My 1.8kw off grid set up, what to do with excess power?

jimmyaz · July 2016

Hey all,

I recently set got my system up and running.... started with 600watts PV but now up to 1.8kw pv... and I am running out of ways to use the excess power. ::( Simply because it's an off grid and run on a subpanel... I can not fully utilized the power. My system can output up to 11kw-12kw a day (thanks to the Arizona sun). But most of the time I can only use 8-9kw or so...

1.8kw pv
Outback Flex80
24v AGM 210ah
2500watts inverter

Currently I am running a 6000btu window AC (10hours a day), fans, washing machine, dish washer, rice cooker, other smart devices. But my system would still absorb 1 hour and float 3-4 hours daily.

I had thought about using the excess power to heat water, but my hot water is natural gas...

and the tank is in good condition, no need to be replace (or at least it doesn't make sense to replace). Any other ideas? My garage is super hot, 105-110F, but it seem like a waste to air conditioning my garage, since it's not insulated.

Here's two videos I have made on my system.

https://www.youtube.com/watch?v=7Zg83n_APiw

https://www.youtube.com/watch?v=NiXZQKBVrqs

BB. · July 2016

That is a pretty good output... For July--I would be surprised if the "average" daily production was higher than ~6 to 9 kWH per day.

-Bill

Johann · July 2016

You could get a electric water heater and place it in-front/ in-line with the gas water heater and pre-heat the water before it is flowing in the gas water heater. This would use some more of your home-made power and lower your gas bill at the same time and if the sun is not there you still have your gas water heater.
Maybe a attic fan or fridge or chest freezer.

dwh · July 2016

https://duckduckgo.com/?q=cold+plate+technology&t=ffsb&ia=web

jimmyaz · July 2016

BB. said:

That is a pretty good output... For July--I would be surprised if the "average" daily production was higher than ~6 to 9 kWH per day.

-Bill

What's the rating of your panel? Your location, would be interesting to know.

Maybe it's because my panel is actually tilt 5degrees NORTH... right now due to the shed slope. I know winter come I need to go the other way, but it seem right now it work great for summer. If I used the power, it average about 10kw daily and if I try hard to use more power, then it 11kw daily. But on cloudy and overcast day, it will do 6-7kw. I have also notice it peak higher wattage on cloudy days, it seem when the panel is cooled, then the sun come out, oh man it's nice... but then that only lasted 10 mins... till the panel heat back up and it dropped.

Johann said:

You could get a electric water heater and place it in-front/ in-line with the gas water heater and pre-heat the water before it is flowing in the gas water heater. This would use some more of your home-made power and lower your gas bill at the same time and if the sun is not there you still have your gas water heater.
Maybe a attic fan or fridge or chest freezer.

Thanks, I picked up a used 20 gallon electric heater yesterday for 70 bucks.. cheapest one I can find, they cost too much new in stock, 300+. Make no sense to do it. I am going to use this as preheat. Do you guys think it's worth it to buy the DC element for my 24volts set up, or it's ok to use the 1400watts 120v element, how much wattage can I expect if I am running the 120v element at 24volts?

Also, do I need to place the preheat tank HIGHER than my full size tank? or would the water pressure take care of the height difference? Right now My 50gal tank is sitting on a stand about 20inches off the floor.

dwh said:

https://duckduckgo.com/?q=cold+plate+technology&t=ffsb&ia=web

Not sure what this is? Cold plate technology?? please explain.

jimmyaz · July 2016

BB. said:

That is a pretty good output... For July--I would be surprised if the "average" daily production was higher than ~6 to 9 kWH per day.

-Bill

Maybe it's because my panel is actually tilt 5degrees NORTH... right now due to the shed slope. I know winter come I need to go the other way, but it seem right now it work great for summer. If I used the power, it average about 10kw daily and if I try hard to use more power, then it 11kw daily. But on cloudy and overcast day, it will do 6-7kw. I have also notice it peak higher wattage on cloudy days, it seem when the panel is cooled, then the sun come out, oh man it's nice... but then that only lasted 10 mins... till the panel heat back up and it dropped.

Johann said:

You could get a electric water heater and place it in-front/ in-line with the gas water heater and pre-heat the water before it is flowing in the gas water heater. This would use some more of your home-made power and lower your gas bill at the same time and if the sun is not there you still have your gas water heater.
Maybe a attic fan or fridge or chest freezer.

Thanks, I picked up a used 20 gallon electric heater yesterday for 70 bucks.. cheapest one I can find, they cost too much new in stock, 300+. Make no sense to do it. I am going to use this as preheat. Do you guys think it's worth it to buy the DC element for my 24volts set up, or it's ok to use the 1400watts 120v element, how much wattage can I expect if I am running the 120v element at 24volts?

Also, do I need to place the preheat tank HIGHER than my full size tank? or would the water pressure take care of the height difference? Right now My 50gal tank is sitting on a stand about 20inches off the floor.

dwh said:

https://duckduckgo.com/?q=cold+plate+technology&t=ffsb&ia=web

Not sure what this is? Cold plate technology?? please explain.

animatt · July 2016

That 1400 watt 120 v element at 24v would be 56watts.
I know you could get 2000w 120v elements but that still would only be 80w at 24v.

