What Size Solar Array Do You Need?

When going solar one of your main questions might be how large your array should be. You’ve probably seen homes with just a few solar modules, and also some with many more covering multiple roofs. What size do you need?

Ideally, your solar array will produce enough solar power to meet your energy needs throughout the year.

Sizing a solar array takes many factors into account – your usage, the solar resource at your location, what can physically fit on your roof, and your budget. 

Analyzing Your Electricity Consumption

When you think about your electricity consumption, you may use more in some months than others.  For example, you might have more summer usage because you are using air conditioning in your home or running a swimming pool.  Or, you might be using electric heat in the winter. A typical usage graph looks something like this:

Solar panels also produce different amounts of energy depending on the time of year–more in the summer due to the longer days. The good news is that the monthly values do not have to match exactly because of Net Metering. Net Metering allows solar customers to use their utility company as an energy bank. In this way, customers receive credit when an array is producing more than a household is using, like on long, sunny days, and drawing on those credits when the solar array is not producing enough to cover energy needs, at night or when it is rainy or cloudy. Therefore, we only have to consider your annual usage.

How Much Power Will your Solar Array Generate?

Many factors contribute to how much energy a solar array will produce, such as, how much shade an array will receive, if there will ever be snow covering the panels, weather, geography, and which direction the panels face. We gather this information during solar site evaluations using a state-of-the-art device, the SunEye 210, made by Solmetrics. You can read more about our process during Solar Site Evaluations here.

After a solar site evaluation, we input the information from the SunEye report into the PVWattsTM calculator. This calculator was created by the National Renewable Energy Laboratory to help solar installers estimate the performance of a solar array at a potential solar site.

The PV Watts report displays estimates of how much power an array is expected to produce over the course of a year using the variables entered in along with historical, local weather information to predict how many sunny, rainy, snowy and cloudy days are expected throughout the year. Then, we can adjust the number of panels in the proposed array until the amount of power expected to be produced covers the amount of energy a household needs based on their energy bill.

Designing the Array

Once we know how big the array needs to be, we move on to the fun part – designing the array. Using a special software, we can show customers a digital rendition of what the solar panels will look like either on the ground or on their roof. We use the images to make sure that the array will fit on the roof and that it looks good to the customer.

Sometimes customers cannot build an array that covers their entire energy consumption. This could be because they do not have enough space on their roof or ground, they don’t have enough shade-free area, or the upfront cost of a large array is simply too expensive at the time. Even if a customer cannot build an array that will cover their whole energy bill, going solar with a smaller array is still a smart option because it will still save them money and reduce carbon pollution.

Should I go Bigger?

Some customers wonder if there is a benefit to building an array that would produce more energy than what their electric bill suggests they would need. The answer is that it is sometimes advisable to build a larger array. One common reason for installing a larger array is if customers anticipate their energy needs will increase. Once customers decide to go solar, they often want to benefit from this new power source as much as possible by switching to electric appliances, electric heat pumps and electric vehicles. It is important to let your solar installer know if you are considering making these changes after you install a solar array so they can adjust their proposals to accommodate for this.

Another reason you may consider a larger array is if you have a place you can divert excess energy. With group net metering you can give your excess solar credits to anyone using the same utility company. Common places that customers will send their extra energy credits are rental properties they own, vacation homes, family members or their favorite local nonprofit.

We hope this discussion has helped to answer some questions about how we size a solar array. Because our work is always customized for your needs, the size will depend on how all of these factors apply to you. Please Contact Us, if you want more information or what to start the solar process.

Checking your Solar Array Production through Green Mountain Power’s Website

Once your solar array is installed, it is easy to forget about it until you receive your monthly utility bill, which now should be a much more pleasant experience thanks to the money you are saving with your solar panels. However, we recommend routinely monitoring your array’s production.  While most of the time your solar array will work as expected and you won’t experience any problems, occasionally glitches do happen. If you tend to only check your array when you look at your utility bill, an entire month may go by before you notice that your solar array is not producing or is under producing energy. Routinely checking how much power your array is producing and familiarizing yourself with monthly and daily averages throughout the year will enable you to spot potential problems quickly and easily. Responding quickly is the key to getting your solar array back up and running as soon as possible.

