### Energy and Power (Full Lecture)

[upbeat music] Good day and welcome to Big Bad Tech I’m your instructor Jim Pytel Today’s topic of discussion is Energy and Power Our objective is to introduce the two closely related concepts of energy and power We’ll discuss the concepts they represent, important differences between them, the units used to quantify these properties, and the means of calculating energy and power First and foremost, energy is not power, and power is not energy If you continue to frequent this channel, understand that I’m unusually firm about this distinction so much so that one might say I’m a messianic jerk about it It will be of tremendous service to keep this distinction in mind because the misunderstanding and misapplication of these two distinct yet closely related concepts is unforgivable Although this lecture is introductory in nature, I am blatantly and emphatically telling you to pay attention as energy and power represent central concepts for this lecture series, and we’ll come back to discuss these concepts again and again and again One of the most effective ways I’ve found to convey the distinction between energy and power is using the analogy of money Money is energy If you’ve got a lot of money, you can do a lot of things, like buy a car, buy a house, or pay a marching band to follow you around all day and play songs that you request The same thing goes for energy If you got a lot of gas in your tank, a fully charged bank of batteries or a reservoir full of impounded water, you could drive a long distance, light a couple lights in your cabin, or light up an entire city How you get that money or energy is via one of two methods, less powerful or more powerful means One, you could work a really poor-paying job for a long, long time, or, you could work a really well-paying job for a short period of time and then just goof around and take up an expensive hobby like horse riding If you take a look at the units, it all makes sense Your pay rate is power, and power is expressed in dollars per hour or energy per unit time The units make sense To calculate how much money you’ve earned at the end of the week, multiply your pay rate by the number of hours you work Dollars per hour times hour yields dollars If you wish to calculate your pay rate following a task, one would manipulate the same question to solve for pay rate Take the sum of money you earned and divide it by the time it took you to earn it Dollars divided by hours yields dollars per hour Finally, if you wish to calculate the number of hours it would take to accumulate a certain amount of money, you manipulate the same question to solve for time, where dollars divided by dollars per hour yields hours What we’ve created is a very simple three-variable relationship The concept of money is placed at the apex of our pyramid as it should be for all good capitalist society with pay rate and time side by side below it To solve for money, take pay rate and multiply it by time because they’re side by side To solve for pay rate, take money and divide it by time because money is over time Finally, to solve for time, take money and divide it by pay rate because money is over pay rate This simple triangular three-variable relationship is very handy, and you’ll find yourself using it over and over again for a number of different concepts, among them Ohm’s law and Pascal’s law, two concepts that respectively govern electrical and hydraulic systems which we’ll examine in great detail in the near future Let’s now tie our monetary analogy to our discussion of energy and power As with money and pay rate, the prime distinction between energy and power is that of time Energy is the amount of work put into a system, i.e., the amount of money you have in the bank Energy can take many forms, among them mechanical, electrical, chemical, and thermal Let’s restrict ourselves to the analysis of mechanical energy right now where energy is measured in units of joules, abbreviated with the capital J where one joule is one newton of force expressed for a distance of one meter Energy can be calculated as force times distance For example, 10 newtons of force expressed for a distance of three meters means 30 newton meters or 30 joules has been expended Power, in contrast, is pay rate Power is how fast energy leaves or comes into a system or the time rate consumption or generation of energy Power is energy over time The SI unit of power is watt, abbreviated with the capital W, which is really one joule over one second, i.e., a unit of energy consumed or generated per unit time The SI unit of time is the second which hopefully doesn’t necessitate explanation These definitions and units imply an important relationship If power is energy over time, energy is power times time I should remind you that the law of conversation of energy

