Online solar calculators can give a rough estimate of how much solar energy you'll need to power your home, but you may want to perform your own size calculations to fine-tune your choices. Below is a step-by-step overview of the process we follow when I want to know what size solar system do i need.

How to determine the size of the solar System in 6 steps.

When determining the size of the solar system, follow these steps to find out the exact plan to meet your energy needs. If you just want a quick estimate without having to do the math, feel free to use our solar calculator.

Step 1: Determine your average monthly electricity consumption.

Statistics show that most people consume more electricity in the summer and winter, when air conditioning or heating is running. If possible, collect your electricity bills for the last 12 months, then add up your kilowatt-hour usage and divide by 12 to come up with a monthly average.

Step 2: Calculate your daily electricity consumption.

Next, divide your monthly kilowatt-hour usage by 30 to estimate your average daily kilowatt-hour usage. The average American household uses about 900 KWH of electricity per month, so we'll use it in our example:

900 KWH /30 days = 30 KWH per day.

Step 3: Estimate how much sunlight your solar panels will get.

The availability of sunlight affects the amount of energy produced by solar panels.

Step four: Explain the inefficiencies.

From there, we needed to add a little overhead to address the inefficiency and degradation rate of solar panels.

The production of solar panels decreases slightly each year, which is outlined in their performance warranty. If your solar panels' performance warranty guarantees 80% performance after 25 years, then their degradation rate is calculated at 20%/25 years, or 0.8% production loss per year. By the end of its life cycle, a 400W rated panel can only output 320 watts of power.

In addition, the solar panels are tested under ideal conditions - a temperature-controlled laboratory without any obstacles. In the real world, solar panels often fail to meet these lab-tested conditions, meaning they produce slightly less electricity than their rated wattage.

Because of these factors, it would be wise to budget for additional solar capacity so that you can reach the target production figure after taking into account the inefficiencies of the system.

20% is a good headroom to explain the inefficiency. Multiply the size of your solar panel by 1.2(120%) to achieve the following:

6 kW x 1.2=7.2 kW solar panel.

Step 5: Full or partial offset?

Most grid-connected homeowners choose to use 100% solar to offset their energy needs. But it is also possible to start with a smaller partial offset system and then scale down as the budget allows.

If partial compensation is your goal, you can explain it here. For example, suppose you want to first offset half of your energy use with solar:

7.2 kW solar panels *0.5=3.6 kW solar panels.

In this case, a 3.6-kilowatt array would cover 50 percent of your energy use, cutting your electricity bill in half.

Step 6: Determine how many solar panels you need.

Once you have your final array size, simply divide by the wattage of solar panels you want to figure out how many panels you'll need.

Using an example of 100% offset for our 7.2 kW(7,200 watts) array, here is a sample system that can meet our needs:

7.2 kW solar panel with 400W Phono solar panel: 7,200 W /400 W =18 panels.

Size of the Solar System: Other considerations.

This should be enough to help you tune a solar system that meets your energy needs. Note, however, that if your utility offers a net metering plan that allows energy resale or variable billing rates, there may be more factors to consider.

A common use case is a utility that charges time-of-use (TOU) rates. Under time-of-use tariffs, electricity bills spike around 5 to 9 p.m. to meet higher demand as people return home from work/school and usage is at its daily peak.

If your utility provider charges a higher timeshare rate, it may be wise to install solar panels on the west side of your roof. While south-facing panels produce more kilowatt-hours of energy, west-facing panels may be more cost-effective overall because they will produce electricity later in the day, offsetting the higher TOU rates at peak times.