With the right installation, battery banks can provide reliable power for years. In this article, you’ll discover how to avoid costly, hard-to-diagnose battery installation mistakes, and you’ll learn a holistic approach that prevents costly errors long before installation.
1. Not Starting with Efficiency
Each additional kWh of energy demand requires extra solar or wind generation, battery storage and backup generation. Thus, it’s cost-effective to start by increasing efficiency.
First steps include replacing inefficient electronics and appliances with Energy Star models, eliminating vampire loads using switchable power strips and adjusting thermostat settings seasonally.
Next, consider adding blown-in insulation to walls and attics. Since nearly half of household energy is used for space heating and air conditioning, this can drastically reduce heating and cooling demands.
Finally, whole-house fans and nighttime ventilation offer inexpensive comfort. And compressor-less Variable Refrigerant Flow HVAC reduces electricity usage by ~90 percent.
2. Improper Sizing
Oversized panels, turbines and batteries waste money, but undersized systems can make everyday living frustrating — and shorten battery life due to deep discharging. The solution? Calculate accurate electrical loads.
After taking steps to improve efficiency, check the past year’s utility bills to estimate power requirements. Affordable devices like Kill-A-Watt accurately monitor individual appliances’ energy usage and reveal vampire loads. From there, the basic calculation for a system’s power needs is: Watts = amps x volts
For instance, if 1,000 watt-hours (1 kWh) a day are needed, a 12-volt / 84 Ah battery bank (1,008-watt capacity) will not address power demands because the battery would be exposed to 100 percent depth of discharge every cycle.
Experts recommend sizing your system based on a maximum of 50 percent depth of discharge (DoD). In the example above, the battery bank would need to be sized to 12 V / 168 Ah — double the estimated Ah requirements.
Note that some battery manufacturers size systems based on 80 percent or 100 percent DoD. This assumption can provide inadequate reserve power for heavy loads during heat waves and frigid winters or for cloudy or foggy days with low solar production. Batteries discharged by more than 80 percent lack reserve capacity to power high-energy appliances or even keep the lights on.
3. Choosing the Wrong Batteries for the Application
There’s no one-size-fits-all battery. Instead, key factors include ambient temperature, technology, desired voltage, maintenance, sustainability/recyclability and cost.
Lead-acid batteries are the most common for renewable systems. Refined over 100-plus years, they’re longer lasting and 50 to 90 percent less expensive than other technologies. According to the EPA, lead-acid batteries are 99 percent recyclable — more recyclable than an aluminum can.
Options include flooded batteries, which offer the highest ROI but require periodic water adjustment and other preventive maintenance, sealed valve-regulated lead-acid (VRLA) batteries and zero-maintenance options that are more expensive.
Lithium-ion batteries don’t require maintenance and offer the highest power density (and thus, lightest weight). For lithium-ion batteries, battery management systems (BMS) are required to prevent overcharging and to reduce the risk of house fires and explosions caused by thermal runaway. Li-ion’s cost per Ah is the highest and they are zero to 60 percent recyclable.
BMS is not required for lead-acid and many other battery chemistries, but BMS is beneficial because features like temperature-based charging, total and per-cell voltage and DoD monitoring help increase capacity and minimize damage caused by temperature extremes.
Whatever technology you choose, only buy deep-cycle, renewable batteries designed specifically for heavy cycling.
4. Improper Wire Sizing
Wire size varies based on amps carried and how many feet electricity must travel. Often, undersized cables are the hard-to-diagnose cause of system failure.
Just as water needs enough pressure to travel through a garden hose, an electric current must have enough voltage to travel. And much like a garden hose, electrical current must exceed pressure (impedance or resistance) caused by wire shape, thickness, length and other variables.
When cables are too small, voltage drops and makes the load work harder. This can cause lights to flicker, heaters to underperform and motors to burn out early. Worse, undersized cables can generate heat and even start fires. A smaller AWG means a larger cable. To calculate ideal wire size, use a “wire gauge calculator” and specify no more than a 3 percent voltage drop.
5. Improper Storage
Batteries last longest at or around 77˚ F. Every 18° F temperature increase drops available cycles by 50 percent. The cold reduces available capacity exactly when solar production is lowest and energy demands are highest.
The only solution to this problem is protecting batteries, but common storage solutions such as insulated coolers and old refrigerators offer little buffer against the cold, and they trap so much summertime heat that battery temperatures often exceed 140° F.
A better solution is storing batteries in a well-insulated, enclosed structure, either inside the home or in a properly vented box in a garage or shed. To do this, arrange batteries to ensure 1/2-in. air gaps and allow for easy maintenance. Never install breakers, switches or spark-producing devices inside an enclosure — this could cause an explosion.
The best approach uses standalone systems such as EMPUS, an insulated structure that maintains ideal operating temperatures year-round, to maximize the lifespan of batteries and electronics.
John Connell is VP of Crown Battery’s SLI Products Group.
— Solar Builder magazine