using excess power to heat water (For Dummies)

[kauaisolarman]

Hello

i have been trying to read on how to use aux to hook up a water heater and use excess PV power to heat water instead of wasting it during absorb and float stages of charge.

after reading and reading i think i understand the concept of hooking up the water heater:

I understand that i can hook up Aux 1 to a SSR and set the diversion settings in the aux 1 control and tell the SSR when to turn on and off depending on my specific voltage settings.

i think that SSR i need to use depends on the heating element i want to use. (this is where i get confused and am not sure to determine how to size/pick the correct heating elements.  im not exactly understanding the ohms thing involved)

am i getting those correct?

i however cannot understand how i can regulate the excess power while in absorb mode.

for example;
my system has enough power to complete a full absorb cycle. At the start of the absorb cycle the required power is 30.5V @ 31A = 950 watts.  my system can produce 1.5kw in peak sun so i have about 550 watts of excess power when the absorb stage starts (obviously more as absorb goes farther along).  problem is once the clouds come out i drop below the 950 watts and come out of absorb.  i cannot understand how this would work with the SSR. will the heating element only pull the "extra" power that the absorb stage is not using or will it start trying to pull power off the battery bank also dropping the voltage? and if so wouldn't that just keep taking me out of absorb and not letting me complete a full charge cycle?

thanks

[sigp2101]

Another dummy wants to know

[ClassicCrazy]

There are some settings in AUX called Waste Not that may be what you are looking for  - you may want to search the forum for WATER HEATING and also using SSR with AUX and search for Waste Not too.

Lots of past discussions on these  topics that will give you some detailed information.

Larry

[kitestrings]

ksman, sigp,

We've been preheating water with "opportunity load" with our Classic and a 3.2 kW PV array for several years now.  It works very well in the summer period especially for us.  We're using a 40 gal Marathon tank, with 1,200w 48VDC elements.  We replaced the stock elements with DC elements and pulse those elements via SS relays.  My preference is to use Aux2, if available, and use the Waste Not Hi feature as Larry suggests (aka 'use-it-or-lose-it, you might google that too).  This lets you program settings relative to your normal charge settings, allowing the typical 3-stage charging to be maintained.

Some cautions - the stock thermal/discs won't break the higher DC current, so don't try that.  You'll want 24V elements if that is your bank voltage.  DC breakers need to be sized for the wire & elements, and solid state relays need to have heat-sinks or they will not last.

One suggestion you might also consider is to raise the temp settings on the tank.  The allowable upper limit temp for this tank is 170F.  If you put a mixing/tempering valve on the outlet it allows you to effectively store more BTUs when available.  This goes against conventional thinking - to avoid mixing cold, and unnecessary heat losses we normally set lower ~120F) - but with PV/diversion the energy source is free, and otherwise untapped.  Ours goes to a LPG instantaneous water heater and we set the outlet temp from the Marathon to meet the max inlet to the LPG unit.

Here is a couple of albeit dated links, but offer some good descriptions of the goal & logic:

http://www.fieldlines.com/index.php/topic,130053.html
http://outbackpower.com/forum/viewtopic.php?f=29&t=2865&hilit=electron&start=25

There are other ways.  This is only one.  Good luck, ks

[kauaisolarman]

thank you again for all the replies.

So i have been reading more and my next question would be:

Why choose Aux 2 (waste not PWM) vs Aux 1 (diversion)?

I have whizbang Jr on Aux 2 and dont want to have to remove it.

i seen another post where they switched from using aux 1 diversion to aux 2 PWM so that they could utilize full PV power even when in absorb mode but i cannot understand why they did this and why it cannot be done with aux 1 and diversion.

i would like the dump load (water heating elements) to always be able to use the excess power when available even when in absorb mode, but i dont want it to take away power and limit the absorb charge (only want it to go on when there is excess power and not take anything from the batteries).

any explanation on why using aux 2 waste not is better than aux 1 for this kind of application

[kitestrings]

Aux1 will work.  The main difference is that Aux1 is a relay action (on- or off), whereas Aux2 uses pulse width modulation (PWM), so it can pulse much faster (hundredths of times per second I believe).  There's a pretty good explanation in the Classic manual, in part:

Aux 1 diversion mode is similar to Aux 2 diversion mode except that it does not PWM, Pulse or buzz at
hundreds of Hz rate. Instead, Aux 1 diversion goes Active at or above the "High" voltage setting, after a
programmable "Delay" time, and goes Inactive when the voltage drops below the "Low" voltage setting
after a programmable "Hold" time. These Delay (or Attack) and Hold times are adjustable in 0.1 Volt
increments.

Our experience has been that Aux2 is more responsive and yields a bit higher "harvest" of available energy.  With Waste Not, it is working relative to your charge settings and only burns off what's available above the battery needs.

