My simple solar system – Part 2…..opppssss and a “duh!”

Well – my solar panels are on the roof, wires run, charge controller running and inverter installed. Just one problem – the system will not fill the role I originally intended. I am usually pretty good at math – but in this particular situation I failed to recognize the results of a simple math equation right in front of me.

First off – my plan was to use the solar panels to charge couple of marine batteries which would then power a very small refrigerator. The fridge is needed for my sons insulin in the event that the grid fails. Here is the problem:

Solar panels produce 45 watts of power for every hour of good sunlight (approx 8)

Refrigerator consumes 140 watts of power per hour 24/7.

Power needed = 3,360 watts daily

Maximum power supplied from solar panels = 360 watts daily

Obviously I am way shy of getting the power that is needed. I just did not so the math at the beginning. In order to make this successful – I need a total of 10 of these systems. That is not going to work. To accomplish what I have set out to do – I will have to rethink this project. I need more power – so a larger system is needed. I also need to source a lower power consumption refrigerator.

Another option is to seek alternate types of refridgerators to start with which consume little to no power.

Regardless of this setback – I still have my solar panels (which I purchased at Harbor Freight). I plan to use the system as it is now configured to perform a variety of roles such as running a radio, power tools such as a drill, and charge batteries.

Having this small system in a grid down situation will be MUCH better than having nothing at all.

More to come……




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40 thoughts on “My simple solar system – Part 2…..opppssss and a “duh!””

  1. dude….why are you running such a large refrigerator to chill insulin ? go get one of those 12v coleman camping “cooler type” setups, and for about 25 watts you can keep your insulin chilled….or better yet get one of those beer (sixpack) coolers for a car and chill insulin for about 5 watts/ both of them run on 12v/ …easy. you are thinking too big with the refrigerator you are using. these camping units have a semiconductor heat transfer plate that runs on dc voltage, and it is very efficient. you could even put some more insulation around them to make them even more efficient. you can adjust the cooling level by playing with the voltage, or using an on/off cycle via timer. hell, you could even wire up a thermostat if you want to. this is your insulin answer.

    keep it up/ dave

      • If your son has diabetes and needs insulin, try to give him FENUGREEK powder, that will lower blood sugar immediately and will not need insulin! forget about the high tech stuff! go to to buy lbs for less than $20, good luck, L

  2. Unopened, not-in-use insulin should be stored in a refrigerator at a temperature of 36-46º F.
    Refrigerator power consumption notes:
    a) Raise the set temperature to 46º F (less power at the higher set point)
    b) Buy the smallest size of refrigerator (smaller size means less power)
    c) Increase the amount of insulation (could add insulation external to the refrigerator)
    d) Lower the ambient temperature (placing the refrigerator in the colder basement or outside in the winter will cause less power consumption).
    e) Power consumption only occurs when the compressor runs so the peak current draw out of a battery is not as important as the average watts over the course of a day or month.
    f) The SUN FROST RF16 typically consumes 15 KWH per month. This translates to an average of 20.8 watts per hour! (expensive refrigerator but really efficient – check out their web site.)
    15 kWh per month
    0.5 kWh per day
    20.8 watts per hour SIZE your solar system for this much available power on Dec 21st.

  3. Rourke,

    You might want to check some RV dealers and see what a RV refridgerator would run. I used to have one that ran on 110 vac, 12 vdc and propane and if I remember right the 12 volt heater was 140 watts for a 3 cubic foot box. These are fairly cheap if you can find a used one but new they are still resonable.


  4. Rourke
    Your soulition might be two fold, 1st a small dorm type refer, and 2nd a root seller. First the smaller fridge should consume less power, and using natural geothermal of a root seller ( after 4ft down you get a constent temp of 56-58 degres) you’ll will have to run it less often. This is just a thought. Something to add to your curent idea. I think you’re on the track.

  5. Why don’t you just use a propane refrigerators. The have small ones that should work. Also, one can go to the camper junkyard and pick one up cheap.

  6. Rourke,

    Look into a propane powered one, they are common in popup campers. They work rather well and propane is easy to stock up on and store. Just a thought.


  7. I have designed small systems for my cabins off grid. A refrigerator has always been out-of-reach off-grid due to the excessive power requirements, however; If you were to visit a truck-stop or two, you’d find some small coolers used by truckers that have a low power use. Look for one that has an 120ac power cord as well as the 12VDC. Run the 120VAC optional power off your current system and rely on the 12VDC power option off your car or truck as a last resort.

    I am not a big fan of harbor freight. If you plan on purchasing additional panels check out ALT E online at:

    This is where the so called “solar dealers” buy their stuff. All top quality.
    Good luck!

  8. Rourke,
    What about getting a smaller fridge like the ones kids get for their dorm rooms? The watts required should be a lot less if you are not trying to run a freezer unit.

  9. I have the same system on the roof of my motor home. It gives me about two hours of computer time (or TV) every evening. You have just highlighted photovoltaic’s biggest problem, i.e. low actual power production. In most parts of the country you would be lucky to get an average of four hours a day from a PV system. The cost benefit ratio for PV is depressing. However, in a SHTF scenario it is better then a gasoline/diesel/NG powered generator. Not for it’s efficiency or cost benefit ration but simply because it works even after society has stopped working. But it still isn’t practical for high energy consumption uses. It will power a couple of LED lights in the evening and allow you to listen to the radio or run your computer for awhile but without a $40,000 investment it won’t power your home.

  10. Ever considered Evaporation Coolers? Zero energy needed or moving parts. When worked properly you could probably get temps cool enough to extend the shelf life of insulin? Possibly use a small fan, powered by the solar panel, to maintain optimal air flow on the cooler? Hope this helps, love the site.

