There is a lot of misinformation about the efficiency of LED lighting. Much of the information out there is not about what LEDs can do today, but rather what they are working toward. In the end, what we all care about, when trying to save energy, is Luminous Efficacy, which is the efficiency of the conversion of electricity into usable light. It's specified in Lumens per Watt.
A good quality fluorescent bulb with an electronic ballast provides on the order of 100 lumens per watt. If it's a dimmable fluorescent, that number can go down quite a bit when dimmed to low levels (down, you ask? Yes, there is a fixed amount of power to run the ballast that doesn't change with dim level, which isn't converted into light). A compact fluorescent is usually in the 50 to 80 lumens per watt, I understand. Only the most exotic prototypes in a lab environment an beat this with LED sources. Most of them are well below what a compact fluorescent can do.
Of course we all want a better light source, so enormous amounts of money (both private and public) is being poured into LED research. I'm sure, in time, the efficacy will improve. I found this nice article about the fundamental sources of heat produced in LEDs, which gives a good outline of where the waste energy is going, but it stops short of giving efficacy numbers. The biggest challenge today, I think, is thermal management. If the LEDs are run at too high a temperature, they will not live up to their promise of long life. CFLs suffer the same problem, and in the wrong kind of fixture they only last a few months instead of the many years they are capable of.
The best way to save energy, now and always, is to turn off lighting that is not needed. While I still train my children to turn off the lights when they are not in the room, they still forget often enough, and the motion detectors I've set up take care of the rest.
Friday, April 17, 2009
Wednesday, April 8, 2009
CFL power quality
Long-term (assuming that CFL bulbs become a substantial percentage of the load on our power grid) the cheap power supplies that are built in most compact fluorescent bulbs will create power quality problems. See this article for some details.
While I agree that it's a problem, having designed power supplies like them, I would assert that it's already been a problem historically, and perhaps is presently, too. The harmonic content generated when a rectifier sits directly on the AC power line, connected to capacitors on the DC side, is pretty nasty. Perhaps counter-intuitively for those of you with an electronics background, the noise becomes worse if you use more capacitance after the rectifier. Think of it this way: a larger capacitor doesn't droop as much between power cycles, so the recharge occurs over a smaller piece of the power line cycle, making a shorter (but higher-amplitude) spike of current. During the remaining power cycle, little or no current is drawn.
While this doesn't represent the traditional inductive or capacitive load (a simple phase lead or lag of current) it's a power quality problem. Capacitor banks on the utility distribution lines will not solve the problem. In the end, the power supplies at the end of the service line must be improved.
As an example of this problem, see this image below of the AC waveform at my house. Compared to a pure sine wave, the peak is significantly clipped. I believe it's due to non-power-factor-corrected power supplies that are in use throughout my neighborhood (and I think the same is true of most parts of the power grid).
While I agree that it's a problem, having designed power supplies like them, I would assert that it's already been a problem historically, and perhaps is presently, too. The harmonic content generated when a rectifier sits directly on the AC power line, connected to capacitors on the DC side, is pretty nasty. Perhaps counter-intuitively for those of you with an electronics background, the noise becomes worse if you use more capacitance after the rectifier. Think of it this way: a larger capacitor doesn't droop as much between power cycles, so the recharge occurs over a smaller piece of the power line cycle, making a shorter (but higher-amplitude) spike of current. During the remaining power cycle, little or no current is drawn.
While this doesn't represent the traditional inductive or capacitive load (a simple phase lead or lag of current) it's a power quality problem. Capacitor banks on the utility distribution lines will not solve the problem. In the end, the power supplies at the end of the service line must be improved.
As an example of this problem, see this image below of the AC waveform at my house. Compared to a pure sine wave, the peak is significantly clipped. I believe it's due to non-power-factor-corrected power supplies that are in use throughout my neighborhood (and I think the same is true of most parts of the power grid).
Wednesday, March 18, 2009
Sustainability and why dimming your lights may not save...
I ran across a series of interesting articles on "sustainability" today. I'm trying to figure out if people are finally joining the sustainability movement because it's becoming more mainstream, or if they really think it's a good idea. Perhaps the higher cost of energy (recently) has been pushing people to save money. Maybe the economic downturn is hitting people so they're trying to save money everywhere they can.
