How to size solar system (to optimize energy consumption and output)

solar system sizing

Green energy is the new way of life while investing in solar power is the most convenient way to source cleaner and greener energy.

The latest solar panels and photovoltaic systems are affordable, easy to install, and even easier to use. By installing the right solar panels, you can efficiently optimize power consumption and energy usage around the house. So, if you’re trying to cut down the cost of electricity bills, you’ve got the sun at your rescue.

However, to get the most out of your solar system, you have to size it properly, and that part can be a bit tricky. You don’t want to end up with a solar system that cannot keep up with your daily energy usage.

That’s why we’re here to lend you a helping hand. In this article, we’ll talk all about how to size solar system, so without any further ado, let’s get started!

What Is Meant By Solar System Size?

The size of a solar system is the capacity of the solar panels to generate electricity. For instance, a solar panel of 300 watts generates 300-wall electricity. Similarly, a 6 kilowatt or 6,000-watt solar panel system will produce electricity of 6,000 watts in standard conditions.

Now, you may ask, what are these standard conditions? To make your solar panels work at the maximum capacity, you need 1,000 watts of sunlight shining on each square meter of the solar panels. Also, you need an optimal temperature of 77℉ to make the panels work properly.

Furthermore, you have to measure the electrical output of the Direct Current (DC) in watts while measuring the solar system size. So, if you have a 300-watt solar panel, it’ll essentially produce 300 watts of Direct Current. And if you put together 20 such panels to build your solar system, the total electrical output will be 6,000 watts or 6 kilowatts under standard conditions.

Identify Constraints While Sizing A Solar System

Before designing your solar system, it is best to identify the possible constraints you might face. Some of the primary constraints while sizing the solar system include budget constraints, space constraints, and energy offset. So, you need to focus on building an affordable, space-efficient system that meets your energy requirements.

Furthermore, the efficiency and peak output of a solar panel massively depend on the sun exposure levels of your local area. Hence, when you are measuring the size of your solar power system, it is imperative to consider the level of sun exposure.

On top of this, the orientation of the solar array plays a vital role in sizing your solar power system. You need to ensure that solar panels have the right tilt angle to perform at their optimal capacity under standard conditions. If the tilt angle is wrong, the solar panels won’t receive enough sunlight, automatically compromising their electrical output.

Ways To Determine The Solar System Size

Now that you know about the possible constraints, it is time to learn about the different methods to calculate the size of your solar power system. In this section, we’ve discussed three methods that you can utilize while calculating the solar system size.


You can use PVWatts to calculate your total annual electrical usage, which can be helpful in measuring the solar system size. This free online software uses weather records and solar radiation measurements to undertake the photovoltaic analysis of your house.

It offers an accurate breakdown of the hourly energy output of your solar power system, making it easier to use PVWatts to calculate the solar estimates. However, it doesn’t directly help you to calculate the size of your solar power system.

PVWatts helps you calculate the solar energy produced per kilowatt of the solar panels. But you can use that value to divide the total annual electricity usage at your home to determine the size.

In this way, you can calculate the size of a solar system that can suitably cover all your energy requirements. That said, the calculations can be a bit cumbersome if you’re using PVWatts.

SolarReviews Calculator

If you’re trying to calculate the solar system size for your residential home, SolarReviews Calculator is arguably the best choice. It uses a diverse database of electricity usage and utility rates to calculate the average solar estimate of your solar power system.

It considers your local address and monthly electricity bills to accurately estimate the size of the solar system that will help cover your monthly electricity usage. Additionally, it quickly estimates the right system size that’ll be best suited to your roof.

Not only that, SolarReviews Calculator provides you with cost estimates for installing a solar system based on its size. You can also view live prices offered by professional solar installers in the area to set up a solar power system. Hence, it is very handy and quite straightforward to use.

Hiring A Professional Installer

The easiest way to estimate the size of your solar system is to hire a professional solar installer. You can simply contact any local solar company to install your solar power system, and they will handle the process without much hassle.

Solar installation companies usually use tools such as PVWatts and offer in-person assessments of the roof to accurately calculate the right size of your solar power system. Any experienced professional installer will estimate the suitable solar system size that’ll help you meet your energy needs around the house.

However, it is best to check the track record and customer reviews of the solar companies before you decide to hire them to size a solar system. You don’t want to waste hundreds of dollars by hiring a professional who fails to calculate the right system size and optimize the target energy output of the solar panels.

Factors Impacting The Solar System Size

When sizing solar PV systems, there are several factors that can impact the calculation. You need to consider these key aspects while calculating the solar system size, and we’ve highlighted some of the major factors below.

Electricity Usage

Electrical usage is the most important factor when it comes to calculating the size of your solar photovoltaic system. You need to calculate the kilowatt-hours (kWh) of electricity usage from your annual power bills.

Once you know the annual power usage of your house, it becomes possible to determine the average monthly and daily usage. The daily kWh energy requirement will seriously impact the size of your power system.

You can use the SolarReviews Calculator for calculating the monthly kWh electric usage. Simply provide the amount of your power usage based on the monthly electric bill, and the SolarReviews Calculator will estimate the pattern of your electricity usage. It will use the electrical usage and utility rate information for your particular area to calculate your annual power usage.

Once the average monthly consumption and the daily energy consumption rates have been calculated, you’ll have a better idea regarding how much power you need. In that way, you can estimate the size of your solar system.

Peak Sun Hours

Depending on your particular location and the local climate, the peak sun hours (PSH) are bound to vary. So, it is always best to look up the solar insolation in your area to estimate the PSH while sizing the solar power system.

To make your solar system operate at optimal capacity, it is essential to ensure that the solar panels are getting the right amount of sunlight. And based on your location and peak sunlight hours, the optimal capacity of the solar panels will vary naturally.

