Energy concepts are flung around on the regular, but many people—myself included—have trouble processing the data. This quick primer should help make sense of it all (or at least a little of it). If you’re a physics geek, apologies for the extreme oversimplification. And as a reminder, we’re talking about electrical energy as it pertains to our daily lives.
Power
Power is a rate, in this case the rate at which energy is transferred.
It is expressed in joules per second, also known as watts.
Light bulbs, home appliances like microwaves, and electric vehicle chargers are labeled in watts or kilowatts (1 kilowatt = 1000 watts).
On a larger scale, power plant capacity is usually listed in megawatts (1 megawatt = 1000 kilowatts = 1 million watts).
For example, you might stumble across a 500-megawatt (MW) power plant or perhaps a regional capacity (all local plants) of 32,000 MW.
Of course, this listed capacity comes after there has already been waste, a concept captured by efficiency. In other words, a certain percentage of what could be available from burning coal, gas, etc. is lost to heat, leaving only the remaining percentage for electricity generation.
Finally, there’s also the issue of capacity factor. Just because a plant has a theoretical capacity, that doesn’t mean it always functions at full power. The concept is easiest to grasp with wind, whose intermittent nature leads to an unimpressive capacity factor (around 33%, or 0.33), meaning actual production is about one third of what would be produced if full power were achieved continuously.
Energy
As power is a rate, it must be multiplied by a unit of time in order to quantify energy.
Had we stuck with expressing power in joules per second, we could have simply multiplied by seconds to express energy in joules.
But convention—at least in the US—is to use watts and kilowatts, meaning energy is typically expressed as watts times hours (watt-hours) or kilowatts times hours (kilowatt-hours).
Your monthly electric bill provides usage in kilowatt-hours (kWhs) and charges a certain number of cents per kWh. As an example, 887 kWh at $0.14 per kWh would equal a monthly bill of $124.18.
Similarly, an electric vehicle’s battery will list its energy storage in kWhs (say 60), and the hope is for the vehicle to yield a healthy number of miles per kWh to avoid frequent charging.
On a grander scale, a very large power plant might produce 18 billion KWhs, or 18 million megawatt-hours (MWh), of energy per year.
Lighting
Sources of artificial light are categorized by luminous efficacy, expressed as lumens per watt (lm/W).
A candle might come in at 0.2 lm/W.
Incandescent light bulbs provide a big jump at 16 lm/W (at 120 volts). Stated another way, a 100-watt light bulb produces 1600 lumens (16 x 100).
Light-emitting diodes (LEDs) now rule the day at around 100 lm/W (at 120 volts). To produce 1600 lumens requires only 16 watts, which over the course of time means far less energy used. It doesn’t hurt that LEDs last much longer too.
Batteries
Contending with the erratic nature of wind and solar power (and the suboptimal capacity factors) would be made much easier if energy storage were possible on a large scale.
Yes, lithium-ion batteries used in electric vehicles can store in the range of kilowatt-hours, and large versions scale to megawatt-hours, but gigawatt-scale storage would be required when discussing national energy policy. (1 gigawatt = 1000 megawatts = 1 million kilowatts = 1 billion watts.)
One word: research.
There you have it—energy concepts, courtesy someone who writes about Olivia Rodrigo.
2 Responses
cool! our solar panels are producing 1MW every month.
Now I know why Paris is city of lights, They produce electricity, but don’t know how to store it, so they burn it at night.( fact_ trust but verify.)
Wow. 1 megawatt-hour a month seems very healthy and probably more than enough to meet household needs! Cool tidbit about Paris—I do know France is known for having a large percentage of its energy come from nuclear.