In any case, the ILLUMRA philosophy still applies: saving energy (for any reason) by automating and controlling devices that use energy. Decades ago it only mattered that the lights worked, the cost of operating them was small in comparison with the light bulb itself (or so everyone assumed). Of course most of the products sold by ILLUMRA (the company, as opposed to this, the blog) involve energy harvesting in one way or another, which ultimately saves wiring, batteries, or both.
In any case, here are links to the articles:
Survey: Americans favor Sustainable Engineering and Manufacturing
Energy cost savings through load shedding (and load balancing)
The power factor issue in the second item will be, I believe, a bigger issue in the future. I've been recently working over ideas for large-scale (building-wide) LED lighting systems. It's critical that the power supplies (ballasts) for the LED lights include power factor correction, and therefore act as "nice" loads on the grid. This will avoid the kinds of noise-induced power quality issues that often occur in large manufacturing environments. Years ago, power supplies in all PCs were not power factor corrected, and contributed to power quality problems (including neutral heating) in office buildings. If someone goes a "too-cheap" route when converting their lighting, they could create as many problems as they solve.
One reason this is so important: Dimmable fluorescents are a nice way to introduce some energy savings (and load-shed capacity) to a building. However, if you use ballasts that support phase-cut dimming on their line inputs (as opposed to 0-10V low voltage control dimming) then the effective power factor will degrade. If a whole office building used this technique to load-shed during a high-demand time-of-day, the net effect may actually increase the electric bill of the facility (because of the power factor and demand charges outlined in the second article above). It's important that while phase-cut dimming is a nice feature on a dimmable ballast (fluorescent or LED) it's not a good way to control a large number of ballasts. A 0-10V solution (wired or wireless) is the best way to go.
In any case, the ILLUMRA philosophy still applies: saving energy (for any reason) by automating and controlling devices that use energy. Decades ago it only mattered that the lights worked, the cost of operating them was small in comparison with the light bulb itself (or so everyone assumed). Of course most of the products sold by ILLUMRA (the company, as opposed to this, the blog) involve energy harvesting in one way or another, which ultimately saves wiring, batteries, or both.
In any case, here are links to the articles:
Survey: Americans favor Sustainable Engineering and Manufacturing
Energy cost savings through load shedding (and load balancing)
The power factor issue in the second item will be, I believe, a bigger issue in the future. I've been recently working over ideas for large-scale (building-wide) LED lighting systems. It's critical that the power supplies (ballasts) for the LED lights include power factor correction, and therefore act as "nice" loads on the grid. This will avoid the kinds of noise-induced power quality issues that often occur in large manufacturing environments. Years ago, power supplies in all PCs were not power factor corrected, and contributed to power quality problems (including neutral heating) in office buildings. If someone goes a "too-cheap" route when converting their lighting, they could create as many problems as they solve.
One reason this is so important: Dimmable fluorescents are a nice way to introduce some energy savings (and load-shed capacity) to a building. However, if you use ballasts that support phase-cut dimming on their line inputs (as opposed to 0-10V low voltage control dimming) then the effective power factor will degrade. If a whole office building used this technique to load-shed during a high-demand time-of-day, the net effect may actually increase the electric bill of the facility (because of the power factor and demand charges outlined in the second article above). It's important that while phase-cut dimming is a nice feature on a dimmable ballast (fluorescent or LED) it's not a good way to control a large number of ballasts. A 0-10V solution (wired or wireless) is the best way to go.
Friday, February 27, 2009
Energy Harvesting - not ready for prime time?
Nice brief summary article relating to energy harvesting technologies:
http://www.greensupplyline.com/214301888
I've got mixed feelings about his assertion that energy harvesting isn't ready for "prime time" yet, though. While I will agree that it's not close to being a technology that fits every application yet, there are certainly some nice niches that fit well.
For example, there are a lot of buildings that can be retrofitted with energy saving lighting controls (California's Title 24 regulation in particular) but the installation cost is high in order to route wiring for occupancy sensors in the room (or even worse, installing a sensor on every fixture). In this case, a wireless, battery-free, energy harvesting motion detector (other manufacturers with the same concept: 1, 2) is a perfect fit. While the equipment cost is higher than that of a wired system, the installation cost is much lower, possibly less expensive overall, but certainly competitive. The sensor harvests solar energy, stores it (enough to run for two days or so in darkness) and operates the occupancy sensor and the radio transmitter.
