My power plan
Use nominal stored energy. Already measured usable output energy is not supported by this model.
Illustrative assumptions. Separate panel yield from losses between the input and battery.
Relate the battery charge window to panel rating, real-world yield, station input limit and charging efficiency.
Use solar view to estimate the energy needed between two battery percentages and the equivalent full-sun time required to store it. Equivalent sun hours describe solar energy, not the clock time between sunrise and sunset.
The estimate is governed by the energy to replace and the useful power that reaches the battery. The panel label helps only until yield losses or the station input ceiling becomes the binding limit.
Understand the calculation path, the strongest inputs and the limits to verify.
Battery Wh between starting and target charge
Nameplate watts adjusted for conditions
Station ceiling and charging efficiency
Equivalent sun hours and indicative days
Nominal battery watt-hours and capacity retention set the retained energy base. The from and to percentages define how much of that energy must be replaced. Charging a partially depleted station is therefore different from assuming every session begins at zero.
The panel rating is reduced by the entered yield factor for orientation, temperature and other aggregate losses. If a station solar-input ceiling is entered, useful input cannot exceed it. Panel voltage, current, connector and series or parallel configuration still require a specification check.
Charging efficiency reduces the power stored in the battery. Dividing charge energy by stored power gives equivalent sun hours; dividing again by entered equivalent sun hours per day gives indicative days. Weather, shade, seasonal variation, charging taper and simultaneous equipment use can extend clock time.
Nominal Wh × retention × (to% − from%)Only the selected portion of retained capacity is replenished.
min(panel W × yield, station input limit)Omit the limit only when you deliberately want an unconstrained energy estimate.
Charge Wh ÷ (useful input W × charge efficiency)Indicative days also depend on entered equivalent sun hours per day.
Change one input at a time and keep the measurement or specification that supports it.
| Input | Effect on the answer | What to verify |
|---|---|---|
| Battery charge window | Controls the watt-hours that must be restored. | Use the actual starting and target percentages. |
| Panel yield | Reduces nameplate panel watts to representative useful input. | Account for orientation, temperature, shade and site conditions. |
| Station input ceiling | Caps useful panel power before charging efficiency. | Check power, voltage and current specifications together. |
| Equivalent sun hours per day | Converts equivalent charging time into indicative solar days. | Use location- and season-specific solar data. |
Solar recharge starts with nominal battery watt-hours, capacity retention and the percentage difference between Charge from and Charge to. That charge window determines the watt-hours to replace. It is independent of panel size, and it avoids assuming that every charging session starts from an empty battery or ends at 100%.
A panel rating is power under reference conditions; a battery label is stored energy. The calculator reduces panel watts by the entered yield, clips useful input at the station ceiling and applies charging efficiency before dividing the charge energy by effective power. This produces equivalent full-sun time rather than ordinary elapsed daylight time.
Panel yield represents aggregate effects such as orientation, temperature, wiring and imperfect irradiance. It is an explicit scenario input, not a weather forecast. Use a conservative value supported by local conditions or compare several scenarios, and keep equivalent sun hours per day separate from the yield percentage so the same loss is not counted twice.
Useful panel power cannot exceed the entered station input limit in this energy model. Once that ceiling binds, more nameplate watts no longer shorten the displayed peak charging time. Electrical compatibility remains a separate check: verify the permitted voltage and current ranges, connectors, polarity, and series or parallel configuration before connecting an array.
Equivalent full-sun hours compress variable solar production into the duration that would deliver the same energy at reference irradiance. Dividing by the entered daily sun value gives an indicative number of solar days, not a clock-time promise. Cloud, shade, charging taper and equipment operating during recharge can all extend the real elapsed time.
Compare battery size, charge window, panel yield and station input clipping.
The engine calculates energy to replace, reduces panel rating by the yield factor, applies the station input ceiling and charging efficiency, then reports equivalent full-sun hours and indicative days at the entered daily sun value.
FULL WORKED CALCULATION
Recharge from 30% to 90% using 240 W of panels while the station accepts at most 180 W.
The panel array is reduced by expected yield and then clipped by the station input ceiling. Once that ceiling binds, adding panel nameplate watts no longer reduces this model’s peak charging time.
Confirm the station’s solar power, voltage and current ranges, then use site- and season-appropriate equivalent sun hours.
CALCULATED EXAMPLE 1
Recharge from 20% to 80% with a 120 W panel, 75% panel yield and 90% charging efficiency.
The result is equivalent full-sun time; daylight clock time will usually be longer.
CALCULATED EXAMPLE 2
Recharge from 10% to 80% using 400 W of panels at 70% panel yield and 90% charging efficiency.
The calculation assumes the stored solar energy is not being consumed by equipment at the same time.
