Originally posted by Diver
View Post
- Visitors can check out the Forum FAQ by clicking this link. You have to register before you can post: click the REGISTER link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. View our Forum Privacy Policy.
- Want to receive the latest contracting news and advice straight to your inbox? Sign up to the ContractorUK newsletter here. Every sign up will also be entered into a draw to WIN £100 Amazon vouchers!
Reply to: Unintuitive to the uninitiated
Collapse
You are not logged in or you do not have permission to access this page. This could be due to one of several reasons:
- You are not logged in. If you are already registered, fill in the form below to log in, or follow the "Sign Up" link to register a new account.
- You may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
- If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.
Logging in...
Previously on "Unintuitive to the uninitiated"
Collapse
-
Originally posted by Diver View PostSurely pitch of blade would be a factor too?
an increase in blade pitch would vary the ratio and thus the output?
So you are right in that it would change the output - but probably downwards
Leave a comment:
-
Surely pitch of blade would be a factor too?
an increase in blade pitch would vary the ratio and thus the output?
Leave a comment:
-
Because the higher you go, the weaker is the Earths magnetic field, which means there is less electricity to extract from the air flow. You can prove this through extrapolation. If the turbine was very high, say 100 miles high, there would be no air flow at all, because it would be in space hence no electricity.
Plus if you made them too tall they would bend over in a strong wind, and effect known as blowing over.
Leave a comment:
-
Unintuitive to the uninitiated
I'm still fascinated by this book http://www.withouthotair.com/ (thanks Cliphead)
Wind turbines
I think it can easily be seen that the power that a wind turbine can extract from the wind will be related to the length of the blades in some way (the square in fact), and perhaps less intuitively that it's also related to the cube of the velocity of the air passing through it (i.e. the wind speed). In fact the formula for calculating the power that can be extracted from the wind is 0.5 * efficiency * airDensity * PI * r^2 *v^3. Or roughly r^2*v^3. So a 1m radius turbine in a 6 m/s wind can produce up to around 200 Watts.
Here's the initially unintuitive bit. In a wind farm, if you pack turbines too close together they become inefficient and it turns out you need at least 5 diameters separation between them to avoid the worst of this effect. The resulting algebra means that the power you can extract from the wind (in a wind farm) then becomes independent of the radius of the blades (cough)! It's just related to wind speed cubed and air density, which by the magic of algebra is also a unit of Watts per square metre. The author (PhD from Caltec, professor at Cambridge, la de da) concludes that this area relates to the amount of land land used and is a constant for a given wind speed. See http://www.withouthotair.com/ page 332 of the PDF book.
At first glance this doesn't seem right. There appears to be a change of interpretation involved here with what the algebra represents (in the first case the area swept by the blades in a vertical plane and now to the area of land used) and it doesn't seem to make sense that power extracted can be independent of the blade radius. For example one might envisage a wind turbine 1 km high that takes up not much more land space than a more vertically challenged version but which has a much larger cross sectional area. Can you see how this works out? (it does) For example why doesn't it help to build higher - in a wind farm - in an attempt to minimise land use?Tags: None
- Home
- News & Features
- First Timers
- IR35 / S660 / BN66
- Employee Benefit Trusts
- Agency Workers Regulations
- MSC Legislation
- Limited Companies
- Dividends
- Umbrella Company
- VAT / Flat Rate VAT
- Job News & Guides
- Money News & Guides
- Guide to Contracts
- Successful Contracting
- Contracting Overseas
- Contractor Calculators
- MVL
- Contractor Expenses
Advertisers
Contractor Services
CUK News
- Streamline Your Retirement with iSIPP: A Solution for Contractor Pensions Sep 1 09:13
- Making the most of pension lump sums: overview for contractors Sep 1 08:36
- Umbrella company tribunal cases are opening up; are your wages subject to unlawful deductions, too? Aug 31 08:38
- Contractors, relabelling 'labour' as 'services' to appear 'fully contracted out' won't dupe IR35 inspectors Aug 31 08:30
- How often does HMRC check tax returns? Aug 30 08:27
- Work-life balance as an IT contractor: 5 top tips from a tech recruiter Aug 30 08:20
- Autumn Statement 2023 tipped to prioritise mental health, in a boost for UK workplaces Aug 29 08:33
- Final reminder for contractors to respond to the umbrella consultation (closing today) Aug 29 08:09
- Top 5 most in demand cyber security contract roles Aug 25 08:38
- Changes to the right to request flexible working are incoming, but how will contractors be affected? Aug 24 08:25
Leave a comment: