Wind power results – 2013/14

I have been monitoring the UK peak power demand every day for the last 12 months, and how that power was delivered. The UK government has invested about £50 billion into Wind energy since 2005,  so how has it performed?

The average Wind component of UK peak power demand was 5.7% over a full year. The maximum power output was 6GW on 21 February 2014 at 18:10, while  the maximum proportion of demand was 16.8% on Sunday 17th August 2014 at 20:08. The minimum proportion was 0.15% on 31st May 2014 when total Wind output was 49MW (0.05GW).

Power delivery by Fuel type to meet Peak demand every day since September 2013. Weekdays peak demand occurs around 18:00 and fat weekdays around 20:00.

Power delivery by Fuel type to meet Peak demand every day since September 2013. Weekdays peak demand occurs around 18:00 and at weekdays occurs around 20:00.

For comparison Nuclear Power averaged 18.1% of demand and never fell below 15%. The bulk of UK power is still met by fossil fuels and it is impossible to imagine a future Grid based purely on Wind power. The mix of coal and gas is interesting. Coal is dominant in Winter while gas dominates in summer. I also monitored the daily energy “trough” or the lowest demand for electricity which usually occurs each day at around 4am . This is shown below.

Power delivery by fuel type at minimum daily power demand (~4am)

Power delivery by fuel type at minimum daily power demand (~4am)

It is Coal that keeps the lights on during winter nights! Gas output is ramped down at night, probably because it is easier to regulate power in Gas power stations. The exception to this is during the summer when several coal power stations would appear to be mothballed.

The statistics for Wind power at night appear better because the overall demand is much less. The average contribution of wind power to minimum demand was 9.8%, and the  maximum Wind supplied was 22.5% on 2nd February at 05:30 (6GW).  However Nuclear also contributes proportionately more at night averaging 30%, which is 10% more than Gas. The difference between the 2 extreme demand curves is shown below over the 13 month period. Note the sharp drop in power demand over the Christmas period.

Daily Peak and Minimum demand  over  a 13 month period Sep 2013 to Oct 2014

Daily Peak and Minimum demand over a 13 month period Sep 2013 to Oct 2014

This analysis makes it clear, to me at least, that the UK should shift the balance of investment towards Nuclear and away from Wind. Even doubling Wind generating capacity to 20GW would still leave some days with essentially zero output, thereby undermining energy security. Furthermore Gas will always be needed with at least the same generating capacity as Wind in order to continuously balance Wind’s erratic output. Nor can energy storage save the day, since it reduces the EROEI for Wind to below sustainable levels.

The data used for this analysis was collected through BM reports – the National Grid balancing mechanism. There are about 10% of wind farms that are not metered by BM so the above figures should probably be adjusted upwards by 10%. The conclusion is the same.

The live monitoring of peak demand over the last 30 days is shown below.

Posted in coal, Energy, nuclear, renewables, Science, Technology, wind farms | Tagged | 30 Comments

The certainty of extreme weather

The Met Office tell us that September was the driest since records began 104 years ago. Last summer was ‘the hottest ever recorded’ in Australia. These extreme records hit the headlines implying that global warming is to blame. However just how likely is it that one extreme weather record or another will be broken due to pure chance? Barometer in today’s Spectator shows how to do the calculation and the results are surprising. I have simply extended the same argument to include Australia and the US.

In the following we consider 3 countries and their regions – The UK, US and Australia. The regions for the UK are England, Northern Ireland, Wales and Scotland. Similarly Australia has 6 states and the US has 50 states. That gives a total of 63 different regions if we also include the whole country itself.

Lets take 4 records that can be broken : hottest, coldest, wettest and driest. During a single year each record can be set yearly, monthly, or seasonally. That equates to 17 different time periods. Therefore for the UK there are a total of 5x4x17=340 records that can be set  during the current year 2014. For Australia there are 6x4x17=408 records and for the US there are a staggering 51x4x17=3468 records.

Now lets assume that all weather records go back 104 years. The probability of a single record being broken in any year is simply 0.0096. So the probability the record will stand during the current year is 0.9904

What is the probability that any of the UK weather records will be broken during the current year ? That is

P = (1 - 0.9904^{340})

There is a 96.3% chance that at least one Met Office record will be broken this year in the UK!

For Australia there is a probability P = (1 - 0.9904^{408}) or 98.1% chance that a record will be broken and for the US there is a probability P = (1 - 0.9904^{3468}) or essentially a 100% chance that a record will be broken!

So in 2014 we can be absolutely certain that at least one state in the US will have its hottest/coldest/driest/wettest month/season/year ever recorded! Such records are totally meaningless.

Posted in AGW, Climate Change, Meteorology, Science | Tagged , | 12 Comments

Tides and Storms

Energy flows from the tropics to the poles. The tropics absorb most of the sun’s radiation and drives heat flow to polar regions where radiative cooling dominates. In winter the Hadley cell moves heat to ~30N via huge convective currents transporting  latent heat from the tropics northwards via a band of powerful thunderstorms . The reverse happens in the northern summer when the tropical Hadley cell  moves southwards towards  the now winter southern hemisphere and it reverses circulation.  David Randall explains this well in his book ‘Atmosphere, Clouds and Climate’ (from which the first 3 figures below are taken).

Hadley

The rising branch of  tropical thunderstorms (ITCZ) is located about 10 deg from the equator in whichever is the summer hemisphere. The release of latent heat warms the troposphere to the moist adiabatic lapse rate. The high warm air moves meridionally and cools by radiating heat, so becoming more dense. It then descends and twists eastward due to the rapidly increasing coriolis forces with latitude. A counter rotating Ferrel cell is driven by the mechanical energy of storms 60 -30 deg and balance mass flow. The JET stream is caused by the coriolis force acting on the descending Hadley circulation accelerated by zonal wind effects. It is concentrated about 12 km up due to lapse rate temperature gradients. The coriolis component of angular momentum M for the earth rotating with angular velocity \Omega  at latitude \phi and zonal wind u is:

M = (\Omega \cos{\phi} + u)a\cos{\phi}

u = 0 at the equator wheras u = 11m/s at 30N

The Jet stream strengthens as the polar night begins. This is closely related to winter storms as the temperature gradient between the tropics and the winter pole increases.  This “thermal wind” in mid latitudes is caused by horizontal temperature gradients which increase strongly in winter. Hydrostatic balance vertically becomes unstable

\frac{\partial P}{\partial z} = -\frac{pg}{RT}

Wind changes rapidly with height when surface temp changes rapidly in the horizontal direction. The Jet stream becomes stronger

temp-gradient

 

If T changes rapidly horizontally then the thermal winds increase strongly with height. This state is termed to be ‘baryclonic’. At 30N in winter the Jet Stream winds starts to increase massively with height. This is because below the Jet Stream the surface temperature gradient increases rapidly towards the ‘night-time’ pole. So the steeper the temperature gradient  the stronger the Jet stream becomes.

zonal-wind

Given a strong Jet Stream and large temperature gradient, conditions are now critical for the formation of big storms. A strong poleward decrease in temperature causes ‘baryclonic instability’. Such storms are technically called ‘baryclonic waves’ and are composed of  cold fronts as polar air moves south under warm tropical air, and warm fronts when simultaneously warm tropical air rises north above cold polar air, all driven by Coriolis forces. Each front causes a rapid change in temperature on the ground. These storms are then accelerated by the release of gravitational potential energy as dense cold air falls downwards feeding kinetic energy to the storm causing strong winds.  When conditions are right for baryclonic instability any small external disturbance will be amplified to trigger the formation of a storm. There is clear evidence that strong spring tides are one important trigger of such storms. Tides provide an asymmetric disturbance which act over large northern zones through  changing tractional tidal forces acting on the atmosphere. An example  of this was the storm on Jan 4-6 last winter.

Formation of storm which hit UK on 5-6 Jan 2014. A strong wave of tractional tides sweeps through the area.

Formation of storm which hit UK on 5-6 Jan 2014. A strong wave of tractional tides sweeps through the area. The new storm seems to have been triggered by a strong kink in the Jet Stream dragging warm air up in the north west Atlantic. By the 4th January this second intense storm is forming fast off over Newfoundland. The tidal forces are very strong and the Jet Stream starts to kink. The previous low pressure system seems to be consumed by  the next as it  grows fast .

In a growing perturbation cold air slides under warm tropical air. Cold air moves down causing a front while warm air on the tropical side moves upwards  causing a warm front. Warm air rises and cold air descends transporting thermal energy upwards and the center of mass of the total air column descends releasing gravitational energy into kinetic energy. This forms a low pressure vortex at the centre.

Hadley cells do not penetrate into middle latitudes. Likewise Baroclonic waves do not penetrate into the tropics. The energy  transported from the tropics by Hadley cells is ‘handed over’ to such baroclonic storms to finish the job by moving the heat onwards to the poles. The Jet stream position defines this boundary between tropical air and polar air. Storms form on the northern side of the Jet Stream at the eastern edge of the Atlantic. The path of these storms is determined by the kinks (Rosby waves) in the Jet Stream.  As the earth rotates, an ever changing gravitational field of  tractional forces sweep across the Atlantic ocean from west to east about every 12 hours.  The effect is similar to a bar magnet sweeping across  a sheet of paper covered in iron filings.  These two videos show how strongly tractional tidal forces can vary both during the lunar month and yearly with gradual changes in lunar declination. The first is updated 2 hourly for August this year and the second shows the direct tide for a fixed position during 2006 when the moon was at its 18.6 year maximum declination.

The southward swirling tidal force acting on the Jet Stream amounts to about 10 metric tons per km. This gravitational force is varying strongly in strength and position during the lunar month. There are two possible effects of tides.

  1. They can distort the Jet Stream causing kinks which change the path of mid latitude storms.
  2. They can seed winter storms by disturbing baroclonic instability at maximum tidal forces. Therefore for lunar tides to effect mid latitude weather we need the following conditions.
  • A sharp horizontal temperature gradient leads to a strong Jet Stream and Baryclonic instability.
  • Increasing spring tides with strong tractional forces at high latitudes can  trigger anticyclonic flow leading to cold/warm fronts and storms moving eastwards.
  • These storms are guided across the Atlantic by the Jet Stream.
  • The Jet Stream itself  is distorted by the same changing tidal ‘tweaks’.
Jet stream flow 3-6 January 2014

Jet stream flow 3-6 January 2014

The strength and position  of storms is enhances by growing instability and changing atmospheric tides over coming days. The same  tractional tidal force field also modifies Rosby waves in the Jet Stream.

Last winter the UK experienced a series of severe storms. The Jet Stream was locked into a pattern whereby the eastern US was extremely cold while warmer air resided over the western Atlantic.  Storms were spun off the boundary between very cold air over Newfoundland and warmer tropical air moving up over the western Atlantic. Each major storm coincided with a maximum tide bringing coastal flooding to the UK as large waves were also enhanced by storm surges.

So there is direct evidence that atmospheric tides can trigger storms.  Nearly all  of last winter’s storms coincided with maximum spring tides. This cannot just be a coincidence. It would be relatively easy to include such tidal forces into GCM weather forecast models. The moon is just one more external force acting on the circulation of the atmosphere. I strongly suspect that medium range weather forecasts would improve significantly if the dynamics of tides were properly taken into account.

Posted in climate science, Physics, Science | Tagged , , , | 3 Comments