EnerMath
All 66 Calculators
Solar & Storage

Off-Grid Solar & Battery System Sizer

Size standalone off-grid solar PV arrays, battery bank Ah/kWh capacity, days of autonomy, MPPT charge controllers, and inverters.

Instant Client-Side Math NREL & DOE Aligned 100% Free & Private

Human Verification Required

Please complete the captcha below to unlock this tool. This helps us prevent automated bots from abusing our calculators.

Technical Overview

What is the Off-Grid Solar & Battery System Sizer?

The Off-Grid Solar & Battery System Sizer is an engineering sizing tool for cabins, remote telecom stations, Tiny Homes, RVs, marine vessels, and standalone agricultural power systems.

Unlike grid-tied solar—which uses the utility grid as a virtual buffer—an off-grid system must be sized for your worst-case winter sun hours and consecutive cloudy days (days of autonomy). This calculator accounts for battery chemistry depth-of-discharge (LFP vs. AGM lead-acid), cold-weather capacity derating, inverter surge ratings, and system voltage (12V, 24V, or 48V).

Get complete balance-of-system specifications including total battery bank kWh and Amp-hours, solar array watts, MPPT charge controller amperage, and backup generator runtime.

Primary Model Inputs

daily load (Wh/day), days of autonomy, DC bus voltage (12V/24V/48V), battery chemistry (LiFePO4 vs AGM), winter sun hours, and peak surge watts

Calculated Engineering Outputs

required battery bank (kWh and Ah), solar PV array size (kW and 400W panel count), MPPT charge controller amps, and inverter kW rating

Mathematical Methodology

Core Engineering Formula & Industry Benchmarks

Bank_Ah = [ (E_daily_Wh ÷ η_inv) × Days_autonomy × f_temp ] ÷ (DoD_max × V_bus)

Uses 85% max Depth of Discharge (DoD) for LiFePO4 vs. 50% DoD for AGM lead-acid, plus a 1.25× NEC continuous current factor for MPPT sizing.

Standard Industry Reference Values

US Residential Installed Cost
$2.65 – $3.15 / Watt DC
Source: NREL Solar Cost Benchmark
Standard System Derating Factor
78% – 84% DC-to-AC
Source: NREL PVWatts v8
LFP Battery Round-Trip Efficiency
90% – 94.5% AC/DC
Source: DOE Energy Storage Handbook
Annual Module Degradation Rate
0.40% – 0.55% / year
Source: NREL Photovoltaic Degradation Compendium
Step-by-Step Guide

How to Use the Off-Grid Solar & Battery System Sizer

1

Gather your baseline utility bills or project specs and enter your values for daily load (Wh/day), days of autonomy, DC bus voltage (12V/24V/48V), battery chemistry (LiFePO4 vs AGM), winter sun hours, and peak surge watts.

2

Adjust the interactive sliders or numeric inputs to match your local utility tariff, climate zone, and system size.

3

Review the real-time calculated metrics—specifically required battery bank (kWh and Ah), solar PV array size (kW and 400W panel count), MPPT charge controller amps, and inverter kW rating.

4

Toggle available incentives (such as the 30% Federal Clean Energy Credit or local utility rebates) to compare gross vs. net payback.

5

Run a sensitivity check by testing conservative, expected, and high-inflation utility rate assumptions.

Real-World Case Study

Worked Example: Off-Grid Solar & Battery System Sizer

Real-World Engineering Scenario: Off-Grid Solar & Battery System Sizer

Baseline Assumptions

An off-grid cabin consuming 4,800 Wh/day with 3 days of autonomy on a 48V LiFePO4 bank and 4.2 winter peak sun hours.

Modeled Outcome

Requires a 20.2 kWh (421 Ah @ 48V) LiFePO4 bank, a 1.98 kW solar array (5 × 400W panels), and a 60A MPPT charge controller.

Engineering Takeaway

Choosing a 48V DC bus over 12V cuts cable current by 75%, reducing copper wire gauge costs and allowing a single MPPT controller to handle 3+ kW of solar.

Domain Intelligence

Key Engineering & Financial Insights

Self-Consumption Beats Export Credits

Under modern net-billing (NEM 3.0) tariffs, consuming your own solar power directly or storing it in an LFP battery is worth 3× to 4× more than exporting midday power to the grid.

DC-to-AC Oversizing Optimization

Sizing your solar array at 1.20× to 1.30× your inverter's continuous AC rating widens the shoulder production curve in morning and late afternoon with <1.5% annual clipping loss.

30% Federal Tax Credit Impact

Applying the 30% Federal Clean Energy Credit (Section 25D residential / Section 48E commercial) directly reduces net capital at risk and shortens simple payback by 2.5 to 3.5 years.

Utility Inflation Compounding

Because retail electricity tariffs historically rise 3.5%–5% per year, your nominal annual solar savings grow every year even after accounting for 0.5%/yr panel aging.

Why Use the Off-Grid Solar & Battery System Sizer?

Convert complex formulas into clear numbers you can act on quickly.

Measure whether your current plan is on track against your goals.

See how changing one variable affects outcomes before committing money.

Stress-test downside scenarios so surprises are less likely later.

Identify hidden cost drivers that reduce long-term financial efficiency.

Prioritize next actions based on measurable impact instead of guesswork.

Create a repeatable decision process you can use month after month.

Improve clarity when discussing options with family, lenders, or advisors.

Track progress over time and correct course early when assumptions change.

Use the results to improve structure and reduce long-term cost.

Technical Q&A

Frequently Asked Questions

The Off-Grid Solar & Battery System Sizer evaluates daily load (Wh/day), days of autonomy, DC bus voltage (12V/24V/48V), battery chemistry (LiFePO4 vs AGM), winter sun hours, and peak surge watts using industry-standard thermodynamic and discounted cash-flow equations (Bank_Ah = [ (E_daily_Wh ÷ η_inv) × Days_autonomy × f_temp ] ÷ (DoD_max × V_bus)). It computes required battery bank (kWh and Ah), solar PV array size (kW and 400W panel count), MPPT charge controller amps, and inverter kW rating in real time directly in your browser so you can stress-test multiple scenarios instantly.
Your local utility tariff structure ($/kWh or fuel price), baseline usage volume, and equipment efficiency rating are the highest-sensitivity drivers. Even a $0.04/kWh shift in electricity rates or a 30% tax credit can shift payback timelines by 2 to 4 years.
Yes—where applicable, our models include toggles or adjustments for the 30% Federal Clean Energy Credit, Energy Efficient Home Improvement credits, and local utility rebates. Always verify your tax liability and local utility program rules before finalizing project financing.
Run three scenarios—conservative, expected, and optimistic—using the exact hardware wattage, SEER2/COP efficiency, and turnkey pricing from each installer's bid. Compare the resulting net payback period and 10-to-25-year cumulative savings rather than looking at upfront price alone.
No. All calculations inside the Off-Grid Solar & Battery System Sizer execute 100% client-side in your browser with <50ms latency. None of your utility bills, property specs, or financial inputs are stored or shared.