“I’ve just been burning fuel, you know. The price and the capabilities, the battery storage haven’t been there (to convert our generator). With (Joule Case) we could get to that point where it made economic sense as well… Being able to run silently really opens up a lot of doors.”
- Sid Gauby, Owner: Slow River Coffee
For the first six years of operation, Sid Gauby and the Slow River Coffee truck relied on an inline diesel generator to provide power to his equipment. But he had been searching for an opportunity to shift to a cleaner solution and after a chance encounter with the Joule Case team at a festival, he found the right fit. Joule Case was able to work with Sid to design a battery solution for Slow River that saved money while allowing Sid to serve his customers in a cleaner, quieter, greener environment. But how did the Sid and the Joule Case team determine how much battery he needed? Below we take a look at the solution that Slow River and Joule Case developed to replace the original diesel generator.
12 kW inline diesel generator
23 kWh Li-ion battery bank
12 KW, 240 VAC split-phase Inverter/Charger
7 175 W Solar panels (1225 W total)
60 A, 48 VDC Charge controller
Before Sid converted to his battery system, he relied on a 12 kW inline diesel generator to power his van. The generator got the job done, but carried a high daily operating cost driven by the cost of diesel. It also required Sid and his customers to live with the background noise and exhaust smell. To determine what was necessary to replace the generator, the Joule Case team first needed to figure out how much load (measured in kW) that Sid would need at any given time. We knew that a 12 kW capacity had worked previously but to ensure that we couldn’t go any lower we also listed out all of his loads and measured the peak load during operation.
Wega Concept 2 Group Espresso machine (4800 W, 240 V)
Bunn Double Brewer (5800 W, 240 V)
3 Blentec Blenders (1500 W)
Bunn MHG Grinder (1320 W)
Mahlkonig K30 Twin (2x 850 W)
Kuuma Water Heater, 6 Gal (1500 W)
True Single Door Undercounter Fridge (230 W)
Flowjet 2.9 GPM 50 PSI Water Pump (90 W)
Although the total wattage of the equipment is nearly 19 kW, the total power that the Joule Case team measured peaked at 11 kW with a steady-state value below 10 kW. To ensure that he had plenty of operational room, Sid opted for a 12 kW Inverter/Charger. This piece of equipment can handle steady-state operation up to 12 kW and manage surges, like those caused by blenders, grinders, pumps, and other similar loads, of up to 36 kW. This surge capacity is one of the many ways that a battery system outperforms generators, which tend to have a surge capacity of fewer than 1.5 times their rated load.
The next step in our process was to determine how large a battery bank Sid would need. A typical day for Sid is a 4-6 hour shift during which he serves 250-300 drinks. We worked with Sid to estimate how much time out of each hour that his equipment was running and then use that to estimate how much energy he is actually using. For example, his espresso machine will use up to 4800 W, but only when he is actually pulling a shot. Even during his peak serving window, we found that Sid was only using his espresso machine for about 20 seconds out of each minute (or ⅓ of the time). By performing a similar analysis we were able to estimate the total battery bank size and landed on a capacity of 23 kWh (kW-hours). After the conversion, we checked back in with Sid to determine how much capacity he used in a typical 4-6 hour shift and found that he ended his day with ¼ to ½ capacity remaining, meaning he could work for several more hours or an estimated 400+ drinks per day.
The final step was to help Sid find solar panels and a charge controller that he could use to help recharge his battery bank. The charge controller is the piece of equipment that converts the output of the solar panels to the correct voltage and current for the battery. Due to the small footprint available on the top of his van, we identified 175 W panels and a 60 A charge controller. Sid opted to install seven panels wired in series for a total array size of 1225 W. Despite the relatively large total load for his van, we found on sunny days, the solar panels extend his operating window by 1-2 hours.
The conversion carried a high upfront cost but allowed Slow River to offset the high cost of diesel (fluctuating from $2.50 to $3.25 per gallon) with electricity from his home (averaging 8.7¢ per kWh) and from the sun (free!). This means that even if he were to recharge only from the grid, a complete “refill” of his battery bank would cost about $2.00 or less than one gallon of diesel. The addition of solar panels not only extended the operational time but allowed Slow River to qualify for the Solar Incentive Tax Credit available to all businesses that pair solar and batteries. A great summary of the Solar ITC can be found on The National Renewable Energy Laboratory website.
Cost of a new 12 kW Quiet Generator: $11,000
Daily Fuel cost (0.75 gal/hr, 5 hours/day, $3/gal): $11.25
Annual Fuel Cost (250 days/year): $2,813
Total Five Year Cost: $25,065
Battery and Solar Option
Cost of Batteries: $14,000
Cost of Solar Array: $1,225
Charge Controller: $500
12 kW Inverter: $3500
Equipment Subtotal: $19,225
Tax Credit: ($4,999)
Net Equipment Cost: $14,226
Daily Recharge Cost ($0.09/kWh): $2.07
Annual Recharge Cost (250 days/year): $518
Total Five Year Cost: $16,816
Even better than the savings is the fact that Sid’s customers don’t have to deal with the noise and fumes from the generator. This creates a more pleasant experience and makes it easier to order. And while Sid normally works during the mornings, he often attends events in the late afternoon or evening. He has been especially involved with the local schools. Having a battery-powered solution means he can park close to the school without distracting his potential customers.
Conversion from a generator to a solar and battery solution can be intimidating, with both complexity and a higher upfront price, but the benefits far outweigh the costs. By converting to a battery solution you end up with a system that provides a better experience for your customers and will save you money over time. If you have interest in a similar solution for your food truck, coffee truck, outdoor concert, or any other event where you are tired of relying on a generator please reach out to the Joule Case team.