8 Common Myths About Commercial Rooftop Solar

Join us as Dan Williams, electrical designer at AEI Madison, discusses the biggest myths around commercial rooftop solar and why making the investment today benefits your future.

The first step to being ecologically friendly is making the move to solar.

Being environmentally conscious requires more than just making the switch over to solar energy. Though it’s a great addition to a home or commercial building, it’s not the first step towards becoming more ecologically friendly.

Analyzing your energy intake and making the commitment to use less energy is the first move. You’ll receive the best payback for every dollar you invest when you start to conserve your energy. Conservation is the first step for any existing business looking to reduce their carbon footprint.

Here are some steps to start:

  1. Get an energy audit.
  2. Maintain your existing equipment (ie: change filters).
  3. Consider re-commissioning systems to improve operation.
  4. Check the building envelope for leaks (audit should help identify areas).
  5. Add insulation (audit should help identify areas).
  6. Consider replacing outdated equipment with energy-efficient and energy star-rated equipment. It may cost more initially but will cost far less over the life span.
  7. Encourage the occupants to reduce their energy consumption by turning off lights, dressing properly for the temperatures and shutting down equipment when unused.

If your business uses a lot of energy and uses it inefficiently, solar panel installation is simply putting an expensive band-aid over the problem. The lower your business’s energy usage, the fewer solar panels you’ll need when it’s time for installation day.

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Dan WilliamsElectrical Designer


Affiliated Engineers, Inc.

Bloomberg New Energy Finance,

How do you know when it’s time to stop investing more in conservation measures and start investing into local energy generation (solar)?

An energy audit is a great place to start. Have the auditor point out the largest problem areas — this will be a starting point for your investment and target the most cost-effective improvements. The audit will show your energy usage in comparison to your peers, providing a valuable point of reference. Finally, spending some time understanding your current energy bills enables you to appreciate how your building adjusts to a new, lower-cost normal. Once you’ve done all of this, consider installing solar PV.

Myth 1 — Solar arrays are too expensive or take too long to pay back the initial investment.

Figure 1,

Adding solar is one of the best business decisions a business or homeowner can make.

The initial price investment of solar photovoltaic panels (PV) can be overwhelming, but, as the market has matured, prices have had a dramatic decrease over the past few years (see chart). This has led to cost parity for utility-scale solar with coal-fired or natural gas plants, with the costs expected to decrease further with market maturation and as production scales up to demand.

Federal tax credits have been in play since 2005–2006 and, due to their popularity, have been extended several times through the years. These tax credits are now expected to be phased out over the next three years (except for a remaining 10% for commercial solar after 2023). The intent was that, as manufacturing scales up, costs decrease and efficiencies rise, with federal tax credits finally coming to an end (next year’s rebates dropping from 30% to 26%). Tax specialists can assist you with reporting solar as a depreciable asset.

The payback time for your solar investment is influenced by a variety of factors but for most, it’s less than ten years – however, payback times vary tremendously based on demand charges, utility net metering rates, local installation costs, and the price you pay per kWh. Bear in mind that most systems have a lifespan well over 25 years.

Consider that, without PV, you’re simply paying the utility company for electricity every month. With PV, you’re paying for the PV system instead of the electricity. With PV, you get free insurance against increasing utility rates and free energy after the system is paid for. We haven’t even mentioned any social equity and positive image that comes from investments in solar. The simplest way to put it is, if you can afford an electric bill, you typically can afford solar.

Myth 2 — Solar energy will power my building if the power grid goes out.

The vast majority of solar photovoltaics (PV) are installed as “grid-tied” systems, designed specifically to shut off in the case of a grid power outage to eliminate the risk of endangering line workers.

In these grid-tied systems, the grid acts as both a source for power when your building isn’t generating enough PV, and a sink to absorb the excess power when your building exceeds your immediate need. Simply put, the grid functions much like a giant, virtual battery that we’re all connected to.

The next most common type of a system is a grid-tied with battery backup. In this type of system, a battery is added to store excess energy to use either to reduce operating costs or to help carry over during an outage. These types of systems are more expensive and more complex to operate. They would typically be seen where a customer has a high peak load or time of use rates and wishes to use batteries to offset those costs.

