Average refrigerator load?

rp3703

I realize this is probably not the best way to go about this but I got a hell of a deal on six 310 watt solar panels for $108 a piece and now I want to design a system around them. So I got a quote a while back from NAWS on a system that would power up to two refrigerators, charge some cell phones and a few lights. They designed me a system for 2600 WH, with 1600 watts of panels, a 3500 watt inverter and four Rolls Surrette S-550(6V 428AH) batteries. Yes I know there’s more to it than that but those are the important parts. Even though I know I have the panels covered, I actually want to reduce my load by one refrigerator and maybe not use all six panels. So my question is, what would be the average load for plain old cheap white, top freezer, bottom fridge, energy star rated refrigerator? 

BB.

Where will the system be installed?

-Bill

jonr

Note that for a refrigerator, you should design for roughly peak daily load, not daily load based on a yearly average.  

Ambient temperature makes a big difference, door opening doesn't.

mvas

Average Monthly Load ...

Refrigerator/Freezer Older units (prior 2000)
Refrigerator (frost-free),   15 cu. Ft. 150 kWh per month $16.50 per month
Freezer (manual defrost), 15 cu. Ft.  90 kWh per month   $9.90 per month

Refrigerator/Freezer Newer Units - Energy Star Refrigerators
Energy Star Refrigerator,                      14 cu. Ft.  34 kWh per month $ 3.80 per month
Energy Star Refrigerator (frost-free),    17 cu. Ft.  35 kWh per month $ 3.85 per month
Energy Star Refrigerator (frost-free),    19 cu. Ft.  46 kWh per month $ 5.06 per month
Energy Star Refrigerator (Side by Side) 21 cu. Ft. 51 kWh per month $ 5.61 per month
Energy Star Refrigerator (frost-free)      24 cu. Ft. 54 kWh per month $ 5.94 per month
Energy Star Refrigerator (Side by Side) 25 cu. Ft. 60 kWh per month $ 6.60 per month

NOTE: Inverter needs to support starting amps of fridge + all other active loads 

mcgivor

Plan on about 1.5 to 2 Kw per day for that basic refrigerator, not including inverter losses. How many times the door is opened during the day will greatly effect the actual consumption.you do realize you are reverse engineering and putting the cart in front of the horse. 

rp3703

The location is in Ontario Canada about 3 hours north of Toronto and about 45min south of Greater Sudbury. Bill, you already figured my loads for lights, cell phone charging and a water pump on this thread.
http://forum.solar-electric.com/discussion/351661/water-pressure-pump/p1
I am only exploring the possibility of adding an electric refrigerator to that list because of the acquisition of these extra solar panels. I have also found a battery supplier where I can get DeKa seconds. I know they are not the best but with this being my first solar install, I don't want to go overboard. I have already picked up two 6V 370AH batteries for $200 a piece and plan to pick up two more to bring the system up to 24V. 

rp3703

So figuring for a 2KWH refrigerator load per day and my 1000 KWH load for all my other stuff, using the numbers Bill used for the load calculations on the other thread, I came up with 593AH of battery storage at 24V. Using a 4hr average amount of sun per day, I came up with 1440 of panel wattage. Does this sound correct?

rp3703

Ok so now I’m confused. If my calculations are correct and it takes 593AH at 24V to run one refrigerator with all my other stuff, how did NAWS figure that 4-6V 428AH batteries would run two refrigerators at 24V?

BB.

I like using 3.3 kWH per day for a refrigerator+lights+washing machine+water pump+laptop computer/tv/etc. for a "near normal" electrical electrical existence in a very conservation minded home.

• 3,300 WH * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storage * 1/0.50 max discharge (better battery life) = 647 AH @ 24 volt battery bank (basically your calculation with 10% more storage)

Size of solar array--Two calculations, first based on minimum rate of charge for battery bank. 5% for weekend/seasonal usage, 10% to 13% for full time off grid--Your system may be better off with the 10% rate of charge--Basically you are running the fridge 24x7, so you are "stealing" some charging current during the day--The 5% minimum rate of charge assumes no concurrent loads:

• 647 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,218 Watt array minimum
  
• 647 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 2,437 Watt array nominal
  
• 647 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 3,168 Watt array "cost effective" maximum
  

And then based on the hours of sun per day--Assuming 4.0 hours of sun minimum for your time at the cabin:

• 3,300 WH per day * 1/0.52 off grid system eff * 1/4.0 hours of sun minimum = 1,587 Watt array "break even" @ 4 hours of sun per day
• 3,000 WH per day * 1/0.52 off grid system eff * 1/4.0 hours of sun minimum = 1,442 Watt array "break even" @ 4 hours of sun per day if you stick with 3,000 WH per day
  

Of course, a refrigerator uses less energy in cool weather (assuming you don't crank up the wood stove in spring/fall and run the fridge "hot")... But I would guess that 1,440 Watts of panel is a bit on the small side...

