Battery Night Planner
A free sizing tool for anyone with solar and battery storage. Add the appliances you run after dark and it will show you whether your battery makes it through to sunrise, what time it would run flat, and what the shortfall costs you over a year.
Will your battery get you through to sunrise?
Once the sun goes down your panels stop producing and the battery carries the house on its own. Whether it lasts until morning comes down to two things: how much storage you genuinely have available, and what you leave running overnight. This calculator puts numbers on both.
Add the appliances you use after dark, tell it roughly how long each one runs, and it works out how many hours your battery lasts, what time it would run flat, how many units you would buy from the grid instead, and what that costs over a year. If you come up short, it tells you how much more storage would close the gap.
It takes about five minutes and nothing is sent anywhere — the figures stay on your own device.
Why you enter hours three times
No household uses the same amount every night, so instead of one guess you fill in three, and the calculator reports on all of them side by side.
Frugal
A careful night. Lights, the fridge, the WiFi, not much else — a mild evening with no heating or cooling running.
Normal
How the house actually runs for most of the year. TV on, a wash to do, hot water heating up.
Comfort
The heavy nights — heating through January, air conditioning through August. This is the one that empties a battery.
Sizing storage on a normal night alone is what catches people out. If the Comfort column runs you flat at two in the morning every winter, that is the number worth acting on.
How to use it
Work down the three cards on the left; the results on the right update as you type.
Set up your battery
Enter how many batteries you have and the rated capacity of each. The reserve is deducted for you, so the green figure underneath is what is genuinely available to run the house overnight.
Set your night window
Sunset to sunrise. On the Costa Blanca that is around 13–14 hours in winter and nearer 9–10 in midsummer. Try both — the winter figure is the one that decides whether your storage is big enough.
Add your appliances
Tap anything in the list to add it, or press Start with a typical home for a head start. Then enter how many hours each item runs during the night, once for each usage style. Wattages are filled in for you — overwrite any you know better.
Read the results
The banner gives the verdict, the three cards show runtime and cost, and the chart shows charge draining through the night. When you are happy, email the results to us or save them as a PDF.
Plan your night
Everything below updates live. Change a figure and watch the results move.
Your battery storage
Enter the rated capacity — the reserve is taken off for you.
Your night window
The stretch between sunset and sunrise your battery has to cover.
Your appliances
Tap an appliance to add it, then enter how many hours it runs between sunset and sunrise — once for each usage style.
Wattages are average draw, not the figure on the rating plate. Anything that cycles on a thermostat or compressor — fridge, A/C, heating, dishwasher — averages well below its plate rating. Overwrite any of them with your own readings.
Add your appliances to begin
Pick the things you run after dark from the list on the left. Results update as you type.
Battery charge through the night
Each line is one usage style, drawn from sunset to sunrise assuming load is spread evenly. Lines flatten onto the reserve floor — they never discharge into it.
What the shortfall costs you
Grid electricity bought after the battery runs flat.
| Usage style | Per night | Per month | Per year |
|---|
What this planner assumes
A quick sizing guide, not a design document. Real installs vary with battery chemistry, inverter losses and how your loads actually cluster through the evening.
Even load across the night
Your total night consumption is spread evenly from sunset to sunrise. In practice the evening peak is heavier, so a battery that looks marginal here will usually empty a little earlier than shown.
Reserve comes off the top
Enter the rated kWh per battery; the reserve percentage is deducted for you, so only what is genuinely available for the night is counted. Most inverters stop discharging around 10% so there is always something left for EPS. The planner assumes the bank starts each night full.
Shortfall bought from the grid
Anything the battery can't cover is priced at your grid rate. Monthly figures use 30.4 nights, yearly figures 365 — so treat them as a worst case if your nights get shorter in summer.