Would seem a purpose built 24v element would be the only way to get useful dc power into your water. Other than converter to ac first.
But the idea of a dc water heating seems like a good one for your smallish inverter.

I think you might want longer absorb times.

jimmyaz · July 2016

animatt said:

That 1400 watt 120 v element at 24v would be 56watts.
I know you could get 2000w 120v elements but that still would only be 80w at 24v.

Would seem a purpose built 24v element would be the only way to get useful dc power into your water. Other than converter to ac first.
But the idea of a dc water heating seems like a good one for your smallish inverter.

I think you might want longer absorb times.

Yeah. I think I will have to get the 24DC element.

But I now have bigger problem need to deal with... My battery are hitting 100-110F daily.... I have been struggling trying to figure a way to cool them. At this rate they won't last.

I am trying to avoid using AC, my inverter is maxing out so I don't want to put any more AC load.

BB. · July 2016

Digging a cellar?

-Bill

jimmyaz · July 2016

BB. said:

Digging a cellar?

-Bill

LOL... I am not digging nothing.... the system is in my garage, concrete slab.

jimmyaz · July 2016

Yesterday I bought a mini fridge for 15bucks and hook it to my battery box and so far it seem to work. Keeping my battery 80F or so when ambient is 100F.

However, this little sucker is old and itself run hot and uses 250watts on start up and 100watt continuous. I am testing to see if I can have it run only during day time when there's solar power to cool the box... and at night shut it off. Hopefully only cooling the battery during midday where it need most due to absorption.

mike95490 · July 2016

rig it to cool the battery as soon as possible in the AM, to get a head start on the heat, and run it as late as possible till you drop out of float

jimmyaz · July 2016

Update:
So I have been running the mini fridge from 7am till 6pm, using about 1kw, it kept my battery box at 79F the entire day. After shutting it off at 6pm, it slowly raised to a max of 94F overnight. Which is a much much better than before... almost 30F difference during day time is good enough for me.

I think the newer mini fridge is a lot more efficient, the Hair 1.7cu I saw only uses 85watts or so.. (vs the old one I pick up, 110-150watts).

vtmaps · July 2016

jimmyaz said:

I think the newer mini fridge is a lot more efficient, the Hair 1.7cu I saw only uses 85watts or so.. (vs the old one I pick up, 110-150watts).

The newer fridge may be more efficient, but not because of those wattage numbers. A conventional fridge compressor cycles on and off. The percent of the time it is on is called the duty cycle.

85 watts with a 60% duty cycle would use more energy than 150 watts with a 30% duty cycle.

--vtMaps

jimmyaz · July 2016

Is it better to have the air space smaller, so it can cool it quicker... or leave more air space so it can keep the cool air longer over night?

vtmaps · July 2016

jimmyaz said:

Is it better to have the air space smaller, so it can cool it quicker... or leave more air space so it can keep the cool air longer over night?

The air has virtually no thermal mass, so it doesn't matter. --vtMaps

jonr · July 2016

Fill the air space with jugs of water and then it will coast longer into the night.

kc8adu · August 2016

having anything but a solar hot water system in AZ seems silly.
maybe a big insulated tank with a diversion heater that kicks in once you hit float.i would be scheduling power hungry loads for those times of excess production.like doing laundry,ect.takes advantage of the overproduction and abundant hot water at the same time.

jimmyaz · August 2016

Guys,

Something is wrong... HELP.

Everything has been running fine, but the last few days I have notice a few issue.

One of a small tower fan I use stop working the other day... When turn on, it just hum, seem like it's stuck. I open it up and the motor indeed very sticky.... so I thought maybe it need some oil, so I give it some and it start running again...

But today, another standard 3 blade fan I use in the garage to keep some air moving... it stop working as well... same issue? What the heck? I am afraid it's my inverter that has been damaging my appliance. I open up this fan and got it running again, but it seem it doesn't run as fast as it use to run. My 6000BTU window AC seem to run, but the fan sound like it's slower as well. I thought for sure that this thing is pure sine wave because it was able to ran my fan way smoother than my old Haborfreight modified sine wave.

http://www.ebay.com/itm/Pure-Sine-Wave-Inverter-2000W-Power-Inverter-24V-to-120V-Off-Grid-LED-Display-/201514136004?hash=item2eeb2db1c4:g:sX8AAOSw14xWQZvi

I have this inverter, it say pure sine wave,, .and has been running for the past 2 month no issue... When I first got it, the output voltage was 129-130, so I ask the manufacture and they can I can adjust a POD inside and that has reduced it down to 125v (lowest it can go).

I have checked the voltage, still out 125V.

The scary part is I have been running my new Samsung washing machine and LG Dish washer.....