states for any closed system, energy can neither be created nor destroyed and only changed in form, therefore the terms consumed and generated come attached with some important disclaimers It would be more appropriate to say that an electrical motor does not consume electrical energy, but rather converts electrical energy into rotating mechanical energy minus losses Additionally it would be more appropriate to say a wind turbine does not generate electrical energy but rather converts the mechanical energy of moving air particles into electrical energy minus losses Regardless, the distinction between energy being power expressed for a period of time, and power being energy consumed or generated per unit of time still holds true This important difference between energy and power bounces off the skulls of many people, and I consider it one of my highest responsibilities as an instructor to force it through their skulls with repeated aggressive hammering Power is energy per unit time, and energy is power times time Graphically we can express this relationship using our three-variable pyramid, with energy at the apex and power and time side by side forming the base To solve for energy in units of joules, take power in units of watts and multiply it by time in units of seconds If a watt is a joule per second, units of seconds cancel, and we’re left with energy in units of joules To solve for power, take energy and divide it by time because energy is over time Units of joules over units of seconds yields joules per second or unit of watts Finally, to solve for time, take energy and divide it by power Units of joules divided by units of joules per second yields units of seconds For those of you with a calculus background, you’ll realize power is the differential or rate of change of energy over time, and energy the integral or area under the power curve For the purposes of this lecture series, we’ll mostly steer clear of differentials and integrals and restrict our analysis to the much simpler algebraic manipulations Let’s try a couple simple illustrated examples Energy is power times time Let’s say you use a 100-watt device for a total of three minutes Three minutes is 180 seconds This device would have consumed 100 watts or 100 joules per second times 180 seconds or 18,000, or more appropriately 18 kilojoules of energy Power is energy over time Let’s say 40 newtons of force has been expressed the distance of five meters Energy is force times distance 40 newtons times five meters equals 200 newton meters or 200 joules of energy input into this system Let’s say it took 10 seconds to put the 200 joules into the system If power is energy over time, this represents 200 joules per 10 seconds or 20 watts of power Finally, time is energy over power Let’s say a 500-watt heater has put 2,500 joules of energy, or more appropriately 2.5 kilojoules of heat energy into a system If time is energy over power, this demonstrates that the heater has been working for a total of five seconds The concepts and the units should make sense One great way of checking your work for energy, power, and time calculations, is to examine these relationships without numbers If energy is power times time, if one had a device of fixed power and increased the time span it was used, the energy requirement should go up Conversely, if one had a device of fixed power and decreased the span of time it were used, the energy requirement should go down If your answers don’t follow these observations you’re doing it wrong and you need to perform a tactical retreat, reassess your situation Let’s try a couple more illustrated examples Consider a task that necessitates 500 newtons of force be expressed a distance of two meters Consider a second task which necessitates 250 newtons of force be expressed a longer distance of four meters Which tasks requires more energy in joules to complete? Energy is force times distance The first task necessitates 500 newtons of force be expressed a distance of two meters 500 newtons times two meters yields 1,000 newton meters or 1,000 joules or more appropriately one kilojoule Similarly the second task necessitates 250 newtons of force be expressed a distance of four meters 250 newtons times four meters also yields 1,000 newton meters or 1,000 joules or more appropriately one kilojoules These calculations imply both tasks necessitate the expenditure of equal amounts of energy, which if you think about it, makes perfect sense Which task would tire you out more? Carrying twice the weight half the distance

or carrying half the weight twice the distance? Theoretically these tasks would be equivalent Let’s now examine the various methods we could use to accomplish a task necessitating one kilojoule of energy of which we have three options Option one, a 500-watt machine, option two, a human working at a moderate pace capable of generating 100 watts of power, and option three, a 20-watt sloth Which of these available options will accomplish the one kilojoule task in less time? It should be obvious that 500-watt machine will be capable of delivering the required one kilojoule of energy in far less time since its power rating or energy per unit time it’s capable of delivering, is much greater than the other two options Calculations support this supposition Time is energy divided by power One kilojoule divided by 500 watts or 500 joules per seconds demonstrates the 500-watt machine is capable of delivering the necessary one kilojoule of energy in the span of two seconds Let’s examine the other last powerful options Consider the 100-watt human times energy divided power One kilojoule divided by 100 watts, 100 joules per second demonstrates the 100-watt human is capable of delivering the necessary one kilojoule