When monitoring your solar array’s energy production, you can use either your inverter manufacturer’s solar monitoring system or you can find the information through your electric provider using their online account platforms. The advantage of using the electric provider’s monitoring tools is that the kWh (kilowatt hours) they report are the exact numbers that you will be billed and credited for. Most of our customers have Green Mountain Power as their electric provider. Below we go step by step through the process of checking your solar array production using Green Mountain Power’s website. 

  1. Go to Green Mountain Power’s website – https://greenmountainpower.com
  2. Click on “My Account”
  3. Login using your Green Mountain Power login information. This step may not be necessary if you have remained logged in from previous sessions. Likewise, if you haven’t used GMP’s website before, GMP may prompt you to set up an account using your account # from your bill and the phone number used to set up your account.
  4. When the “My Account” page opens, you should see information about your account. If you scroll down the page a little bit you should see a chart that looks something like this:
This graph is showing your energy consumption, energy generation, and energy you returned to the grid for each of the last 12 months, plus the current month.

Chart Terms:

Consumed (Orange Bars) – The amount of energy your household or business pulled from the grid. This does not necessarily reflect how much energy was required to run your household during the given time period, as it does not count energy that you used from your array.

Generated (Dark Green Bars) – Total amount of energy produced by your solar array.

Returned (Light Green Bars) – The amount of energy produced by your solar array that was not consumed by your household, and therefore, was returned to the grid. This amount is recorded on your account as “excess generation.”

  1. Click on the bar for the current month and it will open a new graph that will look something like this:
This graph show the energy consumption, generation, and energy you returned to the grid for each day of the current month so far. (Please note there is at least a 24-hour delay on this data.)
  1. A few things to keep an eye out for are no production on days you know were sunny and if there is no production for several days in a row.

Keeping track of your production is the first step in ensuring that your solar array is producing clean energy year-round. If you notice a potential issue, call us. Same Sun of Vermont’s Solar ProFormance Services, LLC provides maintenance and repairs on existing solar arrays, servicing Vermont, New York, and New Hampshire. You can contact Solar ProFormance Services at (802) 775-7900. If you are outside of our servicing area, you can call the manufacturer of your inverter for a list of local solar companies that service your area.

Do I Have a Good Site for Solar?

In the wake of the current pandemic and the country switching to virtual meetings and contact-less delivery, you may be wondering why we can’t or won’t do virtual solar site evaluations. Like the rest of the world, we have had to adapt in response to our new reality and have made changes to ensure that our customers and our staff remain healthy. We only enter customer homes when necessary, we wear masks when in the vicinity of others, and have instituted new cleaning protocols. One thing we have not changed is the quality of service we offer. While we can, and do, gather a lot of information virtually, there is critical information we gather during a site evaluation. That critical information is what allows us to design the best solar array for your home or business. Here we look at what is involved during an in-person solar site evaluation.

During solar site evaluation we want to determine which areas on your property would make a “good” solar site. A “good” solar site is determined by a few factors. Generally, areas that experience minimal shading and face the equator (for us in Vermont, that is South), have the best solar resource.

To calculate these factors, we rely on a state-of-the-art tool called the SunEye 210. This SunEye 210, made by Solmetric, takes a series of measurements at each potential solar site, and provides us with much of the information we need in determining where we should build a solar array.

To do this, the SunEye takes a fisheye image of the skyline and superimposes a Sun Path Diagram to identify any shade-causing obstructions that would interfere with the amount of energy an array would be able to produce. Not only is the SunEye able to project the angle of the sun as it moves throughout the day, but it also projects the change in the sun’s location in the sky throughout the seasons.  The SunEye then instantly calculates how much the shading would impact the efficiency of the solar panels.

