Lithium vs. Lead: Which Battery for the Solar System?
Introduction: It's What's Inside That Counts
Batteries are in some ways like people: they come in different shapes and colours, but ultimately it's what's inside that counts. Over time, many battery concepts have been developed using various material combinations for anode, cathode, electrolyte and separator.
Currently, two technologies are primarily used for storing solar energy:
- Lithium-ion batteries (LIB)
- Lead-acid batteries (LAB)
Both concepts offer advantages and disadvantages for use in solar systems. This article explains which battery type is suitable for which application.
Lithium-Ion Batteries: The Modern Standard
For today's technology, lithium-ion batteries are indispensable. Whether smartphone, electric toothbrush or electric vehicle – this battery type is widespread and increasingly displacing lead batteries.
Operating Principle
The operating principle differs from the galvanic cell only in material composition. As the name suggests, the electrodes contain lithium.
Important distinction:
- Lithium-ion batteries: Lithium as oxygen compound (lithium oxides) – rechargeable
- Lithium-metal batteries: Pure metallic lithium – not rechargeable
Different Cathode Materials
How exactly the lithium is incorporated into the electrodes depends on the chemical structure of the battery. Typically, the lithium compounds are in the cathodes. There are various cathode compositions, each with their own advantages and disadvantages:
| Type | Name | Properties |
|---|---|---|
| LFP | Lithium Iron Phosphate | Longer lifespan, safer, more environmentally friendly |
| NMC | Nickel Manganese Cobalt | High energy density, but more expensive |
| LCO | Lithium Cobalt | High energy density, less safe |
Recommendation for solar systems: LFP cells offer the best compromise between performance and sustainability.
Advantages of Lithium-Ion Batteries
Lithium-ion batteries have become the leading technology in recent years. The following advantages make them particularly attractive for solar systems:
| Advantage | Explanation |
|---|---|
| High energy density | More capacity at the same weight/volume |
| High efficiency | 90–95% roundtrip efficiency |
| Long lifespan | 5,000–10,000 charge cycles |
| High depth of discharge | 80–100% DoD possible |
| No memory effect | Flexible charging possible |
| Maintenance-free | No regular maintenance required |
| Fast charging | Higher C-rates possible |
Disadvantages of Lithium-Ion Batteries
Despite all the advantages, there are some aspects to consider when selecting:
| Disadvantage | Explanation |
|---|---|
| Higher acquisition cost | ~£150–300/kWh (trend falling) |
| Temperature sensitive | Optimal range: 15–25°C |
| Fire risk | If damaged or overcharged (rare with LFP) |
| Recycling challenge | More complex than lead |
Lead-Acid Batteries: The Proven Classic
The lead-acid battery is significantly older than lithium-ion concepts. It was already in use in the 19th century and is still found in many applications today – most famously as the starter battery in cars.
Structure and Operating Principle
The LAB functions fundamentally like any other battery but consists of:
- Lead plates (anode, pure lead)
- Lead oxide plates (cathode)
- Water-sulphuric acid mixture (electrolyte)
Advantages of Lead-Acid Batteries
Even though lead-acid batteries are older, they still have their place. They score particularly well in certain applications with tangible advantages:
| Advantage | Explanation |
|---|---|
| Low acquisition cost | ~£80–150/kWh |
| Proven technology | Over 150 years of experience |
| High robustness | Insensitive to temperature fluctuations |
| Easy recycling | Nearly 100% recycling rate |
| Availability | Available everywhere |
Disadvantages of Lead-Acid Batteries
The disadvantages of lead-acid batteries are the main reason they are increasingly being displaced by lithium-ion technology:
| Disadvantage | Explanation |
|---|---|
| Low energy density | Heavy and bulky |
| Short lifespan | 500–1,500 charge cycles |
| Low depth of discharge | Only 50% DoD recommended |
| Maintenance effort | Regular topping up (for flooded types) |
| Low efficiency | 80–85% roundtrip efficiency |
| Outgassing | Ventilation required |
The Direct Comparison
To facilitate the decision, we compare both technologies directly. The table shows the key differences at a glance:
| Criterion | Lithium-Ion | Lead-Acid |
|---|---|---|
| Energy density | 150–200 Wh/kg | 30–50 Wh/kg |
| Efficiency | 90–95% | 80–85% |
| Lifespan | 5,000–10,000 cycles | 500–1,500 cycles |
| Depth of discharge | 80–100% | 50% |
| Cost/kWh | £150–300 | £80–150 |
| Cost/cycle | £0.03–0.06 | £0.05–0.30 |
| Maintenance | Maintenance-free | Regular |
| Weight | Light | Heavy |
Conclusion: Although lead-acid batteries are cheaper to purchase, lithium-ion batteries are often more economical long-term due to their longer lifespan.
