How to calculate monthly solar power generation for budgeting?

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Understanding Your Energy Needs To calculate your monthly energy needs, start by adding up the total wattage of all your appliances, lights, and other devices. A good rule of thumb is to start with the average daily energy consumption of each appliance and multiply it by the number of hours it’s used per day. For example, if you have a refrigerator that consumes 150 watts and runs for 12 hours a day, its daily energy consumption would be 150 x 12 = 1800 watt-hours (Wh) or 1.8 kilowatt-hours (kWh).
Measuring Solar Irradiance Next, you need to determine the solar irradiance of your location. Solar irradiance is the amount of solar energy that hits a given surface area over a certain period of time. In the US, the average solar irradiance is around 5 peak sun hours (PSH) per day, but this value can vary depending on your latitude, climate, and time of year. You can use online tools or consult with a solar professional to determine the solar irradiance of your location.
Calculating System Size Once you have your energy needs and solar irradiance values, you can use a solar panel calculator or spreadsheet to estimate the energy output for a given system size. A common rule of thumb is to size your system to generate at least 1.25 times your average daily energy needs. This will give you a buffer for cloudy days and other energy-intensive activities. For example, if your average daily energy needs are 12 kWh, you would need a system that can generate at least 12 x 1.25 = 15 kWh per day.