An explosion or earthquake or other disaster of that sort involves the almost instantaneous release of a large quantity of energy. For earthquakes we have a convenient measure in the Richter scale, which measures the shaking amplitude. The Richter scale increases logarithmically, so that an increase in magnitude by 1 means a shaking amplitude 10 times as large. The quantity of energy involved scales as the 3/2 power of that amplitude, so 2 magnitudes on the Richter scale corresponds to an increase in energy release by a factor of 1000. Converting energy to standard metric notation in terms of joules (1 J = 1 kg m^2/s^2), the Richter scale magnitudes come to:

Magnitude 3: 2 GJ (2x10^9 J)
Magnitude 5: 2 TJ (2x10^12 J)
Magnitude 7: 2 PJ (2x10^15 J)
Magnitude 9: 2 EJ (2x10^18 J)

Nuclear explosions are typically measured in units of kilotons of TNT, where 1 kt TNT = 4.2 TJ, i.e. a 1 kiloton explosion should be about double the energy release of a magnitude-5 earthquake, and a 1 MT (megaton) explosion around double the energy release of a magnitude-7 earthquake.

Also worth thinking about in comparison is the non-explosive use of energy, as it runs through the natural world and as we use it for our own purposes. Since a year consists of just over 3x10^7 seconds, a 1 GW power plant over the course of a year produces 3x10^16 J or 30 PJ of electrical energy. That's about 7 times the energy release of the 1 MT explosion, about 15 times the energy release of a magnitude-7 earthquake. That energy release is spread over tens of millions of seconds, not just the few seconds of an explosion, but it's good to remember it is a large quantity of energy.

Human society currently uses about 15 TW of primary energy, or 450 EJ per year. That's over 200 magnitude-9 earthquakes, almost 1 per day. That's a lot of energy.

Earth receives energy from our Sun at a rate of about 174 PW. In a year that's about 5x10^24 J, 5 YJ (yottajoules) or 5 million EJ. That's a magnitude-9 earthquake worth of energy every 12 seconds! Luckily it's spread out over the whole (day-lit) surface of the Earth, so we don't normally experience the magnitude of that energy flow in any dramatic fashion. Still, it's worth remembering how natural energy scales like this tend to dwarf whatever humans do.

So, how do our recent collection of energy-related explosions and disasters compare? Write Comment (0 Comments)

But the meat of the car is the hybrid engine and fuel efficiency. So how does that do? The dashboard monitor tells me how I'm doing, usually somewhere between 40 and 50 miles per gallon. But I wanted to keep better track, so after my first year I decided to start recording my gas purchases; the following graph shows the record:

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(1) Fossil-fuel-based CHP cannot be a long-term solution on climate or energy because they still burn fossil fuels, and therefore still emit a lot of CO2. Reducing that by 20% or even 50% is not enough; we need to take steps that over the next 30-40 years will bring fossil CO2 emissions close to 0.

(2) Efficiency claims for CHP systems are frequently greatly overstated. Heat is lower-quality energy than electricity, and only at high temperatures does it become close to comparable. Efficiency claims for CHP systems that use high-temperature heat are not so far off, but CHP systems that make use of low-temperature waste heat have much lower thermodynamic efficiencies than usually claimed.

The inflated efficiency claims often lead to assertions that CHP is the "largest" or one of the largest potential solutions. But the number of applications that require high-temperature heat where CHP efficiency really is quite high are limited. And the modest efficiency gains with low-temperature waste heat use, which could be much more widely applied, don't lead to very much improvement in overall energy use. [Update: this statement is not quite correct - improving from an effective 6% to 12%, say, is a big improvement even if there's still room for a lot more.] The combining of heat and power production in CHP systems can reduce our fossil CO2 emissions by a few percent, but much more than that is needed in coming decades.  Write Comment (0 Comments)