Cheapest DIY solar setup for powering a refrigerator

[flinx777]

We've had issues recently with our power grid going down from time to time. We've lost food in our refrigerator on too many occassions and I'm looking to build the most basic, affordable, barebones battery/inverter/charge controller/solar panel setup. I've watched enough of Will's video to understand how to build a basic setup, but what I'd love to know from the community is what is the recommended, most affordable parts or kit to build out your own solar setup.

Here are the key points as I understand it:

• 1.5 kWh power drawn each 24 hours by the refrigerator (I purchased a kill a watt meter to record the information).
• 82% efficiency of AC output on a typical inverter (inverters are not 100% efficient).
• 300 watts of panels at 75% efficiency in a typical environment (I live in a very sunny area) pointed at the sun (I'd have to move the panels throughout the day).
• Maybe 10 hours of usable sunlight to charge the batteries, may be 4 to 6 of those hours providing peak power. Obviously, the fall is here and winter will be around the corner and there will be less sunlight.
• I think a 100 Ah battery would be the bare minimum (1.2 kWh) needed.
• I've looked at various charge controllers, but not sure what the best would be for this setup.
• 2, probably 3, 100 watt panels.
• 1000 watt inverter should be enough I'm assuming.

Does this basic setup sound about right? Or would you recommend something to be different? I'm looking for the most affordable (not necessarily the cheapest) components to build a similar setup as what is outlined above. I am willing to change any of those values and would love the community's insight. Also, if there's online calculators you would recommend for scaling up or down depending on variables, I would be more than happy to study this more on my own.

Thanks in advance to a very knowledgeable community!

 

[scoharri]

We've had issues recently with our power grid going down from time to time. We've lost food in our refrigerator on too many occassions and I'm looking to build the most basic, affordable, barebones battery/inverter/charge controller/solar panel setup. I've watched enough of Will's video to understand how to build a basic setup, but what I'd love to know from the community is what is the recommended, most affordable parts or kit to build out your own solar setup.

Here are the key points as I understand it:

• 1.5 kWh power drawn each 24 hours by the refrigerator (I purchased a kill a watt meter to record the information).
• 82% efficiency of AC output on a typical inverter (inverters are not 100% efficient).
• 300 watts of panels at 75% efficiency in a typical environment (I live in a very sunny area) pointed at the sun (I'd have to move the panels throughout the day).
• Maybe 10 hours of usable sunlight to charge the batteries, may be 4 to 6 of those hours providing peak power. Obviously, the fall is here and winter will be around the corner and there will be less sunlight.
• I think a 100 Ah battery would be the bare minimum (1.2 kWh) needed.
• I've looked at various charge controllers, but not sure what the best would be for this setup.
• 2, probably 3, 100 watt panels.
• 1000 watt inverter should be enough I'm assuming.

Does this basic setup sound about right? Or would you recommend something to be different? I'm looking for the most affordable (not necessarily the cheapest) components to build a similar setup as what is outlined above. I am willing to change any of those values and would love the community's insight. Also, if there's online calculators you would recommend for scaling up or down depending on variables, I would be more than happy to study this more on my own.

Thanks in advance to a very knowledgeable community!

Go 2 to 3 times bigger than what you "think" you may need.

 

[Vigo]

All of your key points sound correct or close to it to me.

10 hours 'usable' solar is a bit of a stretch unless you have the panels on a tracker setup or something, but 4hours near peak output probably correct in good solar conditions.

2 maybe 3 x100 watt panels brings up a couple points. If you only count on 2x100 w panels, 4 hours peak solar, and account for efficiency losses, you're nowhere near recharging your 1.2Kwh battery capacity. I would personally cross 200w out of your mind and count on 300+. Which also brings up the point, unless you're trying to make this setup portable, you might be better off buying 1 or more bigger panels rather than 3 100w. Downside would be usually all the 250w+ panels have higher voltage output, which means you can't use a cheap PWM inverter with a 12v battery (assumed from your 1.2kwh / 100ah), it would mandate you use an MPPT charge controller. They're more efficient anyway, but cost more. Question then becomes, if you're looking for CHEAPEST, what is the performance of a system built around a $20 pwm charge controller and more solar watts, vs a $60-100+ MPPT and less solar? I have bought used 260w panels for $38/ea so the difference in price between a pwm and mppt is technically something like 300+w worth of solar dollars if you look at it that way.

