Hacker News Reader

Comment by Animats | Hacker News Reader

This needs a third-party evaluation. Nobody gets that much power from rooftop wind with small devices. Usually you need at least 16 square meters of intake area to get 5KW.

Some similar devices with iffy claims:

- EIP - encased turbine for rooftop mounting [1]

- Sheerwind (active about 2014-2017) Really big funnels. [2] Critique: [3]

If ducting a wind turbine would help, everyone would be doing it.

[1] http://eiptechnologies.com/

[2] https://web.archive.org/web/20171221050330/http://sheerwind....

[3] https://www.youtube.com/watch?v=HtjKXb5gko0

View on HN

When we talk about solar it doesn't really matter if you want to generate 100w, 100kw or 1mw. You're pretty much using the same tech, and the pre-requisite is simple "sunshine".

But wind is more complex. If you want to generate a lot, then you need space (to build a tower), height (higher is better) and size (bigger is MUCH better.) And wind.

But if you just need a little, say 3kw, then you're not looking for the best possible outcome, you're looking for local outcome.

Most of us are location bound. I want to generate energy here - because I use it here. There are constraints (noise, size, height etc.) that I live with.

Sure, I've got solar, my roof is full of that. Let's stipulate that economically I'm better off adding more solar. Let's also stipulate that my roof is "full".

I get quite a few windy days (and windy nights) a year. If I harvest 1kw/h, I'd be happy. If I generate excess I can sell it to the grid.

The obvious answer is still a 3 or 5 bladed conventional wind turbine. But that is both visual, and can be noisy.

Personally, I don't need it to compete economicly with solar. I don't need it to be "perfect wind efficient". All I need is around 3kw capacity (for 1kw output) in a residential friendly package.

Solar has shown that individuals are prepared to spend capital on residential generation. And in sufficient volume to move the grid needle. I'd love to see similar opportunities for those with more wind and less sun.

Note that wind is a good complement to solar, because it's largely driven by the heat from the ground rising upward, so it tends to start picking up in the afternoon/evening as solar starts to dip.

> 1 kw/h

Try again...

Can you elaborate? Some of us flunked out of EE.

It's kWh. Kilowatts multiplied by hours, not kilowatts per hour.

The analogy with units you are familiar with: watts=speed (e.g. knots), energy=distance (e.g. (nautical) miles).

So a kWh of energy is kind of like saying a knot-hour. Or 1 knot for 1 hour, which equals 1 nautical mile.

You can say "I have travelled a distance of 1 knot-hour or 1 knot for an hour". It doesn't make any sense to say "I have travelled a distance of 1 knot/hour or 1 knot per hour". Knot/hour would be a unit of acceleration not distance.

Ok that's probably clear as mud. I also feel like I should make a power units quiz website because so many people get this wrong.

OP was not trying to say kWh. They were trying to say kWh per hour.

1 kWh per hour is 1 kW

Mathematically yes, but linguistically no.

One kWh per hour is the average production of the system. Calling a power generation system "1 kW" implies it maxes out at 1kW. For something like wind or solar which is usually at partial load, a 1kW system will usually not produce 1kWh per hour.

Thus it is appropriate to say "1 kWh per hour" because you will need a ~3kW system to achieve that.

"1kW average"

Yes that would also work.

IMO "kWh per hour" is clearer, because when dealing with power generation those are the units you deal with when you are connected to the grid.

When people talk about their solar generation, they say "I generated X kWh today", not "today my system averaged Y kW over Z hours" and leave the math to the listener. kWh per unit time is common when talking about home energy generation.

I hope you are trolling and not serious.

I'm not. Why would you hope that? Sort of an unkind think to say.

Would you like to elaborate on why you disagree so strongly?

>Sort of an unkind thing to say

I will do better from now on.

OK, first, let me say that I have no objection to your "I generated X kWh today". Neither do I have any strong objection to "kWh per day" or "kWh per month". But I do object to "kWh per hour". I would have the same objection to, "0.6 light-years per year". I would ask people to say, "0.6 times the speed of light" instead.

It is common to need to refer to two different things that happen to have the same "dimension" (electrical power being an example of a dimension and energy being a different dimension). For example, a supermarket needs to distinguish "gross revenue", i.e., how much money it collected by selling things, from "net revenue", which is how much money is left over after subtracting the cost of the supermarket's having bought the things it sold. Note that both gross revenue and net revenue are best measured in dollars (if the market is located in the US). So according to you, if I understand correctly, you think it would be an okay idea for accountants to adopt the convention of using "dollars" as the unit when talking about gross revenue and "dollar-months per month" to signify that we are talking about net revenue. But what are you going to do when we need a third measure that happens to also be denominated in dollars (profit, say)? Are you going to adopt the convention that "dollar-miles per mile" refers to a profit measure?