of energy over a longer span of 10 seconds Consider the 20-watt sloth times energy divided by power, one kilojoule divided by 20 watts or 20 joules per second demonstrates the 20-watt sloth is capable of delivering the necessary one kilojoule of energy over a much longer span of 50 seconds Compare and contrast these results A more powerful device accomplished the same task in less time A less powerful device accomplished the same task in more time It makes sense In keeping with this observation, consider the energy of a triple A battery, a nine-millimeter bullet Which do you think has more energy? Surprisingly a typical triple A battery has much, much more energy than a nine-millimeter bullet Specifications may vary, however, a typical triple A battery might contain around 6,000 joules of energy, whereas a nine-millimeter bullet depending on your proximity of the muzzle might contain only around 500 joules of energy Gun nuts chill out I am well aware of the differences between full metal jackets, soft-points, hollow-points, and fragmentation, frangible variance and their associated lethality index and stopping power, but just go with this 500-joule figure for now The difference between these two devices is obviously associated with their power or their rate of energy transfer Let’s say the triple A battery delivers this energy over a long period of one hour or 3,600 seconds whereas the nine-millimeter bullet delivers its packet of energy over a much, much more rapid time span For the sake of argument, let’s say the bullet does so over 100 milliseconds Again gun nuts, chill out It’s just an example problem in electronics class, not a technical discussion in a Bass Pro parking lot, so you have to forgive any ballistic inaccuracies in the interest of forward progress Power is energy over time For the triple A battery, it’s capable of delivering 6,000 joules over one hour or 60 minutes or 3,600 seconds This yields a relatively low power rating of roughly 1.7 joules per second or 1.7 watts A respectively large quantity of energy is slowly and steadily delivered over a long time The battery would be a suitable means of powering a low-power device like your calculator for a long, long time Let’s now consider the nine-millimeter bullet It is capable of delivering 500 joules in 100 milliseconds 500 joules over 100 milliseconds or .1 seconds yields a much higher power rating of 5,000 joules per second or five kilowatts No wonder bullets cause a trauma on impact A packet of energy is delivered very, very quickly This explains why it’s a recommended practice to power your calculator with a triple A battery rather than shooting it, although at times I’m certain you are tempted to do so Moving on, let’s now examine other units commonly employed in the discussion of power and energy, namely the horsepower and the kilowatt hour First, let’s examine the horsepower In addition to watts, power can also be quantified in units of horsepower, sometimes abbreviated as hp where one horsepower equals 746 watts In the US customary system of units, a horsepower also equals 550 foot pounds force per second As antiquated as this unit may be, I still have the tendency to think in terms of horsepower ’cause it gives me an idea if one can stop a device with your hand, with two hands and a little sweating, or if something will just rip your balls out of your sockets if you ever get tangled up in it Long story short, anything stronger than a horse could probably kill you, and even a quarter of a horse stands a reasonable chance of doing so

if it kicks you in a critical portion of your anatomy Let’s try some basic unit conversions Consider a quarter horsepower of motor In units of watts, this motor would have a power rating of 746 divided by four or 186.5 watts Consider a motor that delivers 560 watts In units of horsepower, this motor has a power rating of 560 over 746 or roughly .75 horsepower Most likely this is a three-quarter motor horsepower Let’s now try an energy, power, and time example necessitating some intermediate unit conversion Consider a two-horsepower motor being used for a span of three hours How much energy in units of joules will it deliver? A two-horsepower motor would have a power rating of two times 746 watts or 1,492 watts or roughly 1.5 kilowatts Three hours represents a span of three times 60 times 60 or 10,800 seconds Energy is power times time 1,492 watts times 10,800 seconds yields 16,113,600 joules or roughly 16.1 megajoules You’ll note that for applications like this, joules are tiny, tiny, annoying, and unwieldy units For this reason, numerous applications make use of a far more convenient unit of energy, the kilowatt hour Pay special attention to the kilowatt hour since in my experience, it presents one of the biggest sources of confusion for those with difficulties distinguishing between the concepts of energy and power The kilowatt hour is a unit of energy It is not a unit of power I know it has a kilowatt in there which is a unit of power, but look at it, it is kilowatts times hour or power times time I say again that kilowatt-hour is a unit of energy It is not a unit of power If you don’t believe me, unwrap each piece of the kilowatt hour one by one and prove it to yourself If one k equals 1,000, one kilowatt hour equals 