Doris B - Power Curve(2)

Progress (and more to learn and some bugs to find).  The Arduino captured a one minute time series of the voltage across a 22 ohm resistor attached to the generator’s output terminals whilst it was hand cranked.  The load on the crank varies during a rotation so there are constant variations in speed and this can be seen in the time-series, the flywheel effect of the wind turbine’s rotor will probably have a smoothing effect.  The circuity between generator and the ADC needs to include a zenor diode to provide some protection for the chip, once that’s in place, the DC biasing can be setup sensibly.  However, the time series was good enough to passed through a Fourier Transform routine which allowed the rotational speed to be estimated.

The speed and voltage data can then be combined into a power curve, the variations in power are due to uneven cranking.  The 22 ohm resistor was chosen because I had one in a box somewhere.  To get peak performance from the generator will require matching the impedance of the load to the impedance of the generator.  The planned load is a USB power pack.

Whilst messing with electronics and Fourier transforms has been instructive, so too has hand cranking the generator, clearly the torque required varies with the value of the resistor, with a 10 ohm resistor the torque required almost pulls the generator of its mounting.

So on the next trip to the beach, I’ll take a bag of resistors and see how they effect the ability of wind to turn the rotor.

Doris B - Power Curve(1)

In order to match the rotor to the generator, it is necessary to understand the behaviour of both. The first step is to grab data, starting with the generator because this can be done on the workbench rather than the beach. Much the same solution can be used for both. Currently, the instrumentation is an Arduino Nano which provides analogue to digital conversion (ADC) and a Raspberry Pi for processing. Electricity and electronics were part of my OND but that was a long time ago, so setting up the tests involved a little vexation, but eventually a Python programme managed to capture a sample of the output of the generator.

Two things became apparent, first the output of the generator is complex and not a simple sine wave, Secondly the starting torque increased significantly from the open circuit value when a resistor was placed across the terminals.

The next step is to analyse the data, the plan is to use a Fourier transform to determine the rotational speed and the area under the curve will provide the energy generated, putting the two together will provide a power curve (I hope). The Ardunio is a brilliant tool and may offer a solution to the high starting torque. If pulse width modulation is applied to the load, the turbine can start with no load and as speed increases the load on it is increased, this in turn could provide a means of optimising performance.

Doris B - First outing

 On Wednesday evening I took Doris B up to Green Ridge and assembled it.  The wind speed was  roughly 5 - 7 m/s.  Whilst held aloft, the rotor was 2.5m above the ground, it turned smoothly and quietly, which was pleasing, an earlier version had struggled to turn at 10 m/s, so progress is being made.  The next step is understand the relationship between the rotor and the generator,  The speed of this type or rotor is proportional to the wind speed and it is important that the rotor turns fast enough for the generator to produce a useful output.  On returning home I ordered some bridge rectifiers and  an Arduino Nano.  The first use of these will be to obtain a power curve for the generator.

My favourite place for messing with this stuff is on the beach at Aldrington, when the wind is from the SW there is little turbulence.  Most of the other people are beach fishermen and we occasionally swap observations on the state of the sea.  There was a curious incident at Green Ridge, a dog walker scooped up his spaniel, carried it over to my rucksack and let the dog have a good sniff, then walked off carrying the dog, I said "good evening" politely.

Doris B - Trial Assembly

10-April-2019 - Completed the partial assembly of the Doris B5/6 small vertical axis wind turbine this morning before giving it a trial outing on the Downs later today. 

The objectives of the initial trials are to determine if it rotates in a wind of 5 m/s and does not disintegrate at 10 m/s. If it survives, the next step will be add some instrumentation and to try and figure out how it works. The design is based on some maths, guesswork and wishful thinking. There have been four previous versions, mostly made of Meccano and sawn up bits of plastic pipe, this one is mainly made of wood. This is not a finished design but part of a process of learning how to make small wind turbines for rural and urban environments, hopefully the design will evolve. The objective for this series is an output of 2.5 watts (similar to a standard USB port) at 5 m/s.

The early days of electricity - Diverse decsions and technologies

Public electricity supplies started to evolve in the UK during the 1880s.  Today electricity is a utility accessible by a high proportion of the population, but in its early days it was part of the luxury goods industry, a unit might cost between 4d and 1s 3d (2p to 6p) which is around £1 in today's money.  Its attraction was that it was convenient and clean and therefore perceived as being healthier than the gas lamps that it was to displace over the next half century.  Arc lamps improved the lighting of streets and public spaces and this gave local authorities an interest in the industry.  The industry grew using both public and private capital, and some local authorities proved to be adept in managing the evolution of a new technology.  Street lighting was often managed by the gas committee, because that was how the streets were lit, so decisions about borrowing substantial sums against the rates were being made by men who were often involved in decisions about the lighting of urinals

The caption on this cartoon was Electricity for the Ballroom

Electricity works, especially those supplying DC had to be close to the consumer because of the limitation of the early distribution systems.  This resulted in generating plant being located in unlikely places like London's Carnaby Street: its contribution to the swinging sixties is well remembered but its power station is long forgotten. The search for early power stations often takes one to the posher parts of town.

