Editorial owner: MCL Solar Knowledge Center. Verification rule: Model-specific performance requires the relevant test report, site data, calculation, and contract documents. Last updated: July 16, 2026.
Key takeaways:
- Compare batteries by rated energy, usable depth of discharge, temperature behavior, traceability, protection, and tested capacity.
- Cycle count is incomplete unless depth of discharge, C-rate, temperature, and capacity end condition are stated.
- Do not convert a cycle claim directly into a guaranteed number of service years.
- Battery autonomy and photovoltaic recovery charging are separate engineering checks.
Battery chemistry and project fit
LiFePO4 is widely used because it can provide a practical balance of thermal stability, cycle performance, and energy density. Other chemistries may be suitable when their charging profile, temperature range, safety controls, service access, and evidence match the project. A chemistry name alone does not prove capacity or life.
Capacity formula
Daily load (Wh) is the sum of LED input power multiplied by hours at each dimming level, plus camera, modem, sensor, heater, and standby loads.
Rated battery energy (Wh) = daily load x autonomy days / (usable DoD x discharge-path efficiency x temperature derating).
Battery capacity (Ah) = rated battery energy / nominal battery voltage.
State every input. Do not divide load by voltage without applying usable DoD, efficiency, and temperature assumptions.
Cycle-life evidence
A cycle-life statement must identify cell model, depth of discharge, charge and discharge C-rate, temperature, rest periods, and the remaining-capacity threshold used to end the test. Calendar aging, daily operating profile, heat exposure, balancing, and enclosure design also affect field life.
Controller compatibility
LiFePO4 does not automatically require MPPT. The controller must provide the correct charging curve, voltage limits, low-temperature strategy where applicable, protections, and system-voltage compatibility. MPPT performance relative to PWM depends on the array-to-battery voltage relationship, temperature, irradiance, and conversion efficiency.
Incoming inspection and acceptance
| Check | Evidence |
|---|---|
| Identity and traceability | Cell model, batch code, supplier record, and pack serial number |
| Rated capacity | Controlled charge and discharge test with voltage, current, temperature, and cutoff values |
| Pack protection | Overcharge, over-discharge, overcurrent, short-circuit, and temperature protection settings |
| Matching and balance | Cell-voltage and internal-resistance records before assembly |
| Environmental protection | Enclosure and connector IP reports for the proposed installation |
| System commissioning | State-of-charge, charging current, load profile, and controller log |
Limitations
Final battery selection requires the project coordinates, worst-month climate data, load profile, autonomy requirement, enclosure temperature, service plan, and the exact cell and pack documentation.
Connect battery selection to the complete energy model
Battery chemistry and nominal capacity should not be reviewed in isolation. A complete sizing record connects five items: the measured nightly load, required autonomy, usable battery energy, location-specific charging energy and the required recovery period after low-solar days.
- Calculate nightly Wh from the approved dimming profile and auxiliary loads.
- Define autonomy as a project input rather than a universal number of rainy days.
- Apply model-specific usable depth of discharge, efficiency, temperature and aging assumptions.
- Check that the selected panel and controller can restore the energy within the agreed recovery period.
- Verify delivered Wh with a controlled pack-level charge and discharge test.
Cycle-life claims must state cell model, test temperature, depth of discharge, charge and discharge rate, end-of-life criterion and whether the statement concerns laboratory cycles or field calendar life.