How Many Solar Panels Will I Need? 

Find Your Answer in 8 Simple Steps!

How many solar panels do you need to provide the energy to support your home and family? It’s a big question because it directly affects the cost of your new solar energy system. Even though prices for solar panels have plummeted in recent years, you still don’t want to overpay.

6 Factors That Determine How Big Your Solar Energy System Should Be

As you make plans for installing a new solar array, here’s a helpful list of the six key factors that affect how many solar panels your home, farm, or business will need.

Factor 1: Your Monthly and Yearly Power Bill

To find how many solar panels you’ll need, first go get your power bill and look for kWhThis is the first thing to look at. It forms the basis for your solar energy production goals.

For instance, if your monthly bill is $100 ($1200 for the year), then you probably don’t need a solar array that produces $2000 worth of energy.

Task 1: Go look at your bills – summer and winter – and see how much you’ve been paying.

Then, if you have them, go look at your rates from five and ten years ago. One bill-payer we looked at is getting charged more than twice as much for energy in 2016 as he was in 2008, and he’s using about the same amount of energy.

Your solar panels will produce consistent power for over 20 years. Factoring in this kind of inflation should be part of your consideration. Your cost savings from solar will increase as time passes, even if your usage doesn’t change.

Factor 2: Your Monthly and Yearly Power Usage

There’s the cost, and then there’s the usage. Your usage is listed in kilowatt-hours – or kWh. Look for it on your power bill.

Usage is separate from the cost for the reason given above. Your usage may not change much for ten years, but the cost per kWh will change. This matters because solar panels produce a certain amount of kWh, and that amount won’t change much. So even though costs rise over time with traditional power, your usage doesn’t have to. In fact, with improve energy efficiency, your usage could actually go down.

You need to think about how your life circumstances might change in ways that increase or decrease your energy usage.

Will you be having kids? They’ll require more energy (and not just from you!)

Planning to add in a hot tub?

Want a new home entertainment system?

A second fridge?

Big computer hardware upgrades or additions?

How about an electric car?

These sorts of things will add significant kWh to your monthly usage. So if you know already you’ve got a couple big “power suckers” in your sights, factor those in to your future energy needs.

Task 2: Think about how your future energy needs will change in 10-20 years.

If you’re averaging 1000 kWh a month now, maybe it will go up to 1200. Or if you’re planning to move to a new and larger home and want to put solar panels on it, that larger home will probably require more energy usage. Again, plan accordingly

From these first two factors you can now set a goal.

Task 3: Set a solar power production goal.

How much of your energy do you want to produce from solar? 80%? 50%? As much as you can afford? All of it?

You want to know this, because that’s ultimately what determines how many solar panels you’ll end up needing. And knowing your kWh usage is the key. If you use 1500 kWh per month, and want to produce 80% of that from solar panels, you’ll need a system that generates 1200 kWh per month.

Keep your goal number in mind as we look at the next four factors.

Factor 3: Inconsistent Power Production

July isn’t December. While we can disagree about which month is our “favorite,” we can’t disagree about which one is better for solar energy production in the northern hemisphere

how many solar panels you need is affected by how much energy you want in summer and winterWhich months are best for solar varies by region, but it isn’t consistent year-round anywhere in the US. Understanding this matters for several reasons:

  • What happens if your system produces excess energy in summer months? Where will the excess go?
  • Does your utility have a net-metering (solar buyback) program?
  • Do you have a way to store the extra energy (solar battery storage)?

If you don’t want to buy battery storage, and if you can’t sell it back to the grid because your utility doesn’t allow it, then producing more energy than you need does you no good whatsoever.

That’s why many people set a goal less than 100%. If your goal is to produce 70% of your energy needs from solar, then it’s unlikely you’ll generate more than you need, even in the summer. And instead of having a zero power bill, you’ll just have a much smaller one. But you’ll avoid the risk of producing energy that doesn’t benefit you.

However, if you do have access to some sort of buyback or net-metering program (like the Tennessee Valley Authority offers its customers, or if you do want to buy solar battery storage, then setting a goal closer to 100% makes more sense.

But just be aware – your solar panels will not produce consistent amounts of energy around the year.

Task 4: Re-consider your goal with excess energy in mind

Factor 4: Your Daily Power Usage – kWh Per Day

Yes, we’re back to your power bill again. But we’re also getting closer to the number you want to know – how many solar panels will you need.

Task 5: Divide monthly power usage by 30 days.

Look at your bill again. If you’re using 1000 kWh per month, that’s 33 kWh per day. You’ll want this number to help determine how many solar panels you’ll need.

