Letting go.....

Whilst messing with some energy management software, I thought it would be instructive to take a broad look at electricity supply.  In reality a diversion into the general and away from the specific is displacement activity.  I'm still getting my head around this stuff, so treat this post with caution.

Go back forty years to the 1970's and coal was the dominant fuel used for electricity generation, nuclear power stations were beginning to come on line and there was a small amount of oil and hydro capacity.  Many large power stations were sited close to the coal fields that supplied them.  Visits to power stations were mandatory for engineering students and I went on two of these and at each one the importance of matching supply and demand was pointed out and illustrated with the same example, that of the Miss World Contest, at the end of this event, several million households all rushed to the kitchen to boil water in electric kettles with which to make tea, creating a massive spike in the demand for energy which had to be met from the "spinning reserve", maybe this was just a good story to amuse visitors, but it sounds credible.  It probably would not amuse my wife and daughter, both of whom have feminist leanings and both of whom have travelled extensively to meet people, which seemed to by the principal aspiration of most Miss World contestants.  To summarise, demand management appeared to be based on the weather, seasons and the TV schedules.

Move on forty years and electricity generation has become much more diverse with gas, wind and solar entering the mix.  Wind is a discontinuous source, on a windy day, wind might account for 10 - 15%  or more of the demand for electricity, on a calm day this can get close to zero.  Looking at the supply of electricity, it appears that gas powered stations act as "back up" for the wind farms, this may not have been the role that investors in gas powered stations envisaged.  In short, the management and economics of electricity generation appear to have become complex.  Variations in strike price for different forms of generation and auctions to maintain capacity do not appear to contribute anything in the way of simplicity.

From the perspective of a naive observer it seems that we are doubling up on generating capacity because of the fickle wind and shifting sun, sustainable sources have to be backed up in some way.  The critical technologies would seem to be demand management and storage both of which could ease the integration of sustainable energy sources and reduce the amount of doubling up.

The peak demand for electricity is during the day and early evening.  The peak demand can either be met from bringing generating capacity on line, or reducing the demand.  The internet of things can make a contribution to managing demand, the frequently quoted example is turning of the fridge in the early evening during evening when many families are cooking meals and doing things with electrical appliances.  It's not beyond the imagination to imagine a system that prioritises the use of energy, turning some things off to free up resources and facilitating tasks that can't wait and then reconnecting them at a more convenient time for the electricity supplier.

There are many ways such a system could be configured.  At one end of the continuum the system boundaries could be drawn at the household or office level, In this case the maximum load on the grid is defined and decisions about its use made by the people inhabiting the unit.  At the other extreme, there could be centralised control.

My guess is that the technology is not the problem, instead it is making it acceptable to the energy consumers.  A key element would be the design of the tariff which would make it attractive for users to stay within the maximum load restriction.  Having discussed this with a few people, including one of my sons, the usual reaction is a lack of willingness to pass control of one's fridge to a third party. the "big ask" of this scheme is to forfeit autonomy for objectives which are remote from the average householder.  These include investing in technology other than generating capacity and improving the management grid management.  For this reason, I would suggest that politicians will be slow champion  this concept.

Exploring the Wind

When I first became interested in sustainable energy, my first thoughts were "haw much wind and solar energy is available.  A large chunk of my life has been spent poking around datasets, mainly those related to hydrocarbon exploration and production, so for me a logical starting point was to seek out sources of wind and cloud data.  This post is collection of personal observations, anyone wishing to acquire a wider knowledge is encouraged to seek out more authoritative material.  For the sake of brevity, nuances and detail have been omitted.

If I was starting again, the first task would be to read a couple of textbooks on global climate and air circulation in particular.  Whilst browsing books at a car boot sale I came across "Climate, Soils and Vegetation" by D.C. Money, this and Wikipedia provided a useful, if belated, context for the maths and stats.

The actual starting point was a sample of Metar and similar weather reports and then attempting to reduce them to Weibull distributions.  One of the locations was an airfield which is approximately 10 km to the west of where I live.  The average wind speed there is around 5 m/s, the surrounding terrain is flat and having stood, with a simple anemometer, on the roof of a WW2 pillbox which overlooks the site, it appears that the air flow is smooth with little turbulence below 10 m/s. In contrast, where I live, the average speed is less than 3 m/s and very turbulent.  Weather data is collected to support human activity, frequently transport, where the objective is to provide pilots, sailors, road users with an indication of what forces of nature they will be exposed to.  This data may not be relevant to other nearby locations with different terrain and land cover.  It is a gross oversimplification, but the average wind speed for a selection of onshore locations  in Western Europe and North America was in the range 4 - 7 m/s with Weibull shape factors in the range 1.3 to 1.8.  The higher the shape factor, the greater the energy yield.  There is an inference that the lower shape factors are associated with complex terrains.  At some point I need to revisit the data and produce a better summary.

Next I looked at offshore data.  Onshore wind is fluid flow over a rough surface, the effects of which extend for a significant height.  In contrast, the fluid friction over water is much reduced.  In the areas between the tropical and polar circulations, the average wind speed might be in the range 6 - 10 m/s with wind speed increasing with poleward distance.  Often the Weibull shape factor is close to 2.0 allowing the use of the Rayleigh distribution (a special case of the Weibull distribution with the shape factor set to 2.0).  The greater energy yield offshore is offset by the higher cost of the installations necessary to capture it. Onshore wind turbines can be erected with general purpose equipment such cranes, diggers and lorries, offshore it is necessary to use specialist vessels for pile driving, lifting and cable laying which are both large and expensive. The nature of offshore structures is determined by the conditions in which they need to survive.  I had a brief career as a merchant seaman and have first hand experience of the violence of an ocean storm.

