“How many solar panels do I need?” Find out here
As solar installers, one of the more common questions we get is: “How many solar panels do I need?”
It may seem like an easy question, but the answer is anything but. It’s going to take some digging by your solar installer to design a system that works for you.
Solar customers in Minnesota can take full advantage of net metering by installing up to 40 kW (AC) of solar, or a little more than 100 panels. That gives you a lot of flexibility in designing a system, depending on the physical space you have on your roof or in your yard, existing energy consumption, and your budget.
Ultimately, you and your solar installer will collaborate on designing the system that’s right for you.
In this blog, we’ll break down some of the information we use to determine how many solar panels you’ll need.
People often misunderstand how solar energy works. If you are tied to the grid, you don’t “need” a certain amount of solar panels to keep the lights on in your house – in fact, you shouldn’t notice any change in day-to-day life at your home.
The solar energy that’s produced from your panels goes where it’s most needed. Unless you have batteries, those electrons can’t be stored and must go somewhere.
If you’re at home while the sun’s shining, your devices are being powered, at least in part, by your solar panels. But at night, when there’s no solar energy to harvest, you’re pulling power from the grid. If you’re producing more solar energy than you need, the electricity is sent back onto the grid and your meter will spin backwards.
The power company is able to track all of this give and take, and your power bill will be based on the difference between what you produced from your solar panels and what you consumed from the grid. If you produced more than you consumed in a given month, the power company will compensate you for that excess energy.
Homeowners that have solar panels and remain attached to the grid in Minnesota are taking advantage of what’s known as net metering. It’s a set of state policies that govern how utility companies bill homeowners with solar panels.
Being tied to the grid means you don’t need solar panels to keep the appliances in your house running. Instead, you’re investing in a solar energy system to reduce your monthly power bills and protect yourself against rising utility rates.
So if solar panels aren’t need to power your home, how do installers size a solar system?
Making an investment
Solar installers are often concerned with a system’s financial implications. And that’s because customers are (rightly) interested in knowing how long it’ll take to pay for itself.
That’s where economics of scale comes into play.
Solar installers often use a system’s “price per watt” as a metric for comparing system price. Generally, larger systems have a lower price per watt because they stretch out labor and permitting costs. Smaller systems with a higher price per watt are less cost effective and may take longer to pay for themselves.
While it’s possible to install one or two panels on your roof, it’s not financially practical to do so. To make your investment worthwhile, you’ll need more. Commonly, grid-tied rooftop solar systems we install are around 6-8 kW, or 15-20 panels.
To receive compensation at what’s known as the “average retail rate,” net metering rules limit the size of solar systems to 40 kW of AC power. AC power is produced by the inverter before it reaches the grid, as opposed to DC power, which is produced by the panels. (Solar systems are more commonly measured by the DC rating of the panels, which tends to be a little higher than the AC rating.)
But each house is different, and we account for several factors when designing solar systems.
One of the first things a solar installer will do when designing a system is determine how much energy you currently use at home. That will help determine how much solar would be required if you wanted to offset your entire electric bill.
The average home in Minnesota uses about 775 kWh per month, or 9,300 per year, according to government data. To produce that much electricity in Duluth, we’d need about an 8 kW system (20 400-watt panels), according to PVWatts.
To come up with that number, I made some assumptions. I assumed that the panels would be placed at a 30-degree angle and pointed directly south. We learned from a previous blog that tilt and azimuth affect solar production somewhat. So if your roof doesn’t face directly south or has some shade, you may need a larger system to offset that energy use.
What if you use more or less than the average home? If you have electric heat, there’s a good chance you use more electricity than homes that use to keep its occupants toasty. But if your home is smaller and well-insulated, you might use less.
That’s why one of the first things a solar installer will ask for is your power bill – so they can determine your existing usage and size your solar system accordingly. Installing a system that produces much more than you use may not be the best choice, since the rate for excess energy is usually a little less than what you pay for it.
Going to the ground
And what if your roof isn’t big enough to hold your desired solar system? That’s another major factor solar installers have to consider when you ask them how many solar panels you’ll need.
In that case, the installer may choose to propose a smaller system that will reduce, but not eliminate, your power bill. While it’s not as exciting to cut your bill in half, the solar system is generating savings that keeps money in your pocket.
On the other hand, your installer may propose a ground mount so you can offset a larger portion of your bill. Ground mounts are generally more expensive, but they are a good option when your roof is less-than-ideal.
As you probably guessed by now, there’s no “right” answer to the question “How many solar panels do I need?” Your house won’t be dependent on the solar to keep the lights on, so the number of panels you’d install would depend on financial considerations and site-specific restrictions, such as roof size.
A reliable solar installer should be able to walk you through your options and design a system that meets your budget and goals.
Read more from Northland’s solar energy experts:
- “How many solar panels do I need?” Find out here
- Solar panel warranty: How to protect your investment
- Getting solar quotes? Here’s how to read your proposal
- Solar tax credits and you: What’s in the new climate change bill
- Designing a new home with solar panels: A guide to maximizing your system