Slow Electricity: The Return of DC Power? (2016)
lowtechmagazine.com
lowtechmagazine.com
One reason DC power is more viable nowadays is (as others here have mentioned) the use of DC-DC converters. They internally actually use AC to do the conversion (usually at much higher frequency to save weight and cost on inductive elements). But they're not super cheap (not cheaper than transformers) and they can also be inefficient.
But part of my problem with this article is it kind of sandbags the efficiency. We can get pretty high efficiency inverters and rectifiers. >90% is common and 95-98% is feasible (and not uncommon). Low voltage DC (like 12V) requires MUCH thicker cables for the same power, which means a lot more copper (and copper mining). Typical line voltage can be very lightweight.
With DC, nothing is really at the same voltage, so you need DC-DC converters all over anyway, so you're not saving anything (although not losing much, either!).
Another important thing that really drives some of the advantages is: breakers, relays, and (much less important) current measurements of existing cables. All these are feasible for both DC and AC, but cheaper and easier with AC. AC is self-extinguishing as it crosses zero 120 times a second. That means you can switch a circuit on or off when the applied voltage is very low, meaning you can use cheaper and lighter power electronics. Plus, at a given voltage, there's a safety advantage as arcs will more easily stop with AC.
I actually think it's funny to see this in a "low tech" blog. DC ubiquity is something really only practical for significant use (i.e. beyond automotive or RV) with modern 21st century power electronics.
This may be the case now, but it's just through historical lack of standardisation, resulting from AC having been the one true standard. It's not inherent to DC.
USB PD is attempting to address this issue. It is standardising voltages for DC-powered devices.
1. Any time you mix motors and electronics, motors produce brownouts and spikes which can cause directly connected electronics to malfunction. DC-DC converter mitigates that. LEDs are particularly prone to overload with just minute increase in voltage and dim/flicker with decrease.
Not inherent to DC but same thing happens with poorly designed appliances that emit RF which then interferes with everything connected to the circuit.
2. Voltages. You can't standardize electronics power supply to 12V because semiconductors are most efficient at lower voltage, which depends on particular technology.
-48V DC has been a thing with telco equipment for decades: it's what a landline telephone uses for signalling.
* https://www.servertech.com/blog/48vdc-power-and-the-backbone...
If we'd use anything DC, it would probably be that.
You can even design the system so that the batteries are in parallel with the power supply and load making the system uninterruptible by default.
A lesser known standard is 110V DC used in electrical substations and switchgear. They cover a lot of ground and cable runs can be hundreds of meters so the higher voltage allows longer distances with minimal line loss.
Power hogs like refrigerators, window-AC units would no doubt still run on 110/220.
But I already have mixed voltage AC in my home: otherwise 110V but purpose-placed 220V for electric stove/oven (in kitchen) and electric clothes dryer (in garage).
In my perfect future only those high-current outlets would remain — the rest of the house would have 12V plugs and lighting.
48V is also being looked at in the auto world as well, at least for "low voltage" stuff:
* https://www.automotiveworld.com/articles/48-volt-likely-to-b...
The IEEE's 802.3bu PoDL can handle sending 12, 24, and 48V, and automotive is one of its deployment spaces:†
* https://blog.siemon.com/standards/ieee-std-802-3bu-2016-powe...
* https://en.wikipedia.org/wiki/Power_over_Ethernet#Standards_...
† 10BASE-T1, 100BASE-T1, 2.5GBASE-T1, 5GBASE-T1, and 10GBASE-T1; .3cz task force is working on 25/50/100 Gb/s.
There are actually scant few things in modern houses that inherently want to run on 60Hz single phase AC - basically just fixed-speed induction motors [1]. And the amount of those are shrinking as more and more appliances get "inverter" technology for the energy savings.
The transformers on the poles are bona fide 60 Hz devices (and I'll take the electricity I can get). Industrial customers with large 3 phase induction motors want 60Hz AC. But for household use, DC would be straightforward.
I agree about the self-extinguishing arcs, although it seems like moving to solid state switches would solve much of that.
[0] power factor correction
[1] And actually, "single phase" induction motors don't even want to run off of a single phase. They all contain capacitors to create a second phase so the motor rotates.
DC-DC converters are cheaper than the classic transformers. There's a reason that you almost never see the classic "big chunk of iron" wall-warts anymore: not only are they inefficient, they're more expensive.
> Low voltage DC (like 12V) requires MUCH thicker cables for the same power, which means a lot more copper (and copper mining). Typical line voltage can be very lightweight.
Yes, a low voltage DC bus doesn't make much sense except for specific applications. Even in small spaces like recreational boats it's more common to use 24V or 48V these days. I think around 50V makes sense, as it's not very dangerous so there are fewer safety regulations. Look at PoE, for example. Unprotected runs of fairly thin cable transmitting up to 52V.
> With DC, nothing is really at the same voltage, so you need DC-DC converters all over anyway, so you're not saving anything (although not losing much, either!).
