The increase in electricity prices along with a decrease in the price of storage systems has led to a rapid expansion of the PV-battery home storage system market. In order to be economically viable PV-storage systems must fulfil certain performance criteria, and the system control strategy has a large impact on the overall system performance.

At KIT the performance of 20 commercially available PV-battery systems has been evaluated based on several criteria, one of these is intelligent control. A detailed study of the relationship between battery ageing and control strategy of 6 of these systems with NMC-based cells is part of the evaluation. It is shown that an intelligent control strategy can prevent calendar ageing. How large the effect is obviously depends on the dimensioning of the system and the sensitivity of capacity fade at different SOC levels. It is observed that a difference in battery lifetime caused by calendar ageing of up to 1.5 years is possible.

In order to complement these results it is interesting to also consider the effects of intelligent control strategies (or the lack thereof) on the PV power fed into the grid. The feed-in of PV power to the grid is often regulated by law, and if the battery is fully charged too early in the day the system operator is forced to throttle the PV-system during the midday peak. An intelligent charging regime with accurate load and generation forecasts can prevent this, but could also lead to a reduction in self-sufficiency if the prediction is incorrect. It is shown that between 62 kWh and 104 kWh per year are lost due to the reason that most storage systems don’t possess a charging strategy to prevent throttling of the PV-generator.

Since the effects of battery ageing and unwanted PV throttling are not independent it is useful to evaluate them in parallel and in combination with results on battery and system efficiency. The goal is to determine the economic impact of intelligent control and the resulting interplay between each of these factors.

• An intelligent control strategy, using forecasts for load and generation, can prevent calendar aging of Li-ion batteries by avoiding prolonged periods at high State of Charge (SOC).
• This intelligent control can extend the battery’s lifetime by as much as 1.5 years compared to standard control strategies.
• Intelligent charging can also prevent the throttling (curtailment) of PV power during midday peaks, which is often required when grid feed-in is legally limited (e.g., to 70% of PV peak power).
• Without such a charging strategy, between 62 kWh and 104 kWh of energy are lost per year due to PV throttling.
• Tests on 20 commercially available systems showed that only 25% possessed a fully developed, intelligent control strategy.