Now the questions about how you will maintain the system... If you are there the whole time running the system and watching battery bank SG / Voltages, and making sure the folks are "wasting power"--You can probably get away with 1,440 Watts of energy--Or at least catch when the battery bank is "not happy" and cut down energy usage and/or power up the backup genset in the morning.

If you will not be there and don't have somebody you can trust to monitor the system--I would tend to suggest you look at ~2,215 (3,000 WH per day) to 2,427 Watt array (3,300 WH per day)--It will give you that extra bit of energy to keep the battery bank happy without having to watch energy consumption/generation like a hawk.

Part of this will be a risk calculation too... Get ~4x series GC 6 volt @ 200 AH batteries * 3x parallel strings for 12 total batteries (~24 volts @ 600 AH) battery bank (mayby $1,200 USD) vs getting some very nice Rolls or other "expensive batteries"... Less expensive batteries, you may take the risk of a smaller array. "Expensive" battery bank that you want to last 8+ years and you not being there "full time" (or running somebody remotely by cell phone and text messages), you might want the additional security of the larger solar array.

Of course, you can build out the system and run it for a month or two--See how everything shakes out--And if more panels are warranted--Then add them when you have time and $$$.

I am sorry I cannot give you a more black and white answer--Just some guidance.

-Bill

Estragon

At around 3kwh your setup sounds about right. A bit more panel for light overcast days wouldn't hurt. My loads and storage are in the same ballpark and I find it works well except in the dead of winter.

400ish ah at 24v might do the job, but wouldn't give as much autonomy. With a bit of conservation I easily go 2-3 days with little sun before needing the generator.

Depending on battery location they may spend most of their life at cool temps. Mine are in an insulated crawlspace and will rarely if ever get to 25C or above, so capacity is lower than rated. Currently charging in full sun they're at 10C and capacity when full is showing on the classics as 300ah vs 350 rating. In winter they'll get below 0C and capacity might get down to 260ish.

rp3703

Tell me if this makes sense. I like your 3.3K with a washing machine added, so I will probably stick with that number. We only visit this location from June to August and from what I found online it says average sunlight per day in Sudbury is 7 hrs. Is it safe to recalculate the panel array using 7hrs instead of 4? Also, we were thinking it may be best to just pull the batteries at the end of each season and take them home. That way, there's no chance of damage from lack of charge during the winter. If we do, would that reduce our required AH any?

rp3703

Hey Estragon, I asked you a question about your water system on this thread.
http://forum.solar-electric.com/discussion/351923/lake-water-treatment#latest
I would really like to hear how you have yours set up.

BB.

For 7 hours of sun per day, you probably would need a two axis tracker:
http://pvwatts.nrel.gov/pvwatts.php

Requested Location

	sudbury canada 2 axis tracking
Weather Data Source	(INTL) NORTH BAY, ONTARIO 75 mi
Latitude	46.35° N
Longitude	79.43° W

Month	Solar Radiation ( kWh / m2 / day )
January	4.24
February	6.15
March	7.55
April	7.50
May	8.62
June	7.94
July	8.88
August	7.35
September	5.84
October	4.59
November	2.34
December	2.74
Annual	6.15

A fixed array system summer:

Requested Location

	sudbury canada fixed, facing south, 30 degrees from horizontal
Weather Data Source	(INTL) NORTH BAY, ONTARIO 75 mi
Latitude	46.35° N
Longitude	79.43° W

Month	Solar Radiation ( kWh / m2 / day )
January	2.98
February	4.45
March	5.61
April	5.43
May	5.93
June	5.48
July	6.02
August	5.28
September	4.17
October	3.37
November	1.87
December	2.02
Annual	4.38

June through August--You are getting closer to 5.28 hours of sun (August), and towards end of August into September, it drops to 4.17 hours per day...

Also, if you have "floor" (minimum daily power consumption)--Such as refrigerator, water, lighting (cannot turn off refrigerator for a day or two of cloudy weather, but you can put off washing, cooking with electricity, etc.)... You should plan on your "floor" to be something like 65%-75% of your "average daily output" (average--some days more power, some days less).

