We present a Java-based embedded data store for edge-to-cloud storage optimized for Smart Grid time-series measurements. The key performance indicators expected of applications and operators of a Smart Grid monitoring and control system - frequent readouts, immutability, statistical indicators - are optimally supported. Furthermore, the data store is tailored for operation on platforms with limited storage and processing resources. We show that our implementation is superior to state of the art and off-the-shelf solutions in data retrieval time and needed storage size.