How on-site solar works
A solar photovoltaic system turns sunlight directly into direct-current electricity. An inverter converts it to alternating current that a plant can use, and the power feeds into the facility’s electrical system alongside what comes from the utility. When the array produces power, the plant draws less from the grid. When it produces more than the site is using, the extra may flow back to the grid, be stored, or be limited, depending on the arrangement and local rules.
The main components are the panels (modules), mounting structures, inverters, wiring and protective equipment, a connection to the site’s electrical distribution, and often monitoring equipment. Many systems have no moving parts, which is one reason upkeep is generally modest compared with rotating machinery.
Where plants put solar
- Rooftops. Large, flat factory and warehouse roofs are the most common location, since they are otherwise unused. The roof must be structurally suitable, in good condition and free of heavy shading. Roof age matters, because replacing a roof under an array is awkward.
- Ground-mounted arrays. Spare land around the site can host an array, provided there is space and the site’s use allows it.
- Parking canopies. Panels over car parks add shade and use space that is already paved.
Benefits plants typically look for
Lower purchased electricity. Energy produced on site displaces energy bought from the utility. Whether this lowers total cost depends on the cost of the system, local electricity prices, incentives and how long the system lasts.
Predictability. Sunlight has no fuel price. After installation, a share of the plant’s electricity cost becomes less exposed to price changes, although the plant still buys power when the sun is not shining.
Daytime match. Many plants run during the day, when solar output is highest. A plant with a steady daytime load can use most of what its array produces on site, which is often the most valuable way to use it. Heavily night-shift operations match solar less well.
Lower associated emissions. Solar generation does not burn fuel at the point of use. Overall environmental effects also depend on manufacturing and end-of-life handling, which are reasons to look at the whole picture.
Resilience in some designs. A solar system alone usually shuts down during a grid outage for safety reasons. With the right equipment, such as batteries and controls, parts of the site may keep running, but this is an added design requirement rather than an automatic benefit.
Limits that shape the design
Space. The power a roof can host is limited by its area. For a large energy-intensive plant, such as a steel or chemical facility, the roof may supply only a small part of total demand. For lighter-load sites it may cover much more.
Weather and time. Output varies with cloud, season and day length, and falls to zero at night. This variability means solar rarely supplies all of a plant’s needs and the grid or other sources remain necessary.
Storage. Batteries and thermal storage can shift energy to later hours, but they add cost, space and maintenance, and their economics need careful study. Thermal energy storage, which stores heat or cold instead of electricity, is another option for some processes.
Grid connection rules. Utilities have requirements for connecting generation, and approvals can take time. Rules about exporting power, charges and compensation differ widely by region and change over time.
Electrical compatibility. Inverters and large motors interact with the facility’s electrical system. Issues such as power quality may need review during design.
Maintenance. Panels need periodic inspection and cleaning in dusty or dirty environments. Inverters usually have shorter lives than panels and may need replacing during the system’s lifetime.
Safety and regulations. Solar systems carry high direct-current voltages even in daylight, so installation and work on them must be done by qualified, certified personnel following manufacturer instructions and local codes. Roof work brings fall hazards, and firefighting access needs to be considered.
Making sense of the economics
A useful way to judge a project is to compare the lifetime cost of the system, including installation, maintenance and inverter replacement, with the value of the electricity it will produce over its life, using conservative assumptions. Reasonable inputs include the plant’s real load profile, an honest estimate of annual output for the site, and the local price of electricity. A simple payback figure is easy to compute but leaves out many factors, as the usual treatment of efficient equipment payback also shows.
Efficiency should come first in most cases. Reducing the plant’s demand before sizing an array means the array can be smaller for the same share of supply. Solar also sits alongside other alternative power sources and the equipment used in broader renewable energy systems, and some plants combine more than one.
Questions to ask before starting
- How much structural capacity and usable area does the roof have, and what condition is it in?
- When does the plant use power, and how closely does that match daylight?
- What does the local utility allow for connection and export?
- What are the incentives, taxes or financing options in this region?
- Who will maintain the system, and what is the plan for the inverters?
Outcomes are uncertain and depend on the site. This is general information; a qualified solar designer and electrical engineer can evaluate a specific facility.