Also, remember that you are using power during the day (refrigerator, possibly other tasks)--5% is my suggested "minimum charging current" available to the battery bank. 5% of 647 AH * 29 volts * 1/0.77 panel eff = 1,218 Watts -- That leaves ~200 Watts of "additional array capacity" to run concurrent loads. The refrigerator will draw ~120 Watts running (25-50% duty cycle)...

Not to say that it cannot be done (smaller array)--Just you will need to manage your power usage vs sun more closely--Some people love doing that, other hate it. And run the genset at times to bump the bank from 50% State of Charge to 80% or so when needed.

At this point, if a fixed array, I would still use 5.0 hour per day for the array calculation--But that leaves you very little headroom for bad weather or a bunch of family and friends plugging in computers, running games on the TV, and such (yea--I know, back to nature to commune with the X-Box....).

For winter--Your batteries will be very happy in the sub zero weather--Assuming they where left >90% charged when you buttoned up the camp. If you have a 1-2% rate of charge:

• 647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.01 rate of charge = 244 Watt array minimum
  
• 647 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.02 rate of charge = 487 Watt array nice for float
  

For example a couple ~240 Watt panels in series with a smaller ~15+ Amp rated MPPT charge controller (just two panels mounted high/vertical for winter charging) should keep the battery bank happy (rest of loads turned off, leave main array+charge controller connected or not--Your choice).

Your batteries will last longer in "cold storage" and will not freeze if charged. Plus their self discharge rate drops when stored cold--By the time you have snow over your array, your batteries will be in "cold storage" and not need any float charging until spring.

-Bill

Lumisol

The number one thing to improve a refrigerator's efficiency is to keep it filled. If you don't have a lot of food, fill it with bottles of water.
Empty space is your enemy.

westbranch

some real life numbers, partly sunny days to hours of full sun over the last 3 weeks starting May 1 till today...  the days > 2.0 kWhr or BOLD are when we have been on site the ones less than that are vacant times,  Fridge is on 24/7 right now.
NF means No Float
first numbers are kWhr and in day order...starting May1
2.1, 1. 7, 1.7, 1.8,   0.1,   2.2, 2.3, 1.9 NF, 1.7, 1.6, 1.5 NF, 1.6,  2.3, 2.1, 3.0,  1.5, 2.0, 1.8, 1.6 
Only 5 days had total input > 1000W (1070, 1108,1113 1226 & 1400),
9 days from 739 to 977W,  (739, 855, 861, 898, 901, 914, 951, 971, 977)
the rest were from 410W to 554W ( 4 days in a row (468, 489, 410, 554), and these days hit float IN OUR ABSENSE..

ADD:
Though the days were warm for early May, we did have the wood stove on for meals and let  it burn out in between except for the night and we stoked a few pieces in and it was still warm in the morning....radiating heat towards the fridge door,     ~7 feet away....
so that is a factor that is absent in the non-occupied times.
Added after reading Estragons comments  hth

mvas

Lumisol said:

The number one thing to improve a refrigerator's efficiency is to keep it filled. If you don't have a lot of food, fill it with bottles of water.
Empty space is your enemy.

The amount of heat that enters through the walls and seals needs to be replaced periodically, regardless of fullness.
Efficiency has little to do with adding warm bottles of water, as you remove the food.
The extra energy used to cool the water, defeats any savings from longer running times (full) vs short start-stops (empty).
Also, a reduction in air flow (full) reduces efficiency.
An inverter type refrigerator already uses low power long cycles - so adding warm bottles of water will cost you money.

The #1 thing to lower your operating cost of your refrigerator is ... Keep the door closed.
Opening the door, while browsing for something to eat, can add 50 kwhr / year = $7.50/yr @ $0.15/kwh On-Grid.
Humid weather will cost even more $'s.
Off-grid will cost even more $'s.

Estragon

Keeping the door closed, and adding extra insulation if possible, is going to make the most difference. Standing in front of the thing deciding if you want an IPA or a G&T just dumps all the cold air on the floor.

Depending on your circumstances though, mass can be important too. Running a fridge during the day when lots of solar power is available with a full load, and turning it off during cool nights can work well, and works best if there is a lot of mass in the fridge during off periods. Did that for years with cooler packs and small batteries.

If I'm reading westbranch's numbers right, there's about 500wh/day worth of cold air spilt on the floor daily. Sounds about right to me.

mcgivor

Be careful not to add insulation to a refrigerator which uses th outer metal skin as the condenser 

Lumisol

mvas said:

Lumisol said:

The number one thing to improve a refrigerator's efficiency is to keep it filled. If you don't have a lot of food, fill it with bottles of water.
Empty space is your enemy.

