Following on from my earlier blog post I have written a journal article on this subject which has recently been published in the “International Journal of Environmental Studies”. The article is available to download here. It also gives a nice description of the mechanisms that can lead to negative electricity prices.
One of the main points is that we should only expect a less efficient storage device to be able to generate a higher revenue if the duration of the negative prices is long enough that a more efficient device with the same charging power would become fully charged before the end of the negative price period. Hence whether an inefficient device can indeed generate a higher revenue depends on the ratio between the charging power and the storage capacity. In the case of bulk storage (with the ability to charge and discharge for many hours) it seems unlikely that this situation will arise and the more efficient the device the more revenue it can generate.