by Thomas Schubert, PE, Electrical Engineer
Almost everyone in the building design industry has worked with Leadership in Energy and Environmental Design (LEED), a green building certification program. When it comes to new construction, the credit with the largest potential points is the building’s total energy usage (LEED v4 EA Credit: Optimize Energy Performance). Even if you aren’t pursuing LEED certification, sustainable building design is important, both from its environmental impact and even more importantly, the building’s lifetime costs.
One of the solutions I propose when I hear an owner wants to obtain LEED certification is to include solar. Adding solar satisfies two separate LEED credits: Renewable Energy Production, by creating green energy, and Optimize Energy Performance, by reducing the building’s total energy usage. With the potential gain of 21 points from these two credits, this single solution can get you half way to a LEED certification! Outside of LEED, solar helps your bottom line by reducing your energy bill.
Types of Solar Systems
There are three basic types of solar systems: on-grid, off-grid, and dual (on and off-grid). On-grid is the most common. Your solar panels produce electricity. This electricity is used by your building to offset your normal electrical use. If at any time you produce more than you use, the remainder goes out on the electrical grid. Off-grid is typically found in more rural areas. The solar panels produce electricity that is used right away or stored for later use. The dual system marries these two concepts with power flowing onto the grid or into your usage as well as on-site electrical storage, which is tapped into if normal electricity is lost. During off-grid mode, the storage is recharged by the solar panels, extending your potential run-time.
There are three basic components to any on-grid system. The first are the solar panels. These you can think of as batteries. When the sun shines, they produce a direct current of energy (DC). The second component is an inverter. This is the box that converts the DC electricity to alternating current (AC), which is used by utility companies and what is distributed throughout most buildings. Multiple panels are tied together in series to increase the voltage, and/or tied together in parallel to increase the current, depending on the inverter’s input requirements. The third component is the connection to your building’s distribution grid and, ultimately, the utility company’s electrical grid. Depending on your local utility’s requirements, you may have a production meter to measure your energy production and a disconnect for the system.
Similar to the on-grid system, the off-grid system contains solar panels as well as an inverter. Since electricity must be used or stored the moment it is produced, this system also has storage. These are typically batteries, but can be anything used to store electricity. A battery charger regulates the current and voltage to and from the batteries. Tying everything together is a battery back-up grid interface. This device is the brains of the system, creating the regulated local electrical grid, directing the electricity to the correct place, and working as a safety check, in case anything goes out of tolerance. As an alternative backup option, a secondary source of electricity – typically a fossil fuel generator – can also be added to the system, depending on the electrical demands, size of storage, size of solar panel arrays and required continual runtime.
Dual on-grid, off-grid: Components
The dual system is the most complicated, tying both ideas into one package. In addition to the components found in the other systems (solar panels, inverter, grid connection, storage, battery charger, battery backup grid interface, generator), this type of system incorporates an automatic transfer switch, with the electrical loads separated into normal-use and critical loads. Under normal use, the grid supplies electricity to your building and the solar array supplements that use. When the grid fails, the battery backup grid interface generates a local grid system, supplying power to all of your building’s critical loads. This setup can again be supplemented with a generator connected through an automatic transfer switch, depending on your needs.
Adding solar to your building can be as simple as placing a few panels on your roof and connecting them to your existing electrical distribution system, or designed to sustain your building through an unexpected loss of normal power. If you are pursuing LEED certification, providing solar as a part of your project will help considerably in achieving your ratings target. Knowing your options will help you make the right decisions.
Got a question about solar? Reach out to Thomas at 717.434.1554 or [email protected]
Thomas Schubert, PE is an electrical engineer with JDB Engineering, Inc. He holds a MS in Electrical Engineering from the Colorado School of Mines and has more than seven years of experience in the design of electrical systems.