The amount of heat that enters through the walls and seals needs to be replaced periodically, regardless of fullness.
Efficiency has little to do with adding warm bottles of water, as you remove the food.
The extra energy used to cool the water, defeats any savings from longer running times (full) vs short start-stops (empty).
Also, a reduction in air flow (full) reduces efficiency.
An inverter type refrigerator already uses low power long cycles - so adding warm bottles of water will cost you money.

The #1 thing to lower your operating cost of your refrigerator is ... Keep the door closed.
Opening the door, while browsing for something to eat, can add 50 kwhr / year = $7.50/yr @ $0.15/kwh On-Grid.
Humid weather will cost even more $'s.
Off-grid will cost even more $'s.

One of water's most significant properties is that it takes a lot of heat to it to make it get hot. Precisely, water has to absorb 4.184 Joules of heat for the temperature of one gram of water to increase 1 degree celsius (°C). For comparison sake, it only takes 0.385 Joules of heat to raise 1 gram of copper 1°C.
What this means is that the water will not warm as quickly as air does so the fridge will not cycle on as often and when you open the door, there is less air exchange from inside to outside and when closed again, the water will take care of re-cooling the air quick so the compressor never even needs to cycle on.
Modern fridges have cameras in them and displays on the door so you never need to open it to 'browse' for a snack.
Here's the one we got.
Link

Lumisol

mcgivor said:

Be careful not to add insulation to a refrigerator which uses th outer metal skin as the condenser 

Yes, that's a good point. I put a small fridge in the RV and have the back and top vented to the cool airflow from outside so it's separated from the inside air that we heat. In summer when it's over 65 out we can shut the bottom and just leave the top for warm air to rise out and away.

mvas

Lumisol said:

One of water's most significant properties is that it takes a lot of heat to it to make it get hot. Precisely, water has to absorb 4.184 Joules of heat for the temperature of one gram of water to increase 1 degree celsius (°C). For comparison sake, it only takes 0.385 Joules of heat to raise 1 gram of copper 1°C.
What this means is that the water will not warm as quickly as air does so the fridge will not cycle on as often and when you open the door, there is less air exchange from inside to outside and when closed again, the water will take care of re-cooling the air quick so the compressor never even needs to cycle on.
Modern fridges have cameras in them and displays on the door so you never need to open it to 'browse' for a snack.
Here's the one we got.
Link

And it takes a lot of energy to get those warm water bottles cold = which costs you money.
Modern refrigerators already have "low power long cycles", so "fullness" does not matter.
Your idea, of inserting warm bottles of water into to fridge to improve efficiency is "an old wives tale" with no merit.
Real World tests & measurements have proved that adding warm bottles of water just to "fill a fridge" is a waste of time & money.

mcgivor

Agreed better to put beer in the refrigerator and reap the harvest 

rp3703

Regardless fellas, with 13-15 people at our place when we visit, our refrigerators will be full at all times.Thanks for the help though.

rp3703

How do you go about sizing required inverter? Does it just need to handle the full load or just the constant fridge load plus a % of the non-constant loads?

jonr

If you leave water bottles in there, then cooling them is a one time event.  Preferably some afternoon when you have excess power anyway (ie, free).     More thermal mass does mean longer cycle times,, which produces some minor increase in efficiency.    Opening the door is a minor issue.   I agree that less internal air circulation, especially against the walls, should have a slight negative effect.  As Estragon says, putting a timer on a refrigerator so that it is off from 4am to sunrise will reduce wear on batteries (probably more important than actual kwh usage).  More thermal mass helps with this.

Most significant issues by far - get an efficient refrigerator and keep the area around the refrigerator cool.

Estragon

Sizing the inverter - the initial startup load to get the compressor motor going and overcome back pressure is generally the main factor. Some fridges (common outside North America) have a lower initial draw than others. Obviously, this starting load would be on top of whatever else you're running.

Estragon

Yes, good point on insulation on skin-cooled fridges. Only possible on units with external coils.

Also a caveat on turning the fridge off at night. It can be counterproductive if it puts the fridge into defrost cycle when turned back on.

mvas

jonr said:

If you leave water bottles in there, then cooling them is a one time event.  Preferably some afternoon when you have excess power anyway (ie, free).     More thermal mass does mean longer cycle times,, which produces some minor increase in efficiency.    Opening the door is a minor issue.   I agree that less internal air circulation, especially against the walls, should have a slight negative effect.  As Estragon says, putting a timer on a refrigerator so that it is off from 4am to sunrise will reduce wear on batteries (probably more important than actual kwh usage).  More thermal mass helps with this.

