Why off-grid systems switch to lithium
Off-grid is the use case lithium was made for: a battery that is cycled hard every single day. Lead-acid hates that, and it shows up in the running cost.
- Deeper daily cycling. To get a reasonable life from lead you keep it above 50 percent; lithium happily uses 80 to 90 percent every day, so a smaller bank does the same work.
- Lower lifetime cost. A lead bank in daily off-grid service often needs replacing every 2 to 4 years. A lithium bank typically runs 10 years, so over the life of the system you avoid buying lead three to five times over.
- Half the size and weight. Because more of the capacity is usable, the lithium bank is roughly half the amp-hours and a fraction of the weight.
- Less generator time. Lithium has higher round-trip efficiency and accepts a high charge current, so it captures a short solar window or a generator run far more effectively than lead.
Sizing the bank: days of autonomy
Work out your average daily energy use in watt-hours, decide how many days you want to ride through bad weather (days of autonomy), then divide by the usable depth of discharge.
12V, 24V or 48V? 12V is fine for a small cabin or shed up to a few kWh. Above roughly 3 to 5 kWh, or with a large inverter, a 24V or 48V bank keeps currents and cable sizes sensible. The finder tool sizes a 12V bank from your loads; for larger systems treat the 12V result as the per-12V building block.
Charge controller and setup
- MPPT lithium profile. Set the solar controller to the lithium profile, about 14.2 to 14.6V bulk and absorption for a 12V pack, with float off or at 13.6V. A lead float voltage holds lithium at the wrong level. See solar setup.
- Monitoring and fusing. Fit a shunt monitor for true state of charge, and size fuses and cable for the higher currents lithium can deliver.
- Cold climates. If the battery space drops below freezing, do not charge without a self-heating pack or a heated enclosure.
- Do not mix chemistries. Build the bank from identical lithium units; do not parallel it with an old lead bank.
Lifetime cost: lithium versus lead off-grid
The sticker price of lithium is higher, but the number that matters off-grid is cost per usable kWh over the life of the system. Daily deep cycling is exactly where lead wears out fastest.
| Lead-acid bank | LiFePO4 bank | |
|---|---|---|
| Usable each day | about 50 percent | 80 to 90 percent |
| Typical life in daily service | 2 to 4 years | about 10 years |
| Replacements over 10 years | 3 to 5 banks | 1 bank |
| Size for the same usable energy | roughly double | baseline |
Size the lithium bank for your off-grid system
Enter your daily loads or your current battery and get a recommended LiFePO4 pack, the usable energy, and the weight saved.
Size my lithium battery