Factor 5: Average Daily “Direct” Sunlight

This is a big one. The same sized solar array in central Canada will produce far less energy than one in South Carolina. The reason is because they don’t get as much direct sunlight – and not just because of cloud cover. They are also at a different position on the earth, meaning the angle of the sunlight hitting Canada is smaller than what hits the Southeastern United States.

What is “direct sunlight?” It’s sunlight that hits a certain spot without interference or obstruction. (Visit our solar dictionary for a complete list of non-technical solar definitions)

Most of the Southeastern US, including Georgia and South Carolina, gets about 5.5 hours of direct sunlight per day. Here, it’s actually highest in the spring and early summer. But the winter has the least amount. Still, 5.5 hours is a good average to use.

And now, you’re ready!

Task 6: Calculate your solar panel system size. (Here’s the math!)

You’ve already got the information you need to do this if you did the first 5 tasks. Here’s a simple equation to use.

kWh per month / (avg sunlight per day * 30) = kW solar system

For example, if you’re using 1000 kWh per month and average 5.5 hours of sunlight per day, that would be 1000 divided by 5.5 * 30, or 1000 / 165 = 6.06 kW

So, to provide 1000 kWh per month in a place that gets 5.5 hours of direct sunlight per day would require a 6.06 kW solar energy system.

For comparison, to produce that much energy in a place with only 3 hours of sunlight per day would require an 11.1 kW solar system – almost twice as big.

To understand what this means, a “6 kW system” means a solar array that produces 6 kWh for every hour of direct sunlight. So a 6 kW system, in a location with 5.5 hours of direct sunlight, makes 33 kWh per day. Remember Factor #4? If your kWh per day is less than this number, then you know your system will cover all your energy needs, on average.

You Are Now Empowered

Now, you have some actual information, and you can use this to get quotes from solar panel installers like us. They can quote you on a 6 kW solar array, for example.

But wait, there’s one more factor to consider. And that factor will be a huge one in their quote.

Remember, the question is how many solar panels will you need, not just how large a system. Your roof can only handle so many panels, right? (Yes, your roof size is a 7th factor, but that one’s kind of obvious. Unless you’re doing a ground installation, you will need the square footage for your roof).

Factor 6: Solar Panel Wattage – Actual Power Production PER PANEL

Different panels produce different amounts of power. And this is why answering the question of how many solar panels a particular house, business, or farm will need can’t be answered for everyone all at once.

Solar panels on the market today range from 45 Watts to 315 Watts. That number is the amount of power that a specific panel produces. So, to power the same 6 kW system, you’d need a lot more 45-W panels than you would 315-W panels. Get the idea?

When you go solar panel shopping, you want to already know the size of system you want, using the process we’ve given here. Because then you can say to the installer, “Give me quotes for an X-kW sized solar array.”

Task 7: Get a solar quote for your ideal system size.

If you have a small roof, you’ll probably want higher-wattage panels because you don’t have the space for tons of them. But, higher-wattage panels cost more. However, you’ll need fewer of them than you would less productive panels.

“So how many solar panels will I need?!!?”

Task 8: Find the number of panels for the wattage you’re considering.

Take your system size number (the one you just calculated, in kW), and follow this simple process:

  • Multiply it by 1000 (because there are 1000 Watts in 1 kW)
  • Decide the wattage of the solar panels you are considering buying
  • Divide #1 by #2

Our example continues: A 6 kW system is a 6000 W system. If I want to buy 300-W solar panels, then 6000 / 300 = 20 solar panels. So to install a 6 kW solar array, which will produce 1000 kWh per month in 5.5 hours of direct sunlight, will require me to buy twenty 300 Watt solar panels.

If you don’t want to buy 300 Watt panels, then recalculate using 250 Watts, or 200 Watts. 6000 divided by 200 equals 30 panels.

Here again is your 8-step process for determining how many solar panels you’ll need to make the energy you want.

Task 1: Go look at your bills – summer and winter – and see how much you’ve been paying.

Task 2: Think about how your future energy needs will change in 10-20 years.

Task 3: Set a solar power production goal.

Task 4: Re-consider your goal with excess energy in mind

Task 5: Divide monthly power usage by 30 days.

Task 6: Calculate your solar panel system size. (Here’s the math!)

Task 7: Get a solar quote for your ideal system size.

Task 8: Find the number of panels for the wattage you’re considering.

Have more questions?

Contact our solar panel installation experts today!

 

Image Credit: Flickr @ Brendan Wood http://www.flickr.com/photos/brendanwood/

 

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2017-02-02T05:45:34+00:00