SUMMARYHigh Throughput Computing (HTC) is a powerful paradigm allowing vast quantities of independent work to be performed simultaneously across many loosely coupled computers. These systems often exploit the idle time available on computers provisioned for other purposes -volunteer computing. However, until recently, little evaluation has been performed on the energy impact of HTC. Many organisations now seek to minimise energy consumption across their IT infrastructure. However, it is unclear how this will affect the usability of HTC systems especially when exploiting volunteer computers. We present here HTC-Sim, a simulation system which allows the evaluation of different energy reduction policies across an HTC system. We model systems which are comprised of both collections of computational resources dedicated to HTC work and resources provided through volunteer computing -a Desktop Grid. We demonstrate that our simulation software scales linearly with increasing HTC workload. We go further to evaluate a number of resource selection policies in terms of the overheads / slowdown incurred, and the energy impact on the HTC system.