Plasmonic catalysis is considered to be a promising sustainable alternative to conventional thermal catalysis. In contrast to traditional thermal catalysis where heat energy (often from combustion processes) is used to accelerate chemical reactions, plasmonic catalysis aims to use light as the sole energy input. The core idea is that light being a superior form of energy, can drive the molecular interfacial processes on the catalyst more efficiently and selectively via generation of dynamic hot carriers. The key question that remains is to what extent light-mediated plasmonic catalysis really outperforms thermal catalysis for a fixed energy input. It is important to realize that plasmonic catalysis in itself already comes with a significant thermal component, since the fate of all the hot carriers that do not participate in the reaction is thermal dissipation. The goal is thus to maximize the contribution of hot carriers to the reaction, rather than to heat dissipation, as the former process is more energy efficient. Several recent reports have attempted to decipher the relative contributions of the hot carrier and the photothermal pathways in plasmonic photocatalysis . Also, comments on these reports have led to interesting scientific exchanges. This discussion continues till date without a clear picture. The antenna-reactor configuration, an idea originated from Halas group , is particularly interesting for plasmonic catalysis, as it can be flexibly applied in different catalytic reactions. In such a configuration, plasmonic nanoparticles act as nano-antennas that collect and concentrate electromagnetic energy, and deliver it to the neighbouring catalytic centres (i.e. reactor or catalyst nanoparticle) that drive the reaction, as shown in Figure . Recently, a number of studies have demonstrated the antennareactor concept with different antenna-catalyst (reactor) combinations such as Au-Ni , Al-Pd , Au-Pd , Al-Cu2O , Cu-Ru , and Au-Pt , for different reactions ranging from dry methane reforming to CO2 conversion. Despite these promising results, a clear distinction between the hot carriers and photothermal contributions has remained a matter of debate, with a number of critical comments and independent articles published addressing the same. It is argued that steep temperature gradients in the substrate and reaction medium close to the illumination spot complicates the measurement of the true nanoparticle temperature. Among these recent studies, the one by Herran et al. is particularly interesting as their bimetallic Au + Pt nanoparticle arrays provide a highly ordered system for systematic investigation. They demonstrated that the rate of dehydrogenation of formic acid was doubled upon light excitation, using a closely packed bimetallic film of Au (i.e. the antenna) and Pt (i.e. the reactor) nanoparticles as the catalyst. The goal of the present analysis is to first dive into the nanoscale energy balance of such antenna-reactors systems, to quantify the photonic energy flow in detail, using the aforementioned study by Herran et al. as a base case. Firstly, their Au + Pt nanoparticle bi-metallic array structure is analyzed beyond what is presented in the original work. Next, a general heat transfer analysis is performed to provide deeper insights into the thermal contribution in these systems, resolving the ambiguity about their true temperature distribution. Finally, a comparative analysis with related nanostructures (including cases in which lossless dielectrics are used as the antenna) as shown in Figure (b) is performed to have a understanding of the performance limits of these systems. The analysis, hence, provides unprecedented insights into the energetics of plasmonic catalysis and specifically antenna-reactor systems. The nanoscale energy balance here is similar to the energy analysis of large scale chemical processes, where the steady state flow and consumption of energy can show the efficiency and performance of individual components without the detailed knowledge of the underlying micro-processes. In the present plasmonic catalytic system, while the underlying temporal quantum processes drive the atomic scale reactions, the steady state energy balance from classical electromagnetic analysis shows the availability of the energy for each nanoscale process. The comparison with the experimental data of Herran et al. thus enables the quantification of the contribution of hot-carrier mediated and photothermal mediated processes. Yellow circles: 22 nm Au nanoparticles, black circles: 3 nm Pt nanoparticles, grey circles : 22 nm GaP nanoparticles. Au-to-Au distance in case A is 2 nm and in case B is 3.5 nm as per Herran et al. In case D, Pt-to-Pt nanoparticle distance is 0.25 nm.