On a typical day in the sunny San Joaquin valley, rooftop solar panels quietly generate clean electricity to lower homeowners’ utility bills and reduce our demand on fossil fuels.
A traditional array of residential panels puts out kilowatts of DC power and connects to a large central inverter that changes the output to AC power for use in your home and back-feeding onto the grid. This series design leaves a few drawbacks which may or may not be relevant on any given installation.
If you have a portion of the array that may receive shade at different periods during the day, that string of panels connected in series is going to share the reduced output, having a large effect on the electrical potential of that string, and thereby the rest of the array.
A Micro-Inverter, however, connects to a single panel, meaning that the inversion from DC to AC power occurs on an individual panel basis. This means that if a panel is shaded for part of the day, only the shaded panel will be affected.
With string inverters, PV (photo-voltaic) panels are be wired in series to connect to a single central inverter. The cumulative amount of electricity from all panels in an array produces potentially deadly DC power on your rooftop that gets routed into your home to the inverter. DC power is dangerous because it is continuous by nature, so if you were to become part of that electrical circuit, DC power tends to grab on and hold you, leading to a potentially fatal outcome.
Because a micro-inverter turns each panel into an independent AC power source, the wiring back to the main electrical system is all AC power. AC power, while dangerous, tends to kick you back from itself, on account of its alternating delivery, so while it will hurt, it tends to strike you off the circuit, so no further damage can occur. It is this design that has led Fire Fighters and other safety-related groups to stand behind the micro-inverter in Solar PV installations.
Because DC panels are wired in series, the total wattage output of the array is limited by the output of the weakest panel in the circuit. If one panel is underperforming due to shading or dust accumulation, the output of all panels is degraded. Equally important, since the inverter itself is actually powered by the DC side of the circuit, it requires that the system reach a minimum output level prior to activating. This means a later turn-on time in the morning and an earlier turn-off time in the evening.
In an array of micro-inverters, the output of an underperforming panel has no effect on the output of adjacent panels. This also permits panels in the same array to be angled differently from one another in order to more efficiently catch solar exposure at different times, or be on different planes of roof due to space constraints. The other added bonus, because the micro-inverter is so much smaller in scale, it requires almost no power to turn on, meaning that it produces earlier in the morning and much later in the evening that its cousin, the string inverter.
Besides the large central inverter, a substantial assortment of components required to install a DC array are made obsolete by the use of micro-inverters, including multiple junction boxes and large amounts of wiring and conduit. This simplified approach lowers installation costs and makes calculating wiring loss and other factors easier.
In the Fresno area, Donald P. Dick Air Conditioning has remained at the forefront of energy-efficient technology such as the micro-inverter for 40 years. Contact us for more information.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about micro-inverters and other HVAC topics, download our free Home Comfort Resource guide.