What do you get when you cross one partner’s love for coffee and baking, with the other’s can-do attitude and draw to renewable energy? A solar-powered café on wheels.
Years ago, Kathy Reinert pondered how best to channel this love for coffee. “Living in a rural community, it was difficult to appease the desire for quality coffee in our small town. After having a passion for coffee for several years, I began looking for options to bring it closer to home. Although the population is low, our area provides a hub of traffic for businesses in the region.”
Taking note of the growing trend toward food trucks in the restaurant industry, the pair began to consider putting Kathy’s ambition on wheels. Unable to justify the cost of a brand new truck, Matt and Kathy embarked on the tedious search for a cost-effective, yet reliable, alternative. After many months of searching, they stumbled upon a van with a body in good condition, but a frame that had seen better days (to put it lightly). After fixing the fist size holes in the frame, assembling prefabricated rails, drilling 100+ holes for mounting the truck components, and a hot dip treatment to prevent corrosion, Kathy’s vision began to materialize.
Powering the Café
To satisfy the tremendous energy demands of a fully operational café, the initial thought was simply to use a 15kW propane generator. The idea was abandoned after Matt and Kathy considered the cost of fuel, maintenance, and noise of a generator. As a Field Engineer servicing commercial-scale wind turbines for Avangrid Renewables, and as a former US Navy nuclear electrician and a master electrician in both MA and CT, Matt soon began exploring renewable alternatives. A battery-based solar solution quickly became the leading contender.
Matt’s system needed enough battery capacity to fully power the café for up to 4 hours each morning. This meant it had to work with a low sun angle and still be able to handle cloud cover. After each shift the truck would return home, giving the solar array time to recharge the batteries, and ideally even send any excess power to the main house panel, thereby offsetting their home energy usage.
Sizing the Battery Bank
In order to determine the required system size, Matt started by creating an incredibly detailed loads list outlining the anticipated surge, continuous duty, and estimated daily runtime of each appliance. These calculations provided us with the two essential figures used to design an appropriately-sized off-grid system: the estimated daily energy consumption (kWh) and the required continuous power and surge rating (kW).
The first of these two calculations would be used to size the battery bank and solar array. The estimated daily energy consumption of the café came out to about 8.7kWh over the course of the 4-hour period that the truck would be out on the road. After accounting for 80% depth of discharge (typical for LiFePO4 batteries), only one “day” worth of storage (knowing that there would be grid power available each night for recharging if necessary), and roughly 90% inverter efficiency, it was determined that about 250Ah of battery capacity at 48V would be required.
8700Wh / 0.8 depth of discharge x 1 day of autonomy / 0.9 inverter efficiency / 48V = 250Ah
Matt hoped to take advantage of the incredibly high cycle life and reliability of the SimpliPhi 3.8kWh LiFePO4 batteries. At 75Ah and 48V apiece, a four-battery bank proved to be the perfect size.
Sizing the Array
Matt and Kathy were limited by the amount of space on the roof of the truck, as is the case with many mobile installations. Normal array sizing calculations might have indicated that a 5kW array would be required.
8.7kWh per day / 2.68 worst case sun hours given no tilt angle / 0.65 system losses = 5kW
This of course does not even account for the fact that the café would only be in operation during early morning hours, not during the peak solar window (9AM – 3PM). Therefore, the best course of action was to choose a module that allowed Matt to fit the highest-possible wattage array on the roof.
For the available roof space, six Hanwha Q. Cell 395W Duo Cell modules would provide the greatest output possible at a reasonable price. Although a 2.37kW array might seem smaller than necessary, remember that the café only needs power for four hours at a time and can spend the rest of the day recharging. If a home solar system runs marathons, this system would be a sprinter. The panels would feed into a single Schneider Conext XW MPPT 60A 150V charge controller to charge the batteries.
2370W solar array / 48V battery bank = 49A minimum charge controller output
Work Smarter, Not Harder
Instead of the bulky and noisy 15kW generator, Kathy and Matt opted for a much smaller and quieter Honda EU7000iS – just in case the solar and battery
power was inadequate. The generator can be controlled by a Schneider Electric Conext AGS for a fully automated source of backup power.
At first it looked as though more than one inverter would be needed to handle the full continuous power and surge demands of the café. With an HVAC, water heater, microwave, coffee grinder, espresso machine, etc., it was no surprise that the total continuous duty rating worked out to about 6kW with a potential peak load of about 19kW if all loads surged at the same time.
Matt decided to power three of the largest and least frequently-used loads with the generator instead of the inverter, which vastly reduced the required size of the inverter. This allowed them to use a single Schneider Conext XW+ 6848 Inverter/Charger to power the loads in the truck, while also allowing for AC charging from the utility grid or the onboard generator if required, cutting down on system cost and complexity. In fact, by the time Matt and Kathy were preparing for the café’s maiden voyage, they realized that if they pre-heated the espresso and drip coffee machine with utility power in the morning, they wouldn’t need to run the generator at all.
Kathy recalls: “The name “All The Perks” came about as we offer several beverage options; the “Perks” serving 2 purposes; coffee percolation and the perks of having a variety! This dream would never have been possible without the support and expertise of my husband, Matt.”
With the system up and running, Matt and Kathy have yet to run the generator and the batteries have not yet dipped below 61% state of charge. The solar panels produce enough power during the day to recharge the batteries, and even offset Matt and Kathy’s daily home energy usage by more than 10kWh on the sunniest days. Although it is incredibly uncommon to have a temporarily grid-interactive system, given Matt’s extensive experience, he was able to install a four pole automatic transfer switch to comply with NEC grounding requirements, and therefore allow for temporary connection and disconnection from the utility grid.
With a healthy mix of passion and determination, Matt and Kathy were able to turn a long-time dream into a reality. An impressively compact, yet slightly oversized, battery-based solar solution has allowed them to not only avoid the noise, size, and cost of a big generator, but to be proud of the clean energy that drives their business.
Stories like these make us proud of what we do and thankful to have played a part in the project. With a month or so of operation under their belts, the couple looks forward to seeing where else they will be able to go as they continue to expand their range and push the limits of their solar-powered café on wheels. Thanks to All The Perks for permission to use the photos. We can’t wait to see what they’ll have brewing for us in the future!