Most of the early dynamos and alternators were turned by reciprocating steam engines.  The early engines were relatively small and built by companies also known for their traction engines and road rollers such as Robey or Fowler.  Until the development of high speed engines such as those of Willans which facilitated direct coupling, the generators were connected to the engine by a belt drive.  Belts would sometime break, in 1882,  the Mansion House was provided with electricity from a generator installed in the basement, where the belt was driven by a gas engine.  During a dinner the belt broke giving the diners the impression they were being attacked by gunfire.  In 1888, the first turbine driven alternator was installed at the Forth Bank power station, close to the centre of Newcastle.

Large generators were steam driven because steam engines could be built to supply hundreds of horsepower and it was a mature technology. At this time steam engines were almost as common as electric motors are today, they powered mills, railways, ships, sawmills, pumps and anything big which needed turning.  Smaller plant in urban areas often used gas engines.  By 1880, most urban and some rural areas had a gas supply and whilst this was mainly used for lighting, it could also used as fuel for engines such as those made by Crossley.  The attraction of gas engines was that there was no need for a boiler and most could be hand cranked into life when needed.  Judging by the number of adverts for fractional horsepower gas engines in pre-1900 magazines, many modest homes may have generated their own electricity from gas.  Such a system is described in a biography of Magnus Volk, the house in which it was installed is comfortable, but not grand.  Many micro systems incorporated a bank of lead acid accumulators making it unnecessary to run the gas engine continuously.

During 1880s and 90s AC and DC systems competed for supremacy.  The AC system would eventually win because it facilitated transmission over long distances allowing big power stations to be sited away from city centres.  However, DC did have the advantage of being able to use lead acid accumulators for storage.  Then as now, the demand for electricity peaked in the early morning and early evening and if only a few hundred homes were being supplied overnight demand could be met from the accumulators allowing the steam plant to be shut down or the boilers banked up.  Accumulators also provided some back-up in the event of plant problems, for this reason, some consumers perceived DC systems as being more reliable.

In the early days, the demand for electricity was measured in kW rather than MW making it possible to supply rural communities using small plant connected to consumers by wires hung from wooden poles. Some of these used water power, Godalming claims the distinction of having the first public electricity supply, this was from a generator turned by a water wheel in a mill. Reeth in Yorkshire had a similar arrangement.

Initially, electricity was an urban industry relying on clusters of high income households, some smaller communities were still not connected to a central generating station until well into the interwar period.  It was during this time that many small electric companies were formed, examples include the Steyning Electric Light Company and the Peacehaven Electric Light and Power company.  I've seen photo's of these companies' plant, both show belt driven generators, in both cases it looks like the motive power is coming from an industrial internal combustion engine, but it is not clear if the fuel was oil or gas.  One of the more interesting of these companies is the High Salvington Electric Light Company, this served a small development of houses on the Downs to the north of Worthing. The generator was turned by a wind mill/turbine similar in design to those of West Texas -the electricity was used to charge up accumulators which in turn supplied the consumers.  There was an oil engine back-up for days when the wind did not blow.  Now that utility scale storage, like Tesla's installation in Adelaide is becoming available, High Salvington can claim to be pioneer in the field of sustainable energy.

A random history of energy economics (3) - The life cycle of fuels

Fuels like any other product have life cycles.  The stages of the classic life cycle are growth, maturity and decline.  For some fuels like wood, the length of the cycle is measured in millennia, that of coal looks like it might be centuries and carbide probably decades.

My understanding of acetylene lamps is that they were developed for cars and motorbikes at the very end of the 19th century.  Whilst electric incandescent lamps could be powered by a lead-acid accumulator, they were not bright enough to allow safe driving at speed.  The attraction of acetylene is that it burns at a high temperature and produces a bright light.  The gas was generated by the action of water on calcium carbide, the lamps were so constructed that a reservoir of water dripped on calcium carbide which was then burnt in a lamp with a reflector.  The brightness of the lamp was controlled by adjusting the water flow, as the gas was generated, the carbide turned to slaked lime.  "Carbide" was sold in garages along with petrol and oil during the 1920's, but as automotive electrics improved and effective headlamps which could be controlled by a switch became a standard fitting, carbide lamps were largely displaced by the 1930s.

