  The growing electricity demand of cloud and edge computing increases
operational costs and will soon have a considerable impact on the environment.
A possible countermeasure is equipping IT infrastructure directly with on-site
renewable energy sources. Yet, particularly smaller data centers may not be
able to use all generated power directly at all times, while feeding it into
the public grid or energy storage is often not an option. To maximize the usage
of renewable excess energy, we propose Cucumber, an admission control policy
that accepts delay-tolerant workloads only if they can be computed within their
deadlines without the use of grid energy. Using probabilistic forecasting of
computational load, energy consumption, and energy production, Cucumber can be
configured towards more optimistic or conservative admission. We evaluate our
approach on two scenarios using real solar production forecasts for Berlin,
Mexico City, and Cape Town in a simulation environment. For scenarios where
excess energy was actually available, our results show that Cucumber's default
configuration achieves acceptance rates close to the optimal case and causes
97.0% of accepted workloads to be powered using excess energy, while more
conservative admission results in 18.5% reduced acceptance at almost zero grid
power usage.
