Modern radio astronomy relies on very large amounts of data that need to be transferred between various parts of astronomical instruments, over distances that are often in the range of tens or hundreds of kilometres. The Square Kilometre Array (SKA) will be the world's largest radio telescope, data rates between its components will exceed Terabits per second. This will impose a huge challenge on its data transport system, especially with regard to power consumption. High-speed data transfers using modern off-the-shelf hardware may impose a significant load on the receiving system with respect to CPU and DRAM usage. The SKA has a strict energy budget which demands a new, custom-designed data transport solution. In this paper we present SoftiWARP UDP, an unreliable datagram-based Remote Direct Memory Access (RDMA) protocol, which can significantly increase the energy-efficiency of high-speed data transfers for radio astronomy. We have implemented a fully functional software prototype of such a protocol, supporting RDMA Read and Write operations and zero-copy capabilities. We present measurements of power consumption and achieved bandwidth and investigate the behaviour of all examined protocols when subjected to packet loss.