Thermal energy grid storage using multi-junction photovoltaics

Abstract

As the cost of renewable energy falls below fossil fuels, the most important challenge to enable widespread sustainable power generation has become making renewables dispatchable. Low cost energy storage can provide this dispatchability, but there is no clear technology that can meet the need. Pumped hydroelectric and compressed air storage have low costs, but they are geographically constrained. Similarly, lithium-ion batteries are becoming ubiquitous, but even their lower bounding asymptote cost is too high to enable cost-competitive dispatchable renewables. Here, we introduce a concept based on thermal energy grid storage (TEGS) using a multijunction photovoltaic heat engine (MPV) with promising initial experimental results that could meet the low cost required to enable cost competitive dispatchable renewables. The approach exploits an important tradeoff between the accession of an extremely low cost per unit energy stored, by storing heat instead of electricity directly, while paying the penalty of a lower round trip efficiency. To understand why this tradeoff is advantageous, we first introduce a framework for evaluating storage technologies that treats round trip efficiency (RTE) as a variable, in addition to cost per unit energy stored (CPE) and cost per unit power (CPP). It is from this perspective that the TEGS-MPV concept offers a compelling economic proposition.

A Cost‐Performance Analysis of a Sodium Heat Engine for Distributed Concentrating Solar Power

“…This difference is mainly driven by the assumptions that are used in the analysis and stated earlier in Section 2; specifically, the battery (EES) round trip efficiency is 81% [ 15 ] versus the TES energy recovery efficiency of 99%. [ 18 ] This suggests that from a capital cost minimization perspective, the Na‐TEC should be coupled with either combusted fuel or TES instead of EES (scenarios B or D). This is not surprising, given that current research efforts are focused on lowering the upfront cost of EES to be competitive with TES.…”

“…This is not surprising, given that current research efforts are focused on lowering the upfront cost of EES to be competitive with TES. [ 18 ]…”

“…Negligible insulation losses are assumed for the TES system (losses <1%). [ 18 ] In order to operate the Na‐TEC at its maximum efficiency, the TES system should be designed such that it can charge and discharge at the evaporator temperature of the Na‐TEC (1150 K). Latent heat storage systems can effectively match the isothermal input requirements of the Na‐TEC.…”

Techno-economic analysis of solar PV power-to-heat-to-power storage and trigeneration in the residential sector

“…Predominately conceived for large grid-electricity storage applications, the potential viability of PHES in the residential sector has not been assessed yet. Other conceptually simpler approaches consider the use of ultra-high temperature (> 1000 ºC) joule heating for sensible- [46] and latent- [41] heat storage combined with a thermophotovoltaic (TPV) power generation. Despite having lower RTE potential (less than ~ 40%), these designs might bring some advantages, as the modularity and the lack of moving parts.…”

“…Regardless of the particular system implementation, it is still unclear under what circumstances a PHPS system could be profitable. In [46], [49] the minimum tolerable RTE of an energy storage system used for grid-electricity storage is estimated at 36% for the case of Pennsylvania-New-Jersey-Maryland grid in 2017. However, this study assumes that the electricity is purchased from the grid, and therefore, the minimum RTE, is entirely determined by the ratio between on-peak and off-peak electrical prices in a very specific case.…”