June 13, 2017

In very simple terms, figuring out “How many solar panels do I need?” is a matter of dividing how much energy a solar panel can provide by how much your business uses. But you didn’t come here for “simple,” you want a real answer.

Okay, let’s dig a little deeper and put some numbers into our formula. Consider the following example:

• A medium-size business uses about 25,000 kilowatt hours (kWh) of electricity each year. That (very) roughly works out to 70 kWh used each day.
• Next you need to know how much electricity solar panels can generate. An average solar panel can produce about 250 watts of peak power (this is also called its “nameplate rating”).
• Finally, you need to know how much peak sunlight you receive each day. In the U.S., that ranges from about 4 to 6 hours of sunlight per day. For our simplified example, let’s call it an average of 5 hours of daily direct sunlight.

Now let’s do the math (Figure 1):

Our basic formula shows a requirement of 14 kW. But we’re not quite done. At the risk of complicating things a little bit more, solar panels generate DC (direct current) electricity. Businesses use AC (alternating current). The conversion from AC to DC power isn’t perfectly efficient, coming in at about 80%. So really you need to generate more than 14 kW (Figure 2). You’ll wind up needing about 17.5 kW to cover 100% of this business’s energy needs.

Now divide the kilowatts you need by a solar panel’s nameplate rating and you’ll get the average number of solar panels needed (Figure 3). This example uses average-quality 250-watt panels:

Okay, let’s recap: A medium-sized business using an average amount of electricity needs about 70 average-quality solar panels to meet 100% of its electricity needs. Average, average, average—but you get the idea.

This demonstrates that calculating how many solar panels your organization needs is not rocket science.

Uncovering the underlying complexity

While it’s easy to find online calculators to plug in information like the example above, the resulting answer to “How many solar panels to power a business?” is a “back-of-a-napkin” calculation at best. Read the fine print and you’ll find plenty of disclaimers about how your particular situation may vary, along with a contact form to fill out for more information (i.e., a sales call).

The truth is, calculating how many commercial solar panels you need likely goes beyond the capabilities of any online app. Take the scenario outlined above. While it may be possible to determine how many solar panels are needed to cover average daily needs—what if your true needs aren’t average? A printing company producing quarterly reports, for example, will show spikes in energy usage four times each year. Can a commercial solar power system set up for average daily use meet the actual electricity demands on days during these peak periods? Does an online calculator understand that the space you have available for solar panels sits in the shadows of nearby trees for a portion of the day? Does a simple app take into account your organization’s financial and environmental goals for going solar? Probably not.

If you’re starting to seriously consider solar (a good assumption since you’re wondering how many panels you'll need), it may be a good time to engage the services of a solar energy consultant or contact a knowledgeable solar provider. They can help educate you about some of the more nuanced factors hidden in the deceptively simple calculation shown above. But whether you decide to hire an energy consultant, talk to a solar company or choose to sort through the options and information yourself, let’s cover the things you should definitely be thinking about.

When average isn’t so average

As mentioned above, understanding the specific, real-world energy needs for your operation is key. Energy fluctuations aren’t limited to month-to-month changes. Chances are, your local utility can help with reports tracking yearly, monthly and even daily usage. You may discover your business is experiencing predictable spikes in electricity use at regular intervals on a daily basis. Rather than installing additional panels to meet peak consumption needs, perhaps a better solution is to attach a commercial solar battery storage system to help level out demand. A little investigating will help you better understand your specific needs and the various solutions available to meet them.

It sounds obvious, but if your objective is to reduce or stabilize your utility bill by a certain amount, you need to identify that specific goal. The number of commercial solar power panels you need will be dramatically different if you’re looking to reduce costs by 50%, as opposed to covering 100% of your energy needs. And if net metering is an option in your area, you may want to install even more panels to take advantage of the credit you could receive by sending unused solar energy back into the grid. Partnering with a solar energy consultant or solar equipment provider who understands your unique objectives is key to calculating your solar panel needs.

Quality vs. quantity

If solar panel A is rated at 200 watts, and solar panel B is rated at 350 watts, it stands to reason that you will need fewer B panels to produce the same amount of solar electricity. Ratings matter, but they only tell part of the story.

A solar panel efficiency rating is also important. It refers to the portion of sunlight energy that is converted into electricity. For example, a panel with a 20% efficiency rate would produce an amount of power equal to 20% of what it receives from the sun. (And 20% is actually very good. Commercially available solar panels currently average a 15% to 24% efficiency rate.) If a solar panel’s photovoltaic (PV) cells are more efficient, fewer panels are needed to meet electricity production goals.

A solar panel’s degradation rate can also impact planning how many solar panels are needed. All solar cells degrade over time. Suffice it to say, the lower the degradation rate, the faster commercial solar savings can be realized. Perhaps more importantly, predicting the amount of solar power that’s expected to be generated over 20 or 30 years (or more) can help determine how many solar panels are needed.

Finally, while not necessarily a factor in how many solar panels are needed, durability is most definitely a factor in how many solar panels need to be purchased over the lifetime of your installation. If you plan to use your system in a harsh environment (e.g., desert heat, mountain snow or coastal sea air), the durability of your solar equipment could be a significant factor. Less expensive panels are no bargain if they need to be replaced more often. And while we’re on this topic, keep in mind that panel warranties matter as well.

Making a statement with solar panels

There are also less tangible factors that can go into determining how many solar panels are needed to power a business. For example, while a rooftop installation may be a viable option, your organization may want to make a more public display of its commitment to corporate sustainability initiatives. A carport installation could visually demonstrate that commitment while also providing shaded parking for employees and customers. Perhaps providing solar-powered vehicle charging stations as part of the installation could help attract socially-conscious employees and clients.  Looking beyond the obvious bottom-line benefits of commercial solar energy can help you see the other potential social and ecological “wins” available—which can translate to bottom-line benefits as well.

Solar panel rocket science?

By now you’ve probably come to the conclusion that answering “How many solar panels do I need?” is not, in fact, rocket science. Hopefully, you’ve also discovered that it involves a much more complex and nuanced calculation than you might otherwise have considered. While it’s important to get to that final figure, it’s even more important to answer the underlying questions hidden within the formula. Only then will you accurately know how many solar panels you need to power a business.

Are solar systems worth it? Evaluating your business’s return on potential solar solutions

Beyond solar panel efficiency: 4 important considerations when evaluating solar panel

Installation investigation: Choosing the right solar design for your organization

The key components of a commercial solar panel warranty

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