Include overnight loads in an ordered solar-energy plan using this page’s inputs.
Battery & Power
Estimate solar battery charging time
Estimate the peak-sun hours and solar days needed to move a battery bank from its starting charge to a target level after solar, controller, battery and equivalent daytime-load effects are included.
Calculation breakdown
Planning estimate only. Peak sun hours are energy-equivalent solar hours, not guaranteed clock hours. Confirm panel, controller and battery voltage/current compatibility, charging settings, temperature limits and manufacturer requirements before relying on the result.
Track an ordered day and night energy balance
Use the original bank, condition, starting charge, target charge, array derating, controller efficiency/current cap and charging efficiency. Enter peak-sun hours and loads separately for each illustrative day below. Original single-day peak-sun hours and equivalent daytime watts are not reapplied. Loads here must already be on the DC-bus/battery-side Wh basis, including any delivery losses.
Separate one refill estimate from an ordered day/night plan
The original calculator estimates equivalent solar production needed to refill a chosen charge interval. Its daytime-load input applies over the entered peak-sun-hour block; overnight consumption is excluded. The additional day/night worksheet carries stored energy through a sequence of supplied solar and load assumptions, exposing why a bank that refills during daylight can still miss a night-end reserve.
Understand the original solar refill model
Nominal bank Wh = bank V × bank Ah. Condition-adjusted energy to store = nominal Wh × condition fraction × (target % − starting %) ÷ 100. Array power after derating = array nameplate W × output-factor fraction. Potential controller output applies controller efficiency to that power.
If a controller output-current cap is entered, its nominal power cap is bank V × limit A. Available controller W is the smaller of that cap and potential output. The original model then subtracts the equivalent daytime load and applies battery charging efficiency to the remaining positive power. Required peak-sun hours = energy to store ÷ stored charging W; estimated solar days divide that requirement by the entered daily peak-sun hours.
Peak-sun hours express equivalent daily energy production, not a number of clock hours during which output remains constant. Choose a location/season assumption appropriate to your question. Do not repeat orientation, shading or other losses in the output factor if your source already includes them. A nominal current cap is not a complete controller compatibility check.
Carry energy through ordered days and nights
The equivalent-energy interpretation is illustrated in the Solar Energy Resource Assessment Handbook (2009). A daily equivalent-energy input does not supply the hour-by-hour weather or load timing needed for a complete operational simulation.
The new worksheet reads bank V/Ah, condition, starting charge, day-end target, array factor, controller assumptions and charging efficiency from above. Each row supplies its own equivalent peak-sun hours, daytime DC-bus load Wh and overnight battery-side load Wh. The original single-day peak-sun hours and daytime watts are not applied again.
Condition-adjusted storage capacity = nominal bank Wh × condition fraction. Initial stored energy = that capacity × starting-charge fraction. For a day, controller energy is modeled controller W × that row’s sun hours. A positive aggregate surplus after daytime loads enters storage after charging efficiency. A deficit drains storage directly. Day-end storage is capped at capacity and floored at zero; the overnight battery-side demand is then subtracted, again flooring storage at zero.
The table compares day-end charge with the original target percentage and night-end charge with the additional planning minimum. That minimum does not stop discharge automatically. Energy that cannot be supplied after storage reaches zero is reported as unserved demand. Surplus above capacity is reported on a stored-energy-equivalent basis rather than being carried into a larger imaginary battery.
A sequence can fail without an empty battery
For a 12 V, 100 Ah bank at full condition starting at 20%, initial storage is 240 Wh. A 300 W array with 75% output factor and 95% controller efficiency gives 213.75 modeled controller watts. At five equivalent sun hours, 100 Wh daytime load and 85% charging efficiency, day-end storage is 1,063.4375 Wh. A 400 Wh battery-side night load leaves 663.4375 Wh, or about 55.286458%.
A following two-sun-hour day with the same loads ends its night at 541.8125 Wh, about 45.151042%. The bank remains above a 20% night minimum, but neither day reached a 100% day-end target. A passing night reserve and a successful full refill are different outcomes.
Use an aggregate model within its limits
Daytime netting cannot reveal an early-morning outage before later generation arrives. It also cannot check momentary load power, intraday controller clipping, battery charge acceptance, charging taper, changing voltage, temperature or a real cutoff. Direct solar-to-load energy is not charged and discharged through an imaginary battery first. Convert AC or regulated-device loads to the specified DC-bus/battery-side Wh before entering them, including the relevant delivery losses once.
Use 1–31 ordered days, sun-hour inputs from 0–24 and daytime/nighttime energy from 0–1,000,000,000 Wh per row. Blank required values are incomplete; explicit zero means none was assumed. Percentages range from 0–100. Exact rational arithmetic precedes six-place display rounding. Source and row edits clear the previous sequence. The illustrative rows are not weather forecasts, and the page does not save a weather or battery log.
Use Battery Charge Time for a bank-side current/headroom estimate or Inverter Battery Backup Time to separate AC load and inverter behavior.