Solar Design for Freezer

Electrohawg · July 2016

Greetings everyone! I stumbled on this site while doing research and was blown away by all the knowledge here. Currently we are looking to design a small system off grid that is capable of supplying power to a deep freezer and a few lights. There will be no utility available so we just want to be able to have a few lights and the ability to keep our food frozen.

We would like to have enough battery for two days at a minimum but am open to suggestions. We are not too worried about other items and would be happy to just have the lights and freezer. Maybe upgrade to more in the future if we thought it was needed.

Now I did purchase a Kill o Watt meter and I put it on the freezer for 24 hours. it used 1.36KWH during the 24 hours. We would use LED lights. and I have not put those on the meter yet but I kind of thought the draw would be low and easy to plan for. My location is in southern Arkansas.

Well, that is all the information I have please feel free to ask questions because I am sure I left some information out that you would need. Thanks in advance for any ideas and assistance.

vtmaps · July 2016

Welcome to the forum,

Planning for two days of no sun is sort of the sweet spot in a design... but you should have a generator for longer periods of clouds.

This system can be built as a 12 volt system, but you mention that you might want to expand the system in the future... in that case you should start out at 24 volts.

A conventional freezer will be the defining load for you... it has a high startup surge which will force you to use a much larger inverter which will have higher self consumption (tare losses). You will need 1000+ watt inverter to start the compressor, but once running a 300 watt inverter would be sufficient.

It might be cost effective to buy an ultra-efficient DC powered freezer (e.g. sundanzer or steca) and get a few DC LED lights.

Your thoughts?

--vtMaps

Electrohawg · July 2016

vtMaps, thanks for the quick reply. I have not though about a DC powered freezer but I will go research it. If I could get away with a smaller solar system that would be a great idea.

So, with the information I have so far with the existing freezer what do you think I would need? Lets say just using a 12VDC system for now. estimating a 2 day back up what size battery bank and solar panels would be needed? I was guessing at using 2 200watt solar panels with about 550 or so amp hours worth of batteries? Is that kind of close or is it way off?

vtmaps · July 2016

Start with your load: 1.36 kwh for the freezer, and I will guess 0.25 kwh for the lights. You will also need maybe 0.35 kwh for the inverter self consumption. let's call it 2 kwh per day. You never want to take the batteries below 50% SOC, so you will need batteries that store 8 kwh.

8000 watthours ÷ 12 volts = 667 amphours (at 12 volts). That would be three parallel stings of golfcart batteries (which is a poor design... avoid parallel batteries). Two of these would do it: https://www.solar-electric.com/6cs-21ps.html

You should aim for a charge rate of 10%. 67 amps of charge current at a charging voltage of 14.8 volts is 991 watts. You can expect to harvest about 77% of your solar panel's ratings, so 991 watts ÷ 77% = 1288 watts of solar panel.

Before I start calculating the size controller, let me hear your thoughts about the numbers so far... perhaps spending $1000 on a DC freezer is looking better?

One more thing... there is a certain charm to using cheap golfcart batteries... three strings would be half the cost of that surrette battery. But over the long haul, the surrette would be cheaper. Another possibility to get the capacity you need is to use four L-16 batteries in a 24 volt configuration.

--vtMaps

Electrohawg · July 2016

Great information. You have giving me a log to digest. But you definitely answered my question. I will read some more of these forum and will need to make some decisions on how to move forward. Thanks for all the help!!

DConlyGuy · July 2016

ive been looking in to the dcf50 sundanzer it in the 600$ plus range, but it says it only uses 280 watts at 12 volts a day or 25 amp hrs a day. it pretty small though

zoneblue · July 2016

1.4kWh/day is im guessing an older model. Modern conventional freezers tend to be sub 1kWh/day. This might as vt said be a sensible place to start. Any kind of refrigeration is a demanding load and once you have that, it doesnt take much more system wise, to power lights, water pump, appliances, and tools. In other words refrigeration is a system defining load. Appliances being cheaper than solar, so it does make a certain kind of sense to get efficient products. Just dont go overboard, some of the super low energy fridges and freezers and like 2000 dollars. Balance in all things. We are starting to see quite commonly "inverter" style fridges, that have no start surge, and can thus run on a 300W inverter. Be worth seeing if you can find a ordinary brand name freezer with inverter tech in and a good energy star rating.

Also look at where the freezer is located. A cool cellar, or veranda, can save quite a bit of power depending on your climate.

