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Comment by quaintdev | Hacker News Reader

> Although that sounds like a very light load, if you run it for 24 hours, it's equivalent to using 84 Watts continuously for one hour.

Its called 84 watt-hours and this is energy consumed in 24 hrs. 3.5 watts is energy consumption rate and is called as power(joules/sec). 84 Wh is not actually lot.

I made a calculator for raspberry pi energy consumption

https://tinyurl.com/nwu6sn4s

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But 84Wh is still enough energy to drive a modern battery-electric vehicle around 500 meters. Kind of puts things into perspective.

I find these numbers really fascinating because it shows how efficient battery-electric vehicles are, especially when you think about things like incandescent bulbs, which easily will run at 50W just to light up a small room.

Don't get me started on cars that display usage in kWh/h per 100km. Yes, you read that right.

Conversely, it shows how sparse kinetic energy is, and that's a good explanation to tell people that would see storage issues solved by damming every stream.

> Don't get me started on cars that display usage in kWh/h per 100km. Yes, you read that right.

ICEs use litres per 100km which I think is where this comes from. And I hate it. miles-per-gallon is much easier to understand I think. I wish we could have split the difference in the EU and just had km-per-litre. I'd rather know how far a tank will get me than how much fuel I'll use to travel exactly 100km

The biggest problem with MPG is its inverse nature makes it a bad unit to use to compare cars.

A 20 MPG car is not twice as efficient as a 10 MPG car.

http://www.mpgillusion.com/p/what-is-mpg-illusion.html

L/100km has the length and volume units reversed, which allows comparisons.

A 20MPG (11.76 l/100km) car is twice as efficient as a 10MPG (23.52 l/100km) car though?

The issue is going from 30 to 20MPG is not the same change as going from 20 to 10MPG, where as the difference between 15 and 10, and 10 and 5 l/100km is the same absolute change.

I might be hung up on the word "illusion". The only difference between miles per gallon and gallons per mile is that the former increases and the latter decreases with efficiency. They are still saying the exact same thing.

"They are still saying the exact same thing."

They are but now I prefer .05 GPM to 20 MPG.

I do as well.

Everyone in the US it seems to like bigger numbers. Just look at the argument some people use to why some people prefer Fahrenheit over Celsius.

... is what I would say, but Tesla seems to be the only one using the sensible Wh/m or Wh/km. All the German ones use the nonsensical kWh/h per 100km.

In fairness, 0 being cold and 100 being hot is pretty intuitive. I would be curious to know how people raised on Celsius feel about Fahrenheit after having lived with it long-term.

> A 20 MPG car is not twice as efficient as a 10 MPG car.

Why not?

The page you linked doesn't talk about "twice as efficient", it talks about an absolute number of gallons saved per distance travelled.

Also, assuming there was no typo, vegardx's point was that "kWh/h per 100km" is invalid. "kWh/h" is the same as "kW", and "kW per 100km" (power per distance) is not describing vehicle efficiency, it's non-sensible. "kWh per 100km" (energy per distance) is.

> And I hate it. miles-per-gallon is much easier to understand I think.

It's just something you're used to.

> I'd rather know how far a tank will get me than how much fuel I'll use to travel exactly 100km

Well, there you go, you're comparing apples to oranges. Unless your tank is exactly one gallon, you've made a conversion when you compute how far a tank will get you. Well, we do the same thing here. I want to travel 500 km? I'll multiply my L/100km by 5 and get how much gas I need. This tells me how many times I'll have to refuel, etc.

true I guess. maybe its just something I'm used to. distance-per-fuel-amount just seems intuitively more useful to me than fuel-amount-per-distance, even if they're two sides to the same coin

I think it'd be incredibly valuable if all vehicles could pick one common unit. Personally I think that need dominates all others. And it suggests to me MPGe is the way to go in the states, to the extend that it makes me want EV "fuel" gauges to be "gallon-equivalents" (33.7kWh). Yes your car only has 2~3 gallons of gas capacity, that's because it's badass & efficient. This is of course (imo: alas) never going to happen.

