Can this setup run my freezer?

Seeria

Hello everyone. I'm very new to this solar thing and not overly electronics brainy. I did a bunch of reading this week and some searching around, then came up with this setup.

What I need is to run a small freezer, 5cu, (max surge seems to be under 1k) and recharge my batteries (the solar and AAAs/electronics). I'll be without electrical hookups 2-3 days in a row, then will either do Rv hookups or run the gen if needed. The big thing here is to keep the freezer working.

Can this setup do it?

1 245watt panel
1 100ah 12v AGM battery
Charge controller, 30amp (450watt), PWM for 12volt
Various rails and mounts
Inverter 1500w (3k peak) pure sine wave DC-AC
Cables (thinking 10 or 8g?) and various extras

Panel would sit directly above the battery/controller/inverter bay and freezer (top of the RV).

Cariboocoot

Re: Can this setup run my freezer?

Welcome to the forum.

The short answer is "no".
The long answer is longer. It's a matter of: A). whether or not the inverter & battery will start the freezer; . whether or not the battery can supply the require Watt hours the freezer will use, and; C). whether or not the panel is sufficient to recharge the battery.

The first one is difficult because we don't know the real start-up demand. You won't capture that with a Kill-A-Watt meter. But then you haven't provided any numbers like that. The cubic capacity of the freezer is irrelevant to how much power it needs: small ones are just as power-hungry as large ones, and sometimes more so.

Normally a refrigeration unit will spike 5X its running current to start, but sometimes less and sometimes more. It isn't even consistent on any given one because the demand will vary with the conditions the compressor has to start under (changes in gas pressure in the line).

A 100 Amp hour 12 Volt battery isn't much in terms of AC Watt hours: about 500. A typical refrigerator or freezer will consume twice that in a day. Yes, even a small one. See the test results on some here: http://forum.solar-electric.com/showthread.php?12272-Just-how-bad-a-small-frige-is

The 245 Watt panel likely isn't going to work on a PWM type controller because it is probably a "GT style" panel with a Vmp of 30 or so. That means much of its power would not be realized using a controller that can't down-convert the extra Voltage into current for the 12 Volt system. As it is a 100 Amp hour battery only needs about 10 Amps to charge with, and that is roughly 175 Watts on a 12 Volt system (current times standard Vmp of 17.5).

When it comes to powering that 1500 Watt inverter, 10 AWG or 8 AWG wire is going to be sadly lacking in supplying the surge current without significant Voltage drop. At 1kW + the current will be over 100 Amps, and even 8 gauge could fry. You might get by with 4 AWG, but 2 AWG would be better (as would any larger size than that).

BB.

Re: Can this setup run my freezer?

Welcome to the forum Seeria!

What would be most helpful is if you can run the freezer on a Kill-a-Watt type meter to measure the average kWatt*Hours per day it uses. Ideally at the freezer/ambient temperatures you plan to use it in.

Freezers are very sensitive to how cold they are set and the room temperature. The wider the spread, the more energy they use.

If the freezer has a Yellow Energy Star/Rating tag--That can also work as starting point (or look up on the web the brand/model of freezer for energy usage).

Generally, even a small freezer will use near 0.8 to 1+ kWH (1,000 Watt*Hours) per day... And if you are camping on the west coast of Oregon--The lack of sun may be an issue too.

Using PV Watts for Eugene Oregon, with the array mounted flat to the roof (typical RV)--Fine for summer, but winter in the northern US will really reduce output:



Month
Solar Radiation
(kWh/m²/day)


1
1.36


2
1.92


3
3.17


4
4.22


5
5.58


6
6.20


7
6.80


8
6.06


9
4.40


10
2.78


11
1.44


12
1.04


Year
3.76




Lets say you want 1,500 Watt*Hours per day... Assuming a minimum of 4 hours of sun per day:

1,500 WH per day * 1/0.52 off grid system eff * 1/4 hours minimum sun per day = 721 Watt array "break even" for 6-7 months a year.

Battery bank sizing... 2 days of storage, and 80% of battery drained (we usually use 50% maximum discharge--But for RVs, 80% will not reduce battery life enough on weekend/week trips to make a difference--Vs a cabin where you live 9+ months a year).

1,500 WH per night * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days of storage * 1/0.80 max discharge = 368 AH @ 12 volt battery bank

The array to charge that battery bank (5% to 13% recommended):

368 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 346 Watt array minimum
368 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 693 Watt array nominal
368 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 901 Watt "cost effective" maximum array

So, taking some wild guesses--You would need a 721 to 901 Watt array with 693+ Watt array "Nominal" for 6+ months of the year full off grid.

In general, for refrigerators--Propane powered refrigerators are hard to beat if you are using them less than ~9 months of the year. Battery banks+Solar Arrays just need a lot of space and weight carrying capacity to supply even modest electric loads.

The sizing for a "good quality" TSW inverter would (typically) be in the 1,200-1,500 watt minimum range--So you have the correct unit sized.

Ask your questions/correct my assumptions and guesses... This is just all a starting point in the sand.

-Bill

drraptor

Re: Can this setup run my freezer?

BB, calculations seems to be bit odd
1,500 * 1/0.85 * 1/12 * 2 * 1/0.80 = 367 not 588

BB.

Re: Can this setup run my freezer?

You are correct Drraptor... ... I used 50% DOD instead of 80% DOD (got the other value stuck in my typing fingers).

Will go fix now. Thank you.

-Bill "trust but verify" B.

mike95490

Re: Can this setup run my freezer?

The other issue you are fighting at start-up, is DC voltage sag in both the battery and wiring, the DC voltage may sag so far in the first 1/2 second, the inverter cuts off before the motor can start. Likely will work with a new battery, but a couple months age and usage, it may fail to start.

My freezer runs at 110watts, but starting is well over 600w, @ 12V that's over 50 amps.

vtmaps

Re: Can this setup run my freezer?

Seeria wrote: »

What I need is to run a small freezer, 5cu, (max surge seems to be under 1k) and recharge my batteries (the solar and AAAs/electronics). I'll be without electrical hookups 2-3 days in a row, then will either do Rv hookups or run the gen if needed. The big thing here is to keep the freezer working.

Many off grid systems have a defining load... a load that the entire system is designed around.

In your case it is the freezer. In order to start up an AC freezer you need a large inverter. Large inverters use power by just being turned on, even if when they have no loads. The inverter you buy for that freezer will consume several hundred watthours per day (tare loss).

Another option is a DC freezer. They can be more efficient that AC freezers and need no inverter. But they are expensive... figure about $1200.

In most off grid systems we recommend a very efficient AC fridge/freezer because there is already a large inverter used for water pumping, laundry, power tools, microwave, etc. The AC freezers are much less expensive than the DC freezers, and with the money you save on an AC freezer you can buy a few more solar panels, battery, etc.

With the loads you mentioned (other than the freezer), you could get by with a very small power system. You will be supersizing your entire system just to run an AC freezer. Perhaps you should consider a DC freezer... look at Sundanzer and Steca for examples. They will use less power than an AC freezer and there will be no tare losses from a large inverter.

Bill mentioned another option that uses virtually no electric power: a propane powered freezer.

--vtMaps