Posted 2014-04-24 15:01:00 GMT
How to compare the cost of energy? Each different source is traditionally traded in different units (kWh, therm, gallon). Here I take the most recent information from the Bureau of Labor Statistics for San Francisco, Oakland, San Jose (the Bay Area) and digest it into kWh.
| Energy source | Cost per kWh in USD cents | Relative cost | Efficiency estimate | Cost per usable kWh | Notes |
|---|---|---|---|---|---|
| Natural gas (utility) | 4.5 | 1 | 25% | (18?) | 29.3 kWh per therm, efficiency estimate based on CNG vehicle which is unfair comparison |
| Petrol (gasoline) | 11.1 | 2.5 | 25-30% | 44.4 | 33.4 kWh per gallon |
| Electricity (mains) | 22.1 | 4.9 | 90% | 24.6 | Most convenient source of energy! |
The cost of obtaining energy from solar installations is becoming competitive with grid electricity but is still much more expensive than other energy sources (particularly natural gas!).
Deciding in practice between which energy source to use is tricky. For example, if you have a plug-in hybrid car, should you charge it from the mains or from a petrol station? That depends on its efficiency per mile traveled from the different sources (normally much higher for electricity) and also on the charging efficiency, as optimistically 10-20% but sometimes even more of the mains charge is wasted and not stored in the battery.
EDIT 20140424: Added estimates of usable energy in terms of efficiency of a motor. For heating, much higher efficiency can be obtained from the cheaper sources like gas (e.g. some people estimate 70-80%).
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