I think the actual units used in EU are, for example, 19kWh/100km (from the BMW iX which does very well for it's size-class). You seem to have an extra /h in your figure. It has the advantage of being a understandable number, relatively well sized in scope. People can think of 100km as a reasonable length in their head that connects distant points. We tend to think in terms of kWh, which is what electricity is typically metered in world wide. It feels like a poor use of a metric system that shouldn't have a bunch of weird prefixes (there's a k above & below the divisor? are you kidding me? 100km? c'mon!!) but the units are people-sized, are things we can work with in our head. And the final number, 19, as in 19 kWh/100km, is reasonably scoped, going up if you're more efficient, going down if you're less efficient.

It's inverse from MPG, putting the range-unit is on the bottom & the energy-unit is on the top. Some people love it: they claim that the difference between like 12 & 24 MPG is hard to appreciate the savings off of, whereas the difference between 24 & 48 MPG looks big but is actually only half as much fuel saved. Personally, I don't really chalk this up as a win, but some people think it's important & I can recognize that potentially it might be helpful.

I still think we should just use 33.7kWh / 1 gallon-of-gas equivalent as the common unit of energy & give everyone a common frame of reference.

Some German cars display current usage as kWh/h, which is just a stupid way of saying kW. If you're using 3kW for one hour, that means you're using 3kWh ... per hour. It just doesn't make any sense to write it like that. They correctly display the average usage over a given distance as kWh/100km.

There's a lot of fuzz in the EV space since everyone is advertising WLTP (previously NADC) numbers as an indicator for range. It uses a standardized test, so this means the numbers should be comparable. But they're not. Some BEVs are much more efficient in cold weather than others, due to things like heat pumps or just better engineering, like aerodynamics. This isn't well reflected in WLTP, and people get disappointed.

You can easily argue for both kWh or Wh. I've always been a proponent of using the smallest units possible, since then everything is just addition, regardless of what you want. With everything being in units of 10, it's fairly easy to do, either way. You could argue that the logical conclusion would be to use Ws/m, which is just ... Joules/m, another SI unit. But then we're using units that most people have no fundamental understanding of.

It would be worthy sacrifice to get rid of miles.

Now let's talk about wheel size. mm/percentage/inches all in one unit...

84 Wh is enough to propel a human on a bicycle about 20 km in about one hour. From this perspective electric cars are ludicrously inefficient ways to get around. Maybe in the future we'll view car dependency as similarly wasteful to using incandescent bulbs everywhere.

Bicycles are something like 99% efficient though so anything will look ludicrously inefficient compared to them.

Have you cycled in the rain or snow? If yes how many times?

Periodically I see colleagues trying to come at work by bicycle. The longest lasting record is one and half year. All the others didn't last after the summer.

Fwiw it would take me 1h of walking to go to work or about 1h20 if I take a couple buses. Or I can take the car and be done in less than 10 minutes.

This is less about the winter and more about the lack of appropriate biking infrastructure. [0]

[0]: Why Canadians Can't Bike in the Winter, but Finnish people can: https://www.youtube.com/watch?v=Uhx-26GfCBU

I think it's mostly about culture and infrastructure. When we lived in Southern Germany, I cycled to work literally 5 days a week for three years (22-25 km per day, depending on the route), yes also when was snowing or raining. I still use cycling as the only means of transportation to the office, but with WFH it's currently only 2-3 days per week. I live in The Netherlands again, where cycling is one of the primary forms of transportation.

Rain: I use rain pants and waterproof jacket/shoes. Snow: bike lanes are cleared, though I did regularly cycle on snowy roads in Germany when they were not cleared yet. Tires with some profile and experience make it very doable.

Honestly, I was with you on the weather aspect. I do go to work daily, rain or shine ... it sucks to drive in the rain and I was lucky to go full HO during a bad winter, but overall it's perfect workable (in central Germany).