In contrast, and ultrasonic sensor uses thousands of times more energy, so to make an energy harvesting vacancy sensor (or occupancy sensor) would require a very large solar panel, enough to make it impractical. So much energy is required, in fact, that it would make a lot of sense to turn the sensor off when the lights are off (unless automatic on is required -- CA Title 24 doesn't allow for that) or at least reduce it's operating duty cycle.
On a related note, there is a movement to revive magnetic coupling to charge cell phones, laptops, and the like. Inductive power coupling is nothing new, it's been around for years. I have a waterproof cordless phone that charges without any electrical contacts, I understand that many electric toothbrushes recharge the same way. In much the same way that Apple made touchscreens new and exciting with the iPod Touch and the iPhone, companies are going to revive magnetic coupling so you can put your laptop on a special pad on (or embedded in) a table or desk and charge without a cord.
While it's convenient, the relatively low efficiency of this power transfer method runs counter to some of the goals of the green movement. On the upside, however, the stray fields from these devices may provide a new mechanism for energy harvesters. Adding a small magnetic pickup coil to an energy harvesting device may, in the future, provide sufficient energy to run these sensors without the need for a solar cell, mechanical, or thermal harvester.
http://www.greensupplyline.com/214301888
I've got mixed feelings about his assertion that energy harvesting isn't ready for "prime time" yet, though. While I will agree that it's not close to being a technology that fits every application yet, there are certainly some nice niches that fit well.
For example, there are a lot of buildings that can be retrofitted with energy saving lighting controls (California's Title 24 regulation in particular) but the installation cost is high in order to route wiring for occupancy sensors in the room (or even worse, installing a sensor on every fixture). In this case, a wireless, battery-free, energy harvesting motion detector (other manufacturers with the same concept: 1, 2) is a perfect fit. While the equipment cost is higher than that of a wired system, the installation cost is much lower, possibly less expensive overall, but certainly competitive. The sensor harvests solar energy, stores it (enough to run for two days or so in darkness) and operates the occupancy sensor and the radio transmitter.
In contrast, and ultrasonic sensor uses thousands of times more energy, so to make an energy harvesting vacancy sensor (or occupancy sensor) would require a very large solar panel, enough to make it impractical. So much energy is required, in fact, that it would make a lot of sense to turn the sensor off when the lights are off (unless automatic on is required -- CA Title 24 doesn't allow for that) or at least reduce it's operating duty cycle.
On a related note, there is a movement to revive magnetic coupling to charge cell phones, laptops, and the like. Inductive power coupling is nothing new, it's been around for years. I have a waterproof cordless phone that charges without any electrical contacts, I understand that many electric toothbrushes recharge the same way. In much the same way that Apple made touchscreens new and exciting with the iPod Touch and the iPhone, companies are going to revive magnetic coupling so you can put your laptop on a special pad on (or embedded in) a table or desk and charge without a cord.
While it's convenient, the relatively low efficiency of this power transfer method runs counter to some of the goals of the green movement. On the upside, however, the stray fields from these devices may provide a new mechanism for energy harvesters. Adding a small magnetic pickup coil to an energy harvesting device may, in the future, provide sufficient energy to run these sensors without the need for a solar cell, mechanical, or thermal harvester.
Monday, February 9, 2009
LED vs. CFL vs. Incandescent
This article I read on edn.com, while it contains nothing I haven't read elsewhere, is a nice summary of the whole migration toward LED lighting. I hope to see LED lights that approach the efficacy (efficiency in terms of lumens per watt) of a good fluorescent light (around 100 lumens per watt). One named in the article was getting closer (about 80) and I've heard of laboratory tests of prototypes that are in the neighborhood of 150 (yes!).
I still want to see an intelligent way to retrofit existing dimming bulbs with dimmable CFL and LED fixtures. I think a bidirectional communication protocol between the bulb and the dimmer might be a way to do it, perhaps over the existing power line. The problem with that method is the extra cost, complexity, and reliability of adding that hardware to the bulbs and the dimmers. A dimmer would probably need to detect the connected load, and either use traditional dimming (for regular bulbs) or leave the power fully on and communicate the dim level, letting the ballast at the load control the brightness.
Perhaps the communication can occur by doing phase cutting, much like regular dimming, but use a 95% brightness level for one digital level (zero or one) and 100% brightness for the other value, and use, in effect, a serial data stream over the power line.