1,000 watt hours If one watt equals one joule per second, one watt hour equals 1,000 joules per second times one hour If one hour equals 60 minutes, and one minute equals 60 seconds, one kilowatt hour is 1,000 joules per second times 3,600 seconds or 3,600,000 joules In summary the kilowatt hour is a unit of energy It is a unit of power, the kilowatt, times the unit of time, the hour Energy is power times time The simplicity of expressing energy in units of kilowatt hours cannot be overstated Consider a four-kilowatt solar ray being exposed to peak sunlight for a period of four hours How much energy does this solar ray produce in units of kilowatt hours? Energy is power times time Rather than converting hours to seconds as we did when calculating energy using units of joules We simply multiply the power in units of kilowatts times the time in units of hours Four kilowatts times four hours yields 16 kilowatt hours It really is that easy If you wanted to go to the trouble, which I have no idea why you would, you could convert this to joules where one kilowatt hour equals 3.6 megajoules, and 16 kilowatt hours would equal 57.6 megajoules You know calculating energy in units of kilowatt hours is astoundingly easy Oftentimes the wattage or power of a particular device is directly specified in the device’s nameplate All you need to do to determine the energies of a particular device is the number of hours you plan on using it For example, considering an 800-watt air conditioner To calculate the daily energy consumption of this air conditioner, simply multiply the wattage rating by the number of hours you use it everyday An 800-watt air conditioner used for eight hours a day uses 800 times eight or 6,400 watt hours of energy or 6.4 kilowatt hours of energy If however you left the 800-watt air conditioner on all day or 24 hours, you’d be billed for 800 times 24 or 19,200 watt hours or 19.2 kilowatt hours of energy Consider a 100-watt incandescent bulb used for eight hours a day This bulb uses 100 times eight or 800 watt hours of energy or .8 kilowatt hours of energy If you were lazy and you left it on all day or for 24 hours,

you’d be billed for 100 watts times 24 hours or 2,400 watt hours or 2.4 kilowatt hours of energy Consider a more efficient 20-watt LED light bulb used for eight hours a day This bulb would use 20 watts times eight hours or 160 watt hours of energy or .16 kilowatt hours of energy If you left it on all day or for 24 hours, you’d be billed for 20 watts times 24 hours or 480 watt hours of .48 kilowatt hours of energy Compare and contrast these last two examples The 100-watt incandescent bulb used five times as much energy as the 20-watt LED light bulb even though they operated for the same length of time It makes sense More power times the same time necessitates more energy even though they are producing the same functional product, namely light of a given intensity Be aware that I’m not so naive to suggest that an LED will be sufficient for all tasks requiring light of a certain quality, let’s say painting a picture or some alone time with your imaginary girlfriend, but I’m confident enough to say that if you simply require light in its most basic form, let’s say task lighting in a factory or to light up your front steps so you don’t bust your ass falling down them, it’d be foolish to use an incandescent bulb to do so principally ’cause the long-term energy cost Additionally compare and contrast the usage patterns Any appliance regardless of type used for 24 hours a day necessitates more energy than an identical device used for only eight hours a day It makes sense Same power more time necessitates more energy This explains why it’s a good economic practice to, one, use efficient devices, i.e., devices that accomplish the same task using less power, and two, use these devices only when it’s necessary, i.e, don’t leave a light on if you don’t need it When you get right down to it, energy is money The more energy you use, the more you pay Nationally, price per kilowatt hour of energy varies depending upon your location from a low of around eight cents per kilowatt hour in regions of the Pacific Northwest, to a high of around 35 cents per kilowatt hour in Hawaii, with a national average of around 12 cents per kilowatt hour at the time of this recording An average house might consume around 30-kilowatt hours of energy daily, although daily energy consumption patterns vary widely from the seven-bedroom McMansions of Salt Lake City chugging 100 kilowatt hours a day, whereas an efficient well-designed modern house with a reasonable number of ecologically and economical conscious people might consume only 10 kilowatt hours Also if you’re on a region characterized by cold winters and temperate summers like Maine or Wisconsin, you might expect larger daily energy consumption in the winter and less in the summer Conversely, if you’re in a region characterized by extremely hot summers and temperate winters like Arizona or Southern Cali, you might expect larger daily energy consumption in the summer and less in the winter Let’s just go with this average daily energy consumption of 30 kilowatt hours per day Given this average price per kilowatt hour and the average amount of kilowatt hours used per day, it’s easy to determine the