Short answer
The return of a solar power plant installed on a factory roof depends on how much of the electricity produced you consume in the facility at the same hour. In a facility that works during the day with a high machine load, most of the production is used directly. Before installation, the load profile, the roof's load-bearing capacity, the transformer and subscription capacity, and fire safety are evaluated together.
Why is self-consumption decisive?
Self-consumption means using the electricity the panels produce in the facility at the same moment, without feeding it to the grid. You do not draw grid electricity for this energy, so it is the most valuable production. Surplus energy fed to the grid is subject to netting rules, and these rules have tightened in recent years with changes such as the move to an hourly basis.
The practical result is this: the system has to be sized not by the monthly total kWh on the bill but by your hourly consumption. A workshop running a single shift and a flour mill running three shifts do not benefit equally from the sun, even if they have the same monthly consumption. In the workshop, consumption is concentrated in the daytime and most of what the panels produce stays on site. In a three-shift facility, night consumption cannot be met by the sun.
Weekends and holidays also count. When the facility is closed, production goes entirely to the grid. The share of these days in the year affects how large the system needs to be.
How is a load profile obtained?
Most facilities with a medium-voltage subscription have their meter data read remotely and keep an hourly consumption record. You can request this data from the distribution company or your supplier. A year of hourly data shows the difference between summer and winter, working hours and holidays.
If there is no hourly data, measurements are taken for a few weeks with an energy analyzer. This shows when large motors start up and the dip at lunch break. If the panel capacity is chosen so that it does not exceed the base consumption left during the day, most of the production is used on site.
Expert note: If you plan to add a new line, a cold room or a compressor in the next two or three years, say so from the start. Higher consumption changes the capacity to be installed and the inverter selection.
Can the roof carry this load?
On most industrial buildings, the roof is sandwich panel or trapezoidal sheet metal over a steel structure. The panels, the mounting structure and wind load all add extra load to the roof. Whether the roof can carry this load is determined by a structural assessment from a civil engineer; it is not decided by eye.
The age of the roof covering is also checked. The panels last a long time; but a system installed on rusted or leaking sheet metal that needs replacing within a few years has to be removed and reinstalled when the roof is renewed. This is both costly and interrupts production. If the roof is going to be renewed, the roof comes first, then the solar plant.
Every point where the sheet is drilled during installation is a waterproofing risk. Clamps or a rail system suited to the sheet type are used, and where drilling is needed, fasteners with gaskets are preferred.
- One year of hourly consumption data
- Weekend and holiday consumption
- Structural assessment of the roof
- Age and condition of the roof covering
- Transformer capacity and connection limit
- Check of the power factor correction panel
- DC cable route and fire compartments
- Safe roof access for cleaning
Transformer, subscription and connection
If the facility has its own transformer, the solar system is usually connected to the low-voltage side of the transformer. The capacity to be installed is evaluated together with the transformer capacity and the limits in the connection agreement. The connection application and approval process go through the distribution company.
Facilities that pay a reactive power penalty should pay attention. Solar production reduces the daytime active energy need but can change the power factor correction balance. The settings and capacity of the correction panel should be checked after the solar plant is commissioned; otherwise the bill may arrive with an unexpected item.
In facilities with more than one building, which building’s roof the panels go on and which panel board they connect to are separate questions. Connecting the production close to the board with the highest consumption reduces cable loss. For a line from a distant warehouse roof to the production building, the cable cross-section, route and protection devices are calculated in the project. This detail is often covered in a single line in quotes; ask in writing which board it will be connected to and with what cable cross-section.
Fire safety and fire department access
A solar system on the roof produces direct current, and the panels are live as long as the sun is out. During a fire, the fire department cannot easily cut this voltage. For this reason, the cabling is planned so as not to increase fire risk.
The points considered in planning are as follows:
- DC cables should pass through the building by the shortest route possible
- Proper sealing where cables cross fire compartments
- Walkways left on the roof for the fire department and maintenance crew
- Inverters and panel boards kept away from flammable material storage
- The switch that shuts the system down in an emergency marked at the entrance
- The building’s fire detection system covering the solar area as well
Dust, heat and maintenance plan
In organized industrial zones, dust, flour or cement dust and chimney soot build up on the roof. Until the first cleaning, this buildup lowers production a little more each day. For cleaning, safe roof access, a water connection and fall protection equipment such as a lifeline are planned during installation.
In Şanlıurfa summers, the surface of a sandwich panel roof gets very hot. Leaving a gap under the panels for air circulation protects efficiency. Inverters should not sit in the sun on the roof, but in the shade or in a ventilated indoor spot.
After the monitoring system is installed, assign someone to follow the production data monthly. A panel fault or a blown fuse in a string shows up as a small drop in total production, and if nobody looks, it goes unnoticed for months.
What to prepare before asking for a quote
The last year’s bills, hourly consumption data if available, the roof plan or at least its dimensions, and transformer and subscription details make the first meeting efficient. In the quote prepared with this information, the installed capacity, the expected annual production and how much of it will be used for self-consumption should be shown separately.
Ask what assumptions the quote’s production estimate is based on. If it is unclear which values were used for panel tilt, orientation, shading and dust loss, it becomes hard to compare two quotes.
Talk about the installation schedule too. Working on the roof of a factory where production continues requires planning for forklift traffic, crane position and occupational safety measures. A short power outage may be needed during connection and commissioning; if the day and time are set in advance according to the production plan, machines do not stop unplanned.
Frequently asked
Can solar panels be installed on a sandwich panel roof?
In most cases they can, but whether the roof can carry the extra load is decided by a structural assessment. Roof holes are kept to a minimum by using fasteners suited to the sheet type.
Does a solar PV plant make sense in a factory with a night shift?
It does if daytime consumption is sufficient, because production covers the daytime consumption. The system size is chosen not according to night consumption but according to the daytime base load that remains.
Is there a power factor penalty after a solar PV plant is installed?
There can be. Because solar production reduces the active energy requirement, the reactive ratios change. The compensation settings need to be checked after the solar plant goes into service.
Let’s calculate based on your facility’s consumption
Share your bills and consumption data; Desa Bilişim will inspect your roof on site and prepare a written quote.