Rules of Thumb for Sizing
Before deciding on a battery, you need to determine the right size:
Rule of Thumb 1: Based on Peak Capacity
Per generated kWp, 0.9 to 1.6 times kWh capacity should be available.
This rule is based on installed module capacity and provides a good starting value for storage sizing:
| System Size | Recommended Capacity |
|---|---|
| 5 kWp | 4.5 – 8 kWh |
| 8 kWp | 7.2 – 12.8 kWh |
| 10 kWp | 9 – 16 kWh |
Rule of Thumb 2: Based on Annual Consumption
Capacity should be approximately 60% of daily electricity consumption.
This alternative is based on actual household consumption and is particularly useful when consumption data is available:
| Annual Consumption | Daily Consumption | Recommended Capacity |
|---|---|---|
| 3,000 kWh | 8.2 kWh | ~5 kWh |
| 5,000 kWh | 13.7 kWh | ~8 kWh |
| 7,000 kWh | 19.2 kWh | ~12 kWh |
When Does Which Technology Make Sense?
Lead-Acid Battery Recommended For:
- Small systems up to 5 kWp
- Balcony solar systems with limited space
- Limited budget
- Off-grid applications (motorhome, garden house)
- Low cycle requirements
Example: At 5 kWp, you need at least 4.5 kWh capacity. In this range, the cost advantage of lead-acid batteries may prevail.
Lithium-Ion Battery Recommended For:
- Medium to large systems from 5 kWp
- Detached houses with 2–4 people
- High daily consumption
- Limited space
- Long-term use (10+ years planned)
- Combination with heat pump or EV
Example: At 10 kWp and 9 kWh minimum capacity, lithium-ion is the better choice – compact, durable and maintenance-free.
Special Case: LFP vs. NMC vs. LCO
If you've decided on lithium-ion, the question of cell chemistry arises. The three most common variants differ significantly in their properties:
| Criterion | LFP | NMC | LCO |
|---|---|---|---|
| Energy density | Medium | High | High |
| Safety | Very high | Medium | Low |
| Lifespan | Very high | Medium | Low |
| Cost | Medium | High | High |
| Temperature stability | Very good | Good | Medium |
| Recommendation | Home storage | E-mobility | Electronics |
Clear winner for solar systems: LFP cells – they offer the best combination of safety, lifespan and cost.
Conclusion
Core Message: The choice between lithium-ion and lead-acid depends on your individual requirements:
- Budget-oriented + small system → Lead-acid
- Long-term + larger system → Lithium-ion (LFP) Prices for lithium-ion batteries are continuously falling whilst the technology keeps improving. For most new solar systems, lithium-ion is the right choice today.
In the next article, you will learn how Power Electronics: Inverters and DC-DC Converters make the battery's DC power usable for your home grid.
The Complete Article Series "Energy Storage for Solar Systems"
- From Frog Legs to Batteries: How Does an Energy Storage System Work? – Fundamentals
- Lithium vs. Lead: Which Battery for the Solar System? – You are here
- Power Electronics: Inverters and DC-DC Converters – Power conversion
- The All-Rounder: Hybrid Inverters – Everything in one device
- AC or DC? System Topologies for Solar Systems – System concepts