Long term, however, low or medium voltage DC power to the lighting loads, with digital control at the point of load, would be more efficient and have fewer points of failure than the current methods.
Just a few random thoughts. I hope to come up with a more coherent post in the near future. It's been a very busy few weeks, so I haven't been able to write a more organized, thoughful post than this.
I still want to see an intelligent way to retrofit existing dimming bulbs with dimmable CFL and LED fixtures. I think a bidirectional communication protocol between the bulb and the dimmer might be a way to do it, perhaps over the existing power line. The problem with that method is the extra cost, complexity, and reliability of adding that hardware to the bulbs and the dimmers. A dimmer would probably need to detect the connected load, and either use traditional dimming (for regular bulbs) or leave the power fully on and communicate the dim level, letting the ballast at the load control the brightness.
Perhaps the communication can occur by doing phase cutting, much like regular dimming, but use a 95% brightness level for one digital level (zero or one) and 100% brightness for the other value, and use, in effect, a serial data stream over the power line.
Long term, however, low or medium voltage DC power to the lighting loads, with digital control at the point of load, would be more efficient and have fewer points of failure than the current methods.
Just a few random thoughts. I hope to come up with a more coherent post in the near future. It's been a very busy few weeks, so I haven't been able to write a more organized, thoughful post than this.
Thursday, January 15, 2009
Electric Cars for Commuting
While I doubt I'll be able to afford one until long after they become available, I'm anxiously awaiting the release of some (almost) pure electric cars. The Chevy (GM) Volt is of particular interest, as it seems to be one of the front runners at this point. It seems that the battery technology is the real weak point at the moment.
From their site:
"All the technology for the car is here today, except for the battery pack. It will use lithium-ion (li-ion) technology. Current hybrids use nickel-metal hydride (NiMh), which carry much less energy per unit weight. The li-ion cell technology exists but putting it into tested and safe packs is what will take some time. There are companies working with GM and trying to get these Li-ion batteries and their packs ready for automotive use."
It's fascinating the different energy storage technologies that have been tried. I recall a city bus that used a large flywheel to recover energy (using regenerative braking) and store it to start the bus back up after each stop. Certainly NiMh batteries see a lot of use in hybrids today, but aren't ideal. Supercapacitors have pretty decent energy storage capacity, but unfortunately petroleum based fuels carry about 100 times the energy (per kg of mass - about 12 kWh vs. 0.12 kWh for Lithium Ion batteries).
Fundamentally, hydrogen is a nice way to store energy, but because it doesn't exist in nature (most of the hydrogen on earth exists in the form of water, H2O) we can only create hydrogen "fuel" by using another energy source to break down water (or some other source of hydrogen, like natural gas). I have only looked briefly at this site, but it seems to have a decent rundown of the requirements to create some amazing solar projects in the southwestern USA.
I'm sure there's some great research going on to find more efficient (and cost-effective) ways to convert solar and other energy forms into hydrogen, because solar (on it's own) isn't a solution to our energy problems. The reason for this is simple: the sun sets at night and peak demand occurs late in the afternoon and into the early evening. For the same reason that electric cars have limited range, we can't store enough energy (with current technology) to keep everything running overnight. If a highly efficient solar-to-hydrogen conversion system can be developed, then storage becomes much easier.
From their site:
"All the technology for the car is here today, except for the battery pack. It will use lithium-ion (li-ion) technology. Current hybrids use nickel-metal hydride (NiMh), which carry much less energy per unit weight. The li-ion cell technology exists but putting it into tested and safe packs is what will take some time. There are companies working with GM and trying to get these Li-ion batteries and their packs ready for automotive use."
It's fascinating the different energy storage technologies that have been tried. I recall a city bus that used a large flywheel to recover energy (using regenerative braking) and store it to start the bus back up after each stop. Certainly NiMh batteries see a lot of use in hybrids today, but aren't ideal. Supercapacitors have pretty decent energy storage capacity, but unfortunately petroleum based fuels carry about 100 times the energy (per kg of mass - about 12 kWh vs. 0.12 kWh for Lithium Ion batteries).
Fundamentally, hydrogen is a nice way to store energy, but because it doesn't exist in nature (most of the hydrogen on earth exists in the form of water, H2O) we can only create hydrogen "fuel" by using another energy source to break down water (or some other source of hydrogen, like natural gas). I have only looked briefly at this site, but it seems to have a decent rundown of the requirements to create some amazing solar projects in the southwestern USA.
