Transforming the electricity grid into a DC/AC hybrid model will enable modern technologies, leading to efficiencies and reducing the nation's carbon foot print, a leading researcher says.
Professor Neville Watson, from the University of Canterbury's School of Electrical and Computer Engineering, is leading the 'Architecture of the Future Low Carbon, Resilient, Electrical Power System' project, which is mapping out the incremental changes needed.
The project has just secured over $13 million of MBIE funding to research the feasibility of a hybrid grid. It will look at how high levels of DC generated by solar and wind power, electric vehicles and battery storage can be integrated into the existing AC grid.
“At the moment a lot of the appliances actually use DC internally because there’s a lot of merit and efficiencies to be gained,” he tells Kathryn Ryan.
He uses the example of a heat pump that, if fed by DC supply, would mean its inverter would be unnecessary. The hybrid model would make household appliances much simpler and less costly.
“The first thing it does is take the AC, converts it to DC and then reconverts it to variable frequency AC, to get the efficiency where you need to drive the compressor at different speeds, which means different frequencies.”
Other modern appliances now have an intermediate DC stage in order to work properly. Basically, he says, the question is whether we can get rid of that first stage and feed DC directly and get a lot of efficiencies.
Watson says there are many advantages to using DC conveyance within the grid.
The project is looking at implementing DC at all levels, transmission around the country, medium voltage, as well as low voltage for the households, he says. DC is more efficient because there is also a lower voltage drop across the line. It can transmit for a given voltage over a longer distance.
“In this project we are looking at where best to change the grid to take use of the advantages of DC.”
Not only does feeding homes with DC make appliances simpler, removing the need for back end technology. It also enables new technology, including panels to generate solar power, which is DC.
“Also, modern wind turbines, because of the advantages of allowing the rotor to rotate at a different speed based on the wind conditions. These modern wind turbines actually convert to DC and then re-invert back to AC at fixed frequency just to interface with our grid," he says.
“Then you have the most obvious one – electric vehicles, and any battery storage, these are going to be DC. So, basically there is going to have lot of advantages with having a DC system that allows a lot of the new technologies to connect directly and a lot more efficiently.”
The scale of the grid system means that any progress made changing its architecture will be incremental. Targets are being looked at leading up to 2050.
A hybrid grid is essential if New Zealand is to meet its targets on global emissions reductions, enabling smarter technologies and accommodating renewable forms of energy, he says.
"The reason it is going to be a hybrid is the transformer for translating the voltage to higher voltage and lower voltage is always going to be necessary because, regardless of AC or DC, there is an optimum voltage level for a given amount of power and transmission distance so there’s a need always to translate voltage to longer distance and higher power levels."