BESS Will Save Us

Last month Transpower published a report Distributed Battery Energy Storage Systems [BESS] in New Zealand. This looked at the use of domestic batteries and EV batteries and their effect on the NZ power grid.

Here are a couple of paragraphs from the key findings and conclusions.

We also found in the course of this investigation that New Zealand’s current power system could accommodate increases in system load due to passive charging associated with the uptake of EVs. A hypothetical low uptake of 64,000 EVs would present no challenges to operation of the power system at a transmission level, and even 2 million EVs could be accommodated under most conditions.

However, our investigation also found that introducing distributed hybrid solar PV BESSs in regions already prone to challenging voltage management issues (the UNI and USI) [Upper North Island/Upper South Island] would not improve the situation; in fact, without proper coordination (for example, limiting injection onto the grid), they could make it worse. Our simulated scenarios in this regard showed that, while BESSs would help to lift the midday trough created when solar PV generation is high, with existing reactive compensation devices and operational measures such as switching out transmission circuits, high voltages would still be difficult to manage to an acceptable level. Any investment in added reactivecompensation devices on the grid would need to keep pace with the uptake of solar PV, to enable the system operator to continue to meet its PPOs [Principal Performance Obligations] in regard to voltage and maintain a reliable power system.


Thus, it is not necessarily all plain sailing, moving into the EV world or the carbon-free totally renewable world even with the batteries Dr 4.5 windfarms Woods is relying on.

There were lots of graphs and calculations in the paper, looking at various scenarios, but what caught my eye were the starting assumptions.

We developed an uptake scenario for the hybrid solar PV BESS we envisaged for individual homes, drawing onthe analysis and findings of our 2017 investigation. We selected the most extreme case that investigation had considered: 4 GW of installed solar PV geographically spread across the country, based on regional population and dwelling information, grid exit point (GXP) distribution factors and solarirradiance data. To provide a sense of scale, 4 GW of installed distributed solar PV represents slightly less than half the currently installed capacity of all other forms of electricity generation in New Zealand; it would generate up to 3,500 MW of electricity in the middle of a sunny summer’s day, and up to 3,000 MW in the middle of a sunny winter’s day. Over an entire year this amount of installed solar PV generation could produce around 20 percent of New Zealand’s annual electricity needs–about 8,000 GWh.

A fully charged small BESS in every home would provide a total of 4 GWh of distributed storage across New Zealand. However, this is roughly equivalent to only 0.7 percent of the nominal controlled hydro energy stored in lake Taup?, and 4 percent of the daily electricity use in New Zealand.

We looked at the impact that BESSs can have on the overall profile of electricity use during the day. To this end, we included two case studies of EV uptake. The first envisaged a nearer-term case of 64,000 EVs (approximately 1.8 percent of New Zealand’s current light vehicle fleet), based on the government’s uptake target for 2022; the second envisaged a longer-term case of 2 million EVs (approximately 55.5 percent of New Zealand’s current light vehicle fleet), aligning with Te Mauri Hiko’s 2050 base scenario. We assumed a geographical distribution of EVs based on scaling existing regional light vehicle registration data available from the Ministry of Transpory.

We have a 3kW PV array on our roof in one of the sunniest parts of New Zealand. The roof is not far off optimum orientation for PV so our figures will be better than the average. Dividing by 1,000,000 for the GW to kW ratio and looking at numbers from the paper compared to the real world numbers from our roof we see:

Summer kWWinter kWTotal kWh
From paper 4GW /1,000,0003.53.08000
From rooftop 3kW array2.51.63600
From paper x 3/42.62.256000
Above real world result4%40%67%

It will be an interesting ride. What sort of incentives will have to be put in place to encourage homeowners to install PV and then a battery and then allow Transpower to control the charging so that they can load and frequency balance the grid?