average cost of energy per day 12 cents per kilowatt hour times 30 kilowatt hours per day yields an average daily cost of $3.60 and an annual cost of 360 times 365 or $1,314 per year Given this average daily energy consumption, let’s now take a look at the average power consumption of a typical home If power is energy over time, you might be tempted to think that a house would steadily draw 30 kilowatt hours divided by 24 hours or 1.25 kilowatts, but you would be absolutely wrong Some periods of a day necessitate massive consumption of power For example in the morning when everyone’s waking up, taking a shower, cooking breakfast, and getting ready for the day This brief period of high power consumption is followed by a longer period of lower power consumption when everyone’s at work or school This period is then followed by another burst of high power consumption when everyone gets home and air conditioners, stoves, washers and dryers start chugging power in massive quantities Finally the day draws to a close and the occupants of the house go to sleep, only the water heater and refrigerator continue to draw power Instantaneous power demand peaks and valleys and peaks and valleys, yet we can say there exists some average power demand which happens to be around 1.25 kilowatts such that over the course of a 24-hour period, the house ultimately consumes 30 kilowatt hours of energy Those of you with a calculus background will realize that the energy is the integral or area under the power curve, i.e., power times time The instantaneous power curve can be a little tricky to calculate, so that’s why the average is used

If you squinch your eyes just right, you’ll note the overrepresented areas in the early morning and late evening are counterbalanced by the under-representation or morning and afternoon If you multiply the average power figure of 1.25 kilowatts by 24 hours, you realize the energy or area under the power curve is 1.25 times 24 or 30 kilowatt hours Don’t get too stressed about the details of this particular example just yet, but rather think of the large point I’m trying to make Power is instantaneous whereas energy is consumed over time Power is the instantaneous rate of change of energy whereas energy is power consumed over time Let’s try an illustrated example of this concept, focusing in on a single household appliance Consider a water heater that over the course of one year or 365 days is known to consume 4,380 kilowatt hours of energy, given the price of 12 cents per kilowatt hour, what’s the annual cost of using this water heater? Additionally what’s the average power consumption of this water heater? Calculating the annual cost is easy 4,380 kilowatt hours times 12 cents per kilowatt hour yields an annual cost of $525.60 Average power should be easy too Power is energy over time One year is 365 days, one day is 24 hours, so one year is 8,760 hours 4,380 kilowatt hours over 8,060 hours use a power rating of .5 kilowatts or more appropriately 500 watts You might reasonably think a water heater continuously steadily draws 500 watts of power and could be powered by a 500-watt generator This, however, is an average power figure only, and totally misrepresents how an actual water heater works Water heater don’t heat water continuously but rather in bursts As a simplified explanation, if water in the tank falls below a certain low value, but heater is applied at full blast until water in the tank has risen above a certain high value, after which the heater is completely turned off and the tank’s insulation, thermal inertia of the water, temporarily hold it inside a specified range The result is a periodic full-on, full-off, bang-bang style control that only on average consumes 500 watts In reality we might expect the water heater to briefly consume massive amounts of power during the heat phase, and then simply turn off during the rest phase until the temperature in the tank falls below the reset value Obviously water usage patterns would influence this periodic cycling As a simplified illustration of this process, let’s say a four-kilowatt water heater operates in a 12 1/2% duty cycle where for 12 1/2% of 60 minutes or 7 1/2 minutes, the four-kilowatt heater runs at full blast, and the remaining 87.5% of 60 minutes of 52.5 minutes, the heater is completely off What you’d experience over the day is regular burst of four-kilowatt power demand followed by an idle state If you summate the on times for a 24-day, i.e., 24 times 7 1/2 minutes or 180 minutes or there hours, it means a four-kilowatt device has been used for a total of three hours or a daily consumption of four kilowatts times three hours or 12 kilowatt hours If the water heater did this everyday for 365 days, it would consume 365 times 12 kilowatt hours or 4,380 kilowatt hours of energy annually Additionally you’d need that minimum of four-kilowatt generator to power this water heater when it was on That generator only working 12 1/2% of the time, and the other time it would sit idle Again those of you with a calculus background will realize energy is the area under the power curve Rather than using instantaneous periodic power burst however, it’s perhaps easier to simply use the average power figure of 500 watts over the 24-hour period which yields 12 kilowatt hours of energy per day Moving on, returning to our discussion of units employed when quantifying energy, the kilowatt hour makes a handy unit for most small scale residential applications However, if the application is smaller in nature like a portable electronics device or sometimes batteries, you might alternatively see units of energy represented in watt seconds or watt hours Watt second is simply a stupid way of writing a joule because one watt times one second is one joule per second times a second which yields joules And a watt hour is a larger packet of joules If one hour equals 3,600 seconds, a watt hour is 3,600 joules, or more appropriately 3.6 kilojoules For example consider a storage battery known to have an energy capacity of 600 watt hours,