~ks

[kitestrings]

Here's a bit more up to date discussion on some of our experiences with both Aux1 & Aux2.  I'm sorry I couldn't recall where this was posted yesterday.  Maybe something of use:

http://www.fieldlines.com/index.php/topic,148575.msg1032997.html#msg1032997

[kauaisolarman]

thank you for the reply kitestrings.

now i can understand the difference between using aux 1 and aux 2.

next question would be abut using AC heating elements vs DC heating elements. I understand that when using the AUX 2 PWM a DC element is preferred because of the rapid on/off state of the element.  Is there any way i can use aux 2 PWM with AC?

only reason for asking is my how water tank is about 40-50 feet away from my battery bank and i dont want to have to run large wiring if i don't need to.

another question is if you were to use aux 1 diversion is there any way to get it to go into divert only after float has been reached?  reading the ouback forum it seems the newer outback controllers have this option.  only reason is my folt voltage is 26.7V and absorb is 30.5 so if i set the diversion voltage to the float voltage it will start diversion before reaching the absorb stage.

if i cannot get the PWM aux 2 route to work i would like to know if there is a possibility to divert in float mode only?

thanks again.  really helpful info.

after i gather all info needed i will try to do a step by step so others can know exactly how to accomplish this.

[kitestrings]

In my mind the biggest reason for using DC is that with AC your tying up more capacity from your inverter, and adding losses which may be be of lesser concern. I'm old school but prefer not to put loads thru the inverter that can be served directly.

I'll defer to others on the float trigger. It may be something that's been added, I just don't know.

Lastly, a guy named "Crewser" wrote a similar white paper if you look for it in the OB thread above. We started this on an OB MX60 and transitioned over to the (superior;>) Classic.

~ks

[ClassicCrazy]

If you wait until it goes to float you could be missing out on a lot of available power  - since it takes a long time to get to float and the current cuts down so much.

Most people don't use AUX 2 because they have a Whizbang on their system. It will give you a much better understanding of your battery health and also control. If you have the Whizbang there are AUX settings that let you turn on a load at for example 90% SOC  and off at another SOC.  If you have Whizbang you can set up ending amps to terminate your absorb instead of using time.

What kind of batteries do you have ? I have lead acid 24v system and 30v is my equalize voltage . Why do you have your absorb voltage set at that ?

Larry

[kauaisolarman]

thanks again guys.

I don't mind running AUX 2 PWM with AC off my inverter as long as its ok for the inverter going on/off like that to satisfy the PWM pulses. (i thought that was the main reason for going DC?)

I am running a set of Interstate GC2 batteries from costco setup for 24V 416AH checked everywhere online and even called interstate to verify the charge voltages.  i am currently using the WBjr to end absorb at 8amps as specified by the manufacturer.

can i run a SSR (AC/DC W/PWM) and WBjr off aux 2 at the same time?

will the PWM SSR Aux 2 route work with 2 CC in Follow Me?  i know kitestrings has a 2 CC setup but from what i can understand from reading the other forum posts the issues are from the wind part of the setup.
if i have 2 CC with 2 seperate PV arrays  doing follow me (to my 24V battery bank) will this AUX 2 PWM SSR "waste not" mode (so you can allow excess dump while in absorb and float mode) work and dump the excess from both seperate arrays? 

[kauaisolarman]

If you wait until it goes to float you could be missing out on a lot of available power  - since it takes a long time to get to float and the current cuts down so much. just wanted to know if that was an option.  ideally i want to setup AUX 2 PWM "waste not" with SSR so i can start using excess power during the absorb stage and not take away from battery charging

Most people don't use AUX 2 because they have a Whizbang on their system. It will give you a much better understanding of your battery health and also control. If you have the Whizbang there are AUX settings that let you turn on a load at for example 90% SOC  and off at another SOC.  If you have Whizbang you can set up ending amps to terminate your absorb instead of using time. if i dont use AUX 2 with the above stated setup how will it just use the Excess power while in absorb mode?or is that not possible with this route

Larry

thanks for the input

[ClassicCrazy]

You can only use Aux2 for Whizbang or for controlling - not both at the same time.

I looked up your batteries and the manufacturer does say to have those voltages that high .  That is much higher than most other battery manufacturers have for their batteries. Interesting .
http://www.batteries-faq.com/activekb/questions.php?questionid=1

Larry

[Westbranch]

A question:  In a multiple Classic system on the same battery bank, is it not possible to use the Follow Me and use the Aux2 in the slave to run the opportunity load?

[kauaisolarman]

yes my thoughts exactly.

is it possible to use AUX 2 "waste not HI/opportunity load" on the slave CC in a follow me setup on the same battery bank?  will the opportunity load be taken from both the different arrays that the CC's are hooked up to or will it only get opportunity load from the CC that aux 2 is being used?