PV opportunity hot water heating

Started by zoneblue, November 17, 2012, 12:28:10 PM

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zoneblue

Hi,

Im putting together an off grid setup at present, and the final decision is the controller. The classic seems to fit my needs generally very well. The system is an 1800Wp system servicing 3kWh/day base loads. But in addition there are large amounts of surplus energy for most of the year.

The main thing i dont understand is how to best use this surplus array output. 
The only thing i found that looks promising was this post http://outbackpower.com/forum/viewtopic.php?f=29&t=2865&start=25

How i think this should work is something like this: as the controller goes into absorb, the off part of the charging square wave turns on a second matching output FET driver that powers the hot water element directly. No external relays or SSRs required, and there would be some means to control the output via the thermostat. This way every amp is used efficiently and theres no strange feedbacks/oscillations as seems likely to occur if an AUX divert approach, and no arbitrary or unnecessary loading placed on the battery bank.

Of course i have no idea how the classic works inside and this may all be silly. Are you considering how this might be better done in the near future? It seems to me that the recent PV price drop changes the game on all this??? Whats my best bet here? Thanks.
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

cpm

I wish I had some good information for ya,

But something strikes me as seriously wrong with the universe if it makes sense to
convert sunlight into electricity to drive resistive loads to heat water.

seriously.

mtdoc

#2
Have a look at THIS thread on the fieldlines forum.

Another option (and more efficient use of PV power) is to use a heat pump water heater such as the Nyle Geyser.  I have one and it works great. Draws about 600-800 watts when running.  When running in my basement with air temp of 55 Degrees F it will take my cold water (50F ?) and heat 50 gallons to 125F in about 3-4 hours.
Array 1: Sanyo HIT225 X 8 on Wattsun tracker. Array 2: Evergreen ES-E-225 X 12 on shed roof. Midnite e-panel with Outback GVFX3648, FNDC and Classic 150 X 2. 436 AH AGMs. Honda eu2000i X 2.

zoneblue

@cpm, with pv prices falling its making more sense to design off grid solar to meet year round needs. This inevitably leaves a serious amount of power that would otherwise be wasted. If you want to get an idea how much power checkout my spreadsheet here:
www.zoneblue.org/files/stand-alone-pv-perf.xls.zip

@mtdoc thanks for that link, thats what im talking about. Ive also now read the classic manual cover  to cover. Does anyone know how the opportunity aux2 setting actually works? How does it prevent the controller constantly dropping out of float?

Guys i see this energy as a waste product. Hence i dont want to either cycle my battery bank, or load my inverter with it. Just putting it to use, as simply efficiently and cheaply as possible. If the SSR was on  the same heatsink as the controller surely it would be cheaper and more integrated.
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

Vic

Hi zoneblue,

So if you are interested in not using the battery bank as a source for this excess power,  then I assume that you are not interested in using the AC output from an inverter either.

Believe that you are thinking of using the DC from the PV array.  It is my opinion that using OFF period of the CC as the ON period to drive a resistive element in a Waterheater could easily upset the voltage regulation of the CC when it is trying to maintain Vabs or Vfloat.

Seems to me that you would need a PWM function that regulates the amount of average current doing into the resistive element.

Ths Classic does have a built-in PWM function on Aux 2, IIRC.  And believe that it must be in the Classic's voltage control loop. This function that is already in the Classic should only need a SSR to control the excess power.

Believe that this prorcess could use either PV DC,  battery DC,  or inverter AC,  with varying degrees of success.

One of the issues with trying to use PV DC is,  that finding a heating element that is tailored to the PV voltage of your system could be a challenge.  There are some elements that are designed for 12 and 24 volt DC systems.   But if your PVs put out,  say around 90 VDC  it would be too much for even two of the 24 V elements in series,  and a bit too low for an element that is looking for 120 VAC,  and so fourth.

And,  cpm,  you are correct in general about using PV electric power to heat water ...  But in a fairly well banalced off grid system,  there are many times where batts are charged,  and  water has been pumped,  etc,  and there is still excess power available.  Having yet another place for the power to go,  especially somewhere that reduces use of Fossil fuel can  be a good thing.