DC-DC buck converters are the simplest, cheapest, and most efficient category of power converters at the moment. (Of course a specific converter may be worse than a specific converter of a different category, but this is broadly true) Buck converters that support up to 50V are only marginally more expensive than lower-voltage ones. As an electronics engineer, I would be very happy if I could get away with only needing buck converters from now on; they're very easy.
If the DC source is required to be galvanically isolated and to have it's own transient suppression than the DC devices can get away with much less input protection than AC devices require. Could be a significant cost savings.
> Another important thing that really drives some of the advantages is: breakers, relays, and (much less important) current measurements of existing cables. [...]
Absolutely. I don't see high voltage/high power DC becoming popular in homes any time soon for that reason. There shouldn't be any difficulty with arcing at 50V though. (Yes, switch contacts still arc but it's not any more difficult than 120VAC) Also high power applications in houses tend to work just fine on AC (motors and restive heaters), though that may be a chicken-and-egg thing.
> One way to solve the problem of high power devices is simply not to use them -- this is the approach that's followed in sailboats, motorhomes and caravans
> Obviously, this strategy implies a change in our way of life. It would mean that electricity is used only for lighting, electronics and refrigeration, while non-electric alternatives are chosen for all other appliances. Not coincidentally, this is quite similar to how DC grids were operated in the late nineteenth century, when the only electric load was for lighting -- first arc lamps and later incandescent bulbs.
> Thus, no dishwasher, but doing the dishes by hand. No washing machine, but doing the laundry in a laundromat or with a manually operated machine. No tumble dryer, but a clothes line. No convenient and time-saving kitchen appliances like electric kettles, microwaves and coffee machines, but a traditional cooking stove operated by (bio)gas, a solar cooker, or a rocket stove. No vacuum cleaner, but a broom and a carpet-beater. No freezer, but fresh ingredients. No electric warm water boiler, but a solar boiler and a small wash at the sink if the sun doesn't shine. No electric car, but a bicycle.
Simple, instead of grocery shopping twice a month, ditch that wasteful freezer and walk to the farmers' market down the block before dinner each night.
Was it cloudy yesterday? Simple!, take a whore-bath¹ at the sink and be thankful your meetings are on Zoom these days :)
Ok, ok, those are caricatures of the final paragraphs, but that's what I hear when the word "simple" is abused that way.
[¹] Or, "PTA", which isn't much nicer. Any ideas on what to call this that's less vulgar, but still derisive?
From memory yes, it's partially about water usage, but dishwashers are in general just pretty good overall about efficiently using energy to maximize "food grime removed" per unit of resources fed in. Even if you're careful with water usage while hand washing, I think a decent dishwasher will beat you.
Another advantage is the dishwasher heats its own water, whereas with hand washing either you need to use a house-wide water heater or preheat water in a kettle or something, which will have its own energy wastes. This of course depends also on how your house's water is heated.
One page I found googling elaborates on these ideas, concluding that you could potentially be more efficient hand washing, but only with a lot of effort: https://www.treehugger.com/built-in-dishwashers-vs-hand-wash...
I once ran the dishwasher with the outlet hose in a bucket because the drain pump was on its way out. I expected to have to empty it several times, but at the end of the cycle there was less water in it than I would use to fill a washing-up bowl to do the dishes by hand (and the amount of dishes it cleaned might have required more than one bowl).
Their rational explanation is probably "how you can be so stupid for not knowing that common knowledge".
And well, even though I am indeed a treehugger, I also knew about the efficency of dishwashers before and also assumed it to be common knowledge, but I would never downvote someone because of a genuine question adding to the conversation.
As for water usage, think first of agriculture, then industry. Only after that do cities come into play. Cities are relatively small water consumers.
>As for water usage, think first of agriculture, then industry. Only after that do cities come into play. Cities are relatively small water consumers.
Where do those agricultural products get sold and eaten?
<insert screeching about "taxing muh negative externalities" here>
There are also some water pumping and treatment costs (more energy), but they can be ignored as insignificant.
I think part of it can also be (at least for me) upbringing. We always handwashed our dishes, and only used the dishwasher a couple times per year for big events.
Firstly, you can't wash with cold water because soap doesn't activate with cold water, hot water also kills bacteria and helps cut through grease.
Fats themselves are hydrophobic and without activated soap you wont get them off... enjoy your "filmy" dishes.
Second, humans expend a lot more energy than you think. The act of standing and using our arms releases varying amounts depending on physical fitness but averages somewhere in the 1kg/h ballpark. https://www.jstage.jst.go.jp/article/jjphysiol/50/2/50_2_199...
Dishwashers use about 1800 Watts and are commonly run for 30 minutes, the average co2 in the USA is 0.92lbs per kWh.
Meaning it's _basically_ the same.
Then there's the freshwater usage, which is the real kicker, because dishwashers use significantly less freshwater, and freshwater filtering is the largest environmental impact of washing dishes (not the direct co2 output).
Bunch of pseudoscience. I've never noticed any difference between washing with cold or not.
hot water also kills bacteria
Ultimately doesn't matter because they're all being washed away by the soap molecules anyway.
The act of standing and using our arms releases...
