By Mark Jones
I was bored as I waited for my “torch” — something that this food truck called its sandwiches — and so random thoughts came and went. This torch name seemed to be an unnecessary gimmick. Fumes directed my next thoughts: fumes from portable generators. Each food truck in the line of food trucks at the farmer’s market was running a generator. The small engine fumes and the noise from the generators ultimately galvanized my thoughts. There must be a better way!
I am a food truck fan. But one universal truth about them is noise and exhaust from small, portable generators. Small generators are a poor way to make electricity. The food truck generators are nominally 2000W units. Five gallons per kilowatt-hour, about 15% efficiency, represents a pretty good upper bound for performance. $0.41/kWh is about what electricity is costing the food trucks at $3.20/gallon gasoline. That is four times the quoted cost of electricity and more than double the delivered residential cost in my area. It is expensive electricity.
Make that expensive and dirty electricity. Municipalities are clamping down on small engines over CO, NOx, hydrocarbons, and particulates. None of the pollution controls on cars appear on small engines. Small engine exhaust, while a fraction of what a car produces, stinks. Those emissions are in addition to the CO2 emissions. Cleaner burning natural gas on the grid is more than 50% efficient even after the 5-7% distribution loss. Small generators produce around 3.9 lb of CO2/kWh, more than four times the Michigan grid emission factor.
Batteries seem to offer a better solution. Charge the batteries from the grid and use batteries to make the food truck experience quiet and fumeless. Flooded lead acid batteries remain the lowest-cost rechargeable batteries. The cost for deep discharge batteries is more than 3.5X the cost of the generator. Throw in the inverter/charger needed, and you are looking at about $1,200 for a DIY system, six times the generator cost. It would weigh nearly 400 pounds, versus less than 70 for the generator and fuel. Rather than sit on the back bumper, as generators often do, the battery system would have to be built into the truck. Lithium-ion batteries are lighter, but more costly. I estimate around $1450 for a DIY system based on deep discharge LFP batteries. Lithium-ion power stations, sometimes called battery generators, offer a nicely packaged but more expensive option. A black Friday deal puts a comparable unit at $2,799, roughly 14 times the gasoline generator. For the added investment, you get a unit that is about the same weight and size as the gasoline generator. Based on a 5-day week and 6 hours per day, a DIY battery system would have about a one-year simple payback. It would be closer to three years for the battery generator. Not a great investment, but not crazy either.
What ultimately keeps batteries out of food trucks is something laptop users have experienced. When the battery is dead, there is no recourse to keep working. It doesn’t matter how many customers are in line — the kitchen will close when the battery dies. Splash a bit more fuel in the generator and all the customers get served. The more flexible solution is the cheaper solution.
For the foreseeable future, food truck fare will come with a side of noise and fumes. Batteries, while they continue to get better, sadly still aren’t good enough to replace inefficient gasoline generators.
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Filed Under: Commentaries • insights • Technical thinking
