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Solar Pantry Part 4: The Plan

At last we've come up with a plan! But before I jump into that, I'd like to summarize this blog series so far (for those just tuning in):

Solar Pantry Part 1: Feasibility
  • In which I count the cost of putting my pantry fridge and freezer on their own solar power system,
  • and learn that it's beyond our budget at the present time.
Solar Pantry Part 2: Analysis 
  • In which I analyze how and why I use my fridges and freezer,
  • and learn that 
    • many of the items I store in these appliances don't actually need refrigeration or freezing.
    • my pantry is simply too warm in summer for good food storage conditions.
  • In which I explore off-grid methods of keeping food without a fridge or freezer,
  • and get a couple of good ideas suitable for us. 

What I realized from these exercises is that my original goal was too narrow. We need to address not just freezing and refrigeration, also we need to improve our food storage conditions in general. In the light of that, Dan and I have come up with a three-phase plan:

Phase 1
  1. Move the freezer from the pantry to our enclosed back porch.
  2. Put the freezer only on solar power.
  3. Replace the old pantry refrigerator with a small chest freezer converted to a refrigerator. It will go on the back porch too.
Phase 2
  1. Update the pantry to make it more energy efficient:
    • better insulation in walls
    • replace old windows with energy efficient ones
  2. Work on ideas to cool the room in summer. Moving the fridge and freezer will certainly help with that. Other ideas:
    • ventilation, cool cupboard?
    • shade the window that gets afternoon sun
    • ice block "air conditioner?" (Ideas at Off Grid World.)
Phase 3
  • Make a root cellar.

Cost analysis for Phase 1 - I couldn't put both my old energy-guzzling fridge plus freezer on solar, but can I manage the freezer only? Based on the readings from my Kill-A-Watt meter, the freezer uses 1600 watts per day. If I've done my calculations correctly, here's what I've come up with. Remember, I only have $1500 for this project, but already have the solar panels.

2, 345-watt solar panels
   ✔
6, 235 AH 6-volt deep cycle batteries
$880
150-volt, 60-amp MPPT charge controller   
$431
1000-watt pure sine wave inverter    
$150  
TOTAL
$1461

Admittedly, there are still a number of other things like panel racks, wiring, connectors, fuses, battery box, etc., but it looks like we have the funds for the major components. Following are a few notes related to the above.

Solar panels. 345 watts, 57 volts each x 2 panels = 690 total watts for the solar panel array.

Wiring. Fortunately, we only have about 25 feet between the panels and battery bank. That will save both in amount and size of wire needed.

Batteries. Why 6-volt? Why not 12-volt? For a couple of reasons. Firstly, because so far I haven't been able to source 12-volt deep cycle batteries locally, and shipping for batteries is very high. Marine and RV batteries sold around here are dual purpose, listing cranking amps and low amp-hours (usually 35 to 55). They aren't cheaper and I'd need more to get more amp-hours. Plus cranking batteries won't take as many recharges as true deep cycle batteries.

The second reason is because 6-volt batteries are more heavy-duty. 6 and 12's are about the same time size. Why aren't the 6-volt smaller? Because they use heavier plates, which means more discharge cycles.

So, wiring two 250 AH 6-volt batteries in series will double the voltage to 12. Wiring the two pairs in parallel will double the amp-hours to 500. That's not quite two day's worth of energy storage, but that's more than I've got on the grid! Plus those four batteries are within my budget, although I'm still trying to shop around.

So far the only place I've been able to find 6-volt lead acid batteries is at Batteries+Bulbs, and I'm having a hard time finding other sources. I miss the days of phone books, when all local options were listed topically in the yellow pages. Search engines favor SEO (search engine optimization), paid ads, and political favoritism, which doesn't help one wanting to explore all the options. [UPDATE: I also found them at Interstate Batteries for the same price. Batteries+ is closer, however, and offers a 10% discount for ordering online.]

Charge controller.
  690 watt solar panel array (57.3 volts)
÷ 12 volt battery bank
= 57.5 amp minimum charge controller (rounded up to 60)
I'm looking at the Outback FLEXmax 60.

Inverter. This converts the DC (direct current) electricity produced by the system for my AC (alternating current) appliances. Thanks to my Kill-A-Watt meter, I know that the freezer uses about 185 watts when it starts up, then quickly drops to 100 to 102 watts and gradually decreases to 87 watts. The freezer light uses 24 watts. Recommendations for sizing inverters vary depending on the solar expert, so I finally decided on a 1000-watt inverter with a 2000-watt surge capacity.

Chest fridge. I first read about converting a chest freezer to a chest fridge in Prepper's Total Grid Failure Handbook. Several readers mentioned using them and how-tos can be found online. Two are at New Life on a Homestead and A Self-Sufficient Life. For now, the chest fridge would be plugged into the grid, until I get a better idea of exactly how much electricity it uses. As a freezer, the model I'm looking at is 5 cubic feet and has an energy rating of 219 kWh per year or roughly 0.6 per day. That translates to 600 watts per day, but surely as a fridge it should consume less(?). An experiment I plan to try is using it as an ice box. If I can freeze enough ice bottles in the freezer, it's possible that I can keep the chest fridge cold enough. We'll see.

5 cubic feet is not very big for a fridge. It will replace the fridge in the pantry, but I'll still have the fridge in the kitchen. I figure this situation will force me to change my habits and routine, plus implement more alternatives to refrigeration. The most perishable items I refrigerate are milk and meat. After that I would say leftovers and salad greens, but really, everything else could be stored elsewhere if I had cooler storage conditions. That's where a cooler pantry and root cellar will come in.

So that's the plan. The first order of business is to clear out the back porch and get ready to move the freezer. It's about due for a defrost anyway. After that we'll just take it one step at a time.

Next  → Solar Pantry Project Part 5: Back Porch Preparations

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