Lol, are you seriously trying to reason that what little energy you burn is more than a dishwasher?
Soap not activating when cold is not "pseudoscience", it's just a fact. Like grease doesn't become liquid unless heated. It's a similar principle.
> Ultimately doesn't matter because they're all being washed away by the soap molecules anyway.
If they bind, but, I'll give you this one.
> Lol, are you seriously trying to reason that what little energy you burn is more than a dishwasher?
Humans are pretty shitty at expending energy. This is one of the largest arguments against cycling long distances (though those arguments I don't agree with, but we're talking about total Co2 output here).
That may be true for most laundry detergents, which have to pull grime out of fabrics, but not simple dish soap. Just look at how well Dawn works to take oil off concrete, for example. Nobody's heating that up.
(essentially, the instructions are to remove the same things from the dishes you would remove if hand washing them in a sink with no disposal...)
I thought the same, and then it turns out that my garbage disposal was broken and obstructing the speedy removal of waste water from my washing machine. Fixed that and now my dishes come out clean.
Once you’ve removed the bones and massive solids, the modern dishwasher can do an astounding job on the rest. Put a little detergent in the prewash (or on a Bosch, just in the tub) and let the machine do the work. (I also grew up washing dishes before putting them in the dishwasher. It’s almost never needed now, but old habits die hard.)
Yes: if your dishwasher has the Energy Star rating then it must use ≤15L of water using the normal cycle per the EPA. This is half the volume of a small sink and a one-third or less of larger ones.
Most people run the water. In the US the average flow rate of a kitchen faucet is 8 L/min (2.2 gpm), so you can quickly use up 15L even just rinsing.
My faucet is very slow, about ~1gpm (I timed it once upon a time because I wanted to be able to put a number to how slow it is). When hand washing I run at maybe 1/4 or less of that. Everyone else in my household runs it at less.
Not many of us would reverse the changes that came with widespread home appliance availability and adoption on either a personal or societal level but every significant change comes at a cost to someone to whom you might well be sympathetic is something worth remembering when looking forward.
For sure it all depends on how you define "basic needs", and how do you divide "work time" from "leisure time".
https://en.wikipedia.org/wiki/Original_affluent_society#%22W...
At some moment I've heard of more recent studies about the myth of the increase in leisure time, but I don't manage to find any good reference now. In any case, I suspect Graeber had a point.
It takes a considerable amount of time.
And before anyone asks she raised five children like that and I'm not the one to try to convince someone who on top of that lived through WWII to change anything in their life.
Washing machine has done more to liberate women than all political efforts combined.
My grandma really spent a lot of time washing clothes, so i dont think this is a significant factor
Women typically would change a bit more often, and generally tried to have fresh panties every day (they would wash them separately from the main laundry). Men who considered themselves sophisticated would change _socks_ every day, but this was a minority. Nobody washed a shirt that they only wore once. Nobody washed pants until they had visible spots or smelled really bad.
And these were civilized XX century households, with access to hot and cold running water, gas, and electricity (but not always a bath or a shower, and rarely a washing machine).
Try wearing the same briefs and socks and shirt for a week, and you will show much you reduce your laundry load...
My grandma took a bath/shower once a week - she grew up when a bath meant bringing water in from outside by hand, heating it on a fire, and then you had to bring it back outside to dump it - I sometimes shower twice a day, and I still use less effort over a week to get clean than my grandma did back in the day.
I like bird bath for this.
I agree with your overall sentiment, I do also aknowledge that we (as a society) are very wasteful with resources. I would like to see some form of incentive for using less power and producing less waste.
My energy provider during the first lockdown actually paid us to use electricity because it was being produced at renerwable plants and would otherwise go unused. We set our washing machine to start during the period they would pay us and did our morning routine a few hours earlier. That small incentive was enough to change our behavior
My question is, if those people actually tried that by themself before suggesting it, or if they just picture the women doing it somewhere.
I mean in this specific instance I can imagine they tried. And I did too, while off grid. It gives you a special connection to your clothes. But suggesting this as a general way of life is a bit offworlds.
And I'm still only in early 20s, not some old dudes.
We debloating our computers all the time, so what's wrong with debloating our houses, and our life ?
https://solar.lowtechmagazine.com/2019/10/mist-showers-susta...
But the person I was answering to, was speaking more broadly of people proposing "awesome simple solutions". Who in my experience seldom lived their solutions.
Not particularly derisive, but I've always called it a “pits & bits” wash. I've heard it called a “got lucky rinse” too, presumably a variant on the whore-bath.
Sponge bath?
> 1. A quick sponge bath by hand, using a wet washcloth or a pre-moistened towelette, to extend the interval between showers or clean up after casual sexual intercourse.
This might be a positive though. Having moved to the UK years ago, the average trip to the supermarket is for around a few days of food, a week at most here. The supermarket is 7 minutes by foot or a 4 by car. It means we buy a lot more fresh items, and this is natural due to the limited amount of freezer space we have (60/40 fridge and no chest freezer in our house). It's arguably better than the experience I had back in Canada plus for the same quality of food, it's much cheaper over here.
