Overvoltage problem in Tasmania
Some solar customers in Tasmania have their recently installed PV system disconnected by electrical inspectors. This page explains the cause of the problem and what customers and solar installers can do about it.
From December 2013, Building Standards and Occupational Licensing (formerly WorkSafe Tasmania) instructed TechSafe inspectors to disconnect solar installations if the solar PV is causing the voltage at the customer’s premises to exceed 253V. The reason for this is that the standard for electrical safety testing only tests that equipment fails safely up to 253V.
This is a very unsatisfactory situation for customers and solar installers. As described below, overvoltage situations are mainly caused by high network supply voltage.
TREA and NECA have been working with TasNetworks on both short and long term solutions to this problem.
Why do overvoltage situations arise?
The nominal supply voltage in Australia is 230 V with an allowable range of 216.2 to 253 V. For various reasons, the Tasmanian network has tended to supply electricity to consumers towards the top of this range. The supply voltage will be different at different locations depending on factors such as local transformer settings and the distance of the customer from the local supply transformer. Supply voltages also vary during the day, tending to be high during the day at times of low load and falling at times of high demand, which for domestic areas will usually be morning and evening, especially in colder weather.
When a solar PV system is exporting power back into the grid it causes a slight voltage rise at the customer premises. The voltage rise depends on many factors, including the length of the line from the customer back to the nearest transformer, the resistance in the supply cables and the amount of power being fed into the grid. The local voltage rise caused by a domestic PV installation will typically be in the 4-10 V range. If the supply voltage was at or near 230 V this rise would very rarely cause any safety concerns. By contrast, for the first 39 solar customers disconnected by TechSafe because of overvoltage concerns, the average network voltage with the solar disconnected was 251.9 V.
What is the solution?
The easiest short term solutions in a local area is to change transformer tap settings to reduce the supply voltage. More complex and expensive solutions include increasing conductor size on supply cables and adding more transformers so that less customers are on an individual transformer.
New inverter standards which require inverters to temporarily not generate power if network voltage is above 255 V can assist in safe operation of the network but mean that customers do not get the full benefit of the system them have installed.
The nature of the electricity grid is changing. Traditionally it was designed to distribute energy in a single direction, from central power stations to customers. The grid of the future will be much more interactive, with homes and business feeding energy into the grid from local generation such as solar PV. There will also potentially be a role for customers to feed back energy stored in batteries to meet peak demand.
We believe that the design and operation of the grid needs to change to accommodate this new reality. Disconnecting installed solar systems, or causing inverters to shut down in overvoltage situations are short term solutions that impose costs unfairly on individual solar owners.
The grid of the future needs to operate safely with energy being generated locally, not just supplied from the high voltage network. This is a medium term objective but strategic planning is needed to drive this transition. It will not be cheap and will need to happen over time, but a smarter, more flexible distribution network will ultimately benefit all customers.
What should you do?
If you are a prospective solar customer:
- Before agreeing to purchase a solar installation, check that your supplier has checked the local distribution network voltage and spoken to TasNetworks if there a potential problem with high network voltage.
- Write to firstname.lastname@example.org and request that he instruct TasNetworks that distribution network voltages should be kept closer to the nominal 230 V so that distributed generation can be connected without causing safety concerns.
If you are a solar installer or solar sales company:
- If you identify a customer supply voltage of 254V or over (without a solar PV system operating), TasNetworks will send a fault crew to investigate. Ring the TasNetworks fault line on 13 2004 and give them your contact details, the measured voltage and where it was taken.
- Also report any measured voltage (without solar) of between 248-253V. TasNetworks will log the situation. They may not investigate immediately, but this will help identify the scale of the problem and help TREA lobby for a better long term solution.