Kerosene (a.k.a. paraffin) as a domestic fuel had a somewhat longer life cycle, it was used for lighting and cooking in late 19th century.  In the era of solid fuel ranges. it facilitated cooking without first having to light a coal fire, although many found the smell unattractive.  Paraffin heaters were widely used well into 1970s and may people remember the Esso's adaption of "the smoke gets in your eyes" for their TV adverts.  Paraffin heaters were generally displaced by low cost gas central heating in the 1970s.

The same pattern of growth, maturity and decline is apparent in the UK coal consumption.  A spokesman for OPEC once commented that the UK did not run out of coal, they just stopped using it.  In the latter part of the 19th century consumption grew as industry, the railways, gas production and other applications expanded.  It remained constant for approximately half a century until the 1970's.  During this time the economy was growing, but technology was evolving which allowed coal to be used more efficiently.  In 1890, electrical power generation had a thermal efficiency well below 5%, by 1970, this was approaching 40%.  The boilers used in the early power stations operated around 150 psi, by 1945 some were operating at 675 psi, the rising temperatures and pressures resultined in higher operating efficiencies.

In the 1960, natural gas (mostly methane) from the North Started to displace coal as a domestic and industrial fuel.

The displacement of coal by natural gas is apparent in the graph below.  Starting around 1830, many towns acquired as gas works either privately or municipally owned, in the early years the principal use was for lighting, but cooking, heating and industrial use increased.  Between 1900 and 1930, electricity, also generated from coal, displaced gas for lighting.    The availability of North Sea gas bought about the extinction of the coal gas works in less than a decade.

Gas turbine power stations, steadily displace coal fired steam technology, a process which accelerated in the 21st century as concerns over the environmental effects of coal grew.

Relevance for Today

The energy mix is constantly changing, the driving force is technology, over two centuries it has included coal, wind, nuclear (after 50 years is this an old technology) and many evolutions within each one.  There is a lot of evolving technology, offshore wind and electrical storage maybe the key elements.  Several cities are talking about petrol or diesel vehicles and only allowing electrical ones, so more change can be expected.

A Random history of energy economics (2) - The Horse and the Lorry

By 1900 railways were the most important element in Britain's transport infrastructure, but they only provided town-to-town communication.  The distribution of goods within a town was done with men with barrows and horses with carts.  In the rural areas "carriers" moved goods and people around with horse drawn wagons.  Horses were widely used well into the 1930s by which time motor transport was firmly established.

I came across some figures comparing the cost of coal distribution from depot to customer by 30 cwt truck and a horse and cart in 1931.  The figures seem to relate to an adequately funded and well run coal business.  Two points about the graphs, first they are for 1931 and are not comparable to costs in 2017 and that the original data is in pounds, shillings and pence which was converted decimal pounds for the benefit of Excel.  I have doctored the data a little for the sake of comparability.  In 1931, the price of domestic coal was between £1.50 and £4.50 per ton depending on the grade, local terrain and market conditions.  Anthracite was the premium product whist Bituminous coal was cheaper, also coke from gas works was widely used.

Both the horse and truck were depreciated over four years and  funded by money at 5%, the horse cost £90 and the truck £250.  The cost structures for both modes of transport is broadly similar, the exceptions are higher capital related costs of the truck, the legal requirements for a license and insurance and maintenance.  Food for the horse and fuel for the truck are similar as are the wages of the driver.

The big difference is the level of productivity, the horse shifts 38.5 tons/week, whilst the truck can do 49.5, but the unit costs are similar at around £0.20/ton.  I suspect that there was a lot of variation within the industry.  If only one man was employed to work with the truck, he would have to work harder than the bloke with the horse and cart, the references I have seen to coal sacks at this time suggest there were 1.25 cwt ( very roughly 62kg or very heavy, I struggle with 25kg bags of sand).  This might have been OK for a youngish man shooting coal into a cellar with street access, much less for an older one shifting the bag from the street to coal store in the scullery at the back of the house.


Some random reading suggests that the domestic coal market was split into three sectors.  At the top end would be customers that bought coal in large quantities, say greater than half a ton, possibly belonging to a "coal club"  which spread the cost more or less evenly over the year, trucks would give an advantage to merchants serving this group.  Those serving customers purchasing less than half a ton and paying the current market price might have a cost advantage from the potentially lower costs of the horse and cart.  At the bottom end of the market would be those purchasing small quantities of coal, possibly as little as 7 pounds would pay high prices to men with barrows.