Grid-Scale Solar Technologies

Introduction

How exactly are the sun's rays harnessed to produce the electricity we use to power our appliances, our lights, and increasingly, our cars? This guide offers municipal officials an overview of the basics of what's involved with grid-scale solar development (GSSD). Having a better understanding of the technology will offer municipal and county officials an easier pathway as they consider solar ordinances in their jurisdictions. Of course, there are also other key factors to assess as possible ordinance development proceeds.

Basic Solar Panel Technology

A solar panel consists of numerous solar cells. Each solar cell contains semiconducting material in which electrons are excited by the sun's rays. This generates direct current (DC). Panels are wired together into solar modules, which are wired together into a solar array to combine their voltage. Electrical current flows along conductors from the array to an inverter. The inverter transforms DC into alternating current (AC), which powers most common electrical appliances. A transformer raises, or steps up, the output voltage from the inverter to the voltage needed in the utility grid.

Current Options in GSS Solar Panels

The solar panels being installed now are monofacial or bifacial. Monofacial panels capture the sun's energy only on the surface that faces the sun. Bifacial panels capture the sun's rays that hit the surface of the panel and also the sun's energy that's reflected off the ground underneath the panel. Bifacial panels are more energy efficient.

Most monofacial panels today are less than 25% efficient. But new technologies are in various stages of development to increase efficiency. Bifacial capacity typically adds 2-5% greater efficiency to the panel but also increases the cost substantially.

Tracking panels are increasingly common. Single-axis tracking panels move about every 10 minutes to maintain maximum exposure to the sun as it moves throughout the day. Dual-axis tracking panels adjust to the sun's movement throughout the day and also to its movement throughout the year. These adjustments help maximize the potential efficiency of the panels. As panels become more efficient, the amount of land needed for GSSD is expected to decrease.

GSS Operational Now in Pennsylvania

As of the end of 2021, four of the eight current grid-scale solar arrays in Pennsylvania are in Franklin County, in the southcentral part of the state. The largest in 2021 was a three-part 500-acre-total ground-mounted solar array that supplies Penn State University with 25% of their power needs across the whole campus system. The 70 MW project located just outside of Chambersburg contains more than 150,000 solar panels.

Also in Franklin County, another site supplies power for SEPTA, the regional public transportation authority serving the Philadelphia area. The site is expected to provide 20% of SEPTA's electricity over the life of the contract.

Transfer of Energy Produced by the Sun in Photovoltaic to End-Users of the Power

A solar array is typically connected to the off-site power grid through three-phase¹ power lines that run to and along the street, either aboveground or belowground, to the nearest substation. From the substation, electricity flows into the power grid via high-voltage transmission lines. Electricity flows from the grid to the "offtaker," which could be a power company or a large industry. Electricity is used by "end users" for residential, commercial, and industrial power needs. A neighborhood transformer steps down the voltage from the transmission lines to that needed by end users.

¹ Homes are usually served by a single-phase power supply. Commercial and industrial facilities usually have a three-phase supply, which accommodates heavy equipment requiring higher power loads.

Three-phase lines are the most common and are typically seen running along roads. They have four lines—three for power and the fourth is a ground wire.

Typical Costs of Grid-Scale Solar Development

GSS developers typically focus on sites where a substation is within 1-3 miles of the site where the electricity from solar is generated. Upgrading infrastructure such as poles to carry the power produced to the substation can cost more than $1 million per mile. The cost to run a new line is $150-200 per foot.

GSS installation costs about $1.13 million per built megawatt. A megawatt of solar panels typically covers about 4-6 acres, depending on the company and the technology used.

Maintenance of GSS Arrays

Washing

The eastern U.S. gets enough rain and snow that this is unnecessary. Some system owners may wash the panels occasionally to increase production, but this is uncommon and would be done only in cases of severe dusty conditions.

Snow Removal

It is rare that snow would need to be removed. The panels are dark and tilted, so with a little sunshine, the snow typically sloughs off within hours except in extreme cold conditions, which can happen on occasion.

Equipment Maintenance and Repair

The solar energy company typically contracts with an operating firm to perform routine technical and troubleshooting maintenance. The operator needs access to the site to handle this, and the site must be accessible by emergency vehicles in case of an accident. The turning radius at the end of the row of panels, also called the setback from end of row to fence line, must be wide enough to handle this traffic. The site must also be accessible to a snowplow in winter.

Vegetation Management

Vegetation under panels must be maintained so it doesn't grow tall enough to shade the panels. This maintenance may be done by an outside contractor or by the landowner under the terms of the lease. Woody plants, vines, and large invasive weeds such as autumn olive and honeysuckle grow too tall and must be periodically mowed if they get established. A mower, weed whacker, or bush hog might be used.

Vegetation may also be managed with livestock, most commonly sheep, which itself creates unique access requirements and emergency management requirements. For more on "agrivoltaics"—the farming of the ground underneath a solar array—see Section 5 (to come). Agrivoltaics are a growing farming practice as more shepherds understand the opportunities to provide this service at a fee to energy companies owning solar facilities.

Photovoltaic Energy Storage and Emerging Storage Technologies Some of the inefficiency of solar energy systems comes when power is produced but not used because the grid isn't "demanding" the power then—supply is greater than demand.

Electricity storage allows power that's not accepted into the grid to be saved for when demand exceeds supply. Most current GSS installations don't have storage capabilities, but it is becoming increasingly common. The most common storage systems use lithium battery technologies similar to the type powering newer electric vehicles.