For instance, the PSH is much higher in Tucson, Arizona, compared to Seattle, Washington. You cannot use the same solar system size to cover all your electrical needs in these two particular areas. Thus, estimate the hours when the sun will be at its peak to design a solar system having the right size.

You can use PVWatts or SolarReviews Calculator to access the suitable database and get all the necessary information regarding the PSH and solar radiation of your location. Also, if you hire a professional installer, they will check all the data for you.

Roof Characteristics

To install solar panels, you need a large usable roof area. The orientation and architecture of your roof will impact the angle and orientation of the solar panel array. These two factors and the direction of the solar panels can majorly impact the kilowatt (kW) output of your solar power system.

You might need to increase the size of your solar system based on the direction of the roof. Solar panels facing south tend to generate 15% more electrical output compared to those facing west or east. So, if you have a west or east-facing roof, you might need to increase the number of panels in the solar system design to enhance energy production.

Furthermore, if you have a limited roof area, you need to install high-efficiency panels that can optimize energy production even when installed in smaller numbers. That said, it is better to leave sufficient roof space so that you can install more solar panels if you need to increase the system size.

System Losses

When you are sizing solar power systems, you have to consider the system losses. You cannot access the full DC electrical output of the solar panels because all solar systems experience some amount of power loss.

Typically, 2% electrical power output is lost when DC electricity gets transmitted to a solar inverter. Also, an additional 3% of power gets lost when the inverter converts the current to AC from DC.

Thus, if you’re using the usual grid-tie solar photovoltaic system, you can access around 95% of the total electricity that the solar panels generate. The remaining 5% of electricity is lost during transmission.

However, you can decrease the power losses by using high-efficiency solar panels and inverters or by reducing wiring. Thus, your system design and equipment can greatly help in optimizing the energy efficiency of solar panels.

Battery Storage

The battery storage of your solar PV system can majorly impact the system size. Now, when we talk about battery storage, there are two main factors for you to consider – battery backup and battery efficiency.

Battery Backup

Do you want to use your solar power system just for emergency purposes? Or do you want it as the primary power source in your house? Depending on your preferences, you need to determine the amount of battery backup that the system will require.

If the solar system is just for emergency usage when your main power source is down, you won’t need any battery backup. In this case, it also won’t have much impact on the system size. However, if you plan to use the solar system as the primary energy source in the house, you need a good battery backup.

It is best to add enough backup power to the system to cover your daily electricity consumption in the latter case. You will need to design a system size that has sufficient backup power to fully recharge the batteries even on rainy or cloudy days when the sunlight is low. Hence, the backup power of your battery can significantly impact the sizing of the solar power system.

Battery Efficiency

As we’ve mentioned earlier, a certain amount of energy is lost within the solar system when the current is converted and transported through it. Similarly, small amounts of power are lost when the electricity enters and leaves the solar battery every time. But, you can reduce the amount of power loss by setting up an energy-efficient battery for your solar system.

For instance, DC-coupled batteries are much more energy-efficient than AC-coupled battery systems. The former shows an average efficiency of around 95%, while the latter has a much lower round-trip efficiency of 90%.

It is always best to go for a high-efficiency battery that can reduce power loss and maintain the peak output of your system. Also, depending on the battery you choose, you need to size the solar power system accordingly to compensate for such power losses.

How Many Solar Panels Are Required?

An easy way out to calculate the required size of the solar PV system is to divide your daily kWh usage with the peak sunlight hours in your locality. Now, divide the kW output value by the efficiency of your solar panels.

In this way, you can estimate the number of solar panels needed to design your solar power system and determine the required system size. The formula is as follows:

(Daily kWh usage/Average PSH) x Efficiency of the solar panels = Size of your solar system

Say, you live in an area with 6 hours of peak sunlight, daily kWh usage is 33 kWh, and the efficiency factor of the solar panels is 1.15. By using the above formula, the estimated DC system size will be 6.2 kW or 6,200 watts.

Thus, you’ll need to install solar panels of 6,200 watts to design a DC solar system that can fulfill your electricity needs efficiently.

Fine-Tune The System Design

To estimate the size of your solar power system accurately, you need to check and fine-tune your system design. The mounting type of your system and type of solar panels can greatly impact the solar system output.

Mount Type

It is best if your roof-mounted system faces the south for maximum exposure to the sunlight. If the tilt angle and direction of the solar panels are not right, you might need to increase the size of your system to optimize solar energy production.

In short, you can save money and enhance the energy efficiency of your solar system by adjusting the angle and direction of the solar panels while mounting them.

However, if the roof mount option isn’t available, you can always look for a pole-mounted or a ground-mounted design. In fact, it is easier to adjust the direction and tilt angle on a flat ground surface compared to a tilted roof.

Type Of Solar Panel

Depending on your available roof area, you can choose a suitable solar panel. If you have a large and open roof, you can easily go for larger panels to enhance the energy output at a much lower cost.

But if your open roof space is limited, it is best to install several smaller solar panels with high energy efficiency. In that way, you get to save money and also leave enough space on the roof if you need to add more solar panels in the future.

Final Thoughts

While sizing your solar panel system, it is always best to calculate the daily energy requirement of your home. And after going through our article, we hope you know a lot more about estimating the daily energy consumption rate.

Furthermore, consider your geographical location and roof architecture while sizing your solar power system. It can seriously help you in estimating the right system size.

We believe these factors will impact the peak output of your system, so refer to our guide to install a solar system of the right size.

Need professional help when it comes to solar panel installation, maintenance or repair? Look for the nearest solar installer in your neighborhood.

Call Now