Good news today! I achieved one of my goals that started me on this journey of harvesting my own power at home. The goal was to bake a loaf of bread using a battery and an inverter. While this isn’t my final goal of actually baking a loaf of bread using 100% self-harvested power it is a worthwhile way point along this particular path.
A few years ago I bought a bread machine so I could easily bake fresh bread at home. A Zojirushi BB-HAC10 1 pound loaf bread machine to be specific. It has served the family well and I’ve fiddled with a whole wheat bread recipe so that it is to my liking.
I think I’m a measurement freak because I found myself hooking my Kill-a-watt inline with the bread machine, curious as to how much it was really costing me in energy to bake a loaf of bread. I won’t spoil the mystery by telling how much it cost just yet.
What I did learn by monitoring with the Kill-a-watt was that the lion’s share of the power is used during the baking cycle. The full process of making the bread from the time the start button is pressed until the bread “pops” out fresh and hot is about 3 1/2 hours. Mixing and kneading between the rising cycles used a very small amount of power. Measurements showed that the heating element used about 450 watts/hour and drew 3.75 amps of current. The heating element appeared to use an 80% duty cycle to keep its oven temperature constant so the high current draw wasn’t continuous during baking.
If at first you don’t succeed
Now translate this all into my failed dream of a no cost solar bakery. My first attempt to bake bread using my 500W modified sine wave inverter and battery from my ’97 Toyota Tacoma failed. While the process appeared to start well, for what reason it failed is currently unknown. My first suspect is the inverter because the impeller in the bread machine failed to spin and mix the ingredients even though the heater did heat the oven to the proper rising temperature. The current requirements for this part of the cycle didn’t seem high enough to even tax the battery. When I checked the voltage it appeared to be in the normal range and the low voltage alert on the inverter never sounded. This leads me to believe that maybe the bread machine required a cleaner power signal than the modified sine wave inverter could provide.
Not knowing for sure if it was the inverter or the battery at fault I decided I needed to replace both with what I thought was more appropriate.
Go big or go home!
I know that having plenty of head room when it comes to electrical systems is a good idea I decided to go big! (not to mention that I already am home so that isn’t really a useful option) I stopped by two local battery shops looking for some advice and to purchase a better battery but to no avail. My first stop resulted in my being referred to the store manager who quickly decided to hedge his bet and recommend his largest deep cycle battery. A little frustrated that he didn’t take the time to think through my needs I said thank you and drove to the second store. I ended leaving a message for the manager at the second store but never got that call back so I was on my own to do research.
While I was still unsure about which type or model of battery to purchase, I felt more confident in the realm of the inverter. I knew the bread machine used 450w/h during the peak of the cycle and that was pretty close to the inverter’s maximum continuous rating of 500W (800W peak). Knowing I wanted to upgrade to a pure sine wave rather than a modified sine wave I did some research online and found a 2000W (3000W peak) inverter that fit a comfortable price point for me. $250 for Home Depot and a few days later a 2000W pure sine wave inverter arrived on my doorstep.
While I was waiting for the inverter to be delivered I continued researching batteries. I decided on a deep cycle gel battery. Since I was going to be moving it around quite a bit I wanted the ruggedness that the gel battery offered. Capacity wise I opted to go with 100Ah. I considered a 200Ah (the big one suggested by the first store manager) but the sheer weight of it meant I would need my wife’s help to move around the house until I find it’s permanent home. I would have loved to buy a light weight lithium battery but the price point is just too high currently
My calculations showed that the total baking cycle consumed about 18Ah @ 12V. Using ohm’s law I considered that 3.75A @ 120V = 33.5A @ 12V during the peak of the bake. Then doing some guessing based on the battery data sheet a 100Ah battery felt about right if the discharge cycle was only 20% to bake the loaf. The current discharge also fell, in what appeared to me, within normal use range. Both of these factors are within the suggested limits to extend battery life.
I was going to order the battery from Home Depot as well as the inverter but by the time I got around to placing the battery order Home Depot was out of stock. Amazon offered the same battery for around $20 less and free next day delivery with Prime. (I assume Amazon had it stocked at a nearby warehouse as the don’t ship these batteries via air freight)
Success
Using Amazon’s next day delivery option the battery actually arrived earlier the same day as the inverter. I’ll detail how I hooked up the battery, inverter and bread machine in another post but the end result was what I considered to be a nominal loaf of whole wheat bread. (The loaf was a bit misshapen, this happens from time to time with a bread machine.)
Oh yea, I almost forgot. I promised to tell you how much it cost using grid power to bake the loaf of bread using the machine. The answer is about 3 cents. The Kill-a-watt reported that it took about 220 watt hours to bake the loaf. At 14 cents/kWh (using the green wind power up sell) * 0.22 = 0.0308. Compare that to nearly $500 for my first loaf. Fortunately for me the cost per loaf will drop dramatically once I hit that 100 loaf mark ($5/loaf). That is “if” I can get a system built to harvest enough potential energy to keep the battery charged.
Conclusion
While being cost effective is in many cases a worthy goal in and of itself, in my case, budget be damned, I’m going to bake me some @#$%& bread! To confess in all honesty, I’ve been procrastinating for years around getting a larger inverter and appropriately sized battery for truly harvesting and using my own power at home. The purchase while larger than I would consider normally is a solid backbone and foundation for future expansion and projects I have planned to harvest and creatively use home power.
Next steps
I’d like to find the root cause as to why my no cost option failed. Here are my next steps to determine what went awry:
- Try baking loaf using 2k pure sine wave inverter and see how far the cycle gets. Will it get all the way through the baking cycle?
- Try baking a loaf using the 500W modified sine wave inverter with the 100Ah Deep Cycle Gel battery.