Usage-Based Kilowatt System Sizing by Season

Qualifying for Solar
Tree With Changing Seasons

While there are many factors that go into the size of your solar installation, one of the biggest factors is energy usage. This doesn’t mean that other factors aren’t important, such as the size of your roof and the direction it faces, but these aren’t nearly as important to your solar savings. 

To help you understand what goes into sizing a solar installation, we’ll cover the specifics of sizing, starting with a simple question, “Does the season matter for a solar installation?”

How Does the Current Season Impact the Solar Installation Process?

In short: it doesn’t. But why is that? To understand the role that the season plays (or doesn’t play, in this case), we’ll need to take a look at the ways that solar companies will estimate the size of your installation. There are a few different ways that this is done, but one key component emerges from the rest — your home’s energy usage. 

How Energy Usage Influences the Size of Your Solar Installation

Energy usage is the most important part of determining whether it’s worth it for your home to go solar. A solar installation’s output is not necessarily linked to its size, nor to the size of your home. An installation that’s half the size of another can still produce just as much electricity, depending on which solar PV modules you install.

Additionally, a home’s size doesn’t necessarily correlate with the energy usage of said home. A smaller home that has six people living in it is going to use more energy than a larger home with only one person living in it. A home with more people will use its appliances more often, which are the main driver of electricity consumption.

Does Energy Use Vary Based On the Season?

Yes and no. Depending on the area where you live, some seasons will be more energy-consuming than others. For example, if you live in Las Vegas, your energy use is going to be much higher in the summer than in the winter because of your air conditioning. In other places, it may be the opposite, where heating during winter is the bulk of your year’s energy use. 

But why did we say no earlier? The answer is simple: because the seasons are cyclical, your energy usage for each year is going to be pretty stable. While you may use less electricity in the winter and more in the summer, after a period of five years, you’re going to have used about the same amount of electricity each year. The EIA’s graph of residential energy use is a perfect example of the cyclical nature of seasonal energy consumption.

Why Does It Matter for Solar Installation Sizing?

When it comes to installing solar, any company worth their salt is going to look at your electricity use over a much longer period than just a few months. There may be fluctuations in your recent energy consumption that don’t represent your typical usage. You may have used more than average or less than average over a couple of months, but then you revert back to the mean.

Sizing Your Solar Installation To Your Average Annual Electricity Consumption

The main reason why your long-term energy use matters are because your solar installation is a long-term investment. Typical solar panels last anywhere from 25 to 40 years while still producing at a good rate. Therefore, a few months of lower or higher energy consumption may give the wrong idea of the size of the system you would need for the next few decades.

What Are the Factors That Matter for Solar Sizing?

Now that we’ve seen why the current season isn’t particularly helpful for determining the size of your solar installation, let’s take a look at the things which are useful. As mentioned above, energy use is the determining factor for the vast majority of homes. In fact, if your home doesn’t use enough electricity, most solar companies will inform you that you’re not going to get the savings you hope for.

But what goes into energy consumption?

How Your Appliances Matter for Energy Use

The main factors for your home’s energy use are your appliances. Some assume that the size of the house itself is going to be the main focus, but the size is a relatively small contributor to your energy use. The only major thing that has a larger house will change is the amount of energy you use for climate control. Otherwise, you’re going to want to focus on your appliances. 

Calculating the Energy Use of Your Appliances

The first step is to calculate how much electricity your appliances are consuming through a home energy audit. This can be done in a couple of different ways. The first, and simplest, the way is to ask your utility for a copy of your power bill. This will show you how much electricity your home took in during the month.

The second way is more complicated but can be done yourself, without the need to wait for your utility to get back to you. This is checking your appliances yourself for their wattage and time of use, then going from there.

What Do Appliance Wattages and Time-Of-Use Mean?

The first step is to find the wattage of your appliances. These can include your washer and dryer, your dishwasher, your lights, and more. Wattage is a simple concept — it describes the number of watts needed to activate the appliance and keep it running. For example, a 60 W light bulb will need 60 W of energy to turn on and will consume 60 W of energy per hour.

Time-of-use is also a simple concept. How long you keep your appliances on will obviously affect the amount of electricity that they use. Using your dishwasher for a single load vs. four loads will lead to completely different amounts of energy used for the day.

Putting Wattage and Time-Of-Use Together

Most appliances will tell you their wattage somewhere on the item itself. If you cannot find it there, then checking the user manual or doing an internet search are both easy ways to find it. Time-of-use is a little more difficult, though also simple in concept. Each day, keep track of the amount of time for which you use an appliance. A few days will give you a good idea of your averages.

Once you’ve done that, you can multiply the total hours you use your appliances daily by their wattage, and you’ll get a good idea of how many watts of electricity your home consumes per day. You can then extrapolate that to get a rough estimate of how much electricity you use per month.

Sizing a Solar Installation Based on Energy Use

Now that you have a good idea of your home’s energy use, you can get an idea of the size of the solar installation that you’ll need. Go Solar Group’s free, online custom quote tool is a good way to get an estimate of what you should expect, based on your monthly usage.

A good solar installation will produce more electricity per month than your home uses in that same period of time. The electricity you produce will first be used to power your home. 

How System Size Takes Net Metering Into Account

Any excess electricity, however, can then be exported to the grid in a process known as net metering. You will then be compensated by your utility company for the excess energy you sent to the grid, usually in the form of credits. These credits can then cover the electricity you pull from the grid at night or during bad weather when your panels aren’t producing much electricity. 

This is why a solar installation will generally produce more electricity than you consume in a month. Net metering is one of the ways in which you can completely eliminate your power bill. An installer should take this into account when sizing your system and giving you a quote. 


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