So it isn't exactly the same as the olden days with wet markets and whatnot, but it's much closer to it (they even have manned meat, fish and deli counters at our local).
Middle class Victorians, in England at least, had things delivered. I imagine that quite a lot of cosplay characters are middle class.
In fact food delivered to homes of all types was a normal feature of life in England when I was a child in the 50s and 60s. Milk, eggs, etc., every weekday morning delivered directly to the door before breakfast, grocery van came to the street once a week, bread van twice, another van came a bit less often selling lemonade and other drinks.
Of course these services were not universally available, we were lucky to live in a moderately affluent town with a prosperous working class.
We didn't have a freezer until 1966 and I'm not sure that we suffered from the lack. But once everyone had both a freezer and a car those services became unprofitable and eventually disappeared.
I think that's key. The wealthy live well enough in pretty much any society. It is the poor who often have the greatest to gain (and lose, when mis-applied) from technological innovations and from having them become widespread.
Making something both simple and easy is a highly sought art.
I think the same applied for the majority of population in underdeveloped / developing countries.
Meanwhile the thing that has actually gotten people out of their cars is the ebike. It turns out it’s much more effective to produce a more convenient and comfortable solution for people rather than just demand that they go back a century or two just because.
0 - It’s also telling that such advocates never seem to actually say who should be stuck doing all the labor that machines like washing machines now do for us. Washing clothes and dishes by hand is hard labor, and someone is going to have to give up their career or free time to do it if we’re going to ban these machines. No extra credit if you figure out who will get stuck with the task…
They are probably not actually closet misogynists or anything like that, they probably just haven’t thought that far ahead.
I agree, this is more probable than the closet misogyny theory. But it's still not exactly a ringing endorsement to say "whoops, we didn't think about who would have to do all that labor once we took away all those labor saving devices!" It's not like this is some hard to predict third order effect, after all.
Overall, the whole argument they're making is kind of silly. Washing clothes by hand sucks, people rushed to buy machines to replace this labor for a damned good reason. If someone's plan for the future involves persuading people to go back to doing labor the vast majority of people don't want to do, then they should prepared for a lot of failure. Given the continued sales of brand new washing machines at my local home improvement store, I would argue that they have failed thus far.
(Ironically, there is probably a good lower-tech argument in making labor saving devices simpler and more reliable. The short lifespan of our appliances is both deeply unpopular and environmentally problematic, and doing anything to make them more repairable would both be good for the environment and incredibly popular.)
Back to their original argument, there's a reason why I hold up the e-bike as an unqualified success that the authors here are incorrectly ignoring. Cycling enthusiasts--myself included--have argued for decades that biking is better and people should switch over to using bikes for more trips. Repeated appeals to the environment, the wallet, and ones health haven't really moved the needle much in this area. Yet it's the high-tech (gasp!) e-bike that appears to be finally getting commuters out of cars and into the saddle. It turns out that while moralizing is fun, actual change involves making compromises towards the convenience and comfort of your average person.
Yeah lol I always find this the funniest part of Low Tech Magazine. While they're always breathlessly moralizing, they rarely think through (or at least write about) the social ramifications of the changes they propose. They do have some interesting ideas though, such as the use of thermal cookers, and burning biomass in a rocket stove may not be the worst idea if you live in an area with a temperate climate and a dirty grid. Perhaps more practical though would be just incentivizing ordering at a restaurant, since a restaurant will be more energy efficient at preparing food than an individual will.
Really? Most restaurants have a grill and deep fry vats hot 100% of the time even when nobody is there.
(Cooking actually takes quite a bit of energy unfortunately and is probably one of the hardest human activities to make carbon neutral. Luckily there's a lot of low-hanging fruit to tackle first before the question of cooking efficiency comes up.)
You're better off just giving poor people here free electricity, which a lot of places do.
This is not my experience. People just put their ebike on a rack and drive it somewhere to ride it for fun.
> This paper reports on a review of the European literature about the impacts of having an electrically-assisted bike available to use, together with results from a trial in the UK city of Brighton, where 80 employees were loaned an electrically-assisted bike for a 6–8 week period. In the Brighton trial, three-quarters of those who were loaned an e-bike used them at least once a week. Across the sample as a whole, average usage was in the order of 15–20 miles per week, and was accompanied by an overall reduction in car mileage of 20%. At the end of the trial, 38% participants expected to cycle more in the future, and at least 70% said that they would like to have an e-bike available for use in the future, and would cycle more if this was the case. This is consistent with the results of the European literature which shows that when e-bikes are made available, they get used; that a proportion of e-bike trips typically substitutes for car use; and that many people who take part in trials become interested in future e-bike use, or cycling more generally.
The real key is that e-bike users will ride further, which expands the range of trips that the owners will consider via bike.
> John MacArthur was the lead author of the NITC report, and told the Electric Bike Report, “While many of the rides we surveyed were for recreation, on average we found that the average trip on an e-bike was nine miles,” adding, “historically on traditional bicycles we see a trip of more than five miles being a barrier.”
