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off-grid battery calculator helps you turn a practical question into a calculation you can inspect. A result is only useful when you understand what went into it: the units, the period covered, the assumptions and the costs or constraints left outside the model. This 2026 guide explains the method behind Off-Grid Solar Battery & Inverter Sizing Calculator, walks through the calculator’s own example and shows how to compare a second scenario without confusing an estimate with a guarantee. You can follow the steps even if you have never used this type of tool before. Start with the example, replace the inputs with your own evidence and keep a note of the assumptions that could change the decision.
Try the calculator with your own figures →
Before you enter numbers
Gather the records that describe the situation you are actually comparing. Use one consistent currency and time period for monetary inputs. Keep measured quantities separate from estimates: a recent bill, a supplier quotation or a recorded average is stronger evidence than a number copied from an unrelated project. Where the future is uncertain, use a range rather than quietly treating one guess as a fact. Write down which inputs came from documents and which were assumptions. This makes your comparison easier to update later.
off-grid battery calculator: Formula and assumptions explained
Add every AC appliance with running watts, daily hours, quantity and total startup watts. Daily Wh is power times hours; inverter sizing uses simultaneous running power, not daily Wh. The largest-group surge option starts all units of one entered row together while other rows are already running; all-start adds every startup load. Battery Wh includes autonomy, discharge limit, inverter loss and battery discharge efficiency, then divides by system voltage for Ah. Solar power covers an average operating day at your entered sun hours and derating; it does not promise recovery after several sunless days. Confirm surge duration, battery current/BMS, temperature effects, wiring and protective equipment with an installer.
daily Wh = Σ(quantity × watts × hours); nominal battery Wh = daily Wh × autonomy / (inverter efficiency × depth of discharge × discharge efficiency); Ah = Wh / voltage
Worked example: read the results
A 100 W load running eight hours uses 800 Wh daily. For two autonomy days,80% usable depth,90% inverter efficiency and 95% battery discharge efficiency, nominal storage is about 2,339 Wh, or 48.73 Ah at 48 V. Continuous load and startup surge are separate inverter checks. A solar estimate for an average day does not guarantee recovery after several cloudy days. Final equipment selection needs electrical protection, temperature and manufacturer review.
Example inputs: check every unit
These are the calculator’s reproducible starting values, not recommended market rates. Replace them before making a real decision. A zero can mean a genuine absence, but it must not stand in for information you have not collected. For a conditional field, first check whether that part of the scenario applies. Keep the same assumptions when checking the example by hand.
- Nominal battery system voltage: 48 V
- Days of battery autonomy: 2
- Usable depth of discharge: 80 %
- Inverter efficiency: 90 %
- Battery discharge efficiency: 95 %
- Daily peak sun hours: 4
- Solar production derating factor: 75 %
- Inverter continuous-power headroom: 20 %
- Starting scenario: largest
| Appliance quantity | Running power per appliance | Run hours per day | Total startup watts per appliance |
|---|---|---|---|
| 1 | 100 | 8 | 300 |
Worked example: read the results
The figures below are calculated from the inputs above using the same engine as the interactive tool. Monetary examples use USD as a neutral label; changing the currency selector does not perform exchange-rate conversion. Small differences in the last decimal can come from display rounding. Compare the meaning and units of an output before comparing its size. A larger result is not automatically a better outcome.
- Daily AC energy: 800 Wh
- Nominal battery capacity: 2339.18 Wh
- Nominal battery capacity in amp-hours: 48.7329 Ah
- Inverter continuous rating target: 120 W
- Inverter surge rating target: 300 W
- Indicative solar array power: 311.891 W
- Continuous battery current: 2.31481 A
How to compare a second scenario
Save the starting calculation, then change one uncertain input while leaving the others unchanged. Record the difference in the main output and explain what caused it. Next, test a realistic unfavorable case rather than only an optimistic case. If your decision reverses after a small change, investigate that input more carefully. Do not combine a low cost from one supplier with a performance claim from a different product unless both can actually occur together. When several assumptions move together, describe the combined scenario clearly rather than presenting it as a precise forecast.
A practical checking routine
Read the field label before copying a number. Check whether the value is per item, per month, per year or a percentage. Keep a copy of your source records. Recalculate one simple part manually to catch a unit error. Review warnings instead of hiding them with a convenient number. Finally, ask whether an important constraint is outside the model. A mathematically correct estimate can still be unsuitable if the inputs describe the wrong situation.
What this 2026 estimate can and cannot tell you
A calculator is most helpful when you have a clear question and comparable inputs. Use this guide to understand the calculation, then use the interactive version to explore your own case. The year in the title identifies this edition of the guide; it does not make an example value an automatically updated 2026 benchmark. Fees, tariffs, contracts, product performance and personal circumstances can change independently of the arithmetic. Where relevant, check the current primary source for your location and the exact product or account involved. Keep any decision based on a forecast provisional until you have checked the main uncertainties. If two scenarios are close, the difference may be less important than an omitted cost, a measurement error or an operational constraint. Record the assumptions behind your preferred option so that a later change can be traced, rather than starting again with an unexplained total.
Frequently asked questions
Are the example rates current market prices?
No. Example inputs demonstrate arithmetic, not live prices, tax rules, salary surveys or sponsor benchmarks. Enter a dated quote, bill, manufacturer specification or verified fee schedule that applies to your situation. Compare a conservative and an optimistic scenario separately.
Why is a result not determined?
Some calculations have no meaningful value when a denominator is zero, savings are non-positive, a target cannot be reached or your data do not bracket an intersection. The tool leaves that result undetermined instead of displaying infinity or inventing a recommendation. Check the method and your inputs.
Does the calculator save my information?
Inputs are calculated in your browser without an account. This calculator does not automatically save inputs. A copied calculation link contains the entered numeric assumptions and rows; anyone with that link can read them. Share only figures you are comfortable making visible. Currency changes relabel amounts without converting them.
Why does changing one input change the answer?
The output depends on the combination of quantities, rates and assumptions described in the method. Recheck the units and compare one change at a time using the worked example as your baseline.
Sources and scope of this guide
Sources explain the underlying concepts, not an endorsement of this website or its results. Method review: 20 October 2026.
Try the calculator with your own figures
Open the calculator, load the example and replace the inputs with your own figures. Compare one alternative before choosing your next step. Use the related tools below when you need to explore a separate part of the same decision.
Off-Grid Solar Battery & Inverter Sizing Calculator →