Calculate your need for solar panels on your boat, caravan, cottage and Off Grid

Solar cells … How many watts do I need?

To find out how many solar panels you need, you should start by calculating your need for power.
Enter in this solar calculator the electrical appliances you have, how many watts they use (this is typically in the manual or printed on the unit) and how many hours you typically use them in a day. Remember that eg. a refrigerator is not running all the time, but perhaps only 25% of the time.
You need the irradiation of sunlight on the place you want the solar cells to work and use the lowest returned figur for the months in which you have power requirements. Incoming radiation can be calculated in this irradiation calculater that covers the entire world.
And then you know how many watts of solar you need. 🙂

Battery capacity

The solar calculator also shows you how much battery capacity you need. It also takes into account that an AGM battery should not be discharged more than 50%. GEL batteries can better handle additional discharge, but it is not recommended.

ATTENTION !! You must use dot instead of a comma in the calculator!

Solar calculator
Green fields is editable System voltage 12 Volt
List of consumers.
Please add power consumers, their watt and running hour per day Watt Running hours per day Power used per day Unit
Eg. Refrigriator (remove or alter this line) 100 6 600 Wh
Eg. LED lights (remove or alter this line) 20 6 120 Wh
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Consumption. Wh/Day 720 Wh
Consumption converted to Ah/Day 60 Ah
System loss/ buffer 20 % 12 Ah
Minimum daily production needed. 72 Ah
Solar irradiance, kWh/m2/day. Find your country and city on the calculator. Choose your panel direction (south, south/west, etc) AND your angel towards the sun. Grap the lowest result for the months of the year you want covered (Eg. You want coverage from may to september and september shows the lowest result. Use the result from september only). Drop the result here (Eg. 3,54 for Denmark, Aarhus, facing south and optimal year round angel)solar irradiance Calculator 5.33
Daily production on a 100 watt panel 417.4456 Wh/Day
Solar Watt needed, when solar alone is used 206.9731 Watt
Recommended Ah. For 5 days of consumption 720 Ah
Minimum Ah. For 2,5 days of consumption 360 Ah