By Robert Doane, VP of Technology & CTO, eNow Inc.
Fleet managers know that all batteries eventually weaken and fail — all types, primary and auxiliary batteries alike. But can battery failure be postponed, and if so, for how long? What are the costs vs. savings for remedies?
In the last decade, mobile solar technology has proven to be a cost-effective solution for many battery power problems. In some applications, solar systems generate savings that provide return on investment within 12-18 months. Here’s what you need to know.
When and why batteries fail
Primary, or starter batteries, on heavy-duty trucks usually expire during the cold of winter. Largely because cold batteries supply reduced cranking power, and cold temperatures thicken motor oil — making it harder for the primary batteries to turn over the engine. But that’s only half the story.
It is during the heat of summer that batteries sustain damage that only becomes obvious in winter. High battery temperatures boil off electrolyte faster – weakening the battery and setting them up to fail in winter. During summer, batteries can also get even hotter due to overcharging by the alternator.
Solar solutions
Recently, advanced mobile solar systems — developed specifically for the trucking industry — have proven to help reverse this problem. The most effective of these systems feature smart, temperature-compensated charging technology that maintains a consistent, healthy state-of-charge (SOC) in all temperatures. This reduces premature battery failure due to overcharging, undercharging and partial charging — and extends battery life by two to three years.
Most applications see a significant reduction in fleet operating and maintenance costs due to reduced battery replacements, downtime, and emergency road service — with full ROI on system cost and installation within 9-18 months. Then bottom-line savings accrue over the 20-year life expectancy of most solar panels.
Thanks to solar systems, liftgate-equipped delivery trucks in urban areas can greatly reduce idling in order to keep their liftgate batteries charged – reducing emissions and fuel consumption.
System basics
Mobile solar systems for trucks include two main components – solar panels and charge controllers – connected by a heavy-duty wire harness and power disconnect switch.
Solar panels or modules contain photovoltaic (PV) cells made from silicon that transform incoming sunlight into electricity rather than heat. They deliver the electricity through a power cable harness to a charge controller located near the batteries, usually in a protective battery box. The newest generation of solar panels is flexible, lightweight, 1/8” thin and range in output from 100 watts to about 400 watts. Completely covered with PTFE film (like Teflon), they are weather-resistant, scratch-resistant, and designed to perform in all temperatures and conditions.
Installation of solar panels on trucks is straight-forward and generally takes an experienced technician two to three hours. Panels are securely mounted to the roof of the tractor or trailer using a combination of high-performance adhesives. Many truck and trailer dealers and up-fitters will install solar systems while you wait.
It is important to match the solar system’s output to the equipment’s power requirements. Key considerations include: the battery capacity and type (flooded lead-acid or AGM) of batteries to be charged, electric load (watt-hours) and desired runtime of the auxiliary equipment (e.g. battery HVAC, hotel load, liftgate capacity, and cycles), and other available charging sources (alternator or shore power). For liftgate applications this tool is helpful.
Generally, we recommend choosing a solar system with more power output than you need — because the amount of sun and clouds varies each day. It is worth noting that, even on cloudy days, advanced solar panels can generate considerable charging power as they convert both visible and invisible wavelengths into electricity.
Charge controllers function as the brains of solar systems and are typically housed in a waterproof aluminum enclosure about the size of a small paperback book. Top-performing charge controllers use a programmable, 4-stage MPPT (Maximum Power Point Tracking) algorithm that ensures optimal battery charging. While more expensive than PWM (Pulse Width Modulation) controllers, MPPT controllers are significantly more efficient and generate more energy from the same size solar panel.
Additionally, advanced charge controllers not only monitor battery voltage but battery temperature. This temperature-compensated charging technology maintains a consistent, healthy state-of-charge (SOC) in all temperatures and virtually eliminates premature battery failure due to destructive charging levels:
- Overcharging batteries causes excess gassing & electrolyte to boil off, reducing life and capacity.
- Undercharging batteries causes “sulfation”, the build-up of lead sulfate crystals on battery plates, resulting in lower capacity & premature failure. (Lead-acid batteries dislike being discharged more than 50%.)
- Hot batteries are common during the summer and require a reduced charge voltage for optimal performance and battery longevity.
- Cold batteries are the opposite, requiring a higher voltage for optimal performance and longevity. (Note: alternators do not compensate for battery temperature.)
Managed charging process
In monitoring battery voltage, an advanced charge controller senses the battery’s state of charge and when needed, delivers a managed charging process:
- Bulk stage, when most of the charge is delivered.
- Absorption stage, a lower charge current that saturates the battery.
- Float stage, when loss due to self-discharge is addressed.
- Equalization. Periodically on flooded batteries, an equalization charge takes place, where all cells in the battery are brought up to full capacity by a short period of over-charging which stirs up the electrolyte by creating gas bubbles.
Costs savings for top applications
Based on the above, solar-based battery charging systems reduce battery replacement and maintenance costs simply by extending battery life, which in turn saves labor costs for removal and installation of batteries. Additional savings include:
- For liftgate applications, where dead or weak batteries are a problem, fleets can expect savings from the reduced need to idle engines to operate liftgates, greater productivity from an increase in liftgate cycles; reductions in truck and driver downtime, emergency road service and liftgate repairs due to premature failure of solenoids and motors. Here is where we see the longest battery life – from 1 year to 4 years.
- For in-cab HVAC and battery APU applications, where drivers must start their engines before their rest period has finished in order to charge the APU batteries and run their HVAC – solar systems will extend the eAPU runtime which reduces if not eliminates engine idling. This saves premature engine overhaul and DP filter maintenance – not to mention fuel consumption between one-half and one gallon per hour. Other cost savings include reductions in emergency road service, penalties for late deliveries and fines for idling.
Can solar help my fleet?
To confirm if solar technology can help solve your fleet’s battery problems and reduce costs, the best practice is to record battery voltage data on multiple vehicles, with and without solar, for at least 30-90 days. This will show a battery’s level of usage and state-of-charge (under, over and optimal charging) during the vehicles’ operation — including parasitic loads, inactivity, engine starts and idling to charge batteries, run liftgates or HVAC. Additionally, this data will help guide the specification of an optimal solar system size.
Solar tech for EV
Even electric trucks need battery power to run 12-volt systems such as HVAC, liftgates, electronics, lighting and hotel loads for driver-comfort systems. For some electric truck applications, it may be cost-effective to use a solar battery-charging system to reduce the load on the powertrain battery — potentially extending a vehicle’s range.
