# Why Solar Panels Can’t Get Much More Efficient (And That’s Okay!): Shockley-Queisser and the limits to converting sunlight into electricity

Commercially available solar panels now routinely convert 20% of the energy contained in sunlight into electricity, a truly remarkable feat of science and engineering, considering that it is theoretically impossible for silicon-based solar cells to be more than 32% efficient. This upper bound, known as the Shockley-Queisser Limit, was first calculated by the eponymous scientists (who actually gave 30% as their original limit) in the Journal of Applied Physics in 1961 [1] (see also updates by Rühle [2]).

Now, if we can answer why solar panels are thus limited, we can understand the essentials of photovoltaics (PV), which have their basis in the photoelectric effect, and p-n semiconductor junctions. While many have never heard of it, the photoelectric effect is of monumental importance, and when Albert Einstein received the 1921 Nobel Prize in physics, it was “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect,” while p-n junctions lie at the foundations of modern electronics, including transistors and LEDs. Indeed, a solar cell is essentially an LED in reverse: Instead of an electric current generating light, light generates electric current!

# The many faces of food waste in the time of coronavirus: Discards, biofuels, meat, and opportunities for change

Enjoy here this post, also on medium.com

#### Introduction and effective waste in the food system

The ongoing COVID-19 pandemic has reshaped the patterns of American life in unprecedented
ways and with stunning rapidity, resulting in many unintended, but not unwelcome, environmental benefits, as skies clear and animals venture into newly empty spaces [1]. On the other hand, the pandemic has also resulted in what appears to be (and is) a shocking crisis of food waste: Acute demand shocks from the almost overnight shift away from food consumption in suddenly closed restaurants and large institutional settings (including schools, universities, and many places of business) towards in-home consumption have resulted in the well-publicized farm-level wastage of whole fields of fresh produce, and the dumping of millions of gallons of fresh dairy [2].

Without commercial customers or the means to quickly reorient to retail supply chains,
and with limited on-farm storage capacity, some farmers have been forced to plow crops under,
bury already harvested produce, or dump milk into manure lagoons. With slaughterhouses now
reeling from COVID-19 as well, slaughter numbers are down and the dire prospect of millions
of livestock meeting their end on-farm without ever reaching a plate is raised, and the USDA now projects Americans will actually decrease their meat consumption in the coming year [3].
And yet, shocking images of rotting crops and animal culls belie a US food system that has long
ultimately wasted, in one form or another, the vast majority (perhaps as much as 80-90%) of all
food calories produced at the farm level, with dramatic consequences for the environment and
both animal and human health and well-being, while the pandemic could paradoxically spur beneficial changes that mitigate such waste.

# Electricity Emissions Factors by Region, Part 1: Background and the Western Region

#### Part the First: Brief Background on Emissions Factors

Electricity generation accounts for almost one-third of US territorial greenhouse gas emissions, and the average US residence consumes just under 11,000 kilowatt-hours (kWh) electricity per year (in addition to other fuels, such as natural gas).  Thus, it is essential to understand the impact of electricity use, and especially how changes in use at the household level will affect emissions.

# Oblivion by any other name: “Biological annihilation” and “defaunation” in the “Anthropocene”

Everything that needs to be said has already been said. But since no one was listening, everything must be said again.

André Gide

I too am reduced to repeating what must be said, and given this nascent blog’s readership, it seems rather likely that it will need saying again.  To wit, George Monbiot recently discussed, in a melancholy but extremely important article (see also the version in The Guardian), the vanishing of so much nature and wild life before his own eyes, in his own lifetime.  It is not mere false nostalgia, and he cites much published work that documents the astonishingly rapid and ongoing global loss of animal life, a process that has been variously (and by respectable scientists, no less!) termed “defaunation” in the “Anthropocene” and, more recently, a “biological annihilation.”

# From 17,000 kWh/year to less than zero: my experience with energy-efficiency and rooftop solar in Mesa, AZ

I wrote several hundred pages of a book that amounted to exhorting people to alter their own habits of residential energy consumption (turn down the heat, you rogues!), as well as upgrade their built environment  (e.g. insulate the attic) and appliances, or even, *gasp*, add solar to their roofs.  All this because the numbers, at least in the abstract, showed that such banal acts of conservation (not counting solar) can reduce the carbon footprint of residential energy use by at least 30-50%, from a baseline average of about 12 metric tonnes (1 tonne = 1 metric ton) of CO$_2$-equivalent (CO$_2$e).  But a demonstration of how, over the course of roughly 5 years, the net energy use in my house actually fell progressively from around 17,000 kWh of electricity per year down to less than zero (net) seems in order.

# Paper of the Day: Poore & Nemecek (2018): Reducing food’s environmental impacts…

#### Synopsis

A new analysis drawing on 570 studies with data covering 38,700 commercial farms shows dramatic variation both worldwide and within-region in the environmental impact across all major foods, but confirms that beef in particular and animal products in general are responsible for the greater part of food’s impact on earth, which adds up to 31% of global warming emissions (including non-food agriculture), and 43% of ice- and desert-free land.  Supplementary material available for free (and is very comprehensive), while the main article is for subscribers only (here).

Poore, J., & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science, 360(6392), 987-992.

# The Inaugural Post

Welcome to EnvironMath!  Hopefully this will become a useful record of (sometimes) mathematically oriented reviews of topics in the environment (and perhaps other areas).  To get started (and to shamelessly self-promote), I’m adding multiple (free) excerpts from my new book, A Fair Share: Doing the Math on Individual Consumption and Global Warming.