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Solar System Sizing: How to Size Your Grid-Tied Solar System?

Installing a solar system is an excellent way to reduce your energy costs and reliance on your grid. But if you want to make the most of your solar system, it’s crucial to size it correctly. Sizing a solar system is a process that involves assessing your energy needs, evaluating your site’s solar potential, and determining the optimal size for your solar system, including the size of inverters.

If you are about to go solar but are unsure how to size your solar system, look no further. In this article, we will walk you step-by-step through solar system sizing, factors to keep in mind while sizing the system, and so on.

A disclaimer at the outset, however. This article only talks about how to size grid-tied solar systems generally installed in U.S. homes. If you want to know about sizing other systems, you may like to read the following:

  • How to size an off-grid system?
  • How to size a hybrid system?

How to Size Your Grid-Tied Solar System?

Unlike sizing an off-grid system, sizing a grid-tied system is relatively easy. You do not have to calculate the battery needs, which can turn quite complex. Just assess your needs, evaluate your location, and find the right solar array and inverter size based on the data.

Let’s start with our first step—estimating your energy needs.

1. Understanding Your Energy Needs

It is simple—look at your electricity bill, and you will have your annual usage. Divide that by 12 to get your average monthly usage. Similarly, divide that figure by 30, and you will get your average daily electricity consumption.

But from here, it gets tricky. What you got above is only an average figure, which may not be quite right for sizing your grid-tied system. On some days you will run some appliances which will consume more electricity, for example, air conditioners in summer and heaters in peak winter. If you size your system on your average daily consumption, your system might fail to meet your demand during peak summer or winter. Especially in winter, as the performance of solar systems drops in winter due to the low number of sun hours.

You will have to calculate your peak daily usage to get a clearer idea of your needs.

Calculating daily peak usage

We do not always use the same amount of electricity throughout the day. At times, the demand is more, such as during the night, when all appliances—lights, refrigerators, televisions, air conditioners, etc.—are running. That’s what we need to calculate to size our system correctly.

Check the power rating of all such devices and add them up. For instance, if you run five 10W lights for 8 hours, one television of 200W for 2 hours, one refrigerator of 400W for 20 hours, and one air conditioner of 1500W for 5 hours, that will be your peak energy usage.

This comes out to be: 5*10*8+200*2+400*5+1500*5=10,300 watt-hours or 10.3 kWh during that time. Note that even though our refrigerator ran for 20 hours, we took it for five because it is during these five hours that we will need the most electricity. Peak usage refers to the highest amount of electricity needed at a certain time. So, our peak hours will no longer apply once the air conditioners are switched off.

You can find the rating on the device or from their data sheets. If it is unavailable or you do not understand the technical details, go for a power meter. Power meters calculate the power rating in real time and more accurately.

You may also like to read: How much does a grid-tied system cost? (ballpark estimates)

2. Assessing Your Site’s Solar Potential

Your site affects your solar system’s size in two ways. First, how much sunlight your state receives? Two, what are your home specifications?

Find your “sun hour.”

The amount of sunlight that a location receives, also known as “sun hours,” directly affects the size requirements of your solar system. Areas with higher sun hours will require smaller solar systems to produce the same amount of power as areas with lower sun hours. This is because solar panels will be able to generate more electricity from the same amount of sunlight.

Note the average annual and monthly sun hours your home receives—we will need them in the next section. You can get an idea from The National Renewable Energy Laboratory here.

Did you know?

Solar panels can generate electricity even when the sun is not shining directly on them, but the amount of electricity generated is less than it would be during peak sun hours.

Your home specifications

The angle at which the system is to be installed and the sun’s direction also affects your solar system’s capacity. For homes in the United States, the ideal angle for solar panels is typically between 20-40 degrees, depending on the location. For instance, homes in Southern states such as Florida and Arizona will typically have a steeper angle (around 30-40 degrees) to optimize solar energy production during the summer, when the sun is higher in the sky. On the other hand, homes in Northern states such as New York and Montana typically have a shallower angle (around 20-30 degrees) to optimize for solar energy production during the winter, when the sun is lower in the sky.

The direction in which solar panels should face depends on the location and available space. In the U.S., facing the solar panels towards the south is generally recommended, as this is where the sun is most intense and consistent throughout the year. This is true for most of the U.S., with some exceptions, like homes in the far southern parts of Arizona, New Mexico, and Texas, where it could be better to orient the panels towards the west due to the high solar intensity.

If your roof angle and direction are a problem, you may consider installing the system on the ground. Ground-mounted systems can be positioned and angled to optimize solar energy production, increasing the system’s overall efficiency. But again, it depends upon the availability of space.

3. Sizing Your Solar System

Now the mathematics is done—you have calculated your daily usage and noted your peak sun hours. Let’s keep your monthly usage as 1000 kWh per month and your average peak sun hours as 5. Your sun hours may be different than this—we have taken this figure for the sake of simplicity.

If you are installing 400-watt solar panels, the energy produced by one solar panel would be 2 kW (400 watts x 5 sun hours). Per month, it would be 60 kW. Divide your monthly consumption, i.e., 1000 by 60, and we will need around a solar array consisting of 17 solar panels. That means the size of your system must be 6.8 kW to meet your monthly needs.

But this is a simple answer, where we have assumed that your solar system is performing at its full potential. As we discussed in section 2, the full potential of a solar system can be realized only when it is installed at the right angle, facing the sun directly. You may need a bigger system for the same consumption if the angle or direction is not appropriate.

Sizing your inverter

Ideally, you should keep the inverter size the same as your system size. In this case, you will need a 6.8 kW inverter.

But experts recommend keeping the size of your inverter above the system size. The reason is that inverters are not 100% efficient. Some of the power is lost in the conversion process, while the inverter itself consumes some. Also, the performance of inverters drops as the mercury goes up. So, it would be best if you kept a 15% window for the inverter to maneuver and keep you comfortably powered.

You may also like to read: Installing a grid-tied system? Here are 7 things you need to know

The effect of net metering on your grid-tied system size

Net metering is a billing mechanism that helps you connect your system to the grid. Through this arrangement, you can sell your excess electricity to the grid.

If your state has a net metering policy, this means that you’ll need a bigger system to match your electricity consumption. Doing so will bring your electricity bill to the bare minimum, as the grid will buy the excess electricity your system generates. In return, you can use their electricity at night or when the weather affects your system’s performance.

If no net metering is available, you may consider installing a smaller system only to meet your needs during sun hours. Perhaps, a 4 kW system would work well for you.

This was all about how to size your grid-tied system. Remember that sizing your solar system is not as simple as it sounds. To make the most of your system and to let it reach its full potential, we recommend consulting a professional solar installation company to do the job. They will take care of everything—from inspection to documentation to giving you the right-sized system.

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