Frequently Asked Questions

How an Inverter can be affected by Grid Voltage

If your solar grid inverter turns off and on during a bright sunny day, the reason is not necessarily the fault of the inverter; it could be the high voltage of the grid it is connected to.

The Australian Standard AS4777.3 requires that any inverter connected to an Australian electricity grid network must have an inverter grid disconnection feature should the grid voltage be too high or too low as well as disconnect altogether should the grid be not visible to the inverter at all (eg: black out).

The standard requires that the inverter temporarily disconnect should the voltage measured at the output of the inverter be outside of the 200VAC to 270VAC range when it is measured within a 2 second period.

In Western Australia, Western Power is responsible for the delivery of power via the grid network.

For a single phase household connection the 5 minute inverter under voltage limit range is 200VAC ~ 225VAC and for a 3 phase inverter it is 350VAC ~ 390VAC.

For a single phase household connection the 5 minute inverter over voltage limit range is 254VAC ~ 270VAC and for 3 phase inverter it is 440VAC ~ 470VAC.

Over frequency is 52Hz and under frequency is 47.5Hz.

In most cases the inverter manufacturers will have their single phase high voltage setting in the 255VAC ~ 265VAC range.

So any transient voltage spike lasting more than 2 seconds will have the effect of sending the inverter into protection mode and when the inverter re-connects, this has the effect of further increasing the apparent grid voltage, so it is possible that this could happen over and over again given the right conditions of high solar system penetration in an area and high solar radiation.

This will be even further evident especially if the inverter is some distance from the connection point to the mains grid connection point, where as soon as the inverter tries to send power back to the grid in export mode.

If the cable sizing is small diameter, then this will be even worse, especially in a single phase inverter output configuration at high system power.

With the great uptake of solar power systems in residential areas around Australia, this phenomenon is becoming all too real for many solar power owners.

Western Australian energy retailer, Synergy, has tried to circumvent this problem by limiting qualification to their Renewable Energy Buyback Scheme to 5kW maximum inverter output size. In Brisbane, for example, electrical distributors have limited the number of solar power installations in any given street, specifically to avoid this ‘cut in ~ cut out’ phenomenon.

Naturally when this cyclic on/off situation happens, it means that the inverter is not supply power neither the home nor exporting any excess back to the grid.

In residential 3 phase systems, recent Western Power directives have meant that if a home has a 3 phase supply (and 40% or Perth homes do for example) then the system supplier needs to supply either 2 or 3 inverters to deliver the solar power across 2 or 3 of the incoming phases, or to install a single three phase inverter so that the exported power is ‘balanced across the phases’. If using multiple inverters, the potential imbalance must be less than 2.5kW between the phases.

At Renewable Energy International, we always discuss these issues during our site visit to ensure that our customers get a system that works as effectively as possible.

John Hall
Managing Director
1 June 2012

Solar Module & System Performance

When determining the correct system for installation to residential premises, it is important to realise the difference between the output of a solar module when quoted at Standard Test Conditions (STC) and what the real life performance of that solar module is when consideration is given to the following factors:

  1. Manufacturer’s Output Tolerance: the power output for all solar modules is specified in watts with a typical power tolerance of +/- 3% and a solar cell operating temperature of 25 degrees Celsius. Cell temperature should not be confused with operating ambient air temperature. For example an ambient temperature of say 30 degrees C, translates to an approximate 50 degree C operating cell temperature. Therefore a typical 190W solar module could have an actual nominal rating of 184.3W.
  2. De-rating due to Dirt: Any air borne dirt or bird dung accumulation on the solar module over a period of time will have a de-rating effect on the solar modules’ output. This will vary due to location but an acceptable figure of 5% from the already de-rated figure of 184.3W would not be uncommon. This then would further de-rate the solar module to 175.09W.
  3. De-rating due to Temperature: As mentioned in Australian Standard AS4059.2, and above in 1, cell performance will alter at higher working temperatures by a set formula. For our mono-crystalline solar modules, for every degree above 25 degrees C the output power will drop by 0.43% as a direct result of the drop in output voltage of the solar module. Using the accepted formula of ftemp = 1-[y x (Tcell eff y –Tstc)], a solar module operating at 30 degrees C will drop power by a further 12.9%. Therefore the previously de-rated figure of 175.09W will now drop to 152.50W as the effective power at the inverter.
  4. Inverter Efficiency: The final factor for what is actually produced as AC power for either home consumption or export to the grid is the inverter efficiency. This important factor is one reason Renewable Energy International, selects only the most efficient inverters available. Our current range of inverters have a maximum efficiency of between 96.8% to 97.6% and a Euro efficiency of between 95.8% and 97.1%. As the Euro efficiency is a more realistic gauge, this takes 3.55% (average figure) from the 152.50W solar module de-rating now with an effective AC power of 147.08W.

