Slow Electricity: The Return of DC Power? (2016) • Hacker News Board

Re: Slow Electricity: The Return of DC Power? (2016)

#131

Post by bob1029 » Wed, Aug 18, 2021, 10:44 AM UTC

skybrian wrote: post #62

I'm not sure I care whether it's AC or DC, but it might be nice to have some parallel off-the-grid wiring that comes from a solar-charged battery and will run during a power outage. What would work best for this?

I've been looking at stuff in this space and there are a few options on the market (most out of stock at the moment).

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.

Re: Slow Electricity: The Return of DC Power? (2016)

#132

Post by bob1029 » Wed, Aug 18, 2021, 10:49 AM UTC

dreamcompiler wrote: post #65

baybal2 wrote: post #9

Almost every type of DC-DC conversion requires some intermediate AC conversion anyway. 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…

But that intermediate AC is square (not sinusoidal) which means the transistors spend almost no time in the linear range, which means they generate very little heat. And the frequency is much higher than 60Hz too. It's a very different kind of AC, with much more controllable and more efficient electronics. Transformers still have their place but they're still basically big dumb (uncontrollable) chunks of copper and i…

> which means they generate very little heat

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%).

Re: Slow Electricity: The Return of DC Power? (2016)

#133

Post by throw0101a » Wed, Aug 18, 2021, 10:52 AM UTC

nielsbot wrote: post #93

tootie wrote: post #66

Earlier quoted context omitted.

It's frequently much more energy intensive too. Cars are a lot more efficient than horses and dishwashers are more efficient than hand washing.

Can you explain how dish washers are more efficient than hand washing? Is it about water use? What if you don’t run the water while you soap your dishes and only rinse them in a rinse tub?

> Is it about water use? What if you don’t run the water while you soap your dishes and only rinse them in a rinse tub?

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.

Re: Slow Electricity: The Return of DC Power? (2016)

#134

Post by dijit » Wed, Aug 18, 2021, 10:53 AM UTC

JohnWhigham wrote: post #124

nielsbot wrote: post #93

Earlier quoted context omitted.

Can you explain how dish washers are more efficient than hand washing? Is it about water use? What if you don’t run the water while you soap your dishes and only rinse them in a rinse tub?

If you're careful about water usage and use cold water, you'll always beat a dishwasher. Another thing people often forget about dishwashers: you're supposed to pre-scrub the hard shit off the dishes. Well, you just did half the mechanical work yourself, why not finish it? 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…

I grew up handwashing too but I disagree with your assertion.

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).

Re: Slow Electricity: The Return of DC Power? (2016)

#135

Post by starfallg » Wed, Aug 18, 2021, 10:55 AM UTC

function_seven wrote: post #44

IlliOnato wrote: post #37

I read the whole article with sympathetic interest, until the conclusion: > 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…

I get unreasonably angry when Victorian cosplayers think they've found the solution to our wasteful modern life. Simply eschew modern conveniences and spend hours each week beating your clothes against a rock! 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…

> 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.

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).

Re: Slow Electricity: The Return of DC Power? (2016)

#136

Post by c_o_n_v_e_x » Wed, Aug 18, 2021, 10:56 AM UTC

The contrast of articles currently on the HN front page is amusing.

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

Re: Slow Electricity: The Return of DC Power? (2016)

#137

Post by throw0101a » Wed, Aug 18, 2021, 11:01 AM UTC

Robotbeat wrote: post #28

So, I used to be "team DC" as well, but after learning up a bit, I realized there are still a lot of advantages to AC in the 21st Century. 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 cheap…

> 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.

-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.

Re: Slow Electricity: The Return of DC Power? (2016)

#138

Post by bob1029 » Wed, Aug 18, 2021, 11:02 AM UTC

wyager wrote: post #5

This doesn’t make any sense. Power transmission with DC still requires high voltage for any reasonable efficiency. Then you have to convert it back down to a residential voltage (still probably >100V for conductor material efficiency) and then devices have to convert that down to low voltage. So you’re not actually saving any conversion steps. On top of that, you have to use DC-DC power electronics, which are much mo…

> On top of that, you have to use DC-DC power electronics, which are much more expensive than transformers etc. at high power levels.

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.

Re: Slow Electricity: The Return of DC Power? (2016)

#139

Post by throw0101a » Wed, Aug 18, 2021, 11:04 AM UTC

klondike_ wrote: post #85

DC wiring is already standard in many office buildings in the form of power over Ethernet (PoE). It powers access points, lighting, and infrastructure, and high power variants can do 100W+. Since it's under 50V, the IT guy can install it without a qualified electrician. High power loads like motors and heaters will continue to require AC but I see no reason why small loads can't use PoE. I would love to see it take o…

> It powers access points, lighting, and infrastructure, and high power variants can do 100W+.

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...

Re: Slow Electricity: The Return of DC Power? (2016)

#140

Post by rob_c » Wed, Aug 18, 2021, 11:08 AM UTC

Well yes, but frankly given the small losses due to modern conversion systems being so efficient I think we're worrying about catching that last small%age if energy losses.

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.