Finally, there are off-grid or stand-alone systems that are sized for and designed to operate for extended periods of time without a utility connection. For example, a college campus that has their own generation assets as well as solar PV or wind assets. These systems are quite complex and require detailed planning to ensure that the lights can stay on. Stand-alone systems are seen in situations where either the grid is unreliable or where there is a need to protect assets like research.

Simple grid-tied systems are the least complicated and least expensive and can provide the most generation per dollar invested. So, unless you have a special need for islanding or battery storage (until battery costs decrease more), your money is better off spent installing a simple grid-tied system with focus on installing more PV on your building.

PV arrays on roof of parking garage

Myth 3 — PV arrays must be installed on the roof of a building.

Whether you have a new or existing building, the roof is typically the simplest and lowest cost place to locate panels. Roofs are ready-made support systems for panels, eliminating the cost of building a structure and provide a convenient path to connect to the buildings electrical system. That said, electricity doesn’t care where it comes from and solar panels just need to see the sun. So, panels can be installed both on the building or elsewhere on your building site.

Consider using solar panels as parking canopies, a roof for a gazebo, walk path, or just as a free-standing solar field. These off-roof types of installation have the added cost of a structure but they also come with added benefits. Solar parking canopies keep the hot sun off from employee vehicles and also provide a bit of rain cover. A gazebo is a great gathering place in the shade. A solar field can show your corporate neighbors and community your commitment to renewable energy.

If you don’t immediately plan to add solar to a new building, it is advantageous to install a few conduits to the roof or out to your site to be solar-ready in the near future.

Myth 4 — PV arrays must face south.

Looking back in time, solar panels were much more expensive than they are today. Since they were so expensive, panels were typically placed to face south because that was the direction that would generate the most energy. It wasn’t until recently that other directions were considered.

Though there is a penalty of approximately 15% generation loss to face panels east or west, panel prices have dropped so much that it now makes financial sense to install panels on both the east and west faces of a roof as well as the south. This opens other areas of rooftops that weren’t considered in the past and increases the overall, available site PV.

Myth 5 — Big systems require big inverters.

Just as solar panel prices have increased, the options for inverters have increased as well. Solar designers now have multiple types of inverters in their toolkit to help design the best, optimized system for each customer.

The large, centralized inverter was once the king of large commercial PV systems – but now we can design large systems using multiple mid-sized string inverters designed be mounted on the rooftop. This allows for more flexibility in the system architecture and eliminates the need to space plan for a large inverter inside the building. This modular approach to inverters means that any single inverter can be shut down for maintenance without shutting off the rest of the system. Plus, these smaller inverters can typically be maintained by an electrician or maintenance staff vs. specialized personnel for large centralized inverters. String inverters have multiple maximum power point tracking systems (MPPT) that can maximize the power output of that string, increasing the overall system output.

Myth 6 — Solar panels and inverters require significant maintenance.

Panels generally require very little maintenance and last 25 years or more. If you live in a place where it snows, leave the snow to melt on its own. The amount of energy lost vs the amount of effort spent cleaning them off does not typically pay off. In the summer months, solar is self-cleaning when it rains. If you live in a very dry environment where dust can collect during dry spells, you can occasionally spray them with water to wash off accumulated dust and increase their output.

Inverters are more complicated than solar panels and require some maintenance. They require yearly checkups consisting of cleaning and checking connections (make sure to review your specific manufacturer’s recommendations). That said, a remote monitoring system can provide input on your inverter health straight to your computer and greatly simplify your maintenance program. You can help protect your inverter assets by placing them in a more protected environment, though it’s not necessary. Manufacturers are making them more robust and able to be installed most anywhere on a roof.

The first year or two after installation should be covered under a warranty granted by the installing company and is a great time to catch any loose connections. Also, consider purchasing an extended manufacturer warranty at the time of purchase.

Myth 8 — Solar panels output decreases over time, making them less efficient.

This is true, but it’s not as bad as you might think. The output of solar panels does decrease over time due to something called Light Induced Degradation or LID. With LID, over time, the panels become a little less efficient each year. The average panel depreciation ranges from 0.3% to 0.5% per year and manufacturers will guarantee an end-of-life output. For example, LG’s new NeON panel warranty documents have a 0.3% degradation with a guarantee of 90.8% of output at the end of 25 years.