> Additionally, the electric assist of the e-bike helps to generate more trips, longer trips and different types of bicycle trips. These findings are represented by the high value attributed to being able to avoid or tackle hills easier, ride farther and faster with less effort, and being able to carry more cargo or children when needed.
Assuming that the 9 mile limit holds, that is a pretty long distance in most cities. I live in the suburban edge of a small city, and downtown is only 6.4 miles away for me. Even when I lived in LA, 9 miles was more than enough for 80% of my trips or so.
Tech products footprint is either during consumption (most of the devices requiring heat or cold) or during production (the other devices like smartphones).
Obviously this rule is a trend and countries with low carbon electricity are exceptions.
While most people are OK for lasting a smartphone a bit longer, the same logic would imply to reduce the heat/cold consumption.
So yeah in this sense, a freezer is a luxe we can't afford.
The 380-volt DC sounded nice, so long as DC to DC is more efficient than AC to DC, but I have no idea if that’s true.
Consumer devices vary, but it’s a safe bet that modern cool-to-the-touch GaN power adapters are far more efficient than those old black bricks from the 1990s.
Saving a few % just isn’t worth all the incompatibility and inconvenience of rewiring your entire house for.
380-volt DC sounds dangerous!
(Though I do think that Americans uses clothes dryers _much_ more than they should. Most other G20 countries do not. In our household we hang dry any load of laundry that doesn't involve our heavy blankets, and that usually ends up extending the life of our laundry as well, while taking just a few additional minutes. (See, "often impractical" not "always impractical").)
And a kettle is so low impact anyway. It uses a high amount of power for a very short time and spends almost all of its life turned off. The faster you heat the water the less waste there is as it cools during the heat process.
It is not obvious at all and requires calculations.
When you use electric kettle you use energy which was obtained mostly from coal and gas (60% of it in the US) and efficiency of the conversion is less than about 40% on average (limited by efficiency of a steam turbine). Then about 8% of this power is lost during transportation/distribution.
When gas is burned in a gas stove 100% of its energy converted to heat. The only problem - some fraction of this energy heats a room instead of a kettle. But it is not bad if you had to heat room anyway (where I live 8-10 months out of 12 I'd prefer indoor temperature to be higher then it is).
I expect this loss to be smaller than 50%, but I've not found credible numbers for this.
Efficiency for an oven may be low because it measurably heats a kitchen, but ovens is another story.
Time-wise I'd think it's quite comparable, in my experience.
This of course depends on sizes and quality of kettle/pot. Wide pot, with large surface area and a quality heatspreader on the bottom will get the water boiling more quickly. Also covering a pot is a must.
Sometimes when I'm in a hurry I split the water between a pot and el. kettle, to get a boiling 2l of water faster, and there's no huge difference in time to boil.
But somehow gas doesn't have to be accounted for and just comes for free.
Heating water in a domestic setting on a gas stove is incredibly inefficient and you don't even need a calculator to know why - put your hand adjacent to the stove and feel the heat being lost. This is not a small fraction, it is significant unless you run the stove really low and spread that heat over a large area.
Now put your hand and any point outside an electric kettle and see how much heat you can feel. Almost none.
This isn't really as complicated as you're making it out to be.
Gas stove is nominally competitive, but as soon as you start adding renewables to the power mix or considering indoor air quality & venting, electric seems like the path forward to me.
Besides, why you need to boil water for tea or coffee? These days tap water is safe for drink, and if you want to add extra flavor, you can chew your tea leaves or coffee beans... ;-)
Edit : Don't downvote. I am just the messenger. I just wanted to spare the googling to someone
I've had one of [1] these for years and it hasn't let me down yet.
[1]: https://www.ikea.com/us/en/p/frost-drying-rack-indoor-outdoo...
In those places it is typically forbidden to hang clothes outside their specific places because it is not aesthetically pleasing.
There are many reasons for this. Some of them are cultural, and other are legal.
Many Americans simply don't remember drying clothes on a clothes hanger outside, and aren't used to hanging them indoors as many Europeans do. And to be fair, indoor clothing hanging is time consuming in comparison to "transfer clothes from one machine to another".
But what many don't know is that it's often banned in many home owners' associations, and banned in many apartment leases, meaning that hanging your clothes outside is actually a luxury that many simply can't partake in.
That seems extremely inappropariate. Are there no restrictions on what they can ban, like can they ban children or cooking curries?
I just refuse to live in one which solves it for me.
The reason that both HOAs and landlords disallow outdoor clothes drying is that it's seen as an eyesore. People associate clotheslines full of clothes with images of testaments in NYC in the 1920s and representing overpopulation and or immigration.
Landlords in particular don't want people hanging things from the apartments- even objects like small satellite dishes are often not allowed.
What many don't know is that in the US, many of these rules are simply null and void:
https://www.sightline.org/2012/02/21/clothesline-bans-void-i...
The challenge is that this requires a great deal of work on the part of the homeowner, and in doing so they would be entering into a conflict with the HOA. They would win in a court, but they would need to put up the money to fight in court. Even if/when they won, the HOA would make life unpleasant for them and likely retaliate in some other way.