Just opinions,  YMMV,   Vic
Off Grid - Sys 1: 2ea SW+ 5548, Surrette 4KS25 1280 AH, 5.25 KW PV, Classic 150,WB, Beta Barcelona, Beta KID
Sys 2: SW+ 5548s, 4KS25s, 5.88 KW PV, 2 ea. Classic 150, WB, HB CC-needs remote Monitoring/Control, site=remote.
 MN Bkrs/Bxs/Combiners. Thanks MN for Great Products/Svc/Support&This Forum!!

TomW

Quote from: cpm on November 17, 2012, 05:12:49 PM

But something strikes me as seriously wrong with the universe if it makes sense to
convert sunlight into electricity to drive resistive loads to heat water.

seriously.

There are a few good reasons for doing this.

Burning up excess power is the biggest one.

I agree it would be kind of short sighted to deliberately turn sunlight into high grade electricity to turn around and use it to  create heat when you can do a relatively low tech solar heating setup for pretty cheap.

Not everything is as simple as we would like.

Just Sayin.

Tom
Do NOT mistake me for any kind of "expert".

( ͡° ͜ʖ ͡°)


24 Trina 310 watt modules, SMA SunnyBoy 7.7 KW Grid Tie inverter.

I thought that they were angels, but much to my surprise, We climbed aboard their starship and headed for the skies

boB


Another idea I have heard of, and kind of like the idea is to use extra energy to make hydrogen.

Not sure how you store that hydrogen but it could be used in several different ways I suppose.

boB
K7IQ 🌛  He/She/Me

zoneblue

#7
Quote from: Vic on November 17, 2012, 06:06:07 PM
Believe that you are thinking of using the DC from the PV array.

Yes so that the inverter capacity can remain free for base loads.  And avoiding the inverter losses, which maybe more than the DC wiring losses?

Quote from: Vic on November 17, 2012, 06:06:07 PM
It is my opinion that using OFF period of the CC as the ON period to drive a resistive element in a Waterheater could easily upset the voltage regulation of the CC when it is trying to maintain Vabs or Vfloat.

This is my point, if the controller essentially sent everything it wasnt using for charging to hot water, then all this fiddling with matching the pulse width would be a non issue.

The battery bank only has finite cycles and by guessing the AUX settings doesnt the mismatch mean you are inevitably cycling the battery more?

And the difficulty of finding the right size DC element? That would improve if it was easier to do, no?.

Quote from: Vic on November 17, 2012, 06:06:07 PM
Believe that this prorcess could use either PV DC,  battery DC,  or inverter AC,  with varying degrees of success.

You only have to read the two threads mentioned above to see how hit and miss getting the AUX/PWM/ SSR combination working sensibly is.

Im still interested to know how the midnite AUX2 works. How does it know the difference between loads and charge?  how to avoid cooking, say AGMs by long absorbs etc? By constantly messing with the load, how does it have any clue at all where the battery is in the charge process?

Anyway coming back to the OP,  are we saying that the AUX/SSR method is the current best way to achieve this?

6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

mtdoc

#8
To directly power a resistive water heating element with DC current, I think you would want to use a diversion controller like a Morningstar TS 45 or Xantrex C40 (these also work as PWM controllers). 

Just like the diversion load used for hydro or wind  systems, you would connect the diversion controller to your battery bank and the water heating element.  I believe there are several options for how the Aux port from the Classic could be set up to trigger this diversion. 

You still need to go through the batteries but if set up correctly you would not be cycling them.  Personally I think Chris Olson's method using a SSR and the "waste not high" Aux function is more elegant and probably much more efficient. With his method you are not cycling the batteries either. 

