Freezer for Off Grid PV

[BritishPete]

I have two identical 5 cu ft freezers, one is used as a fridge which I am sure is nothing new here except perhaps that I have added stackable shelving to make it really easy to access foods. This one of mine averages 180w per day.

the second one is used as a freezer BUT it is powered through an electronic time clock and has it's thermostat bypassed.
The time clock is set for 6 daylight hours per (8 hr) day and then 10 minutes on every hour for the remaining 16 hours.
This results in very little energy being used from the battery bank while still maintaining a maximum of -12C temperature.
As (Very slow) bacterial growth does not start until -9.6C it is quite safe and saves a lot of battery drain.

[Sunking]

Well it would cost 1/10 the money buying it from FPL.

[BritishPete]

Well it would cost 1/10 the money buying it from FPL.

Not sure how you figure that; Mine is FREE. How much is 1/10 of free?

Note this was posted in the Off Grid Forum.

[BritishPete]

We could do some cost engineering here too. FPL/TECO monthly meter/service rental (without consuming anything) is about $12 per month. So my 100 watts x 16 hours at 10 minutes x 30 days = 8Kw per month total means my FPL price per KWhr would be $1.50. Of course first I would have to convince them to follow my RV around with their service.

[Sunking]

Not sure how you figure that; Mine is FREE. How much is 1/10 of free?

Simple I work with numbers, not feelings and emotions. As pointed out buying the electricity will cost you about a $1/month.


So you need about .3Kwh per day right? That will cost you about $1200 for the panels, charge controller, and battery. That does not include any misc materials and hardware. Of that $1200 the batteries will cost you around $350, and need replaced in 5 years or less.

So for the first 5 years:

If buying from the POCO will cost you .3 Kwh x $0.12/Kwh x 1825 days = $65.70
If you go the solar route about $1200.

So just how do you figure it is free?

My guess is because you feel that way.

[BritishPete]

Follow me with a power supply LOL! WOW! What are you doing on an Off Grid Site? and how could you possibly know the life of my battery bank without knowing type of battery and DOD

Plus in my math 5 years at $12 a month equals $720. What do you know I don't?

I work with numbers too but from the PRACTICAL side, 0.3Kwhr per day cost me less than $100 in panels, where are you buying yours from?

[BritishPete]

Panel cost $1.79 per watt, average insolation (In Florida) 6 hours per day = 6 watt hours per $1.79. 300 watts therefore = $89 purchase price, 40A PWM controller $45, batteries existing anyway but would cost $100 per Kwhr to replace so $60 for 300 watts (to 50%DOD and your 5 years)

Total less than $200 compared to TECO $720 for the first 5 years and $60 per subsequent 5 years while TECO will still be $720.

Is that numbers too?

[Sunking]

Is that numbers too?

They sure are, but they are Make Believe. You di dno tuse correct math and formulas in any of your calculations.

In addition you did not account for battery system efficiency of 50%, used Average Insolation, and not given any allowance for cloudy day recovery.

With a battery system you have to generate 2 watt hours for every 1 watt hour used.
For a battery system you have to use December/January Insolation, otherwise you go dark in winter. In central Florida you get 3.8 Sun Hours.

So to generate 300 wh you need a panel wattage of [300 wh x 2] / 3.8 Sun hours = 150 watts. Round up 20% for cloudy day recovery = 180 watts. Pay attention here because this is where you really screwed up the math. To find the correct panel wattage the formula is [ Watt Hours x 2] / Sun Hours + 20% = Panel Wattage.

So you need:

180 watt solar panel = $1.79/watt x 180 watts = $320
15 Amp Charge Controller = $100
12 Volt 125 AH Battery = $350
500 watt True Sine Wave Inverter = $100
Est Total = $870

So you are getting off cheap living in Florida.

Total less than $200 compared to TECO $720.

Who the heck is TECO? At 12-cents/Kwh using 300 watt hours/day for 5 years = .3 Kwh/day x $.12/Kwh x 1825 days = $65.70

At $720 from TECO the Kwh cost would have to be $720 / 547 Kwh = $1.316/Kwh.

$720 for 547 Kwh. LOL.

[BritishPete]

If your job is using numbers I am sorry for you. I know PRACTICALLY what I use and how much it cost me. Sounds as if this is a customer sales pitch to me.

Maybe you should re-read my post to see why it would cost $720; METER RENTAL !!! $12 per month.

[BritishPete]

Anyway back to the real world; Anybody have any serious questions regarding my post on reducing freezer battery load? I also want to sell 125AH batteries at $350 LOL! I'd be rich in no time or you could try Trojan 105RE's 1.5Kwhr for $150. and 8 year life with my 30%DOD (that's 30% discharge) and 80% efficiency

[Sunking]

Maybe you should re-read my post to see why it would cost $720; METER RENTAL !!! $12 per month.

Oops my bad, it is an RV. That being the case you do not need any solar, just a battery isolator using the alternator. Run the engine 5 minutes per day and you are done. Or you can do the solar thing if you do not like your money.

[BritishPete]

LOL! The freezer is not my ONLY load, I produce and need 7 Kwhr per day from my panels. That would be a lot of fuel and inefficient use of my RV motor. However the topic is FREEZERS and saving battery power.

I could also (more cheaply) use my generator but at a far greater cost than my expected battery replacement costs.

So I joined an Off Grid forum today to talk about the BENEFITS of Off Grid. I gave up a 7 acre farm and a $600 a month utility bill now it's FREE (or $60 every 5 years to keep you happy)

Actually I have 12 Kwhr total of Trojan T105RE battery at a cost of $900 and a life expectancy of 8 years to my 30% discharge so $110 per year for all. Stll beats the heck out of Utility.

[Sunking]

utility bill now it's FREE (or $60 every 5 years to keep you happy)

You are dreaming. To use 1 Kwh per day at 12 volts requires a 440 AH battery every few years. I really do not care if you believe me or not because in a very short time you will learn that the hard way. A good 5 year 12 volt 440 AH battery will cost you $600 to $800

[BritishPete]

You are dreaming. To use 1 Kwh per day at 12 volts requires a 440 AH battery every few years. I really do not care if you believe me or not because in a very short time you will learn that the hard way. A good 5 year 12 volt 440 AH battery will cost you $600 to $800

Once again READ my post. Did I ever say the 7 kwhr was coming out of the battery? Most of my power is used during insolation time. Your numbers tally almost exactly with mine; I use 2 Kwhr per day battery and I have 1000AH.


PLEASE! Back to freezers now.

[Mike90250]

...PLEASE! Back to freezers now.

So, are you using a 120VAC for the freezer, or 12VDC ? Check out the home style energy star freezers, and see what their daily/annual power consumption is.

To get better cooling - insure the coils / hot side have pleanty of cooling air flow, don't put hot product into the freezer... you nkow the whole drill.

Insulation, can you add some externally ? Oftne the small, micro stuff has very low quality insulation.