There was a famous physicist (Steven Weinberg, I think) who criticized Windows for giving science and technology a bad reputation. In particular, he worried that young people would react to the buggy behavior of Windows by becoming sour on the whole edifice of science and technology and would try less hard to learn science. I guess my main objection to "dollar-months per month" and to "kWh per hour" is like that: I worry that it will prevent (via confusion) some fraction of people from learning enough about accounting and the fundamentals of electricity to wield words like "gross revenue", "net revenue", "energy" and "electrical power" effectively. (One of the sources of my worry is my imagining how I personally would've reacted to coming across "kWh per hour" long ago before I had mastered the concepts of watts, energy and power.)

To bring this back to where we began, if there are two different quantities of interest, namely, the advertised "capacity" of the panel versus the power a consumer can realistically expect to get out of the panel on a typical day, I would ask that people settle on some short phrases for both -- similar to "gross revenue" and "net revenue" -- and to denominate both quantities in kW (or kWh per month maybe).

I kind of agree. But anyway kW/h is wrong either way.

Yes, I entirely agree with that.

> because so many people get this wrong.

All these terms are just so unintuitive for a mere mortal like me.

Energy? Power? The difference between those two words has as much importance to the common person as the difference between "empathy" vs "compassion", or "theory" vs "hypothesis", or "less" vs "fewer".

kW being a "stuff over time", but kWh being "amount of stuff"? I don't doubt the math checks out if you expand all units, but I'm as dumb as a wet rock so it took me a while to get this.

---

If people wanted me to understand this way sooner, they should have started asking me to think in terms of "kcal" (kilocalories).

At least I know that kcal is an "amount of stuff" because it's something you hear if you talk about food. And there's no mention of "hour" anywhere in the name (like with "kWh"), so the name doesn't have anything misleading.

Then just tell me that "860.421kcal/h = 1kW" (the numbers don't really matter), and ask me to solve for kcal.

When I move the "h" from the left to the right, and the equation becomes "860.421kcal = 1kW * h", everything will click.

---

Food has kcal, so kcal is something that can be stored. When the equation has "kcal" on the left, it has "kW * h" on the right, so that means batteries store "kW * h".

When I think of "kW" alone, I will remember that the "* h" moved to the left side and became "/h".

I might forget stuff, but I know what food is, and I know that there exists an equation, at one side there's "kcal", at the other side there's "kW", and there's an "h" somewhere in there.

And "kcal * h" will look wrong af, so I will remember that if the "h" at the left side, it will be "kcal/h".

Result: Now I have an intuition for this.

(EDIT: Escaping, and add some separators to hopefully make the comment easier to read.)

> All these terms are just so unintuitive for a mere mortal like me. Energy? Power?

Yeah in fairness I think most people never have to deal with these units and they're used interchangeably colloquially.

kW = power. This is a rate of work. How quickly work is happening. Intuitively, cycling hard = high power, cycling with low effort = low power.

kWh = energy. 1 kWh is literally 1kW for an hour. If you are cycling pretty hard with a power of 0.1 kW for 10 hours, you have generated 1 kWh (0.1 * 10). If you cycle inhumanly hard (0.2 kW) for 3 hours you have generated 0.6 kWh (0.2 * 3).

That's it. Now some examples:

* Solar panel peak power. This is the maximum power output of the solar panels. For cycling it would be the hardest you can possibly cycle. Apparently the record for cycling is 2.7 kW! (But not for very long; unlike solar panels people get tired.)

* Battery capacity. This is in kWh. They store a finite amount of energy. If you have a battery containing 10 kWh you can eek it out slowly - if you only draw 0.1kW from it it will last 100 hours. Or you can dump all the energy in half an hour and it will output 20 kW.

The only really complicated one is battery factory output capacity, which approximately 0% of journalists understand. This is measured in Watts... because if you produce 1kWh batteries, and you make one per hour... 1kWh/ 1h is 1 kW! In other words if the batteries from the factory magically came out fully charged and you just used them as a power station without recharging them, then how much power could that power station provide? Yeah that one is a bit confusing.

What is kw/h?

What is kw/h with a lowercase w? I’m familiar with W which stands for Watt, a unit of power. Could it simply be a typo like in GP’s comment who misspelled kWh?

I want a setup that generates 1 Kω/H.

1 kiloscrotums per hour is way more than any man would need.

The rate of change of your power consumption?

kilo-wut?'s per hour ;)

I was going to say the same - there was a big fad for building-top wind generators and then everyone figured out that the airflow over a building is really turbulent, which makes it pretty shit for power generation.

Ask anyone who sails; trees and buildings shield a lot of wind out to surprisingly far away. The reason the big boys work well is because they are much higher above the ground where the wind is stronger and more consistent. That's also why companies are trying to make kite and blimp based generators work.

Only place I've seen the rooftop turbines work was at an airport where the giant open space around the terminal buildings means winds are more even and lower to the ground.

It feels like off-grid people mostly use it as a supplement for the stormy bouts where winds are often strong when solar yield is low...or as a backup in case their solar system breaks. They're happy if they meet the needs of their fridge, for example. Modern fridges use an average of less than 100W; lower if they're not self-defrosting.

