Want to power refrigerator and freezer in case of grid power outage for several days, please let me know if my calculations are correct.

loac

New Member
So I have been watching lot's of Will's videos and they are super helpful to a beginner like me. I also found a site called PVeducation.com which did a good job of spelling out the process of sizing your PV and batteries. I attached the image below of my calculations. I am a complete beginner so please let me know if I calculated something incorrectly!

The amount of battery amp hours needed to do this seems really excessive at 1012 AH @ 24v. The batteries alone would cost about $10,000 dollars which is way out of my budget so hopefully I just calculated wrong.

Thanks in advance for your help!
 

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DThames

Photon Sorcerer
A quick look at your numbers and they don't look out of line. However....5 days with no sun is not likely. But on a heavy overcast, your power can be as low as 5% based on my observations. However, it is pretty odd in most locations to have heavy overcast all day for days in a row. When it does happen a gas generator can make up the difference and keep your battery size down.

Also, for things like freezers, if the power is out you can cover them with blankets when the compressor is not running and they will hold for hours between 'cycles'. Running one only during the day when you have some sun would also reduce battery demand. If your typical power outage is in winter and your freezer is in the unheated space of the house, that is an additional help.

More solar panels can help make up a difference during the day so you might run your freezer all day without touching the battery and unplug and cover it with blankets at night. Things like that will help, if you don't want to spend big on batteries.
 

MisterSandals

Participation Medalist
2041Wh per day looks a bit high...

2041Wh / 24h = 85W average.

My experience is that my fridge and freezer each run about 20 min per hour (33%).
If yours is similar that would be (85W /.33) = 255W when "running" (and assuming 0W when idling)

This is a lot more than my 27cuft GE Energystar refrigerator/freezer (2 ice makers, water dispenser, door electronic display). I recall 125W when running and about 25W idling. This comes to (125 x .33) + (25 x .66) = 41.25W + 16.5W = 57.75W average
Fun with numbers: 57.75W x 24h = 1386Wh x 365h/y = 505890Wh per year

Just another data point.
 

kenryan

Solar Enthusiast
The thing that sticks out to me is that the refrigerator/freezer (size not given) uses 50% more power than the large freezer. Something seems off there.

Regardless, in a situation like this, a backup generator makes a lot of sense. If you consistently have 5 consecutive days with no sun, then perhaps your location is not suitable for solar.

I live in Anchorage, Alaska. Here, solar is very practical in the summer and very impractical in the winter. But because we have a grid and can offset our use, we can build a solar system without a battery component, and size the panels for summer usage. The result is no electric bill in the summer, and no change to the electric bill in the winter, and about a 15 year payback on the system cost. Sometimes, grid tied solar with no battery can make the most sense.
 

loac

New Member
A quick look at your numbers and they don't look out of line. However....5 days with no sun is not likely. But on a heavy overcast, your power can be as low as 5% based on my observations. However, it is pretty odd in most locations to have heavy overcast all day for days in a row. When it does happen a gas generator can make up the difference and keep your battery size down.

Also, for things like freezers, if the power is out you can cover them with blankets when the compressor is not running and they will hold for hours between 'cycles'. Running one only during the day when you have some sun would also reduce battery demand. If your typical power outage is in winter and your freezer is in the unheated space of the house, that is an additional help.

More solar panels can help make up a difference during the day so you might run your freezer all day without touching the battery and unplug and cover it with blankets at night. Things like that will help, if you don't want to spend big on batteries.
Thanks for the response. I agree that the 5 days without sun is very unlikely, especially here in Phoenix area. I will probably reduce that to 1 day. I can't really afford more anyway and don't want to go too crazy on my first system.
 

loac

New Member
The thing that sticks out to me is that the refrigerator/freezer (size not given) uses 50% more power than the large freezer. Something seems off there.

Regardless, in a situation like this, a backup generator makes a lot of sense. If you consistently have 5 consecutive days with no sun, then perhaps your location is not suitable for solar.

I live in Anchorage, Alaska. Here, solar is very practical in the summer and very impractical in the winter. But because we have a grid and can offset our use, we can build a solar system without a battery component, and size the panels for summer usage. The result is no electric bill in the summer, and no change to the electric bill in the winter, and about a 15 year payback on the system cost. Sometimes, grid tied solar with no battery can make the most sense.
Yeah, I'm not sure why it is such a large number. It is a subzero fridge/freezer so maybe the fancy ones like that take more power. I tool the yearly KW/hr rating from the manufacturer so it probably pretty close.
 
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