Section 6: PV System Components Flashcards
What are string inverters?
Typically 1-4 strings of PV connect to an inverter without using separate combiners.
Converts DC to AC
25 kW and less usually
May be gounded or ungrounded
What are grounded inverters?
These are inverters with a grounded conductor, which is white neutral wire
Has a Ground Fault Circuit Interruption (GCFI) fuse
What is a ground fault circuit interruption?
A ground fault circuit interrupter (GFCI) or Residual Current Device (RCD) is a device that shuts off an electric power circuit when it detects that current is flowing along an unintended path, such as through water or a person.
How to ungrounded inverters work?
Transformerless, non-isolated, no white current carrying conductor,
A “grounded” PV power source has either the positive or negative DC-carrying conductor connected to ground (called the “DC system ground”). An “ungrounded” PV system has neither the positive nor negative DC current-carrying conductor connected to ground. However, just like the grounded system, it still has equipment grounding. While “ungrounded” is the terminology used in the NEC, many in the solar industry call these arrays “floating,” because of the confusion that can ensue over the variety of PV terminology containing the word “ground.” Floating means that neither the positive nor negative conductors on the DC side of the system have a direct connection to ground.
What are 2 Channel MPPT inverters?
These can track maximum power voltage separately and can have separate string sizes.
More efficient with multiple strings.
Can help minimize effects of shading due to bypass diodes and different input voltages.
What are micro-inverters?
Micro-inverters have dominated the market over the last several years. They have solved a lot of problems inherent with string inverter type systems.
Each module has its own inverter, so we are immediately converting AC power to DC power right at the module.
Series string are no longer required at the inverter.
MPPT at module level.
When power goes out, wires are safe going throug hte building.
Rapid shutdown compliant.
Enphase is the main micro-inverter on in the market
What are pros and cons of micro-inverters?
Pros: module level MPPT most shade tolerant no big inverter installation no DC knowledge or components
Cons:
more expensive
changing more inverters at end of lifecycles
lower voltage means more voltage drop percentage or more copper…so we have to increase the size of our conductor running from the J box down to the main service panel
What is a multimodal inverter?
Multimodal system takes grid-tied and off-grid system together. You can feed power back into the grid, or use the power to charge a battery backup system. Multi-modal will deliver power even when the grid is down.
What is a bipolar inverter?
Positive and negative grounded arrays. Unusual except for large inverters
What are central inverters?
Central inverters are extremely large, designed for utility scale pv systems. Delivered on flatbed trucks
Includes combiner for PC output circuits
Installed on concrete pads.
Often connected to medium voltage (1000s of volts)
What are interactive inverters?
Interactive inverters means inverters that can work interactively with the utility grid. They condition power so that it’s compatible with the grid’s utility power.
Simply a term that says we are working interactively with the grid and can send grid quality power back into the system. Just about every inverter sold these days is considered an interactive inverter.
Will anti-island, or turn off, when there is not steady clean AC voltage and frequency
What are battery inverters?
Also known as standalone inverters. Often include charge control integration. They take power from batteries, condition it, invert it, and send it to loads inside the home. Must have charge control to protect batteries from over charge or over discharge. Lowest battery component determines high battery current.
What are power optimizers?
Can be underneath or co-located with the module.
Allow for MPPT at the module level
Many of the same benefits of micro-inverters, but less expensive and still require a wall-mounted inverter
Can include rapid shutdown, which makes the PV output circuit much safer when the PV system is shut down
What are charge controllers?
Charge controllers protect the batteries from overcharge and over discharge.
They are located between PV and batteries.
MPPT charge controllers have higher voltage on PV side, lower voltage on battery side.
What’s the deal with pv batteries?
Batteries are part of off-grid systems to store power to be used at night.
Batteries used differ quite a bit from you might find in your automobile. Deep cycle batteries used in pv systems are designed to provide a steady amount of current over a long period of time, as opposed to high amounts of power over a short period of time.
Most common is lead acid batteries. They use PV deep cycle. 10-15 year lifespan if sized correctly