While it's an added cost to buy a heat pump water heater,  the efficiency you gain from doing so would far outweigh the small efficiency losses in the inverter/batteries. On the other hand if your inverter size is such that it can already barely handle your peak loads then your concern about overloading the inverter is valid.
Array 1: Sanyo HIT225 X 8 on Wattsun tracker. Array 2: Evergreen ES-E-225 X 12 on shed roof. Midnite e-panel with Outback GVFX3648, FNDC and Classic 150 X 2. 436 AH AGMs. Honda eu2000i X 2.

zoneblue

Quote from: mtdoc on November 17, 2012, 08:22:06 PM
To directly power a resistive water heating element with DC current, I think you would want to use a diversion controller like a Morningstar TS 45... you would connect the diversion controller to your battery bank and the water heating element.  I believe there are several options for how the Aux port from the Classic could be set up to trigger this diversion. 

thanks, any ideas where to start reading on that? A TS60 is cheap enough, im happy with that if it will play nicely with the 150 classic.

QuoteChris Olson's method using a SSR and the "waste not high" Aux function is more elegant and probably much more efficient. With his method you are not cycling the batteries either. 

I cant find any reference to 'waste not high' in the manual. There's opportunity hi and lo. Diversion hi and lo. And what is there is pretty brief. Is this documented elsewhere?

Cheers


p40

Aux 2 Function. Output/Input   

OUTPUT = 12V/0V Signal

FLOAT LOW       Aux2 off when in Float
FLOAT HIGH      Aux2 on when in Float
DAY LIGHT       Aux2 on at dawn off at dusk
NITE LIGHT       Aux2 on at dusk off at dawn
CLIPPER CONTROL    PWM Control for Clipper
Pv V ON LOW      PWM sig below Pv in setpoint
Pv V ON HIGH      PWM sig above Pv in setpoint
TOGGLE TEST      Aux2 cycled 1 sec interval
OPPORTUNITY LO     PWM divert rltv chg state lo
OPPORTUNITY HI      PWM divert rltv chg state hi
DIVERSION LO      PWM Divert on Bat voltage lo
DIVERSION HI      PWM Divert on bat voltage hi
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

boB

Quote from: zoneblue on November 17, 2012, 08:37:07 PM

OPPORTUNITY LO     PWM divert rltv chg state lo
OPPORTUNITY HI      PWM divert rltv chg state hi



What was the software version or date for this MNGP ?

boB
K7IQ 🌛  He/She/Me

zoneblue

I clicked main nav, documents, manuals, classic manual. Is there a newer manual?
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

boB

Quote from: zoneblue on November 18, 2012, 04:07:38 AM
I clicked main nav, documents, manuals, classic manual. Is there a newer manual?

No newer manual.  OK, swap those words "Opportunity" with "Waste Not".

Thank you for pointing out this error in the manual !!

boB
K7IQ 🌛  He/She/Me

Eric L

#13
Quote
You only have to read the two threads mentioned above to see how hit and miss getting the AUX/PWM/ SSR combination working sensibly is.

I've been using that function (which I found out about initially form this forum) for about two months and it's working very well. As I mentioned in the linked "Fieldlines" thread above, I had some early problems with my inverter AC voltage fluctuating too much, but that's largely resolved. There is still some flickering in CFL bulbs when the heating element is on in the "waste not hi" PWM mode, but remember that the element is only on during the day, usually during the brightest part of the afternoon, so the flickering is not a significant issue, since the lights aren't on then except in one windowless bathroom. The battery charging cycles complete normally.

By doing this, I spent about $40 in parts (SSR and some wire) to get hot water from the surplus power my panels were producing, which has basically been enough to take our water heater off grid (probably around 5-10% of heating now is on grid power). Hard to imagine a way to do it more cheaply, and even if it doesn't work out for some reason, it's not like you've made a huge investment.


Since installing this, my pv production measured at the Classics has gone up significantly, and I think I'm close to using almost every watt-hour that my panels produce. Right now (November) a sunny day sees them producing over 4 KWh per KW of panel. Pretty cool if you ask me.

Halfcrazy

I do basically the same thing. I ave 2 SSR's in the house that are run by 2 Classics using Waste Not PWM, I also have a single large SSR in the house driven by Waste Not NON PWM. In the summer the large SSR drives my 40 gallon water heater, in the Winter the 2 SSR's drive 4000 watts of electric heat. This works well although it does use the inverters so there is some loss there. DC diversion is very elegant but not always practical. In my case the batteries are 150ft from the house.

Ryan
Changing the way wind turbines operate one smoke filled box at a time