Solar Inverters vs Batteries: Myths About Backup Power

Many homeowners install solar and expect backup power automatically. That expectation often comes from mixing up what a solar inverter does and what a solar battery does. The inverter converts electricity. The battery stores electricity. Both are valuable, but they solve different problems. This piece separates myths from facts, adds technical detail, and gives you practical sizing steps for a reliable backup setup.

Myth 1: A solar inverter equals backup power

Myth: “I have an inverter, so my lights stay on during an outage.”

Fact: A grid-tied inverter converts DC from solar panels into AC, but it does not generate energy on its own. Most standard inverters shut down during an outage to prevent unsafe backfeed into utility lines (anti-islanding). As explained by the International Energy Agency, PV modules output DC and need inverters to deliver AC to typical loads, and these inverters are part of the system’s balance-of-system components, not energy sources themselves. See Solar Energy Perspectives.

Advanced “smart” inverters add grid support features such as voltage and frequency regulation. This helps stability during normal operation and high solar penetration. The U.S. Department of Energy notes that smart inverters provide reactive power support and data that help operators balance the grid. See EERE Success Story—EPRI Lays Foundation for Smart Inverter Technology. Even with these features, backup still requires an energy source: a battery or a generator.

What provides true backup

• A grid-forming hybrid inverter that can island your home safely
• A battery bank sized for your critical loads
• Optionally, a generator input for extended outages

IEA summarizes how PV systems can ride through grid disturbances if configured, but they still need local energy during longer interruptions. See Status of Power System Transformation 2018 - Technical Annexes.

Myth 2: Any battery will run my home for days

Myth: “Install a battery once and forget it. It runs everything for days.”

Fact: Runtime depends on three numbers: usable battery capacity (kWh), inverter output limit (kW), and your average load (kW). A common formula helps:

Estimated runtime (hours) = Usable capacity (kWh) ÷ Average load (kW)

Usable capacity is not the sticker size. Many lithium batteries, including LiFePO4, allow 90–95% usable capacity without harming life. Lead-acid often uses 50% to protect lifespan. LiFePO4 also offers high cycle life and stable thermal behavior, making it well suited for daily cycling and backup use.

Sample runtimes with typical critical loads

Battery bank (nominal)	Usable capacity (assume 90%)	Average critical load 0.5 kW	Average critical load 1.0 kW	Average critical load 3.0 kW
5 kWh	4.5 kWh	~9 hours	~4.5 hours	~1.5 hours
10 kWh	9.0 kWh	~18 hours	~9 hours	~3 hours
15 kWh	13.5 kWh	~27 hours	~13.5 hours	~4.5 hours

Inverter power also limits what you can run at the same time. A 6 kW hybrid inverter can deliver up to 6 kW continuously; large appliances with high surge (pumps, compressors) may require higher overload capability for a few seconds. Many LiFePO4 systems allow 0.5C–1C discharge rates; always match battery discharge ratings to inverter demand.

Design tips for right-sized backup

• Split loads: move only essentials to a critical loads panel (lights, fridge, Wi‑Fi, gas furnace fan, well pump).
• Set conservative assumptions: use winter solar production and a realistic overnight load.
• Prefer LiFePO4 for safety, long cycle life, and deep usable capacity.

IEA highlights how distributed batteries can increase self-consumption and reduce backfeed, making distributed solar more system-friendly. See Next Generation Wind and Solar Power.

Myth 3: Solar always recharges the battery during outages

Myth: “If the grid is down, my panels will refill the battery every day.”

Fact: Solar generation depends on sun hours, weather, array size, roof orientation, and temperature. In storms, output can drop sharply. You also need a grid-forming hybrid inverter or charge controller to operate the array in island mode. Many standard grid-tied inverters shut off during outages by design.

What makes outage charging dependable

• Grid-forming capability: The inverter must set local voltage and frequency. DOE describes how advanced inverters manage voltage and frequency to support operations. See EPRI smart inverter technology.
• Right charge rates: Ensure PV power and inverter charge limits can recharge the bank between outages, not just maintain it.
• Energy budget: Reduce loads on cloudy days. Prioritize essentials via automation or manual switches.
• Fallback plan: Consider a generator input for multi-day storms or winter periods.

IEA notes PV can “ride through” short disturbances if configured, yet sustained outages require local energy. See Status of Power System Transformation 2018 - Technical Annexes.

Myth 4: Solar needs 1:1 backup from storage or conventional plants

Myth: “Every unit of solar needs an equal unit of backup.”

Fact: At the grid level, this is a well-documented misconception. The IEA explains that system integration challenges emerge gradually and can be managed with a range of tools: flexible conventional plants, transmission, demand response, and smarter operations. Storage helps, but a strict 1:1 rule is not required. See Getting Wind and Solar onto the Grid.

That same logic scales to buildings. A home does not need batteries sized to cover every load indefinitely. Focus on critical circuits, sensible automation, and enough storage to bridge typical outage durations in your area.

