The maximum theoretical performance of unconcentrated solar photovoltaic and thermoelectric generator systems

TL;DR

This paper analyzes the theoretical maximum efficiencies of non-concentrated photovoltaic and thermoelectric generator systems, considering combined and tandem configurations, and identifies the conditions for efficiency gains over standalone PV systems.

Contribution

It presents an analytical model based on Shockley-Queisser limits and TEG parameters to determine maximum efficiencies and conditions for performance improvements in combined PV-TEG systems.

Findings

Maximum efficiency increase is 4.5 percentage points for combined systems.

Maximum efficiency increase is 1.8 percentage points for tandem systems.

A minimum TEG figure of merit ($zT$) is required for combined systems to outperform standalone PVs.

Abstract

The maximum efficiency for photovoltaic (PV) and thermoelectric generator (TEG) systems without concentration is investigated. Both a combined system where the TEG is mounted directly on the back of the PV and a tandem system where the incoming sunlight is split, and the short wavelength radiation is sent to the PV and the long wavelength to the TEG, are considered. An analytical model based on the Shockley-Queisser efficiency limit for PVs and the TEG figure of merit parameter $zT$ is presented. It is shown that for non-concentrated sunlight, even if the TEG operates at the Carnot efficiency and the PV performance is assumed independent of temperature, the maximum increase in efficiency is 4.5 percentage points (pp.) for the combined case and 1.8 pp. for the tandem case compared to a stand alone PV. For a more realistic case with a temperature dependent PV and a realistic TEG, the gain in performance is much lower. For the combined PV and TEG system it is shown that a minimum $zT$ value is needed in order for the system to be more efficient than a stand alone PV system.