Caculating kilowatts need to buy a right solar power system

Determining the number of solar panels that you need for a home involves considering some several factors. To know exactly the number of solar panels you require, take into consideration the amount of energy you use, roof’s surface area, peak sunlight and the climate in your region. You should also consider the wattage and photovoltaic panels’ relative efficiency.

When you want to determine the energy required for your household, check at previous utility bills. If you want to know the number of solar panels necessary, you multiply the peak sunlight hours in your area by the hourly energy requirement of the household and dividing the result by the wattage of the panel. You can use a high voltage and low voltage if you want to determine the range. You will also have to consider the amount of sunlight that the roof gets, battery storage and roof size.

Most solar power system manufacturers can calculate for you. However, here are some of the things to consider if you want to figure out for yourself.

  1. The watts you use currently

Your electricity bill will show this. It can be given regarding kWh or something similar. Look for the period that it represents but usually its 30 days. If the bill doesn’t show the number of kWh used, check the beginning and ending readings of the meter. Subtract the reading from the previous time from the current one.

If you want the hourly or daily usage and the bill don’t show the daily average, divide the annual or monthly by 365 days or 30 days respectively. Divide the result by 24 if you want the hourly average. The answer that you will get is in kWh.

A home in a temperate climate can use about 200 kWh every month, and a larger house where there are air conditioners might use about 2000 kWh per month since air conditioners account for more energy use. An average home in the US consumes approximately 900 kWh each month. That’s like 30 kWh each day or 1.25 kWh each hour.

The average daily usage is the target average for calculating the solar needs. It is the number of kWh that you will need the solar power system to generate if you want 100% of the energy requirement.

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You should note that solar panels don’t always operate at its maximum efficiency. For instance, it can be affected by weather conditions reducing its efficiency. It is recommended to add 25% cushion to the daily average if you want to have all the energy you require.

  1. The number of hours that you receive sunlight

The amount of energy produced by a solar power system is affected by peak sunlight hours. Some areas receive more peak hours than others. However, it doesn’t mean that areas with low peak hours can’t go solar. It means that more solar panels are required. Divide the average hourly wattage by peaks hours per day. You will get the amount of energy that your solar panels produce each hour. A US home that uses 900 kWh each month in an area with five hours of peak sunlight would require 6,250 W system.

  1. Panel output efficiency

There are different solar panels. Photovoltaic solar panels come in wattages that range from 150 – 370 watts each panel. This depends on efficiency, cell technology, and panel size. Efficiency is how well a solar panel can convert sunlight into electricity.

For instance, a solar cell that has no grids on their front can absorb more sunlight than other conventional cells. They also don’t suffer from delamination issues. The construction of the cells makes them more resistant and stronger. They can resist cracking and corrosion. Having a micro inverter on individual solar panel helps in optimizing power conversion.

Due to the extensive variations in efficiency and quality, it can be complicated to generalize on which solar panel is the best for you or the number of solar panels to get for your home.

As the efficiency of solar panels increases, the wattage produced goes higher too. This means that you will need fewer panels and you will still get the same energy output.

Conventional panels produce around 250 watts each panel. However, they have a different level of efficiency. You can get the most efficient solar panels if you want to have few panels.

If you want to know the number of solar panels that you will need, divide the hourly wattage requirement by your panel’s wattage.

  1. The effect of the size of the panel

The size of the panel and their numbers would come into consideration when you have unusually shaped or small roof. If you have a large roof, you can sacrifice efficiency and get larger panels at a lower cost. However, if the usable area is limited, or if some parts are shaded, then you will need smaller and fewer panels with higher efficiency.

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Most residential solar panels have dimensions of about 39 inches x 65 inches(1m x 1m7) . There are some variations among manufacturers. These dimensions have been used for more than many years, but the output and efficiency have kept changing as more efficient panels have been designed. Some designs have no gaps in between panels and they use invisible mounting and framing hardware to have the rooftop footprint attractive, efficient and tight.


When you have considered these four factors, you will be able to calculate the kilowatts that you will need when you are looking for the right solar power system. Also, a professional will have to assess the roof architecture and angle to the sun to determine how the panels will be arranged for you to achieve the daily energy required.

You will also have to consider net metering since you want to know your ROI for a solar system. Net metering shows how a utility company credits someone for producing excess solar power and lets you use the credits when using the power grid during the night when you don’t have a battery for storing power.



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