Inverter vs battery: roles and specs at a glance

Component	Primary role	Key specs	What it does not do
Solar inverter (grid-tied)	Convert DC (PV) to AC; feed grid; track maximum power point	AC power rating (kW), efficiency, MPPT range, smart functions (Volt/VAR)	Provide energy during outages (standard units shut down for safety)
Hybrid/grid-forming inverter	Convert DC to AC; charge/discharge battery; island critical loads	AC power (kW), surge, battery charge/discharge limits, transfer speed	Store energy (needs a battery or generator to supply energy)
Battery (LiFePO4)	Store energy for backup and peak shaving	Usable capacity (kWh), cycle life, C‑rate, BMS safety features	Convert DC to AC; manage grid voltage/frequency

For foundational background on PV conversion and inverters as BOS components, see IEA’s Solar Energy Perspectives. For smart inverter capabilities and why they matter for stable operation, see DOE’s EPRI smart inverter technology. For general solar basics, see DOE’s topic hub Solar Energy and EIA’s explainer Photovoltaics and electricity.

Practical sizing for reliable backup

Step 1: List and trim critical loads

• Create a critical loads subpanel. Include lighting, fridge, router, medical devices, and heating fan. Exclude EV charging, electric ovens, and central AC unless you size for them.
• Estimate average draw in kW across 24 hours. Smart plugs or a whole‑home monitor help.

Step 2: Pick an inverter that can start and run those loads

• Match continuous kW to your expected simultaneous load.
• Check surge ratings for motors and compressors (2–6x for a few seconds).
• Choose hybrid inverters with grid-forming and rapid transfer to keep critical circuits live.

Step 3: Size the battery for your outage target

• Use the runtime formula. For a 1 kW average critical load, 10 kWh usable gives about 9–10 hours.
• For daily cycling and safety, LiFePO4 batteries offer long life and high usable capacity.

Step 4: Right-size the PV array and charging

• Aim to replenish overnight usage during the next day under typical conditions.
• Verify inverter charge limits and MPPT range fit your array.
• Consider seasonal output. Winter sun can be 30–60% lower in some regions.

Step 5: Plan for edge cases

• Add a protected outlet for a small generator if you face multi‑day storms.
• Use load management: time-shift laundry and dishwashers to sunny hours.
• Ensure code compliance and anti‑islanding protections. Work with qualified installers.

Real‑life configuration example

Scenario: A home wants backup for lighting, fridge, gas furnace fan, Wi‑Fi, and a well pump. Average critical load: 0.9 kW; short surges up to 3 kW.

• Hybrid inverter: 6 kW continuous, 10 kW 10‑second surge, grid-forming.
• Battery: 15 kWh LiFePO4 (usable ~13.5 kWh). Estimated runtime ~15 hours at 0.9 kW average.
• PV array: 7 kW DC on a mixed east/west roof. On a clear day, expect 20–35 kWh depending on season and location.
• Controls: Critical loads panel plus a simple “storm mode” to cut non‑essentials.

Outcome: During a daytime outage, the PV covers most loads and tops the battery. Overnight, the battery carries essentials with margin. In a multi‑day storm, a small generator can be connected to extend runtime and keep the battery healthy.

Where integrated products fit

Homeowners who value simplicity often choose an integrated energy storage system that combines a LiFePO4 battery, a hybrid inverter, and PV integration in one cabinet. This reduces wiring complexity, accelerates commissioning, and streamlines remote monitoring. For off‑grid cabins or farms, turnkey solar kits pair panels, a hybrid inverter, and scalable batteries to match seasonal use.

LiFePO4 batteries offer stable chemistry, high performance, and strong safety characteristics. Scalable modules allow customers to start small and grow capacity as needs change. This aligns with a practical path to energy independence: reliable and expandable power, not oversizing on day one.

Key takeaways

• Inverters convert; batteries store. An inverter alone does not provide backup power.
• Backup performance is math. kWh divided by kW sets runtime; inverter kW sets what you can run at once.
• Smart, grid-forming inverters and LiFePO4 batteries create dependable backup, with PV recharging during daylight.
• Storage helps, but strict 1:1 backup rules are a myth. System flexibility and smart operations matter at every scale.

Cited insights for deeper reading

• PV produces DC and requires inverters; BOS context: Solar Energy Perspectives
• Myths on 1:1 backup and “storage is a must-have” at system level: Getting Wind and Solar onto the Grid
• Ride‑through behavior and inverter settings for reliability: Status of Power System Transformation 2018 - Technical Annexes
• Distributed storage increases self-consumption and reduces backfeed: Next Generation Wind and Solar Power
• Smart inverter functions and grid support benefits: EERE Success Story—EPRI Lays Foundation for Smart Inverter Technology
• General solar basics and technology background: U.S. DOE — Solar Energy and EIA — Photovoltaics and electricity