If you want governments to do whatever needs to be done to limit climate change, you also need to be willing to "pay the price" in the form of reduced material comfort.
Besides, there are quite a few people (a big chunk of the world population actually) living today without dish washers, without microwaves and without coffee machines.
Which is why nothing significant has been done, nor will it.
Instead of driving to the gym and bike 1h you may commute by bike (with enough safe paths its pretty nice, not perfect but pretty nice and health improvements come very rapidly as a bonus).
I have no idea where they got that picture either. Edison's Pearl St. station did not work that way, and that was the first power station. The generator shown is Edison's famous "long-waisted Mary Ann". But Edison never built a one generator per bulb power station. He was able to calculate ROI [1]. This is probably some conceptual drawing of what would have been necessary had the "subdivision of the electric light" (a hot issue around 1889)[2] had not been accomplished.
"In other words, a DC electrical system could make a solar PV system more energy efficient." Not clear that it matters much in terms of raw conversion efficiency. Solar inverters are now up around 96-98% efficiency. If you're going to have batteries, you need something that handles battery charging, discharging, and some constant output, and while you can get all that stuff for 12VDC or 24VDC, it's not any more efficient than outputting 120VAC.
The real argument they're making is to save power by using small boat or RV sized appliances. They're available, efficient, undersized, and about 3x as expensive as line-powered units.[3]
[1] https://www.hup.harvard.edu/catalog.php?isbn=9780674423640
The best inverters convert solar DC to household AC at 97.6 % efficiency. [1]
Adding more solar is a question of adding another panel.
The inversion loss is a small price to pay for safe power. [2]
DC is probably not coming back as a way to wire houses and buildings.
[1] https://www4.enphase.com/sites/default/files/downloads/suppo...
[2] https://www.businessinsider.com/tesla-solar-panel-fires-beco...
It's more convenient to simply plug into a low voltage DC current wiring with a LED fixture than to install a AC-DC converter.
It's certainly something I've entertained doing for my own place.
otherwise you chain a bunch of panels together in series and track the max power point there. This means that you don't quite optimise for each panel
The only reason PoE makes sense at all is because it uses 48V, but due to the flimsy cables the losses are still 15-20%. Not great.
802.3bt Type 4 allows for sending 100W down Cat 6A cables, but only 71W is available at the other end. That's highly inefficient.
* https://en.wikipedia.org/wiki/Power_over_Ethernet#Standard_i...
Power over Ethernet would be a pretty cool way of doing it if it was practical...that way you get the data to control the lights as well as the power to run them.
Does anything like this exist in a way that won't get me fired by the builder for even mentioning it?
Just be aware many jurisdictions have minimum lighting requirements that your low voltage lights may not meet, but you could always just leave those lights off
I’m also looking at whole house USB-PD, https://voltekinc.com/dc-power-advantage/
I had a battery fridge in a caravan (trailer) and it was very small and pretty rubbish, certainly not suitable for home. However, for a short stay, it could keep some basic foods cool enough to be safe.
As others have said, although it is fine on paper, as soon as you start talking about significant power, you are talking lots of amps, which means more risk of overheating and fire, potentially significantly larger (and therefore expensive) cabling and all of the switchgear that can support a few amps AC will not support the same current at DC so all your switchers are larger/electronic. There is also an issue of RFI which could be significant if you are switching high current DC loads.
[1] https://www.boatus.com/expert-advice/expert-advice-archive/2...
V=RI and W=VI
WireLossInWatt = RI²
at 120V you need 1A so you lose 1²A² × 7ohms = 7W
at 12V you need 10A so you lose 10²A² × 7ohms = 700W
Heating all of your house wiring to 90C is a) dangerous, and b) expensive. Even if you're doing less than 20A, decreasing the voltage by a factor of 5 still increases energy loss in cabling by a factor of 25.
Thermostats and doorbells are low-voltage AC. The transformer is standard. If you can find 24-volt AC lights, an open-minded electrician should be able to figure it out.
Related: My old house built in the 1960s had an intercom system that was ripped out by a previous owner. I found a warm transformer attached to a bare bulb light socket in the basement with nothing else running from it. I happily removed it.
We'll see how things go, but on paper at least this makes a lot of sense if you don't try to run things at 12V (why do people still try?). 48V is a voltage that is still safe, but cuts your amperage and losses to reasonable numbers.
While designing my own LED drivers, I found that most LED panels will internally work with a Vf of 36V, which you can efficiently get from your 48V installation.
Even in an AC-powered home, if you have lots of LED lighting in one place, it makes sense to use a single high-power converter to get 48V DC and then drive LEDs off that. Small AC to DC converters are inefficient.
At least here Europe/Italy there are bus-based systems from various manufacturers.
Example:
https://professionisti.bticino.it/catalogo-prodotti/myhome-i...
(not too bad in google translate)
Basically normal wires (here 220-250 V AC) Live+Neutral+Ground and a signal (bus) 2 wire cable arrive to each and every electrical box/light point.
