What to do when the sun is not shining. Photovoltaics (PVs) plus batteries plus grid (Gas and coal turbines) backup are expensive. Concentrated solar power (CSP) is considered a “nearly obsolete” technology, yet it is the only technology that is based on a heat engine, that can replace fossil fuel heat engines. In a few consecutive days with poor solar radiation, the heat engine can be driven by green hydrogen or gas for 24/7/365 full dispatchable electricity. Today, CSP is an expansive utility scale power plant (0.09$/kWh) with reliability and financing challenges.

A modular-CSP (MCSP) is made of an array of small receivers where the heliostats shift from one receiver to the other along the day targeting the receiver next to the sun. This way the field efficiency is doubled, and no costly huge tower, resulting half the cost of a central CSP (0.045$/kWh). The modularity, also supports an exponentially growing market, as in PVs, with a potential for a global impact in a few decades. We work to demonstrate M-CSP in lab scale, analyze its performances along the year, and develop its control system for supporting baseload, dispatchable, stable, and low cost, solar energy. M-CSP requires a small and efficient external heat engine that doesn’t exist. See the next topic for our solution.

M-CSP requires a small (<1MW) and efficient (>40%) external-heat engine, not existing today due to thermodynamic considerations. Such an engine will also increase the green hydrogen production capacity factor, which will reduce its cost to the level of gray Hydrogen, and will allow to harvest waste heat.

In all heat engines that we know, only gases are used, and for two roles; i.) Perform the work by expansion and compression. ii.) Transfer the energy into the engine. This 2nd role is challenging for external heat sources, because gases carry negligible thermal energy per volume (volumetric heat capacity), and tend to behave as an ideal gas. This results in a non-isothermal expansion/compression, which is counterproductive since the temperature drop arrests the expansion and drastically reduces the efficiency.

Increasing energy density by three orders of magnitude and inducing isothermal gas expansion is what we solve by demonstrating the first dual-phase (HTL & gas bubbles) engine where the HTL supplies the heat along with the gas expansion.

In our engine, HTL such as molten salt flows in a nozzle with a thermal energy density that is orders of magnitude higher than gasses (per volume). Pressurized bubbles of air are injected into the nozzle and expand isothermally due to the negligible heat capacity of each bubble compared to its large surface area. The bubble’s expansion accelerates the HTL in the nozzle converting the heat and pressure into kinetic energy of the HTL. Converting the kinetic energy of fluids into electricity is extremely simple and achieved by hydroelectric-like technology, which has a tag price that is a fraction of the cost of steam turbines.

for winning the 2nd place in the Hackathon on utility-scale energy storage.
The team evaluated liquid air technology for seasonal energy storage. Their solution used a solar powered thermoacoustic engine to liquify air at a round trip efficiency (from sun to liquid air and back to electricity) of 15%, comparable to a combined PV + pumped-hydro system. This cost effective approach allows for long-life, high energy density, reliability, and geographic flexibility not found in traditional utility scale energy storage technologies.

for wining the 1^st place in the Hackathon on green energy utility scale storage.  The team showed how thermochemical storage Ca(OH)₂/CaO that has more than 77% energy cycle efficiency (in retrieving heat at 500C) without the need for catalysator.

It is also cost effective, non-toxic, stored at room temperature, which is perfect for seasonal storage.  Together with our concept for M-CSP and a reversible reactor at the heat demand location (industrial consumers) this concept can solve 25% of the world global energy consumption.

Planck’s law of thermal radiation depends on the temperature, T, and the emissivity, ε, which is the coupling of heat to radiation depending on both phonon-electron nonradiative-interactions and electron-photon radiative-interactions. In contrast, absorptivity, α, only depends on the electron-photon radiative-interactions. At thermodynamic equilibrium, nonradiative-interactions are balanced, resulting in Kirchhoff’s law of thermal radiation, ε=α. At non-equilibrium, Quantum efficiency (QE) describes the statistics of photon emission, which like emissivity depends on both radiative and nonradiative interactions. We theoretically and experimentally demonstrate a prime equation relating these properties in the form of:

ε=α(1-QE), which is reduced to Kirchhoff’s law at equilibrium.
Read more… “NATURE Phot – Generalized Kirchhoff Law”