While you may think it easy to identify shading in an area, it can sometimes be quite tricky. For example, our Solar Consultant, Scott Stahler, described a time during a site evaluation when a house did not seem to have any shade in the vicinity to cause obstructions. Upon using the SunEye, he realized that the potential solar site had significant shading from nearby mountains during parts of the day and year! While a mountain is not an obstruction that could be removed, if shade is coming from nearby trees, the SunEye can help determine whether tree removal is worthwhile by simulating what the solar resource would be when they are gone.

If it turns out that your first-choice location for a future solar site is less than ideal, we can identify other potential sites. Often, people have ideal solar locations that they have not thought of. For example, perhaps there is an accessory building such as a barn, garage or guest house that can be used.

Or, you may have ideal land for a ground mount and not even realize it. We can help identify and evaluate multiple potential solar array locations.

We will also take roof and/or ground measurements to calculate the number of solar modules that can physically be installed. In this way, we can compare the size of the array and its anticipated generation with our evaluation of your current and future electricity consumption. For example, plans to install heat pumps or purchase an electric or hybrid vehicle will impact your usage. Look for a future blog post that will explain the methodology we use to design the array to fit your needs.

After we take all the measurements and gather the information we need, we will take some time to draw up a proposal for your future solar array. We custom design each system to meet your energy needs and ensure you will be happy with your array for years to come. If you have questions, or would like a solar evaluation done on your property, Contact Us today!

Same Sun is Hiring!

Same Sun is looking for dedicated professionals to join our team. Based in Rutland, and operating statewide.

A resume, cover letter and a minimum of 3 job references are required for consideration. Please email to jobs@samesunvt.com.

PV Installation Foreman

The PV Installation Foreman’s primary job is to lead a crew in safely installing solar-electric systems to the highest level of quality and code compliance, follow plan sets and job specifications, and provide frontline customer service at the jobsite. While mostly focused on residential projects, the job will at times include small-scale commercial projects as well. Previous PV and/or building trade experience highly preferred.

Read the full job description here.

Solar Designer

The Solar Designer’s primary job is to support the Operations and Project Management teams by developing customer specific design packages, including basic site plans, one-line electrical drawings, array layouts and grid interconnection details. While mostly focused on residential projects, the job will at times include small-scale commercial projects.  Prior solar installation and/or design experience required.  NABCEP certification and/or Solar S-license (or equivalent state license) highly preferred.

Read the full job description here.

Solar+Storage Forum on the Green in Woodstock


On  Thursday, October 24th from 5:30 pm to 7:00 pm,  Same Sun of Vermont will be hosting a forum at 16 The Green, Woodstock, Vermont to showcase their installation of solar and battery backup system at this historic home, built in 1823. 

Elements specific to this unique property, as well as those common to all solar and battery storage installations will be explained, including:

  • a design that minimizes visibility in the center of the Village;
  • the process of informing the Design Review Board and the feedback we received; 
  • the environmental and financial benefits of solar power;
  • the costs and engineering of a battery backup system.

Light refreshments will be served, with a presentation from 6 pm to 6:30. 

If you can’t make it but know someone that is interested in solar, please pass this along.

Reservations are required; please email, call 802-775-7900 or use the Contact Us form on this website.

We look forward to seeing you!

Marlene & Philip Allen
Same Sun of Vermont, Inc.

Summer 2019 Promotion

Go Solar in 2019, Pay in 2021! Call now for a FREE site visit to reserve your custom solar installation. Enjoy no-payment, no-interest financing for 18 months; if your system is installed in the fall/winter of 2019, you will not have to pay until 2021. Take advantage of your tax credit and months of electric bill savings, before having to make any payment.

Front of Summer Promotion mailer
Back of Summer Promotion Mailer

May 14th Solar Event at the Paramount Theatre

Please join us for a FREE Solar Event at the Paramount Theatre, located at 30 Center Street in Rutland, from 4 to 7pm on Tuesday, May 14th, with a presentation at 6pm. We will explain the process of going solar, what the benefits will be, and why this may be the last, best time to sign up for a site visit to take advantage of the best incentives before a July 1st deadline.

Food and drinks will be provided by Roots the Restaurant, there will be door prizes and gifts. Don’t miss a fun and informative afternoon. RSVPs will be appreciated.

We hope to see you there!