Batteries and energy storage — when they make sense, when they don't

Batteries get marketed as an inevitable companion to solar. They aren't. In many situations — reliable grid, favourable net-metering, predictable daytime load — batteries don't pay back before their own end of life.

In other situations — frequent outages, time-of-use tariffs with wide peak/off-peak spreads, remote sites — batteries are transformational.

This guide covers how to tell which applies to you.

What batteries actually do

A solar battery stores energy so you can use it when the sun isn't producing. That's the simple version. In practice, batteries do four different jobs:

Time-shifting: store daytime solar for evening use, typically to capture the difference between peak and off-peak electricity rates.
Backup: provide power during grid outages, when an otherwise-healthy solar system would shut off.
Self-sufficiency: minimise grid imports, even when there isn't an outage. Relevant when export compensation is poor.
Arbitrage: charge from the grid at off-peak rates, discharge during peak rates. Separate from solar but often combined.

A battery spec'd for one of these jobs may not be right for another. Which job matters most drives sizing, chemistry, and cost.

The four good reasons to add a battery

1. Your grid is unreliable

If your site experiences frequent outages (more than a few hours per month), and those outages are costly (spoiled inventory, lost production, safety concerns), a battery earns its keep through backup alone.

2. Your tariff has a wide peak/off-peak spread

Time-of-use tariffs where peak rates are 2–3× off-peak rates make time-shifting economical. Store daytime solar, discharge during the peak window, save the rate difference.

3. Net-metering is poor or unavailable

In markets where exported solar earns little (or nothing, or costs you), storing surplus for on-site use captures value that would otherwise be wasted. The battery becomes the "return path" for energy you'd otherwise lose.

4. You have critical loads that can't go down

Medical equipment, refrigerated inventory, servers, climate-sensitive livestock or greenhouse operations — if the cost of an outage is very high, the battery's backup value alone can justify it.

Bad reasons to add a battery

"It seems like the modern thing to do."
"I want to be independent from the utility."
"The salesperson said it would pay back in 5 years."
"I want to use 100% of my own solar."

These are feelings. They can lead to real value, but only if they coincide with one of the four economic drivers above. Batteries bought on emotion usually disappoint.

Battery chemistries

Three chemistries dominate the solar battery market today:

Lithium Iron Phosphate (LiFePO4 / LFP)

The current standard for residential and small commercial. Long cycle life (4,000–6,000+ cycles), safe chemistry (thermally stable, low fire risk), good performance at high temperatures. Slightly heavier per kWh than other lithium chemistries. Typical warranty: 10 years.

Lithium Nickel Manganese Cobalt (NMC)

Higher energy density than LFP (smaller footprint for same capacity). Shorter cycle life (~2,000–3,000 cycles). More thermal management required. Used mostly where space is tight. Typical warranty: 10 years.

Lead-acid (AGM, Gel, flooded)

Legacy chemistry still used in some off-grid applications. Cheap upfront. Short cycle life (500–1,500 cycles), limited depth of discharge (~50%), higher maintenance. Typical life: 4–8 years. Mostly replaced by LFP now, except at the very low end or for specific off-grid use cases.

For most residential and commercial applications in 2026, LFP is the default answer.

Sizing a battery

Battery sizing is job-specific. The right size for backup is different from the right size for time-shifting.

For backup (critical loads during outages)

Calculate the daily energy demand of only the loads you want to keep running (fridge, lights, a few outlets, maybe a fan). For a typical residential critical-load setup, 5–10 kWh of battery capacity covers a day. "Whole-home backup" typically needs 20–40+ kWh and costs accordingly.

For time-shifting

Size to store the solar surplus your load can't absorb during the day, for discharge during the peak-rate evening window. Typical home: 10–20 kWh. Commercial: larger, depending on load profile.

For self-sufficiency

Size for overnight consumption — roughly half a day's electricity use. More than this adds cost without proportional benefit, because you can't fill the battery during cloudy days anyway.

Start smaller than the salesperson suggests

Oversized batteries are the most common mistake. Better to install a right-sized system now and add capacity later than to over-commit capital upfront. Most modern battery systems are modular — additional capacity can be added to match actual need as you learn your usage patterns.

The economics

Battery economics are highly market-dependent and change fast. Some general patterns in 2026:

A backup-only battery earns its keep through value-of-uptime, not cents-per-kWh math. If outages are expensive, the payback can be almost immediate.
A time-shift battery in a market with a 3× peak/off-peak spread typically pays back within its 10-year warranty life. In a market with a 1.5× spread, it usually doesn't.
A self-sufficiency battery in a market with good net-metering is rarely economic. In a market with bad net-metering, it often is.
Stacked use cases (backup + time-shift + self-sufficiency) are the strongest economic case.

Before committing, get a proposal that shows the projected annual savings broken down by each use case. "This battery will save you X per year" without that breakdown is a sales number.

Frequently asked questions

Most LFP batteries carry 10-year warranties, with expected lifetime of 10–15 years. Degradation is gradual — typical warranties guarantee 70–80% capacity remaining at year 10. NMC batteries typically degrade faster. Lead-acid lasts 4–8 years.

Modern LFP batteries are very thermally stable and widely used in residential settings. Installation codes require specific fire separation and ventilation. A properly-installed battery is lower-risk than many appliances already in homes. NMC chemistries have higher fire-risk and are typically installed in dedicated enclosures or outdoors.

Sometimes easily, sometimes not. If your existing inverter is hybrid-ready, adding a battery is straightforward. If it's a standard string inverter, you'll need to replace the inverter or add a separate AC-coupled battery system. The former is usually cheaper; the latter preserves the existing PV kit.

Batteries usually fail gradually (diminished capacity) rather than catastrophically. Warranty coverage typically covers failures below a threshold (often 70% capacity). End-of-life batteries can be recycled in most jurisdictions — battery recycling has become a mature industry.