Most significant issues by far - get an efficient refrigerator and keep the area around the refrigerator cool.

The statement made was ...
"The #1 thing to increase the refrigerator's efficiency is to add water bottles".
Tests have proven that the total kwhr used over a one year period is not reduced.

Yet, excessive opening the door will add an extra 50+ kwhr per year - proven.

You will have to remove those water bottles, to put more food back in - it is not a one-time event.
If your fridge is constantly filled with water bottles then get a smaller lower kw-hr fridge and save real money.

Then you start talking about "Opportunity Cooling - when the sun is shining" and "reducing battery drain at nigh with a timer" which has nothing to do with making the refrigerator operate more efficiently over a long period of say one year. You are simply time-shifting when the exact same amount of total power is consumed by your refrigerator, while the efficiency of the refrigerator remains the same.  Inverter type and many newer refrigerators already have "low power, long on-time cycles", so no there is efficiency gain here. Yes, you can manipulate when the fridge or any appliance is ON, to coincide with your particular energy production rules, but that does not make that appliance "more efficient".  The efficiency of your appliances has not changed, it is you that has changed.  Your ( minimized energy consumption ) lifestyle, is now controlled by your limited energy production.

BB.

My "cheap" fridge/freezers use a mechanical timer with (what seems to be) a 12 hour cycle... Turning off at night just delays whatever cycle it was in before continuing the next day.

Bigger issue is probably the swing in the average temperature of the refrigerator and freezers. An old thread with even older data on optimum freezer temperature (tested for 6 months of storage):

Question - Best Freezer Temperature

Quick answer, Zero F is optimum. Even 5F noticeable increase in decay of markers.

I also would watch too much swing in freezer temperatures--You can get freezer burn (as air is "re-chilled", plastic bag is colder than contents, get freezer burn/draws moisture from food and deposits on bag/air space as free ice--dehydrating your frozen food over time).

And in the above thread, some quick math on freezers and opening the door... Very roughly, if you assume all cold air is lost in vertical freezer of 15 cuft with only 5 cuft of food--You loose about 0.3% of the mass of "cold" in the freezer that needs to be chilled back down to zero F--And air does not have latent heat of freezing, so it is not as bad as water which you also have to turn to ice to get to zero F.

Open the door 10x per day for freezer it is the same effect as placing less than 3% (by weight) new food/water in freezer to freeze. Not a whole lot to worry about.

As a comparison, if you place 1 lb of room temperature food in the freezer, it cold warm 6 lbs of frozen food from 0F to 32F (not thawing). Another good reason to not put a freezer on a timer if you have a tendency to put new room temperature food in the freezer when it is shut down at night (i.e., only run the freezer during daylight hours to save on your battery bank cycling). You will raise the temperature of your frozen food and exacerbate freezer burn/dehydration because of the "wide" temperature swings.

And if you make lots of ice (drinks, for ice chests, etc.)--That significantly increases energy consumption too.

-Bill

jonr

There are various valid ways to measure efficiency other than kwh/year.  For example, my $/year efficiency (including purchase price) would take a horrible hit if I bought a new one just because mine is slightly larger than I need.  Might as well add water jugs.

This source found .0092 kwh per door opening (a minor 17 kwh/year for an extra 5 openings/day) and a large effect of room temperature.

http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-239-92/

Lumisol

mvas said:

Lumisol said:

One of water's most significant properties is that it takes a lot of heat to it to make it get hot. Precisely, water has to absorb 4.184 Joules of heat for the temperature of one gram of water to increase 1 degree celsius (°C). For comparison sake, it only takes 0.385 Joules of heat to raise 1 gram of copper 1°C.
What this means is that the water will not warm as quickly as air does so the fridge will not cycle on as often and when you open the door, there is less air exchange from inside to outside and when closed again, the water will take care of re-cooling the air quick so the compressor never even needs to cycle on.
Modern fridges have cameras in them and displays on the door so you never need to open it to 'browse' for a snack.
Here's the one we got.
Link

And it takes a lot of energy to get those warm water bottles cold = which costs you money.
Modern refrigerators already have "low power long cycles", so "fullness" does not matter.
Your idea, of inserting warm bottles of water into to fridge to improve efficiency is "an old wives tale" with no merit.
Real World tests & measurements have proved that adding warm bottles of water just to "fill a fridge" is a waste of time & money.

Use cold bottles from an ice chest or in our case from floating in the creek.
No one said add warm water, that's silly.