I spent 5 years working in wind microgeneration (but with helical turbines) and entirely agree.

Rooftop solar works because it's cheap and simple to set up. Wind is not that. The structural and installation requirements result in relatively high fixed costs. To offset that you need to scale the size of the turbine, and maximise the time they spend spinning. You can only go so big on buildings and the built environment reduces your capacity factor because there's loads of buildings blocking the wind.

In an urban environment is there enough updraft from "heat island" effects to harvest the energy?

I kinda assume not else someone would have done it already, but maybe my assumption is wrong because it wasn't economic before and could be now.

There is some but not nearly enough to generate useful amounts of wind.

This agrees with what little I remember. Energy you can get out depends on swept area, and these don't have much of that (different rules apply to funnel designs like this one but the concept is still applicable). Wind close to the ground is too turbulent to get much power out of as well (imagine how many times it can change from blow to suck and back in a minute). They could have solved these problems, but I didn't see anything very different at their website, just creative funneling of air through a turbine. I wish them luck though.

In 2013, I had an internship at a kind of industrial incubator and fund in Kongsberg, Norway[https://kongsberginnovasjon.no/?lang=en]. Although that was 11 years ago now, and a lot has certainly changed in the industry, physics has not.

At the time, they had an explicit focus on alternative energy technologies, so recieved a lot of proposals similar to this. I do not remember the details of my analyses anymore, but I do remember that every single one of them was rejected because none of them passed a basic back-of-the-envelope plausibility evaluation.

These projects basically fail because their output is poor compared to other solutions of similar or even lower cost.

It is also important to consider how much energy it takes to manufacture their solution in the first place. How long does it take for them to actually become net carbon negative? Does it even happen in the lifetime of the product? Sometimes the answer is no (in which case, what is even the point?)

The point might be as simple as a big building wanting reduced bills or energy independence without thinking one iota about the environment. It can also be to just signal that your big building is progressive and innovative, to attract companies to your commercial real estate.

Here's another one, Ventum VX175: https://ventumdynamics.com/

Regarding what you said about ducting, I don't think that's a fair assessment. Really big turbines are the biggest bang for your buck, but they aren't exactly duct-able. And on the flip side, really big turbines can't be built in a lot of places. So the question is, does ducting help smaller scale turbines, and will placing smaller scale turbines where big turbines won't fit going to be worthwhile?

> So the question is, does ducting help smaller scale turbines, and will placing smaller scale turbines where big turbines won't fit going to be worthwhile?

Simple ducting does help some. A group at Clarkson has been working on this. They have a wind tunnel, so they can get solid data. [1] They have a simple duct around a standard wind turbine. This gives the effect of more intake area, and they get almost twice the output power. Unclear if this is cheaper than just increasing the blade length.

Many people have been down this road. There are many, many variants on experimental ducted wind turbines. Just search for "ducted wind turbine". There are very few installations. Here's one of the few.[2] They're demo installations on college campuses.

[1] https://www.youtube.com/watch?v=EXxA-RkwuRY

[2] https://www.ductedwind.com/blog

There has been several startups for the past decades who have tried this an disappeared afterwards.The real and legitimate research, development and improvement of wind turbines have been plagued by fad wind turbines. Fad wind turbines fly around Amazon selling big claims at breakneck speeds.

I've been interested in this company that has made vertical axis wind turbines for harsh conditions for 40 years: https://windside.com/gallery/

They have very slowly started to sell to wider market. Clearly they have never aimed at being cheapest, but their advertised maintenance free installation is a big plus. And also that the models can generate electricity at wind speeds from 2m/s to 60m/s.

The evaluation just needs to be for longevity, repairability and maintenance needs/costs. The big purpose of wind for a lot of small scale installs is to augment solar for night time and/or continuous base load assistance to it, and not as a primary source of generation.

I'd immediately get something that just gives me a tiny 300w on average as it means my 5kwh battery lasts 5 hours at night instead of 3 (made up numbers). That puts me soooo close to being full off grid it's not even funny.

People talking about return on investment, payback periods etc are completely screwing over the uptake of solar and other non renewable sources.

Yes, their generation numbers are not definitively defined in TFA, not even as a concrete typical range.

For those who are looking for a more intuitive understanding of what 5kW is, that's 6.7HP.

More comparisons: the power of water cookers, (a single) electric stove top and fan heaters are usually in the order of 2kW (at least in Europe with 230V AC)

5kW is just enough power for a 5 HP motor at 230v 3-phase (12.5A), and not quite enough power for a 5 HP motor @ 208v 3-phase (13.8A). If #14 wire was allowed for branch circuits in commercial construction, you could use those as your conductors, that’s how small these things are.

NEMA motor ampacity table: https://www.galco.com/circuit/fla_rate.htm

They also have a hurricane upgrade package.

Now we're cookin with gas

Reply on news.ycombinator.com