As countries across the world are pushing towards the increased use of renewable sources of energy the burning of biomass fuels makes up an important part of this strategy. Many coal fired power stations have been converted to co-firing and in some cases are being completely biomass fuelled. However, due to their variability in size, shape and the complex nature of gas-solids two-phase flow the monitoring of biomass particles in a pneumatic conveying pipeline is difficult. This paper presents the results of experimental investigations carried out using a novel electrostatic sensor array that is capable of measuring the particle velocity and concentration profiles over the whole diameter of the pipe. Experimental tests were carried out on horizontal and vertical pipe sections with different particle sizes of a common biomass fuel - willow, over a range of flow conditions. Results from the experiments indicate that smaller biomass particles have more stable flow characteristics across the whole diameter of the pipe. (C) 2014 Elsevier Ltd. All rights reserved.