Grid vs Battery Calculator | Compare Net Metering & Battery Savings

What this tool compares: two ways to use the same solar system. Net metering sends every spare unit of solar to the grid during the day and draws it back at night, paying only the net difference. Hybrid storage keeps some of that spare solar in a battery for the evening instead. Both scenarios run against the same daily solar production, daytime usage share, import rate and export rate.

Daily simulation: the battery is modelled day by day for a full 365-day year. Each day the solar system charges the battery from excess generation (up to the usable capacity), the night load is served from the battery first, and the charge state carries over from day to day — so a battery charged in a sunny week still helps on an overcast one. A battery/inverter power rating (kW) can cap how much energy the battery can deliver each day (rating × 5 h full-rated window). Why 5 hours? This is a modelling simplification, not a physical battery limit: it assumes roughly five hours of effective full-power charging during the solar day and a similar evening discharge window. It approximates a typical sunny-day energy throughput for the inverter; if your loads spread over more hours at lower power, the cap simply does not bind. Results are rolled up to months and years for the charts and totals.

Solar generation model: when coordinates are available, monthly solar production is consumed from the same Solar Metrix climate model used by the Energy Yield calculator — Open-Meteo hourly tilted irradiance with temperature derating at your location's optimal tilt and azimuth. Without coordinates (or if the live model is unavailable, e.g. offline), the tool falls back to a latitude-band estimate (145 near the equator, 135 to 40°, 110 to 55°, 85 beyond) with fixed seasonal factors, and the solar size is rounded to the nearest 0.5 kWp — the same sizing method used across the Solar Metrix calculators. You can override your system size (kWp) or enter your actual monthly generation to use measured production instead. The monthly chart shows grouped bars (net-metering vs hybrid bill); no manufactured fluctuation is added.

Grid export & credit model: when grid export is on, surplus solar is sold back at your export rate in both scenarios; when it's off it is curtailed (wasted). Export credit is a simplified energy-credit model — one flat rate applied to exported kWh. Actual net-metering rules, caps and credit rates vary by utility, region and policy, so treat this as a planning estimate and verify with your utility before deciding.

Battery chemistry: battery capacity is converted as Ah × V ÷ 1000 = kWh. The chemistry presets are typical planning assumptions, not specifications: Lithium LFP assumes 95% round-trip efficiency with 90% usable depth-of-discharge; Tubular lead-acid assumes 80% efficiency with 50% usable depth. Usable capacity = nominal × DoD (the round-trip efficiency is a conversion loss applied when charging, not a capacity loss). The model also applies an inverter/PCS efficiency, so the system round-trip efficiency = battery RTE × inverter efficiency (e.g. 95% × 97% ≈ 92%) — this is the figure used in the energy flow and savings.

Break-even, aging & the 10-year net benefit: electricity prices rise at your chosen escalation (Low 5% / Base 8% / High 12% per year) — your result is highly sensitive to this assumption. Aging is always included: capacity fades linearly each year at your fade rate (never below 60% of nameplate), and this decline is already reflected in the financial result. An estimated battery replacement is scheduled when cycle life or calendar life runs out: replacement year = min(calendar life, cycle life ÷ (equivalent full cycles per day × 365)), where equivalent full cycles per day = energy discharged per day ÷ usable capacity (nominal × DoD). This is an estimate based on the selected cycle-life and calendar-life assumptions — actual battery life varies with usage and climate. Each replacement year deducts your replacement cost (% of a new battery), and an annual maintenance cost (% of battery cost per year) is deducted every year. Two payback figures are reported: the simple payback at today's tariff, and the realistic payback that includes price rises, fade and replacements. The headline 10-Year Net Benefit = savings − initial cost − replacement − degradation − maintenance. The 10-year cost chart crosses when the Solar + Battery option becomes cheaper than Solar + Grid — that crossing is the true break-even.

All data stays in your browser. Nothing is sent to any server except the country lookup, used only to pick your currency.