By John Connell, VP of SLI products at Crown Battery Manufacturing Co.
It’s easy for batteries to thrive in laboratory conditions or computer simulations. Too often, these perfect conditions are the source of marketing claims like 10-year guarantees.
But the real world isn’t as forgiving. In the field, experimental battery designs can fail early. And extreme temperatures, deep cycling and poor maintenance can slash any battery’s lifespan — leaving solar system owners in the dark.
That’s why trustworthy manufacturers test batteries in extreme real-world applications and analyze how they perform, charge and fail.
During the past two decades, Crown Battery has installed numerous sets of test batteries in mission-critical locations, including off-grid homes, hospitals, factories and mines across North America. These batteries are digitally monitored and analyzed, chemically assayed, put under scanning electron microscopes, x-rayed and torn down for R&D and engineering purposes.
These battery torture tests revealed core lessons about what really matters for renewable energy batteries, and you don’t have to spend tens of thousands of hours or millions of dollars to benefit from this research.
Here’s how you can maximize operating cycles, performance and reliability:
- Start with the right batteries for your system
- Protect them from harsh conditions
- Avoid deep discharge
- Consider a battery management system (BMS)
- Automate maintenance
1. Select the right batteries for your system
Which battery chemistry is right for you? Lead-acid batteries and lithium-ion systems are among the more popular choices.
Flooded lead-acid batteries offer the lowest per kilowatt-hour (kWh) cost and require regular maintenance. Absorbent glass mat (AGM) lead-acid batteries have near-zero maintenance but a higher cost per amp-hour. All lead-acid batteries are 99% recyclable.
Lithium-ion batteries also offer near-zero maintenance and feature the highest power density. Their cost is also higher. Lithium-ion’s power density makes some chemistries prone to thermal runaway and fires, and it is 0%-60% down-cyclable.
There’s no perfect battery. But for most applications, lead-acid batteries offer a good combination of reliability, ROI and real-world proof (more than 100 years’ of field-testing and optimization). Most lead-acid batteries look nearly identical on the outside, but engineering and manufacturing differences on the inside profoundly impact maintenance, performance and longevity.
Here’s what to look for with lead-acid batteries:
- Renewable energy-optimized design: Regular or car batteries aren’t designed for the deep discharging requirements of renewable energy.
- Heavy plates and more active material allow for more chemical reactions and longer life.
- Computerized lead-oxide production, paste mixing and curing improve quality and consistency.
- Robotic assembly bolsters reliability and reduces maintenance.
- Cast-on-strap (COS) welding offers 100-times the precision of manual welding for lower maintenance and more uptime.
- Aerospace vision systems enhance quality control.
2. Give me shelter
Extreme temperatures hurt batteries. Batteries last the longest and perform best around 77°F. Cold weather compromises battery temperature, performance, charge acceptance and temporary capacity. Hot weather slashes lifespan and performance.
Alarmingly, common lead-acid “battery boxes” like insulated coolers and fridges often worsen temperature extremes.
Where should you store batteries?
- Dry environments with moderate temperatures (50° to 85°F) are best.
- AGM and other no- or low-maintenance batteries can be stored inside the home or building.
- Flooded batteries are best stored in secured, vented boxes in a shed or garage.
How should you store lead-acid batteries?
- Store batteries off the floor in a dry, well-insulated enclosure with proper ventilation. This will prolong battery life and reduce temperature damage.
- Ensure batteries are away from electrical outlets, breakers and other potential sources of sparks.
- Mount a dry chemical fire extinguisher in a well-marked location.
- Always lock your battery box.
- For ventilation recommendations, see National Electrical Code, Article 490.9(A).
If you’re unable to protect batteries from cold weather, install a larger battery bank to compensate for diminished capacity.
3. Avoid deep discharge
There’s a dangerous trend in renewable energy system design. Some unscrupulous salespeople are sizing systems for 80% depth of discharge (DOD) — often to rig buying criteria toward higher-cost-per-kWh batteries.
Even if a particular battery technology can discharge deeper in the lab, you can’t afford to risk it. That’s because every battery needs reserve power in case of increased electrical demand or reduced energy production (for instance, during cloudy, foggy or windless days).
Besides, while safe DOD levels vary, all lead-acid batteries die early when they discharge too deeply. A good solution is to size batteries for no more than 50% depth of discharge.
A few rules:
- To stay below 50% DOD, size your system for two-times the true amp-hours needed, regardless of battery chemistry.
- If batteries are discharging below 50%, install extra batteries.
- Specify three to six days’ stored energy (batteries and/or backup generator) when going off-grid.
- Never exceed 80% DOD (50% DOD is optimal for enhanced power reserves and longevity).
4. Look into battery management systems (BMS)
During Crown Battery’s product torture tests, we closely monitor batteries’ internal health using battery management systems (BMS).
You can do the same in your system; a BMS can boost lifespan and capacity, reduce damage from extreme temperatures and save time on maintenance. Common BMS features are DOD monitoring, temperature warning sensors, total and per-cell voltage and more.
While a battery management system is a powerful tool for lead-acid systems, it is a necessity for lithium-ion systems to prevent overcharging and decrease the risk of thermal runaway.
5. Make maintenance automatic
Routine maintenance maximizes battery life and reliability. And every battery — even no- or low-maintenance models — must be inspected regularly according to manufacturer guidelines.
Routine lead-acid battery maintenance may include:
- Cleaning battery terminals and inspecting cables.
- Inspecting electrolyte levels and watering batteries.
- Equalizing batteries (scheduled overcharging) to desulfate plates and achieve voltage parity.
- Floating daily when possible.
To make maintenance easy, invest in the right tools, schedule it in your calendar and record what maintenance you performed.
You don’t have to test thousands of batteries to discover which battery strategies work best. With these five lessons, your batteries will last longer, and you’ll spend less time and money on them.