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
How does battery cycle life relate to depth of discharge?
The more we discharge a battery, the shorter its life cycle is going to be.
Depth of discharge drops as number of discharges increases
How does voltage relate to depth of discharge in batteries?
As % discharged increases, voltage drops.
How are batteries tested?
Hydrometer: measures specific gravity of each cell in a battery
Refractormeter: does the same thing
Load tester and digital multimeter also used
How do you clean batteries?
Equalization, which is the controlled overcharging of a battery.
Overcharging can cause the off gassing of hydrogen, which creates possibility of explosion
What are some other battery technologies?
Lithium: 3.6 to 3.8 V per cell
NiMH: 1.2 V or 1.25V per cell
Flow batteries: ion exchange occurs as two fluids flow past semipermeable membranes
What are conductors and how are they sized?
Conductors refer to the wires that move energy all over the place.
Typically copper (or aluminum) protected by insulation.
Sizing: the larger the number, the smaller the wire.
14 AWG<12AWG<10AWG etc. Once we hit zero, wires get bigger as numbers get bigger
AWG stands for American Wire Gauge
How do wire colors work?
Neutral is white or silver
Earth/grounding wire is green, bar, or green and yellow
What is conduit/raceway?
Conduit is a type of raceway
Conduit is pipe made for protecting conductors
Electrical metallic tubing (EMT) is the most common conduit in the US.
Metal raceway, or MC cable, is required for PV source and output circuit conductors inside a building up until the first readily accessible DC disconnect
We must put “photovoltaic circuit” labels on PV circuit conduit
What is a combiner box?
Combines PV source circuits into a single PV output circuit via large metallic boxes called busbars
What is junction box?
Used when transitioning from one wire to another
What is an overcurrent protection device (OCPD)?
Products conductors when there is too much current. OCPD will open the circuit due to high amount of heat. They make sure that max voltage is not exceeded.
Circuit breakers are reusable and disconnect.
Fuses are disposable and less expensive
What are disconnects?
Disconnects are used to turn off power.
Open circuit = off. Handle up = on, down = off.
AC disconnects should not be used when DC components are called for.
What are terminals?
Terminals are used to connect wires to PV equipment. Usually screw terminals.
What is revenue-grade monitoring?
Built in inverter monitoring. +/- 5% accuracy.
A meter specified as being revenue-grade is one that meets the requirements outlined in the ANSI standard C-12.1-2008.
What are off-grid pv components?
PV
Battery/stand-alone inverter
Charge controller
Battery bank
Racking system
Remaining Balance of System (BOS): (wires, junction boxes, disconnects, conduit, circuit breakers, fuses, etc)
What are the components of a grid-tied system?
PV
interactive inverter
mounting system
remaining BOS: (wires, junction boxes, disconnects, conduit, circuit breakers, fuses, etc
What are grid-tied battery backup components ?
PV
Inverter
Charge controller
Battery bank
Subpanel for backed up loads
Racking system
Remaining Balance of System (BOS): (wires, junction boxes, disconnects, conduit, circuit breakers, fuses, etc)