But then you wrote that you walk just 1h to work ... That can't be more than 20 minutes by bike. (My commute is 30 minutes by foot, 15 by car, 1:30h public transport... But due to the road layout it takes me just 10 minutes on average by bike.)

I drove to work for 10 years, although I did skip winter season, riving on ice is NOT fun

> Fwiw it would take me 1h of walking to go to work or about 1h20 if I take a couple buses. Or I can take the car and be done in less than 10 minutes.

That's kinda the problem. Even here with pretty good infrastructure car is 50 minutes in peak traffic, metro + walk to metro station + few stops of tram is 1h. If I go like 2h after peak it's 35 minutes...

But how many parsecs does it take to do a Kessel run?

For a comparison, 50W doesn't seem like much, right? Maybe if you're older you had 50W incandescent light bulbs in your house. Normal thing.

Let's say a WISP wanted to run a very basic off grid relay site with some radios that are 8-12W DC load each and a router that's 15W. Total around 50W 24x7x365. ((50 x 24 x 31)) / 1000

That's 37.2 kWh per month.

You need a surprisingly large amount of solar panels to generate a reliable 45-50 kwH per month to refill a battery bank every day when the sun comes up, in November, December, January, February at latitude 45N or above. Like, really, a lot more than you might think. Four or more 370W 72-cell.

PVwatts says a 4-module array of 370w panels, including AC losses, will produce about 100kWh in January at 45N FWIW

That's assuming perfect sun exposure on a roof or ground moving with no shadowing at any time of the day and at the optimal tilt.

Pvwatts says that usable energy from a 1480W system at 43.6N in Boise ID might be more like 77kWh a month in December, the shortest sunlight month of the year.

An off grid system generally needs to be calculated to survive December. January will be a few percent better as days start getting longer.

Realistically, to get through entire week long periods of snow and overcast, if I had a load that was 50kWh a month I would want a 75-80kWh a month predicted PV production system to make it worry free in December.

Going against the trend here but I still use incandescent bulbs in key places like my desk and so on. I find LED to give a terrible light (not the whole spectrum), but they are getting harder and harder to find.

Incandescent bulbs are not full spectrum, though. They are on the warm end of the color temperature scale, much more "orange" than mid-day sunlight.

The good news is that you can get LED bulbs in any color temperature you like. My house is full of "warm white" LED bulbs and I could not tell any difference in brightness or color when I swapped them in for incandescent many years ago.

The difference is colour rendering and the nature of the spectrum.

An incandescent bulb is, by definition, emitting black body radiation - it’s a nice curve encompassing a good chunk of the spectrum, but as you say biased towards the red end.

LEDs tend to emit discrete quantised frequencies of light, as a result both of the dopants in the LEDs and the phosphors used on bulbs.

They have got better, due to better phosphors, but they still don’t render colour as well as incandescent bulbs.

That said, I’m all LED here as I cannot afford within our energy budget to burn a kilowatt or more on lighting.

They are continuous black body spectrum which we got used to

> LED to give a terrible light

Let's stop spreading this myth. Cheap LED lights can have terrible spectrum. Good LED lights have a better spectrum than incandescent.

I should have phrased it differently. See madaxe's comment:

> The difference is colour rendering and the nature of the spectrum.

If you compare it with your own eyes, you should definitely be able to see it.

Here's a good article explaining in-depth how and why LED light looks different from incandescent.

https://nymag.com/strategist/article/led-light-bulbs-investi...

> If you compare it with your own eyes, you should definitely be able to see it.

People buy cheap LEDs and then say this. Buy good quality LED bulbs and you will see no difference.

There are a few specialty LED lightbulbs made with (old-fashioned) yellow glass that offer a warm (yellowish depending on the room) and comfortable light.

Finding LED that have light that doesn't look bad is unnecessarily complicated sadly

Agree it doesn't feel like a lot. We run our house, including a decent sized pool pump, off solar for most of the day. A Pi seems like very small fry in the scheme of things.

Getting something like this up and running in a few short hours of Dutch summer sun just shows that everyone should be trying it (that includes me).

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