Any advise?

thanks guys

kc8adu · August 2016

cheap fans often fail like that.not a bit unusual.
i see lots of cheap plastic stuff on the curb waiting to go to the landfill.
some motors dont do well on inverters.
but going sticky is just poor quality oil.
you might be able to take it apart,clean the bearings,shaft,and packing with carb cleaner.then re oil with a good synthetic.i use mobil 1 0w20.
my 20's western electric,30's robbins and meyer,and 40's emerson all work just fine on inverters.and get run year round.

jimmyaz · August 2016

Is it true that a hand held voltage meter can not measure Pure sine wave correctly? would always read higher voltage than it actually is?

This is what I have... not cheap Harbor freight one...

http://www.tequipment.net/Greenlee/DM-860A/Multimeters/?Source=googleshopping&gclid=CP6uj4eat84CFVKUfgodC9YCIg

westbranch · August 2016

You should ask Greenlee, they are not know for cheap tools either...

jimmyaz · August 2016

A technician at Midnite solar told me so, he said something about a standard voltage meter wouldn't be able to measure pure sine wave correctly.... need a expensive oscilloscope to measure it correctly.

He even said I may have lower the voltage too low if I based on the hand held meter. Now I'm confused as hell. When I use my Greenlee meter to measure the Grid power at my location, it show 120Volt exact. Using it to measure my inveter output say 128V.

westbranch · August 2016

that's way above my pay grade...?? Why do you want '' that number'' for ?

Raj174 · August 2016

You have a high quality meter that would be used by a professional in the electrical field. It is a true RMS meter, so it measures AC voltage accurately.

Desert Rat · August 2016

jimmyaz said:

... I have been struggling trying to figure a way to cool them.

I have my batteries in a water bath and keep the water level just below the tops of the batteries. I've set up several systems this way, and even with ambient temps as high as 110, the water never gets hotter than 85-87 degrees. That's here in the Chihuahuan desert; I suspect in Arizona your results would be similar.

jimmyaz · August 2016

Desert Rat said:

jimmyaz said:

... I have been struggling trying to figure a way to cool them.
I have my batteries in a water bath and keep the water level just below the tops of the batteries. I've set up several systems this way, and even with ambient temps as high as 110, the water never gets hotter than 85-87 degrees. That's here in the Chihuahuan desert; I suspect in Arizona your results would be similar.

Really? the battery case can stand longevity submerse in water? I never had thought this was possible... lol.

WaterWheel · August 2016

Desert Rat said:

jimmyaz said:

... I have been struggling trying to figure a way to cool them.
I have my batteries in a water bath and keep the water level just below the tops of the batteries. I've set up several systems this way, and even with ambient temps as high as 110, the water never gets hotter than 85-87 degrees. That's here in the Chihuahuan desert; I suspect in Arizona your results would be similar.

interesting...... anybody else tried something like this water bath? This time of year my batteries sometimes get up to 105 in a well ventilated box.

Marc Kurth · August 2016

@Desert Rat - Help me understand how are you keeping the water at 85-87 degrees with a 110 deg ambient.

Yes, I understand vapor pressure differentials and related evaporation rates, but it occurs to me that a standing tank of water will closely approach ambient dry bulb, given time. Now add heat generated by the batteries during charging and you get more temperature rise.

With enough water circulation (and airflow) to force some evap cooling - it all comes together. In fact, it should be easy to hold the water to about 5-7 degrees above the wet bulb temperature this way. But, I have not tried it.

How have you done your systems?

Thanks in advance,
Marc

Desert Rat · August 2016

With the extremely low humidity here in the Chihuahuan Desert, evaporation alone keeps the water cool. If memory serves, I've set up seven battery banks this way. A couple are in waterproofed concrete enclosures and others are in plastic tubs or wooden boxes with pond liners. No water circulation or forced air is needed. Two of the banks are set below grade level, and this is good for a few more degrees of cooling. All but one are outdoors and covered. The lids/covers are not airtight; they are loose enough to allow evaporation.

Johann · August 2016

jimmyaz said:

animatt said:

That 1400 watt 120 v element at 24v would be 56watts.
I know you could get 2000w 120v elements but that still would only be 80w at 24v.

Would seem a purpose built 24v element would be the only way to get useful dc power into your water. Other than converter to ac first.
But the idea of a dc water heating seems like a good one for your smallish inverter.

I think you might want longer absorb times.

Yeah. I think I will have to get the 24DC element.

But I now have bigger problem need to deal with... My battery are hitting 100-110F daily.... I have been struggling trying to figure a way to cool them. At this rate they won't last.

I am trying to avoid using AC, my inverter is maxing out so I don't want to put any more AC load.

You could get a inverter just for the heater. The thermostat from the heater could turn a inverter on and off and if needed or wanted you could have a timer or sensor like a voltage sensor in line with it. The output (120/ 240 volt) from the inverter could be hooked up to the heat element and you would have a controlled power source that is used by demand and you would have full power at the heat element and at the same time can use a small #12 wire for the 1400 watt 120v heat element .

If you get a 600 watt 24 volt heat element, that is still pulling 25 amps. So you may end up with an bigger wire depending on distance and the thermostat will burn up at those DC amps.

My 1.8kw off grid set up, what to do with excess power?

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