  11. Our pop-up camper has a dual-fuel refrigerator – electric and propane. We have used the propane fuel several times and the refrigerator works great. Just a thought.

  12. Rourke-
    Given the importance of the issue you are trying to mediate, I’d suggest a
    DC fridge…a bit pricey, but is much more SOLAR system friendly. Trying to power an AC power hog, while a 12 or 24-volt DC system is available, is working uphill.

  13. I can see from your picture that your using vented wet cell batteries. Just wondering if your marine batteries are deep cycle or standard starting batteries? Deep cycle are a must in this application. Also GEL and AGM (absorbent glass mat) offer some nice advantages over wet cell (price is not one of them). What refrigerator are you using, a small dorm room style or an rv type?

    • Slaveboy –

      I am using a small dorm style with no freezer. As far as the type – I honestly do not know – I thought that being Marine it was a deep cycle. Hmmmmm……could be another “duh”.


  14. Something to consider is one of the personal mini refrigerators that are meant to keep a couple of cans cold. You can find them on Amazon for about $30-$40. Your system still wouldn’t power it completely, but with some additional insulation it may be enough to help stabilize insulin.

    There are also low power fridges that will only pull about 45 watts, but they are pretty expensive.

    With a little creative engineering, I think you could make this work. 🙂

  15. May I ask how much the total system cost you ? I am thinking of putting in a small system like this to power a few things and to keep the battery charged on my generator . Also have you thought of using a propane refrigerator ? You can get some large or small ones at a camper supply place and a 100 gal tank will run one forever if that is all that is hooked to it . Just some thoughts
    .Hope that helps
    Robert W

  16. You might want to consider a used RV refrigerator that operates on 12 volts. You should be able to find people that strip out RV’s and campers for parts and sell them on craigslist for as little as $20.

  17. How about this: Designate a small under the table type for critical needs? Perhaps the wattage will be less and fall closer to the caps of your system. I use these types of small coolers in my place of business, just a thought.

  18. What about a smaller fridge like the ones kids get for their college dorms? A small fridge without a freezer should use less watts and may be just what you need for the single purpose of a safe long term storage of insulin.

    • VTpaladin – Thanks for the ideas – that actually is what I am using. A very small fridge with no freezer.

      Take care – Rourke

  19. Hello, Some things to consider. It may be more effective to just run a generator for about an hour twice a day to power the fridge. Inverter gennys are very fuel efficient and quiet. Don’t forget your vehicle can be used as a generator if you attach an inverter to it. Also consider a small propane powered rv refrigerator in combo with 2-100 lb propane tanks. They can be found used quite cheaply and that much propane would last a long time. HTH

  20. Rourke, here’s a little info on batteries. A standard car/marine battery is designed to start the motor and really thats about it. They are not designed for repeated discharge / recharge. Running them below half charged capacity multiple times will eventually damage them. Deep-Cycle batteries have fewer but thicker lead plates. They are designed to run electrical equipment and therefore can be nearly completely discharged / recharged repeatedly without damage. I noticed you had your setup in a plastic tote, not a good idea. Wet cell batteries vent Hydrogen which will collect in your tote. Hydrogen is not only flammable but explosive. You can buy HYDROCAPS that will replace the vent caps on a wet cell battery, they are supposed to eliminate the Hydrogen venting out. Then a tote would be ok but I still wouldn’t have other electronic devices in the tote with the batteries. Gel and AGM batteries are a even better option but are far more expensive. You can find plenty of info about them on the net……. good luck

  21. To all who suggested a propane refer. Thats all well and good and propane refers are pretty efficient however it used a non-renewable power source. Solar can be recharged while eventually the propane will run out.

    Personally I’m looking at 12v solar specific refers, yes very spendy. But they are designed from the start to use the 12v that I can supply from just about anywhere.

  22. I know people have made suggestions but my Energy Star fridge draws a constant 17 watts, rarely does it every have to kick up to 150 with every day use of the door opening and closing.

  23. How cold does it have to get? For instance, there is a natural method that will work well in some environments. It’s explained over at lifehacker…

  24. Ran across this insulin info that may be of interest. Search for “Frio”.

    I have been thinking of what kind of a power budget is available from solar panels, inverters, and batteries and decided I had to reduce my power requirements. My first priority was water from my well as a long-term supplement to stored water, particularly since my existing setup used so much power.

    After my old well pipe developed a hole in it, I decided to replace my old 220vac pump that pulled a surge current of 12-15A with a more energy efficient model. My well guy pointed me at Grundfos SQ and SQE pumps, so I got one and replaced my old working pump. Now, if worse comes to worse I have a working spare (altho not easily replaceable by any means) since I kept the old pump. BTW, this is a good site to help diagnose plumbing issues:

    The pump I selected runs on 120vac and uses a clutch to slowly ramp up its current usage. We tested it and it pulled no more than 7A at any time during a 15-30 minute test. Still quite a load for a battery and inverter to provide, but a lot fewer watts than the old pump. The new pump is also so quiet that I can no longer tell when it’s running. Not necessarily a great thing if things go wrong, as the only clue I had a hole in my well pipe was that the old pump ran a lot more than normal.

    With the install and hardware cost, this is my major prep purchase for the year. They’re not cheap, but neither are normal well pumps. Now if I can just find a good use for the old steel well pipe I scavenged.

    From my notes during the install, the new pump is the 1/2 HP 3″ pump head 10SQ-160 and motor Model B P10938. Obviously mine is not the only choice.

    Best wishes,


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