In addition to capturing temperature and dew point data, weather balloons also record wind speed and direction.  Unlike airports and buoys which usually report once an hour typically providing 8760 observations per year, an upper air sounding station might generate 200 - 300 observations per year for a given altitude.  At about 800m the flow of air is not influenced by the nature of the earth's surface and this known as the planetary boundary layer.  For North America and Europe, the average wind speed at 800m was often in excess of 10 m/s and the distribution similar to that for offshore locations.  I am intrigued by the concept of airborne wind turbines, machines which generate electricity can be summarised as being large chunks of metal, Doing this safely and economically is fascinating technical challenge.

Close to earth are personal weather stations.  For large scale installations turbines can be mounted on masts which gets them away from the turbulent zone close to the surface, but for small installations, once you get above a few metres from the ground, the cost of the mast becomes significant, not to mention the attitude of local residents.  Many PWS are located in urban or residential areas, they often suggest low average wind speeds, lots of turbulence and long periods of calm.

Whilst I'm sadly fond of software and databases, the hours spent with them were suggesting complexity.  I found two ways of exploring this.  The first was simply to cycle around the local coastal area with a wind speed meter.  Close to the coast the wind when blowing off the sea was smooth and similar to that reported by the local airfield.  In urban parts, it was weak and turbulent (however, destructive gusts can and do occur in such places).  On the surrounding ridges and hills, the wind speed had some relationship to that on the coast but was noticeably more turbulent.  Taking a kite on these expeditions made them more fun.  If you fly a kite people will smile at you and look happy whilst messing with an anemometer (or small model Savonius wind turbine)  is a solitary activity.

A variation on this theme is to observe the angle of trees.  In an area where the wind speeds are low, trees grow vertically, as the wind speed increases they take on a slant away from the direction of the prevailing wind, the countryside records the weather.

The second route was to look at the location of windmills.  During the 19th many windmills were constructed, mainly to grind corn but also for pumping, sawing timber and towards the end of the period a few were used for generating electricity.  The siting of a mill was critical to its economic success and therefore it is reasonable to assume that millwrights had a good knowledge of the interaction of wind and terrain.  I'm still working on this, but it is appears that ridge and plains were the favoured locations.   I'm still looking at this, but it appears that many early airfields were also build on shallow hills and ridge with the runways oriented along the direction of the prevailing wind, thus giving aircraft with low power/weight ratios compared to today's standards some assistance in getting aloft.

Wind is not constant and the energy available for conversion is proportional to the cube of its velocity, for example, wind blowing at 7.5 m/s represents approx 3.4 time more energy than at 5.0 m/s and at 10 m/s this increases to 8.0.  Wind energy arrives in "pulses" sometime separated by days or even weeks and subject to seasonal variation.

The old order changeth, yielding way to new

I was recently looking for a second hand PC power supply for a project which is so late I'm too embarrassed to talk about it.  Whilst walking the dog, I came across a box next to a wheelie bin, I knew it was not a PC, but it was probable that it would contain some sort of power supply, whilst it was not ideal it could save a ride into town.  When I got it home it revealed itself as a CD drive with SCSI connectors conveniently marked as having been acquired in 1993.  Against my better judgement, I powered it up with an energy meter in the line after which it drew a steady 10 watts.  From my experience, this type of device would mainly be used for installing software and performing system backups, when in use it might draw 20 - 30 watts, but only for as long as it takes to write a CD (which in 1993 could be quite a long time).  Back in the 90's a lot of computing was based on servers and local area networks (LANs), there were file servers, print servers, mail servers, database servers etc. etc. spread over one to many grey boxes depending on the size of the enterprise.  At that time I did not take much interest in energy consumption, however for a brief period, three of us worked in my house with a server and some PCs, suffice to say, the central heating was redundant.  Later we moved to offices with a server room which we also used for drying wet clothing.  To summarize, there was a lot of waste heat.

Raspberry Pi - consumption 3 - 5 watts

I'm currently messing with some energy management software which runs on a Raspberry Pi, this device has exceeded expectations, not least because of its energy consumption, I have not done any serious measurements, but I guess it takes something like 3 - 5 watts and nothing is warm to the touch.  The Pi uses a web server to output to my mobile phone.  Like the Pi, the phone is also good with energy.  An aging laptop and an LCD monitor complete my working environment and these are profligate in comparison with the phone and the Pi but even they don't compete with the central heating.

A computing peripheral from the past - Consumption 10 watts at idle.

Another element in computer energy us is the growth of the clouds.  Data centres use a lot of energy but they make it possible to share resources which have been optimised to minimize their energy consumption.  Servers in small offices used to be sized to meet the peak demand, but most of the time (including overnight and weekends) were just a convenient place to keep a mug of coffee warm.  For a few GB of data, cloud storage probably offers a better energy result than operating a dedicated in-house server

Whilst energy costs and footprint have been a factor in the increasing the efficiency of computing devices, equally important is that many applications, most notably the mobile phone won't work unless they are good at energy.

The doctrine of unforeseen circumstances now kicks in, I occasionally heat my work room with a coal fire, sometime augmented with wood I've picked up whilst walking the dog.