theoretically this battery could power a 600-watt device for one full hour or 300-watt device for two hours or 1.2-kilowatt device for 30 minutes or any other combination of power and time that ultimately yields a product of 600 watt hours of energy This, by the way, is theoretical capacity only, and isn’t entirely true especially for high power demands As we demonstrated, triple A battery is ordinarily limited to an extremely slow rate of energy transfer per unit time, i.e., low power, and can’t be expected to deliver a high power burst as with a bullet I suppose you could throw a battery at an aggressor’s head but I suspect that might only make them mad We’ll examine battery performance characteristics in greater details in later lectures If the application is considerably larger, for example the daily and annual energy output of a large generation facility, you’ll sometimes see figures in the megawatt hour or gigawatt hour range Given your understanding of engineering prefixes, you will note that 1,000 watt hours equals one kilowatt hour 1,000 kilowatt hours equals one megawatt hour And finally 1,000 megawatt hours equals one gigawatt hour Consider a single 50-megawatt turbine inside a larger hydroelectric dam that runs at full capacity for 24 hours How much energy does this turbine produce in one day? Energy is power times time 50 megawatts times 24 hours yields 1,200 megawatt hours, or more appropriately 1.2 gigawatt hours If you wanted to put this in terms of kilowatt hours, this would be equal to 1,200,000 kilowatt hours Consider a two-megawatt wind turbine that runs at full capacity for only eight hours a day How much energy does it produce? Energy is power times time Two megawatts times eight hours yield 16 megawatt hours, which if you want to put it in terms of kilowatt hours, would equal 16,000 kilowatt hours If you were to sell each kilowatt hour at a wholesale price of five cents per kilowatt hour, this means the turbine would produce 16,000 kilowatt hours times five cents per kilowatt hour or $800, meaning the turbine is effectively generating $100 an hour every hour it’s in full production No wonder such a high priority is placed on the efficient operation, maintenance, and timely repair of these machines Other questions I’m frequently asked about wind turbines, why are they so big? Why are they so tall? Why are they painted white? How many houses can a turbine power? I think the last one deserves some comment in this particular lecture The average dunderpate beebopping down the street does not understand the difference between energy and power and often uses these two concepts interchangeably You, however, understand the difference To make this a solvable problem, let’s assume the following We’re using a two-megawatt wind turbine that operates at full capacity for eight hours a day As we demonstrated, it would produce 16,000 kilowatt hours per day The average daily energy consumption of a typical house is 30 kilowatt hours And finally, each house does in fact steadily consumed a flat rate power figure of 1.25 kilowatts We know this last point isn’t true because of our earlier discussions about instantaneous power demand at particular points in a day, however, let’s just say the instantaneous demands of all the houses we’re really considering does average out to a steady state draw of 1.25 kilowatts each For example, not everybody is popping a load of wet clothes in their dryer, vacuuming the floor, and making a smoothie at the same time, but rather these events occur out of sync with one another such that it makes it appear as if each house draws an average 1.25 kilowatts of power Given the original phrasing of this question, let’s answer this question How many houses can a two-megawatt turbine power given an average power consumption of 1.25 kilowatts each? This two-megawatt turbine could theoretically power two megawatts or 2,000 kilowatts divided by 1.25 kilowatts per house or 1,600 houses or can it? You’ll note a major flaw in this assumption Notably this community would only be powered when the wind was blowing, meaning for the remainder 16 hours of the day when the turbine was not operating, the houses would be dark This is to suggest that in order to continuously and reliably power this community on a 24-hour basis, a mix of energy sources like wind, water, solar, coal-fired power plants, and natural gas turbines need to work together Not only are renewable resources like wind and solar intermittent in nature, they’re also unschedulable Intermittent and unschedulable by the way doesn’t mean unpredictable For example, if this community knew the wind forecast in advance, they could turn off the gas turbines and turn on the wind turbine when it was windy and turn on the gas turbine

