Metal nanoparticles (MNP) supporting surface plasmon excitations have demonstrated efficiency improvements in solar cells through large angle scattering and light trapping. However, tarnishing of silver can degrade the scattering properties of the MNP, thereby limiting the potential for light trapping. In this work, we study the impact of ageing on the performance of silver MNPs over time. Our experimental results reveal that the degradation in photocurrent due to ageing can be as high as 7%, when compared to the case of freshly deposited silver MNPs. Simulation results further confirm that the degradation is indeed due to surface tarnish, which behaves as an undesirable over-coating layer. Our results highlight the sensitivity of the MNPs light trapping performance to varying properties of the dielectric material that surrounds them. It is important to prevent exposure of the MNPs to air to avoid tarnish. The use of encapsulation, over-coating, or embedding materials that have the potential to chemically alter the MNP surface should also be avoided. Experimental results reveal a method to mitigate these negative effects.