Honestly, based on your accounting of the situation already being fairly thorough, i doubt you will go wrong with your choices. About the only way you could screw up a purchase would be to buy an inverter that couldn't start the fridge compressor. If you buy too little battery or solar you just add more to it or shrink the 'run time' until it fits your current capacity, no real loss there since you continue to use the purchased components. But if you buy an inverter that can't start the fridge and you can't return or exchange it for full credit, that is actual money lost to a mistake. So i'd make sure you hit that target, and then upsize the solar and battery with whatever's left.

 

[Doggydogworld]

Do you need to handle 24 hour outages or multi-week ones? How frequent?

Less than 24 hours I'd use water bottles and gelpacks. For a few multi-day outages per year I'd buy a used generator. You don't have to run it continuously, just an hour or so every few hours.

Startup amps will determine your inverter and battery size. I'd guess a 2000W inverter and a 12V / 200Ah battery, but there's a recent thread where a guy couldn't run his fridge with a similar system. Maybe he had a bad connection or something, but it might be a hard-to-debug issue due to poor power factor at startup.

I strongly doubt 300W of panels will generate 1.5 kWh per day in winter. And you need a lot more than 1.5 kWh from the panels due to losses in the charge controller, battery and inverter. Another recent thread involved a guy getting less than 1.5 kWh/day out of 800W of panels. That's this month, not winter. He's also in a sunny location. Don't know the problem, but that was measured at his PWM controller. MPPT would do better, but not 2-3x better. Use PVWatts to get estimates for winter months at your exact location.

 

[Mattb4]

Check your refer for the FLA. It can be found inside the door. That will give you starting current. Depending on quality of inverter you likely will want to double that for running current to cover inverter overhead. For instance my small refrigerator lists FLA of 8.5a. That is 1020w so I would want a 2000w/4000w surge inverter.

Batteries should have enough amp-hour to cover the loads (inverter is a load both just at idle and during operation) for the whole day plus the next day during any time the panels are not making enough to cover load. If lead acid batteries do not forget that you only want to use half the amp hour they are rated for.

Panels almost never deliver full rated watts. 75% is about a good average in full sun. These need to both supply loads and recharge your battery from previous non sun periods.

If you want a shoestring setup you might look at my review of the EAsun 3kw AIO in the Offgrid Inverter Forum. Hard to get much cheaper and have some reliability.

 

[Vigo]

The first thing i ever ran truly around the clock off my solar system was my fridge. I hate to be overly optimistic and lead you astray but i'd be REAL surprised if a 1000w inverter couldn't start the average fridge. I know it depends on a million things, but.. my fridge only uses about 120w with the compressor running. I actually tried running it off a 400w inverter the size of my hand at one point and if i remember correctly it could start the compressor.. sometimes. More than never. Which leads me to believe i'd be way into the safe zone with 1000w on my personal fridge (it's hooked up to 10,000w of inverter now but that's beside the point). Unfortunately since 1000w inverters are close enough to the cheap end of inverters in general, you're still going to run into some that can't do anything close to what they say they can do even if they're 'sized' accurately based on your appliance ratings or even direct measurements of your exact fridge. If you were buying a 3000+w inverter the chances of it doing what it says it does go up dramatically, not that that helps you save any money. Upsizing 'to be safe' is a good idea but when you say 'the cheapest way' i hate to just make throwing more money at it my main recommendation. ? But usually the cheapest way to do something is to break a few eggs while figuring out what the actual minimum you can get away with really is. I once tripled the wheel horsepower of a minivan with the stock pistons in it, but i broke a lot of pistons in other engines before i got to that point! Bare minimum is a bit of an art form. If you want it to work well on the first try, you really should 'take what you think you need and double it'.

 

[Ampster]

Check your refer for the FLA. It can be found inside the door. That will give you starting current. Depending on quality of inverter you likely will want to double that for running current to cover inverter overhead. For instance my small refrigerator lists FLA of 8.5a. That is 1020w so I would want a 2000w/4000w surge inverter.

If the OP is lucky to have a more modern refrigerator with an inverter driven compressor with little startup surge, he may be able to get by with a smaller inverter. His Kill A Watt may tell him that info..

 

[flinx777]

If the OP is lucky to have a more modern refrigerator with an inverter driven compressor with little startup surge, he may be able to get by with a smaller inverter. His Kill A Watt may tell him that info..

Excellent point! I'll plug it back in and monitor the start up surge values. Thanks for pointing that out.

 

[Ampster]

Excellent point! I'll plug it back in and monitor the start up surge values. Thanks for pointing that out.

You may be able to tell by just watching the load. If it modulates, it is probably Energy Star and inverter driven. If it is on then off it will likely have a surge.