Note the above calculations assume a solar insolation figure of 1000W/m2

John Hall’s Rule of Thumb has always been “Nominal rating less 20%” for quick calculations on effective peak solar module performance.

So a 190W module less 20% equals 152W or if the +/-3% is applied, then (190W -3%)-20% = 147.44W. This matches the previous calculations.

Annual Performance Differences due to Direction of the Solar Array

It is also important to understand the performance variation due to the direction the solar array is facing (azimuth). In the southern hemisphere, all solar modules face north (towards the equator) for maximum year round performance.

Any variation to due north has a slight change to the annual performance of the solar array; but by how much?

Using an example of 16 x 185W solar modules on a 20 degree roof, Perth weather data and a transformer-less inverter with a Euro efficiency of 96.3%, the annual performance data shown in the table below is observed.

As can be seen there is very little difference between NW all the way through to NE on an annualised basis.

For solar arrays that are installed West or East an annualised power drop of 10% is not considered to be of a magnitude that should preclude an installation.

Direction Annual Units (kWh) Variation in Annual Power
North 4997 0%
North West 4842 2.7%
West 4479 10%
East 4499 9.6%
North East 4856 2.43%

Annual Performance Differences due to Roof Angle

Using the same solar power system described above, the table below shows the annualised performance difference at differing roof angles, when the solar array faces due north.

The other major consideration in regards to angle of inclination also relates to the accumulation of dirt and bird dung and the ability of natural rainfall to ensure the glass surface of the solar modules stay relatively clean and not hold the dirt.

Roof Angle Annual Units (kWh) Variation in Annual Power
35° 4891 -2%
30° 4951 -1%
25° 4980 +1%
20° 4977 0%
15° 4944 -1%
10° 4876 -2%

Solar PV Connection Process

When can my solar PV system be connected to the network?

Your system can be connected once all of the applicable connection eligibility criteria have been met. This includes:

  • application to your electricity retailer to ensure that your contract is appropriate
  • application to Western Power for technical approval of your proposed system
  • Western Power has approved your system
  • Western Power approved metering is installed Note: systems installed before 15 February 2013 are allowed to be connected prior to Western Power approved metering being installed.

Do I need to contact my electricity retailer if I want to have a solar PV system installed?

Yes, you must contact your retailer when looking to install a solar PV system, even if you do not wish to participate in a buyback scheme. All electricity customers have a contract with their retailer and this must be adjusted to allow for generation. If a customer does not contact their retailer they will be in breach of their contract; and also the approval given by Western Power.

What needs to happen to the meter at my property prior to the connection of a solar PV system?

The Electricity Industry Metering Code (2012) requires a Western Power approved bi-directional electricity meter to be installed before connection of your solar PV system to the network. The existing meter at your property will need to be changed or reconfigured — this is arranged via your electricity retailer. Systems installed before 15 February 2013 are able to be connected prior to bi-directional metering being installed.

What is a bi-directional meter?

A bi-directional meter is a meter that is capable of measuring electricity flowing two ways, and is programmed to record net electricity consumption and generation at your property.

How do I know if the existing meter at my property needs to be changed or reconfigured to allow for a solar PV system to be connected?

All meter types (electronic and mechanical, old and new) must be either changed or re- configured. From 15 February 2013 this is required to be undertaken before your solar PV system is connected to the network.

Who changes or reconfigures the meter before a solar PV system is connected?

Western Power will change or reconfigure the meter when requested by your electricity retailer. Western Power will leave a card in your letterbox once this service is completed, so that you can contact your solar installer to proceed with connection of your system.

How long will it take for Western Power to change or reconfigure the meter?

Western Power will use best endeavours to complete this service within five business days of the request from the retailer in metropolitan areas and within 10 business days for country areas. Some customers may experience extended timeframes where meter installation conditions require a specialist crew to complete the service.

What are the consequences of connecting a solar PV system to the Western Power network without a bi-directional meter?

Under the Electricity Industry Metering Code (2012) this is meter interference. From 15 February 2013, if bi-directional flows occur at a connection point without a bi-directional meter the customer, property owner and the electrical contractor that commissioned the system may be prosecuted in accordance with the Energy Operators Act 1979.

In addition to this, if your solar PV system is connected without the installation of a bi- directional meter Western Power will be unable to determine an actual value for your electricity consumption and, in accordance with the Electricity Industry Metering Code, will estimate your consumption and apply a substituted reading. Western Power will not estimate energy generation credits and a zero generation reading will be applied.

Note: systems installed before 15 February 2013 are able to be connected prior to bi-directional metering being installed.

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