Then you can install into the box any kind of device, switches, outlets, etc., and you can configure them.
The bus wires (the protocol is called SCS):
https://en.wikipedia.org/wiki/Bus_SCS
allows also (low power) 27 V DC trasmission.
The protocol and compliant devices were first introduced between 1996 and 2000 and are by now well tested and reliable:
https://en.wikipedia.org/wiki/OpenWebNet
Legrand also uses the same protocol:
https://developer.legrand.com/documentation/open-web-net-for...
> AC won, mainly because of its higher efficiency when transported over long distances.
AC is not actually more efficient at long distance transmission, it’s less efficient due to the skin effect. AC is just easier to convert.
1) The line connects two synchronized grids. It's much easier to convert electricity to DC and back to AC on receiving end, than to synchronize grids or to implement something similar with AC.
2) The line runs under sea water for a significant distance. Due to the conductivity losses DC is more efficient in such contexts that AC.
And surprise, a lot of DC-DC topologies require a transformer too.
Transformers still soundly beat solid state conversion on cost, and efficiency at above the wall outlet voltages.
You can't run away from that entirely. If you were to give a free hand to a good EE to redesign the electric grid from scratch, I doubt the result will differ much from what the world has already.
Transformers still have their place but they're still basically big dumb (uncontrollable) chunks of copper and iron.
This is incredibly important to note. Buck-boost converters enjoy efficiencies beyond 90% in even the most pedestrian implementations. This makes their efficiency directly competitive with transformer-based designs (95-99%).
So everyone saying how it's fantasy to expect peoples behaviour to change, just remember if you haven't tried it you are likely highly over estimating how much effort it is, and not aware of many of the unexpected advantages.
As much as I personally hate them, would it not be better to install 120% of solar cells required to match the load upfront. Given the energy is free at generation write off this small inefficiency as being built into the system. It's not like the sun will come after you for capturing more than your fair share.
This feels like a problem for 2100 imo once we've moved to much lower carbon supplies.
There is an argument for using DC over AC but avoiding conversion losses is not a compelling part of it.
Is this actually true though? I just bought a reel of 30 high power mosfets from digikey for ~$450. Each of these bad boys can rock ~1kW continuous switched output/input. Magnetics for the HV boost section of a 30KW DC-DC converter circuit are a mild additional cost.
Compare this to how much money you would have to spend for a more traditional copper & iron monstrosity of similar rating (well over $1000).
Weight is also a huge factor when you start talking about megawatts.
This is absolutely untrue. You may be safer from shocks, but it's a much _worse_ fire hazard. The currents need to be higher at lower voltages. Higher voltages need less current for the same power, decreasing the fire risk.
(Water heating dominates the energy used in those, the mechanical sloshing around takes trivial power compared to it).
There's not many people living in these areas though like the sibling comment points out.
What would work best for this?
Check out options like the Yeti 6000x. You can buy a transfer switch to go with it for powering a few circuits. The 6kwh battery could run things like your fridge and computers for at least a day.
As I type this my house is running from a backup generator. The power company has their repair crew in route to whatever the issue is. I'm looking into how/if I can add solar to the system as well.
They have an automatic transfer switch built in for anti-islanding (your mains entry goes through it), so it disconnects you from the grid if it goes down but your local side still operates. I think it can also have two AC outputs, one for loads powered by either grid or battery, and one that is only on when the grid is present (if you have a grid). You can use any type of battery so you’re not locked in (LiFePO4 are some of the best at the moment).
I have an AC solar inverter and 5kW of panels on my roof, which would be about enough, but I’m going to add another four panels (bit less than 1.5kW) that are DC-coupled through an MPPT charter (Victron SmartSolar MPPT) to solve the bootstrap problem for prolonged outages (which are very rare here, but still). Not sure if that’s the normal term, but I mean where the batteries run out, so without the grid to put some charge in them, the inverter/charger can’t produce an AC waveform for the PV inverter to lock to, so the PV inverter won’t switch on. Having some solar on the DC charger lets that work.
I camp a bit and spend more than enough time dealing with 12V lighting, recharging drone batteries from car/aux batteries, etc. Always end up wondering how much of my house actually needs AC, where in the house that occurs (fridge, ducted heating/cooling unit?) and what could get by without it. More and more of my power tools are battery based too. Would AC to the kitchen and garage be enough?
I still do think AC is still advantageous in a lot of ways for power grids though, just not on that particular point.
We have this article that discusses changing home design in order to limit cabling losses (crazy) and not using "high power" appliances that we associate with modern life... and another article discussing Livermore labs achieving net positive fusion, a milestone that seemingly hints we're on the cusp of a carbon free renaissance of power generation.
Schrodinger comes to mind
I wonder what would happen if we redesigned the grid today? Would it be AC or DC? If AC, would it be a higher frequency? (Smaller transformers) Is modern DC-DC voltage conversation easier than AC-DC? What voltages would we use?
The biggest factor is AC is a lot safer. Switches and branch protection devices (fuses) work best on AC. For low voltage DC we can make them work, but for high voltages we don't - instead we put in the protection on an AC side, then convert that to DC.
