How Do You Measure Commercial Solar Energy Production?

See How Much One Business in Statesboro, GA Expects to Produce

As a business considering installing a solar array, you have more at stake, and more to gain, than a typical home residence. With that in mind, you need a way to quantifiably monitor your commercial solar production – the economic and energy output you’ll be getting from your array after it’s installed.

Commercial facilities are usually larger than residences, and can therefore install bigger solar production arrays and gain larger financial savings. But the upfront costs are comparatively larger too.

So how will you know it was worth it after you install the solar panels?

There are two metrics you can use to answer this. Whether you own a small or medium-sized business, these metrics will show you if your new solar array is producing a solid return on investment.

Before we get to those, let’s look at some numbers and give a quick example to help you get in the right frame of reference.

Commercial Solar Basics

When solar power systems are installed, they are labeled by the amount of power they’re expected to produce. For example, a 10kW system is expected to produce 10kWh of energy – that’s 10kW produced for each hour of sunlight.

So if you average 5 hours of direct sunlight in a day (typical for Georgia and South Carolina), a 10kW solar energy system should produce 50kWh for the day.

For some fun math, look at your monthly energy bill and see how many kilowatt-hours you’re using per month. Divide that number by 30 and you have your kWh per day. Divide that by the hours of sunlight, and you can see what size system it would take, approximately, to neutralize your electric bill – in theory.

Statesboro, GA Basic Business Example

We created an energy-savings projection for a business in Statesboro. They’re consuming about 11,000 kWh per month, or just over 360kWh per day, spending nearly $20,000 a year on electricity. According to this math, assuming 5 hours of sunlight (a reasonable expectation in Georgia), the business could wipe out their electric bill with a 72kW system (360/5).

This particular business is looking at a 55kW solar array, which would cover about 65% of their bill.

Even with 65%, they would pay off their solar system in five years and save over $400,000 over the next 25 years. And their solar array will produce about 235 kWh per day, taking a big bite from their carbon footprint.

These projections should give you a sense of what it might look like for your business. But now let’s see how you can measure the actual performance of your commercial solar energy system on an ongoing basis, after it’s installed.

Two Metrics to Measure Commercial Solar Production and Efficiency

Energy Yield

To quantifiably measure your actual commercial solar production, the first metric is the Energy Yield.

This is the amount of power produced divided by the power of the system installed. So, if a 10kW system produces 12kWh, then its Energy Yield would be 1.2.

Why the difference? Because all the predictions and solar efficiency ratings that come with solar panel installations are based on lab testing. But at your business location, things will be different. You have intermittent cloud cover, temporary partial shading, restricted angles of sunlight reception, a certain orientation of your building, and other factors that the lab can’t predict.

With a well-installed system, you hope to do better than the predictions, and this does often happen. But there are no guarantees.

The Energy Yield tells you how your commercial solar system is performing in terms of actual energy production.

Performance Ratio

Energy Yield is actual. The performance ratio compares that with what you should get in theory, but still at your specific location. It’s the actual over the theoretical at your location, and it will be a percentage less than 100%.

To get this figure, you take the Energy Yield, and divide it by what we might call the “Irradiance ratio”. What’s irradiance?

Direct Normal Irradiance (DNI) is the amount of solar energy falling per square meter each day at a specific location. For example, a DNI of 3 means 3 kwH of solar energy hits each square meter per day. A higher DNI means more energy.

Irradiance is affected by all the real world factors listed up above, and more. It’s also affected by system losses. These can come from the wiring, the soiling, the inverter, and other technical issues that you usually can’t control.

To get the “irradiance ratio”, you divide the measured irradiance at your location by the standard reference.

Then you take the Energy Yield and divide it by this ratio, and you get the Performance Ratio. A good number is anything over 80%.

This means your system is performing at above 80% of its ideal performance. No system will ever reach 100%, because some system losses are unavoidable. When you go through the PVWatts calculator (see box below), you’ll notice this solar calculator takes those losses into account.