When turning off your solar system can make you money

Nudged along by Anthony Seipolt‘s post on AGL Australia offering a new retail tariff incentivising residential customers to turn off their solar systems in return for some cash (importantly, more cash than they’d otherwise get from their feed in tariff), here’s a very rough and ready look at some Gridcognition simulation data to see when and why that approach might make sense.

Although it’s not explicit in the AGL post Anthony linked to, the assumption here is that residential customers will be paid to curtail solar generation during periods of negative pricing in the wholesale energy markets.

To test this out we’ve modelled the wholesale energy supply costs for one year for a residential property with a 6.5kW solar PV system. Through the magic of simulation we’ve located the home in Melbourne, Adelaide, Brisbane and Sydney, exposing it to both the regional pool price for energy as well as the local irradiance data to drive the solar generation. Three scenarios were assessed:

1. No solar export allowed (maybe the network provider forbid it). The retailer still needs to purchase energy to meet the residual home demand though.
2. Free solar export allowed. As above but the retailer can now sell the exported energy at the corresponding wholesale price.
3. Solar generation is curtailed when wholesale prices fall negative. Importantly, we’re curtailing the entire generation, not just export, meaning the retailer will be making money as the home owner uses energy.

First chart provides a summary of the cashflows for each site for each scenario.

The second chart shows an indicative week of interval data for the Adelaide home. Why Adelaide? Well South Australia has experienced the most significant negative pricing events over the last 12 months. The week of data below if from September 2021 with the green colour highlighting periods where wholesale prices were below $0.