.  The transistor of the opto pulls the gate up to 12V.  Those data sheets always give the resistance with at least 10V of drive. They need to be slammed hard to pass current without heating.  Optos are slow, the reason we drive them at low frequency. Trade off is a bigger capacitor bank (not that big or expensive) for non critical part layout, no EMI, and minimal parts. Here is the basic schematic of the heater driver.  My fingers are getting tired.

Offline lighthunter

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Hi all!,  just in case anyone has need.  I finally found an affordable DC rated relay capable of switching up to 400v safely.
I first found the relay on ebay for $38 usd but later noticed another supply has them for $20. Some places charge as much as $180.  Panasonic makes it. The contacts are chamber nclosed and gas filled with a permanent magnet to the side to extinguish the arc. Seems to work good for me. I wanted for remote control of array power in case of fire anyone can disable utility and solar from one location. Could also be used to switch or divert an array for power controlling.

**Edit**
The aaa bat is just for size reference. The relay coil is 24v and current measured by vdrop  4v on 100r with 24v on coil = .96w coil pd @24vdc.
LH

Offline eidolon

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That's good to know.  And it is battery powered! 

I wish those ET modules were better as far as speed. They literally have a LED inside and a solar panel to create FET gate voltage. As such they are fairly slow speed and I wonder if they will burn up if placed on a Midnight diversion output.  I made some isolated FET switches with an opto isolator driving a 100K resistor for gate drive.  Used a 9V battery for gate power.  So little current the battery lasts its shelf life.

Offline MadScientist267

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Gate drive for FET (unlike base drive in bipolar) only uses current when it's changed. In effect, you're charging a capacitor. You could (and should) replace that 100k with something of much lower value so it switches quickly. Opto may be slow, but 100k at the gate gives it a run for its money, you can bet on that  :o

Also, there's no reason to use a "solar panel" inside the confines of an optically controlled switch in the way you describe... The reason semiconductors are all encased in completely opaque material in whatever form it takes (typically an epoxy), isn't just for physical protection from the elements and structural support... it's because they are directly sensitive to light in and of themselves.
Wanted: Schrödinger's cat, dead and alive.

Offline eidolon

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You are obviously not aware of the VOM1271 which creates voltage to drive a FET and is likely similar to what is used in many of the FET modules.  They are slow turn on,but turn off is shortened.  Many other devices use the principles you talk about.  Solar panels are just big crappy diodes. Even a LED generates voltage.

One time transitions generally aren't a problem with a FET.  It's quick and dirty.  You could add a 4049 tied in parallel as a driver.  Do they still make those?  Everyone should burn up a few FET to get an education.