CALCULATED EXAMPLE 3
Recharge from 20% to 90% using 400 W of panels, 80% yield and 92% charging efficiency.
A 350 W input ceiling is entered so clipping remains visible in the result.
Calculated by the same engine as the tool.
| Scenario | Entered plan | Calculated answer |
|---|---|---|
| 2,000 Wh station with 400 W solar | Recharge from 20% to 80% using 400 W of panels at 75% yield and 90% charging efficiency. | Energy to replace: 1,140 Wh · Stored solar power: 270 W · Equivalent sun time: 4.22 h · At entered sun per day: 0.84 d |
| Small 300 Wh station with 80 W solar | Recharge from 25% to 85% using an 80 W panel at 70% yield and 90% charging efficiency. | Energy to replace: 180 Wh · Stored solar power: 50.4 W · Equivalent sun time: 3.57 h · At entered sun per day: 1.02 d |
Unless a row states an input limit, each row uses a 20–80% charge window, 100% retained capacity, 80% panel yield, 90% charging efficiency and four equivalent sun hours per day.
| Scenario | Inputs | Engine result |
|---|---|---|
| 500 Wh battery with 100 W solar | 20–80% charge; 80% panel yield; 90% charging efficiency | Energy: 300 WhSun time: 4.17 h |
| 1,000 Wh battery with 200 W solar | 20–80% charge; 80% panel yield; 90% charging efficiency | Energy: 600 WhSun time: 4.17 h |
| 1,000 Wh battery with 400 W solar | 20–80% charge; 80% panel yield; 90% charging efficiency | Energy: 600 WhSun time: 2.08 h |
| 2,000 Wh battery with 400 W solar | 20–80% charge; 80% panel yield; 90% charging efficiency | Energy: 1,200 WhSun time: 4.17 h |
| 2,000 Wh battery with an input limit | 800 W array; 500 W station limit; 20–80% charge | Energy: 1,200 WhSun time: 2.67 h |
Equivalent sun time is an energy measure. Weather, shading, orientation, charging taper and equipment operating during recharge are outside these examples.
Interpret equivalent sun hours, panel rating, input clipping and simultaneous use.
The answer depends on the battery percentage window, panel yield, charging efficiency and station input limit. With these values entered, the result reports equivalent full-sun hours and indicative solar days.
No. They compress a variable solar day into the equivalent duration at reference irradiance. Morning, evening, cloud, shade and panel angle make clock time longer than this energy-equivalent duration.
Only while useful input also doubles. The station input ceiling may clip the larger array, and panel yield and charging efficiency still apply.
It is the maximum power the charging input can accept under compatible electrical conditions. In this energy model, useful panel power is clipped at that ceiling before charging efficiency is applied.
This model assumes the entered solar energy goes into charging and no equipment consumes it at the same time. Simultaneous use requires subtracting battery-side load from useful charging power in a time-based model.
The calculator multiplies retained nominal capacity by the 60-percentage-point charge window. It then divides that energy by stored solar power after panel yield, input clipping and charging losses.
Represent expected aggregate conditions with a conservative panel-yield factor or test several scenarios. A single energy estimate is not a weather forecast and does not model hour-by-hour irradiance.
This calculator evaluates watts only. The array must also remain within the station’s voltage and current ranges, connector requirements and permitted series or parallel configuration.
Power Planning Model v1 · 48 saved checks · reviewed 14 September 2026.
MODEL CHECK
We run 48 saved examples, edge cases and combined checks before release. Each modeled relationship is mapped to an official primary source and at least one saved scenario. When we compare a published example, we first use the same inputs and assumptions.
All explicit loss factors are neutralized so the model must reduce to energy divided by accepted charging power.
The model keeps equivalent full-sun energy separate from elapsed daylight and weather forecasting.
Desk-validated means the documented arithmetic, exact boundaries and model invariants reproduce the stated results. It does not certify a product or predict weather, battery condition or field performance.
References used by this page, what is calculated and what still needs a specification or measurement.
Reviewed 14 September 2026. These references support the terminology and methods. Equipment presets and default efficiency values are examples, not facts about every product.
Pages 3, 4 and 11 state E = P × t, P = E ÷ t and electrical P = V × I. This validates dimensions, not equipment performance.
Reference for energy units and the nominal-voltage requirement when starting from amp-hours. No product recommendation.
Context for solar losses and uncertainty. This tool uses a simpler local energy-budget model; it does not call or reproduce PVWatts.
This solar model does not forecast weather or hourly irradiance, simulate shade, charging taper, battery temperature, simultaneous equipment use or panel electrical compatibility. Equivalent sun time is an energy requirement; verify array voltage, current, connectors and site conditions separately.