Renewable Energy: Sizing Up Solar PV

By Max Lopp
From the September 2013 issue of Today’s Facility Manager

Renewable energy can be a powerful way for organizations to lower energy costs significantly and reduce their carbon footprint. Solar power is among the most commonly tapped renewable energy sources—and its benefits are among the most well documented. However, before taking the solar power plunge, facility managers (fms) should consider a number of factors related to solar photovoltaic (PV) technology. These include its potential impact as well as what’s needed for the technology itself and financing options, among other items.

The first step in evaluating the potential for an on-site solar PV installation is to examine available real estate. Rooftop space is typically available and makes the most sense, making these installations the most common. Rooftop installations can also be more convenient given electrical requirements.

Rooftops do present challenges, however. The structure may require reinforcement to hold the additional weight of the solar arrays, for example. Additionally, strict Occupational Safety & Health Administration (OSHA) regulations, such as required walking space between the equipment and the edge of the roof, can reduce viable roof space and increase installation costs.

If a rooftop isn’t an option, installing the PV array in a field or open lot near the facility is an alternative. However, field installations can require additional security measures, such as fencing to protect the system from possible vandalism. These types of installations also require maintenance like regular tree and grass trimmings to reduce shading that could impact energy generation. Extensive electrical work may also be required to transmit the power from the solar array back to the facility.

When evaluating real estate options, it’s also critical to determine the amount of energy the solar PV system must generate. On average, an installation will need about 120 square feet of space to generate one kilowatt-hour (kWh). For illustration, assume a school uses about 20 kWh per day. Power generated by the solar arrays should have the capacity to offset 80% to 90% of the building’s total energy consumption for an installation to be financially feasible. As a result, for this particular school, the solar arrays should supply at least 16 kWh per day and would require about 1,920 square feet of space.

Estimating the potential savings impact of solar PV can be difficult without an expert because of building and location variables that can hinder an installation’s efficiency. Common variables that can factor in include the amount of sun exposure available in the region and panel performance degradation over time.

Fortunately, tools are available to assist in estimating the impact of a solar PV installation, including the National Renewable Energy Laboratory’s (NREL) Solar PV Watt Calculator. With some basic data (including the size of the PV installation, building location, and the PV panel type), it’s possible to get a solid idea. (Access NREL’s PV Watt Calculator online.)

When determining what solar PV technology to purchase, it’s important to keep key factors in mind including the panel’s estimated lifespan, the nominal panel output, and its degradation rate. Today, the most standard PV technology includes 300 watt panels with a lifespan of about 20 years. Most standard panel output efficiency will degrade about 1.8% to 2.5% in the first year, and about 0.5% to 0.7% per year over the panels’ remaining lifetime. In general, a reliable solar PV panel should not degrade more than 20% overall over the course of its 20 year lifespan.

Financing is another important consideration. Some states and other entities have solar renewable incentive programs that can help make solar PV installations financially viable. Additionally, various financing agreements can help specific types of organizations tackle solar PV installation costs. For example, an organization may be able to use power purchase agreements (PPAs) and performance contracts. A PPA allows a third-party service provider to install, operate, and own the solar PV system, and it then sells the generated power back to the facility. Performance contracts enable organizations to finance the installation over a 10 to 20 year contract with the guaranteed cost savings that the system will produce. The annual cost savings is also guaranteed by the company that installs and services the system, which reduces the risk for the fm’s organization.


Tapping solar energy may not be an ideal option for all organizations. The benefits can be significant, but the process can be more challenging than an fm may realize. Understanding the nuances and challenges of installing solar PV systems can help fms make informed decisions.

Lopp is an energy and environmental engineer for Honeywell Building Solutions.


  1. Many companies want to asses solar feasibility to lock in electrical rates and for sustainability and branding reasons. As Max points out, it’s wise (and free!) to get a professional to screen your site (roof and/or ground mount) for engineering and financial feasibility. Solar PV is a mainstream industry and there are many resources to find qualified installers nearby. They will know how best to capitalize on financial incentives, as well. Permitting is more or less easy depending on how experienced the local AHJ is, so selecting a good developer/installer is key here too.

    Interestingly, the issue of roof load is more “lift” (wind) than weight – most roof construction can easily bear the load of PV panels and brackets. However, Orlando FL, Chicago, and other high-wind locations have successful projects! Roof age and condition are more important factors, in terms of timing for replacement and the cost of reinstalling the solar system.

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