I found a comment that explains it:
"The users in the study were using pricing to their advantage. They were buying power in low demand times (low price) and discharging the battery to avoid buying electricity in high demand times (high price).
The problem is that high or low price doesn't necessarily correlate to high or low carbon so while the arbitrage can save the consumer some money they may not be reducing their carbon footprint and in some cases were actually increasing it." - username Statistical