Also you can't exactly have a USB-C PD power strip of 10+ plugs without it costing a fortune because of all the negotiation needed per-port. Now they're onto some GaN bullshit just to make the PD adapters smaller.
The standards are a shitshow, there are incredible number of non-compliant USB-C cables.
802.3at PoE is slightly better, you can get 24+ ports for a couple hundred bucks, most cables advertised to meet PoE specs do in fact meet them.
But really the best would be straight up 48V on 2 rails and a bunch of plugs. No negotiation, no bullshit, no GaN, just 2 wires. Equipment, cabling, power strips would be dirt cheap. Individual devices can have very compact, efficient buck converters to get the voltage they actually need.
Well, I don't. The 100W PD plugs I own cost typically $60 or more. Put yours on Amazon if they can do 100W and I'll happily buy them.
And if it doesn't support full 100W it's a PITA because that's more thing the user has to think about.
Isn’t that what the “old” PoE was before 802.3at/f? Just plain non negotiated 48V over a cable with RJ45 plugs?
I don't necessarily think it's wise to do 5 amps over USB-C, but it is a standardized DC outlet. Personally, USB-A is still a more useful power outlet, but nobody is insane enough to shove 240W over it.
You can even get Anderson Powerpole wall sockets: https://powerwerx.com/powerpole-connector-outlet-box-coverpl...
I lived on a boat for a while and I used almost exclusively DC - it worked out pretty well. I used hard wiring and cigarette lighter plugs and that worked fine. The problem with wiring a house is that DC losses start to be huge over decent distances (100+ feet starts to be really tough.) I feel like that's one reason why DC is only really standard on cars/boats/motorhomes.
Transitioning to this sort of system would actually be simple, you'd just have to make DC power supply boxes that plug into a regular 110 or 220 AC outlet -- sort of like multi-port USB power adapters, but designed for more power and probably higher voltages: perhaps +/- 12 volts and ground.
A more sophisticated system might be that the DC power supply can supply a different voltage/current to each port, and it negotiates with the device to supply to current power. (I think this is basically how DC fast chargers for EVs work -- the car tells the charger what it can accept, and the charger supplies that the car.)
Maybe "dumb" devices that don't know how to do the handshake just default to 5v DC or something.
It can. Cree's JR5050 24‐V LEDs run on 24V. They have 30V and 36V versions as well.
You might have several LEDs in series and they might very well have a voltage drop across all of them of 24V or even much higher when maintaining an operational amount of current.
I'm using my ipad while plugged into a 120V USB charger, and the charger isn't even warm.
120VAC plugs e.g. standard IEC computer power plugs can be hit with bricks and rammed into furniture while they are plugged in and they won't get damaged. All forces of impact get transferred to the chassis, not the PCB. That's good design.
I break about a USB-C cable a week because they just aren't designed for the ruggedness that consumer use cases demand, which are typically higher than military.
I don’t know… that seems excessive, even people I’ve known to handle all of their stuff like it’s free have managed to go mostly through 1-2 cables a year.
Reality is if you go out at all you've probably figured out that phones only come with 1/2 day of real battery life (because they do the damn factory tests with full bars of reception, not real world 1-bar reception), and you needed to charge a phone stuffed in one pocket with a battery in the other pocket, connected by a USB-C cable, and bike, ski, run, hike, climb rocks, whatever it is. Or had to use a laptop in a bus where an asshole plops their heavy ass next to you and you accidentally ram your laptop and USB-C connector into the side wall. Or because pants are designed with only 2 instead of 3 front pockets, one is occupied by wallet and another by a big fat keyring, you have no cohice but to put phone in your back pocket and battery in the other back pocket with a wire between the two and sit on it while plugged in. Or had to stuff your charging phone and battery into a jacket, crumple the whole thing and stuff it into a TSA bin. Or children bite your cables. Or dogs. Or the phone was in the car with a suction cup holder and fell off ramming its USB-C cable into some hard part of the car floor. THIS is daily consumer life.
If one hasn't experienced the above, they probably sit in an office all day and work out in a gym and are oblivious to the realities of active lifestyles and how they are highly incompatible with physically weak connectors like USB-C.
They should look at Zojirushi water boiler magnetic plugs. You can yank them all you want and they don't deform. They're designed to be yanked off accidentally by children without bringing down a pot of boiling water from the counter. They just need to miniaturize the concept.
Maybe Apple's battery life is That Much Better, but I've been led to believe it no longer is.
For chewed cables I agree. But again to actually make a resilient cable it would need to be thicker than most modern phones, the connector is not the weak point here.
Also you could easily miniaturize an IEC power cable, it's the material and design that makes it good, not the size. Rubbery plastic and all forces transferred to housing not the PCB.
12V would need some fat wiring to avoid incurring voltage drops for normal amounts of loads.
48V is nice because you can use much thinner wiring, and it's about the highest "safe" voltage to accidentally touch with normal dry skin.
Sorry to be so pessimistic on my first post, but I don't see this happening for a long, long time.