System Components
The following illustrations provide a concept of how the components fit together to form a system; a line diagram and picture of the whole system (excluding panels and frame) is shown at the bottom of the page.
whole system (excluding panels and frame) is shown at the bottom of the page.
A standard grid connect system consists of panels, inverter, roof mounting, circuit breakers, meter, and the wire that links them.
Non-standard systems (not covered in this document) include:
- Larger systems, fuses, isolation devices may also be used.
- Standalone systems, a battery regulator and separate maximum power point tracker may be used.
- Trackers that point the panels toward the sun. This increases the amount of energy yield from the panels, but the costs, ground-space, and maintenance requirements of trackers are unjustified in most residential situations.
Standard system components are explained in the following sub-sections.
Panels
While panels designed for stand-alone power systems can be used in grid connect systems, specifically designed panels are more often used in grid connect applications. Solar panels for grid-connect are typically higher voltage than those in stand-alone power systems.Panels are electrically linked together in series to form a "string" and parallel to form a solar array.
When you expand a system (i.e. increase it from 1 kW to 2 kW), it is possible in some circumstances to use different brand of panels from the originally-installed panels, so long as they have similar characteristics. To maximise energy production, it pays to use the same panels as those originally installed.
Efficiency
In order of efficiency, mono-crystalline (13 - 15%) are slightly more efficient than poly-crystalline (13 - 14%), which are about twice as efficient as amorphous panels (5-8%).
Panel efficiency is only of concern on a constrained roof. If the roof will easily hold a 1.5 kW system, it doesn't matter much if the area taken up is 10% larger; either way, you still get a 1.5 kW system. Of greater concern is the energy yield, which depends upon the other factors including the performance of the panels and inverter, and the nature and quality of installation.
Research focuses upon improving panel efficiency, but this doesn't necessarily mean that more efficient panels will be any cheaper. Of primary concern for a rational customer should be the performance and purchase security per dollar invested, plus other considerations including panel warranty, performance warranty, and quality assurance measures.
Future Sustainability utilise mono-crystalline panels. Mono-crystalline silicon panels are the most efficient technology, furthermore the Hyundai panels are some of the most efficient in the world! Most importantly when it comes to customer purchasing decisions is that Hyundai are a significant brand name in the world market and are the largest heavy industries manufacturer in the world. This gives customers the confidence that they have a brand name partner in Hyundai for their full 25 year performance warranty.
Characteristics
Panels work better at lower temperatures. For this reason, the framing system creates a gap between the panels and the roof; increased ventilation from using a raised frame can increase performance.
PV panels' power rating is their peak output Wattage at "Standard Test Conditions" (25C, 1000 W/m2). However, these overstate the typical output of the panels under normal conditions. As a consequence of this and other conversion losses in the inverter and wiring, the output from a 1000W system may often only be 800W. This is common across all solar systems. At the end of the day, customers should compare systems performance by their energy yield (kWh/year), not by their nameplate rating (kWp).
Inverters
The inverter converts the solar panels' DC electricity into 240V AC electricity
The inverter also synchronises this AC electricity with the grid, and monitors the grid to shut down the solar power system in event of blackout (for reasons of safety of power line workers).
The inverter also contains a Maximum Power Point Tracker (MPPT) to get the most power out of the panels for the current panel temperature and solar radiation level. The MPPT operates most efficiently when all panels face the same direction6 .
Inverters have a typical DC-to-AC conversion efficiency of 93-96%.
The inverter dimensions vary by brand and inverter capacity (kW).
Inverters turn themselves off at night to conserve power.
The inverters make a small amount of noise, typically less than a fridge compressor. Because the system operates from sunrise to sunset, it is best to locate inverters away from living or sleeping rooms.
The inverter works best when it is kept cool. For this reason it's preferable (but not crucial) to locate the inverter out of the direct sunlight and in a well-ventilated space.
The inverter may be sized larger than the solar array in order to provide future expansion capability. The inverter's range of acceptable input voltage and current places some constraints on over-sizing.
Roof Mounting
PV panels are attached to the roof with a roof mounting system.
The roof mounting system typically consists of a pair of rails that are affixed to the roof with feet.
- On metal roofs, the feet are screwed to the roof battens
- On tile roofs, a tile foot is clamped and/or screwed to the batten, and the tile slid back down over the foot
- On flat roofs, a raised frame may be used to elevate the system to a more optimum angle.
PV panels are placed side by side and are affixed to the rails with clamps
The PV system is quite lightweight and does not require roof reinforcement
The roof mounting system is designed to withstand the force of the wind. Flush-mount systems do not create much wind load.
Switches
Isolation devices are required to safely disconnect the solar power system for maintenance, during electrical work, or during an emergency such as a house fire.
These typically consist of an AC circuit breaker in the electrical switchboard to which the inverter is connected, and a DC circuit breaker mounted near or on the inverter.
In some states, a DC circuit breaker is required on the roof also.
On larger systems, fuses and other string protection devices may be required.
Wiring
The solar panels are connected to one another to form a string
On larger systems, multiple stings might be connected in parallel
The wires between the solar array and the inverter are run through the roof cavity or along the outside of the house back to the inverter via an isolation switch.
The inverter output is wired to an electrical switchboard/meter board (fuse box), via an AC circuit breaker.
Shorter wiring runs mean fewer losses.
Meter
The inverter can be connected to the house’s electricity meter in two different configurations – "gross" and "net".
In the most common "net" connection, the inverter output is connected on the customer’s side of the electricity meter, and a meter is installed that measures net import and export (see image below left)
- The import register of the meter measures how much power has been imported from the grid (the sum of instantaneous electricity consumption less what the PV system produces).
- When electricity production exceeds on-site electricity consumption, the export register of the meter measures how much power has been export to the grid (the sum of instantaneous electricity production, less what was consumed on site).
- The power company reads both meter registers and applies the feed-in tariff (if applicable) to the export, and the standard rate to the import.
- The customer imports a smaller amount of power from the grid, and may export power to the grid at a premium rate in states with net feed-in tariffs (Vic, Qld, SA)
In a gross connection, the entire output of the inverter is connected to a separate "gross" meter, leaving the existing import electricity unchanged. (see image below right)
- Customers’ existing import electricity meter will still read the same amount of import electricity as before, as electricity will flow from out of their gross export meter and back into their house (or to the grid if their house’s power consumption is met).
- The power company reads both meters and applies the feed-in tariff (if applicable) to the gross export meter, and the standard rate to the import meter.
- In states with gross Feed-in Tariffs (NSW, ACT), the customer earns a premium amount for all solar power generated.
In NSW and ACT, the inverter must be wired to the house’s main meter board ("gross metering") in order for the customer to receive the premium solar bonus or Feed-in Tariff.
In other states, the inverter can be connected to the house’s main meter board or any sub-board ("net metering")