Most new solar projects will have battery storage facilities. These are optimally placed within the solar array, rather than at the edge, because of equipment noise, mainly from cooling fans.

Municipal officials should be aware that in the future, solar companies may want to install newer types of energy storage technologies at existing solar arrays. This could require additional land and setback allowances to accommodate noise, light, vehicular traffic, and other impacts.

Battery Storage

Battery storage is currently the most common kind of electricity storage. It is now commercially viable, and prices declined by about 27% per year between 2015 and 2019. About 20% of the projects currently in the PJM queue include a plan for battery storage.

The quest to increase battery efficiency, reduce the use of rare earth metals, and incorporate more materials produced within the U.S. is the subject of ongoing research.

Other Energy Storage Technologies

Hydrogen is another kind of energy storage in development. Hydrogen would be stored in a tank and moved to where it would be used as a liquid fuel, expanding the scope of possibilities for solar-generated power. There are several types of hydrogen storage, but green hydrogen is most relevant to GSSD.

Green hydrogen uses excess electrical capacity from solar energy to split water into hydrogen and oxygen. The hydrogen can be stored in tanks until the power is needed. This form of energy storage is not yet commercially viable in the U.S. Its development is further along in Europe, but its potential use in the U.S., including in Pennsylvania, is rapidly advancing.

Co-location of green hydrogen storage at a GSSD could be a zoning consideration. This form of energy storage would require trucks to haul out the produced hydrogen, which would bring more people into the solar facility and have implications for transportation infrastructure nearby.

Municipal officials should keep in mind that there could be additional accessory land use considerations for possible co-located energy storage systems, as they find greater commercialization across the state in the future. Energy storage is a potential spinoff of a solar array, analogous to the need for compressor stations after initial development of shale gas wells, with accompanying noise and potential need for emergency response.

Conclusion

Solar technology will likely expand in areas where it is most economical. The 2021 Solar Futures study, from the U.S. Department of Energy, laid out a possibility for the U.S. energy future: "New tools that increase grid flexibility, like storage and advanced inverters, as well as transmission expansion, will help to move solar energy to all pockets of America. Wind and solar combined will provide 75% of electricity by 2035 and 90% by 2050, transforming the electricity system."

For More Information

Battery Storage in the United States: An Update on Market Trends. 2021.

Health and Safety Impacts of Solar Photovoltaics. 2017. North Carolina Clean Energy Technology Center, North Carolina State University.

Low-Conflict Solar. Alyssa Edwards, Lightsource bp. Penn State Solar Law Symposium, June 17, 2021.

Photovoltaic Energy Factsheet. 2021. Center for Sustainable Systems, University of Michigan.

Solar in PA: A Developer's Perspective. Phillip Guerra, Forefront Power. Penn State Solar Law Symposium, June 17, 2021.

Solar Energy Development in Pennsylvania—What's Currently Happening and What's Expected. Penn State Extension webinar, Aug. 5, 2020.

Solar Photovoltaic Technologies Basics. Solar Energy Technologies Office, U.S. Department of Energy. n.d.

Notes "Most monofacial panels today are less than 25% efficient." (in Current Options in GSS Solar Panels)

Source: Photovoltaic Energy Factsheet. 2021. Center for Sustainable Systems, University of Michigan.

Information on Penn State's solar arrays in Franklin County (in GSS Operational Now in Pennsylvania)

Source: Solar Projects at Penn State. Penn State Sustainability Institute. n.d.

Information on SEPTA's solar array in Franklin County (in GSS Operational Now in Pennsylvania)

Source: Alyssa Edwards, Lightsource bp. Low-conflict Solar. Penn State Solar Law Symposium: Utility-Scale Solar Development for Lawyers, Landowners and Others. June 17, 2021.

"The cost to run a new line is $150-200 per foot." (in GSS Operational Now in Pennsylvania)

Source: Phillip Guerra, Forefront Power. Solar in PA: A Developer's Perspective. Penn State Solar Law Symposium: Utility-Scale Solar Development for Lawyers, Landowners and Others. June 17, 2021.

"GSS installation costs about $1.13 million per built megawatt." (in How Much Does Grid-Scale Solar Development Typically Cost?)

Source: PA DEP estimate from Dan Brockett. Prices, Economics, and Impacts of Utility-Scale Solar Leasing in Pennsylvania. Penn State Extension webinar, May 4, 2021.

Battery storage "prices have declined by about 27% per year between 2015 and 2019." (in How Is Solar Energy Currently Being Stored, and What Storage Technologies Are Now Emerging?)

Source: Battery Storage in the United States: An Update on Market Trends. 2021. U.S. Energy Information Administration.

2021 Solar Futures study from the U.S. Department of Energy (in Conclusion)

Disclaimer

By Thomas B. Murphy, Director, Penn State Marcellus Center for Outreach and Research, and Joy R. Drohan, Eco-Write, LLC.

This material is based upon work supported by the United States Department of Energy, Office of Energy Efficiency and Renewable Energy, under State Energy Program Award Number DE‑EE0008293.

This material was prepared with the support and funding of the Pennsylvania Department of Environmental Protection (DEP) and the US Department of Energy's (DOE) State Energy Program. Any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the DEP or DOE. This report was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof.

Additional support provided by the Penn State College of Agricultural Sciences, the Penn State Marcellus Center for Outreach and Research, and the Penn State College of Earth and Mineral Sciences.