Solar Rooftop Arrays- What about Warehouses?

This article was written in partnership with the Cumberland County Planning Office. Special Thanks to Author Elizabeth Grant!


The average size for new warehouses constructed in the South Mountain region is 500,000 – 1,000,000 square feet. This is a large footprint of developed area and combined with stormwater facilities necessary to manage the impervious surfaces, these facilities can occupy significant acreage. When new warehouse development plans are presented at public meetings, residents often have questions about why they are needed in our communities and who will benefit from these developments. One creative solution to increase the public benefit from these sites would be to utilize the footprint of these buildings for roof-mounted photo voltaic (PV) solar arrays, to provide renewable energy on developed sites and avoid conversion of farmland or open space.

A utility or grid scale solar installation is a facility which generates solar power and feeds it to the power grid. The Solar Energy Industries Association (SEIA) defines a project as utility scale if it generates greater than 1 megawatt (MW) of solar energy. Pennsylvania’s Solar Future Plan (PSFP, 2018) calls for 10% of in-state electric consumption generated by in-state solar energy by 2030, which requires 11 gigawatts of solar power (GW). The plan anticipates that 65-90 percent of the solar generation will be through utility scale projects. It is estimated that 89 square miles (56,800 acres) to 124 square miles (79,200 acres) of land in Pennsylvania is needed to accomplish this goal (PSFP, Executive Summary, xvi). Rooftop systems are not accounted for in these estimates. A study in 2008 estimated that 27 GW could be accommodated with existing rooftop space across the state, which would more than provide for the 11 GW goal if rooftop solar was widely adopted.  New studies for this generation potential are certainly warranted due to the expansion of warehousing in Pennsylvania.

If communities do not embrace planning for where these installations are to be situated, and facilitate placement of facilities on developed sites, solar development may significantly impact viewsheds and remove land from agricultural production across the state.

Cumberland County is taking on this question as it implements its Climate Action Plan with the assistance of a Shared Energy Manager (SEM), Wilson Engineering Services, which was provided by the Department of Environmental Protection (DEP). The SEM is helping Cumberland County evaluate energy needs for county operations and opportunities to incorporate expanded energy alternatives and efficiency measures for its facilities. To date, the county has facilitated six focus meetings with industry experts to define the needs to increase solar in developed areas and clarify the role of state and local government in promoting and supporting that effort.

The group has compiled a list of challenges currently faced and considerations that warehouse developers need to increase adoption of solar on these sites. The goal is to compile these into an analysis and develop recommendations and a plan to share the information gleaned with stakeholders across the region and state.

The challenges include:

  • Uncertainty of end user and energy needs of warehouse facilities
  • Current legislation limiting power generation to 3 MW for net metering (with limited distribution capability)
  • Structural questions for existing warehouse roofs
  • Lack of adequate infrastructure for electrical generation and distribution
  • Relatively low costs for fossil-fuel electric generation

The needs for developers to increase adoption include:

  • Cost analysis which demonstrates investment payback within 5–10-year period
  • Education for design/build professionals to present feasibility considerations to developers
  • Clear path for permitting approvals and process for connecting to the utility
  • Technical specifications recommended for the project under considerations

Most warehouses are built speculatively, and during construction the end user or tenant for the warehouse may not be known. From a technical perspective, the best time to install solar is when the building is designed or built. Whether solar installation would be compatible or likely to substantially increase the value of the site may be difficult to assess when a developer is determining whether to make the investment. One solution is to make the construction of the structure solar-ready, at a potential added cost of $50,000-$100,000, so that the roof is confirmed to be structurally capable of bearing solar panels, there will be sufficient space reserved for HVAC and other building maintenance needs, and there is adequate distribution infrastructure installed should the site be used to generate energy in the future.

Warehouses also may not be able to consume all the power that could be generated from their rooftops, and the cost to install panels to satisfy their energy needs alone may be prohibitive. Tenants who are intensive energy users, such as manufacturing or cold storage facilities, may likely have the energy usage needs to benefit the most directly from this investment. Net metering is a policy where the owner of a system receives credit for excess energy generated. The Public Utility Commission has put limits on the size of non-residential solar arrays for net metering at 3 MW AC, which translates to 330,000 square feet of usable rooftop space for solar. This is potentially only a third of the available space on a warehouse roof. It is currently not economical to install a solar array that does not participate in net metering, because the value generated is much greater than the value of simply delivering solar energy onto the grid. Community solar legislation would make it attractive to utilize the balance of the space on warehouse rooftops and allow for the energy and value generated to be shared by the local community.

Some of the promising areas where government could help include incentives and tax credits. New Jersey is moving in the direction of rebates for solar development in specific land use types including industrial, abandoned mines, and commercial sites.   Another area with promise is in extending the federal tax credit, which is currently on a graduated downward scale. The current tax credit of 26% could be stepped up to 30%. The majority of solar projects today would not be economically feasible if not for the federal tax credit. Local municipalities could create density bonuses or other incentives for developers that incorporate solar energy development in their plans.

Education for facilities managers who might be hesitant to apply panels to existing roofs could include weight rating – most solar panels add 4-6 lbs. per square foot, which most roofing is able to accommodate. There are also non-penetrating solar panel systems which may alleviate some of the concerns about panels damaging roofing. For those who need to replace their roof and seek to apply panels during that time, there are white roofing materials which allow for use of bifacial solar panels to get even greater energy generation. In some instances, this roofing material can be funded as part of the overall solar installation project due to this energy generation potential. Photovoltaic film may be another solution for those with structural concerns because this would not require additional reinforcement.

Technical recommendations all need to be tailored to specific project sites and cost analysis performed per project. In some cases, where warehouses or other facilities are owned by the same developer, it may be advantageous to examine virtual net metering or meter aggregation opportunities within 2 miles of where the solar energy is generated which is allowable under current legislation. Convening technical expertise in solar energy generation with industrial and commercial design/build firms and developers can bring more of these projects into fruition in our region. Municipalities and local governments can consider how to incentivize these practices to meet local and state goals for renewable energy.