Electrohawg · August 2016

vtmaps said:

Start with your load: 1.36 kwh for the freezer, and I will guess 0.25 kwh for the lights. You will also need maybe 0.35 kwh for the inverter self consumption. let's call it 2 kwh per day. You never want to take the batteries below 50% SOC, so you will need batteries that store 8 kwh.

8000 watthours ÷ 12 volts = 667 amphours (at 12 volts). That would be three parallel stings of golfcart batteries (which is a poor design... avoid parallel batteries). Two of these would do it: https://www.solar-electric.com/6cs-21ps.html

You should aim for a charge rate of 10%. 67 amps of charge current at a charging voltage of 14.8 volts is 991 watts. You can expect to harvest about 77% of your solar panel's ratings, so 991 watts ÷ 77% = 1288 watts of solar panel.

Before I start calculating the size controller, let me hear your thoughts about the numbers so far... perhaps spending $1000 on a DC freezer is looking better?

One more thing... there is a certain charm to using cheap golfcart batteries... three strings would be half the cost of that surrette battery. But over the long haul, the surrette would be cheaper. Another possibility to get the capacity you need is to use four L-16 batteries in a 24 volt configuration.

--vtMaps

I haven't forgot about this yet! Just been trying to learn a bit more about the different options. The biggest surprise so far has been the cost and numerous different options of batteries. Anyway, vtmaps, was hoping you could drop some more knowledge on me for sizing the controller. Also, if i were not planning to add more loads in the future where there be any benefit to moving up to 24VDC?

Thanks in advance for the assist!.

vtmaps · August 2016

If we stick with the numbers I used above, you will need an 80 amp controller such as Midnite Classic, Outback FM80 or the new Magnum PT100. If you build a 24 volt system, you will only need a 40 amp controller.

Regarding 12 vs 24 volts, that may depend on the batteries. For example, you could use 4 L-16 batteries. They have the same storage capacity whether configured as 12 or 24 volts, but at 24 volts they are a single series string, whereas at 12 volts they are in series/parallel. A single string is a more optimal design.

I think you should consider a different freezer. If you spent $1000 on a new freezer, you would probably save more than $1000 building your power system. It's usually cheaper to conserve a watthour than to generate and store a watthour.

--vtMaps

TURNEROFFROAD · August 2016

Great info.. I'm a greenhorn on all this as well Electrohawg where are ya from... I'm from South Arkansas as well

jonr · August 2016

Supposedly LG is now producing an inverter based freezer:

https://www.bellanaija.com/2016/01/lg-electronics-innovative-new-home-appliances-are-just-what-you-need-in-2016-fridges-freezers-washing-machines-microwaves-vacuum-cleaners/

softdown · August 2016

Lots in interests in freezers and their power consumption. Freezers are getting more efficient all the time. A couple days ago I bought a 14 cubic foot Danby chest freezer from Costco. Found it interesting that last years 7 cubic foot Danby chest freezers costs $25/year to operate. I almost slobbered at the $35/year figure for the 14 cubic foot freezer.

Start up surge is 220 watts and appeared to last for 1/2 second. It runs at a steady 80 watts while cooling. In ~1 1/2 hours...it dropped the temperature from 60F to 10F. Extremely quiet and with a keyed lock.

I don't work for Costco or Danby. Just relating the figures on one of the latest freezer offerings. Also...I think Costco quit carrying this freezer after a very short time. I bought the last one. Other stores no longer carried it. Looked like a distributor undercut what the sales price is supposed to be?

Amazon carries it: https://www.amazon.com/Danby-DCF145A1WDD-Designer-Thermostat-Efficient/dp/B01F8KCI0Q/ref=sr_1_9?ie=UTF8&qid=1471826670&sr=8-9&keywords=danby+chest+freezer

just starting · August 2016

Softdown is that on a kilowatt meter?

softdown · August 2016

just starting said:

Softdown is that on a kilowatt meter?

Yes it is.

just starting · September 2016

Can you get a week's worth of full kWh per day?

Electrohawg · September 2016

TURNEROFFROAD said:

Great info.. I'm a greenhorn on all this as well Electrohawg where are ya from... I'm from South Arkansas as well

am from the woodlawn area.

Electrohawg · September 2016

the deep freezer I am using is a Sears Model (253.290428010). It is an upright and is pretty large. Physically it is larger than my refrigerator.

I have almost decided on all the equipment I am going to purchase. I have decided to go with a 24 volt system as I feel it is the most expandable for my needs. What I have not decided on is the batteries. When I really take a look at all the options and the price range it is a bit of a daunting task. That and it hurts the wallet!

I could purchase the DC powered freezer and may do that in the future. However for now will plan on a system that will handle what I have now.

Solar Design for Freezer

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