and turn off the wind turbine when it wasn’t What’s the advantage of this mixed approach? Easy, you’re not burning expensive gas when the free wind is blowing Let’s answer this question from a different perspective, that of energy Let me rephrase the question ever so slightly How many houses’ daily energy needs can a two-megawatt turbine operating at full capacity for eight hours satisfy given each house consumes 30 kilowatt hours of energy everyday? As we demonstrated, a two-megawatt turbine operating at full capacity for eight hours produces 16,000 kilowatt hours Given each house consumes 30 kilowatt hours each day, this means this turbine can satisfy the daily energy needs of 16,000 divided by 30 or roughly 533 houses or does it? The problem again is matching the instantaneous power requirements of a house with the instantaneous power output of the turbine The turbine produces way more power than instantaneous needs of 533 houses for eight hours, and then just goes dark when the wind stops There is a workable solution to this problem too Consider letting the wind turbine operate intermittently throughout the day and dump excess overproduction into a battery bank to be withdrawn when the wind dies What’s the advantage of this approach? Easy, you’re not burning any gas at all Other techniques that could allow the transition to an all-renewable grid might be the grid itself Consider several communities each consisting of 533 houses and a two-megawatt wind turbine linked to each other via a transmission grid Granted it may not be windy in regions A and C, but in region C where it is windy, the output of this turbine can be directed to A, B, and C matching the instantaneous power output of the turbine with the instantaneous power demands for all three communities When weather patterns shift and it’s windy in region A, and not B and C, the output of this community’s turbine is directed to A, B, and C Add to this transmission scheme localized battery storage in regions A, B, and C When it’s windy in two or more regions, any excess power stored in these battery banks to account for the inevitable day when the wind refuses to blow in any of these regions Keep in mind energy storage needn’t be limited to electrochemical means as in batteries but can also take the form of pumped hydro storage when in the event of excess power production, water is pumped uphill, and in the event of need, it’s allowed to run downhill and turn a hydroelectric turbine Add to this simplistic wind generation scheme, additional supporting renewable sources like solar, biofuels, and geothermal This scheme is not as farfetched as you might think We have the technology, we have solar panels, wind turbines, batteries, and a transmission grid To make this a reality, we need political will and economic muscle to overcome the significant technical challenges this presents This will not be easy nor inexpensive by any measure Intermittent and unschedulable renewable resources like solar and wind necessitates a sufficiently large population of distributed generation sites Batteries and reservoirs must be constructed with sufficient scale, and the transmission grid needs to be upgraded to handle this level of coordination Vocal detractors are quick to point out the complexity and cost of such a future Listen, I never said it was going to be cheap and easy In fact I’m telling you upfront the switch to renewables would be the most expensive and most complicated leap we’ve ever made However, the future of business as usual is horrifying to consider Think of a world with more and more and more people and less and less resources You do the math I don’t mean to end this lecture on a down note, but I do want to emphasize that society needs energy to function All forms of energy extraction come at a price The way I see it we can pay this cost via two radically different approaches One, the hard and dirty way Fighting increasingly frequent conflicts to ensure our continued access to limited petroleum supplies, or two, the soft and clean way, make our own energy inside our own communities using abundant renewable resources My intention in publishing these lectures is to give you the skills necessary to contribute towards solving a complex challenge that has lasting implications for our nations future In conclusion this lecture examined energy and power at an introductory level We learned power is energy per unit time, and energy is power times time We introduced units used to measure energy, namely the joule and the kilowatt hour, and learned to convert power measurements expressed in units of horsepower and watts Remember to review these concepts as often as you need to really drive it home Imagine how well lab will go if you know what you’re doing Thank you very much for your attention and interest And we’ll see you again during the next lecture of our series Remember to tell your lazy lab partner about this resource, be sure to check out the Big Bad Tech channel for additional resources and updates

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