I'm sure there's some great research going on to find more efficient (and cost-effective) ways to convert solar and other energy forms into hydrogen, because solar (on it's own) isn't a solution to our energy problems. The reason for this is simple: the sun sets at night and peak demand occurs late in the afternoon and into the early evening. For the same reason that electric cars have limited range, we can't store enough energy (with current technology) to keep everything running overnight. If a highly efficient solar-to-hydrogen conversion system can be developed, then storage becomes much easier.
Thursday, December 11, 2008
Daylight Saving - Does it really save energy?
For a more thorough analysis of this subject, there are some studies currently underway and other useful info around the web, but I'm not sure if they make this point well enough. Try this link or Google "daylight saving energy" for more info.
Based on some of the information about peak electrical demand in California (see my other posts about some data that came out of UC-Davis) I'm not convinced that daylight saving actually saves energy as much as it used to. When previous studies were done, central air conditioning was not nearly as common as it is today (many of the studies date back to the 1970s). I believe that central air is a large contributor to the peak demand when people return home from work in the afternoon, even more so when they use a programmable thermostat to set the temperature higher while they are at work. Without a programmable thermostat, the overall energy usage is much higher, because the A/C unit runs more during the day. However, a programmable thermostat changes the setpoint around the time you get home, effectively turning on the A/C for an extended period right at that time, increasing demand a lot, even though the overall usage throughout the day is lower.
Daylight saving effectively gets everyone home from work one hour earlier (as far as where the sun is in the sky) and therefore closer to the hottest part of the day. At this point, more energy is needed to cool the home to a comfortable temperature, while if people returned home an hour later (without daylight saving) the house wouldn't be as hot because the sun is lower in the sky. Of course the evening lighting load will be greater, because the sun goes down, but certainly that's a smaller load (overall) than the A/C unit.
This is an idea that may sound completely backward, but consider it for a moment. Assume for a moment that it is true that programmable thermostats cause most A/C units in California to turn on at about the same time each summer afternoon (within an hour or two of each other) and then they run for an extended period of time to cool the buildings. Now what if, instead of using demand response controls to disable some of those A/C units to reduce peak demand, you instead use a demand response control to turn some of those A/C units on earlier, cooling some of the homes earlier than others, so they won't need it later when all the other units kick on. It's the exact opposite of a typical demand response system, but in terms of reducing peak demand, it may be exactly the right thing to do.
I really think that new studies will show that daylight saving is no longer helping our energy usage (especially on the basis of peak demand) as much as it used to (if at all).
Based on some of the information about peak electrical demand in California (see my other posts about some data that came out of UC-Davis) I'm not convinced that daylight saving actually saves energy as much as it used to. When previous studies were done, central air conditioning was not nearly as common as it is today (many of the studies date back to the 1970s). I believe that central air is a large contributor to the peak demand when people return home from work in the afternoon, even more so when they use a programmable thermostat to set the temperature higher while they are at work. Without a programmable thermostat, the overall energy usage is much higher, because the A/C unit runs more during the day. However, a programmable thermostat changes the setpoint around the time you get home, effectively turning on the A/C for an extended period right at that time, increasing demand a lot, even though the overall usage throughout the day is lower.
Daylight saving effectively gets everyone home from work one hour earlier (as far as where the sun is in the sky) and therefore closer to the hottest part of the day. At this point, more energy is needed to cool the home to a comfortable temperature, while if people returned home an hour later (without daylight saving) the house wouldn't be as hot because the sun is lower in the sky. Of course the evening lighting load will be greater, because the sun goes down, but certainly that's a smaller load (overall) than the A/C unit.
This is an idea that may sound completely backward, but consider it for a moment. Assume for a moment that it is true that programmable thermostats cause most A/C units in California to turn on at about the same time each summer afternoon (within an hour or two of each other) and then they run for an extended period of time to cool the buildings. Now what if, instead of using demand response controls to disable some of those A/C units to reduce peak demand, you instead use a demand response control to turn some of those A/C units on earlier, cooling some of the homes earlier than others, so they won't need it later when all the other units kick on. It's the exact opposite of a typical demand response system, but in terms of reducing peak demand, it may be exactly the right thing to do.
I really think that new studies will show that daylight saving is no longer helping our energy usage (especially on the basis of peak demand) as much as it used to (if at all).
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