Wind power close to the city centre

When I first worked on this image of historic windmill sites around Brighton I was more interested in the terrain:.

Most mills are located on ridges or close to the coast to take advantage of the smooth air flow coming off the sea to the southwest.  Equally interesting is that they within the urban parts of Brighton and Hove whose population grew rapidly in the 19th century.  In paintings, wind and water mills are usually depicted in rural settings and most surviving structures are in rural areas where nobody wants a block of flats.  Yet in many big towns, flour milling was an urban industry.  The Moulin Rouge in Paris maybe better known for its performance of selections from the works of Offenbach, but the theatre was built on the site of one of the many windmills providing the Parisians with flour.  19th century milling techniques produced flour with a short shelf life, flour produced in modern plant will keep for several months, thus it made sense to have mills close to the bakeries.

Well into the 20th century, corn was cut in the fields during August and September and then gathered up into sheaves to dry and later stacked in such a way to protect it from the weather.  There it remained until labour was available for threshing to separate the grain from the stalks.  Originally, threshing was done manually and provided employment farm labourers when there was no other work available.  As with many other agricultural tasks, machines were invented to do the work.  During the Second World War, one of the tasks of women in the Land Army was to operate threshing machines which were moved and powered by tractors.

The peak of windmill building took place in the first half of the 19th Century, the graph below was estimated from an article in Wikipedia:

Most mills were built when demand for food in the expanding cities was growing and farming was a prosperous industry.  In the second half of the 19th Century, two trends emerged which were to bring about the demise of wind powered flower milling, both of which are related to the rise of steam power.  Steam ships enabled bulk cargoes to be moved across the oceans cheaply, this allowed the large wheat producing regions of North America to access the British market which in turn led to a fall in prices and a recession in British farming. The ports where the imported grain was landed also had access to coal from the mining areas of North East England and South Wales.  Thus flour milling became one of the industries based on sea ports alongside electricity generation and gas works.

This post is related to my interest in the economics of sustainable energy.  Whilst wind is the only thing that a modern electricity generating wind turbine has in common with a flour producing wind mill, I thought it would be interesting to attempt to understand the economics of windmills.  First, it seems that whilst milling might be seasonal, it was not directly related to agricultural production.   Flour could not be stored for long but grain could, so the mills needed to operate throughout the year.  Secondly, windmills declined because of the lower cost of alternatives, of which the availability of cheap transport was a significant element.  Also, as town expanded, the sites occupied by windmills had greater value as sites for housing.

Historic Windmill Sites

When I first became interested in sustainable energy it seemed that it was a data-rich industry, whilst good quality meteorological data is available in long time series, a lot of it comes from aerodromes which are flat, unobstructed spaces.  Solar devices are relatively independent of terrain, however, the output of wind turbines is determined by terrain.  Within a few kilometers of where I live, the wind speed can vary between 0 and 10 m/s according to location, where the terrain ranges from seafront, urban areas, exposed ridges and sheltered valleys.  Whilst industrial scale wind turbines for electricity generation are a relatively recent development, the wind was a significant source of energy in the 19th Century for milling and pumping applications.  There were approximately 20 windmill sites within what is now the Brighton and Hove city limits with several more within a few kilometers.  It is interesting to look at the location of these mills in the context of terrain.

The graphic below was mainly compiled from two sources:

• Timothy Carder's excellent "The Encyclopedia of Brighton" which was published in 1990 by East Sussex County Libraries.
• SRTM 1 arc second elevation data.  The 1 arc second data became available in 2014, prior to that only 3 arc second data was available for areas outside the US.  I very much appreciate this data being available.

The shading is relative and based on one of the ColorBrewer schemes with linear interpolation between the intervals, this is a convenient way of working with continuous data.

The graphic clearly shows that the favored location for windmills was either on the coast or along the chalk ridges that extend southwards from the Downs, only one appears to be located in a sheltered location.  Siting a windmill or turbine requires access to land, thus available locations may not always by the optimum ones.  The Google Earth screenshot below illustrates the competing uses for land.  In this case, the contours were generated using the SRTM 3 arc second data set.

Post mills are relatively portable, the machinery is mounted in a wooden structure which rotates around a post, a picture in a local museum shows one being moved on a sled drawn by oxen.  During their lifetimes five mills were moved to new sites either in one piece or in separate loads.  I have not studied the history of milling in the town, but I'm guessing that the early mills were built in the late 18th century to serve Brighton's growing population, however, as the demand for building land grew, the mills were displaced.  The screenshot shows the change of location of four mills, a fifth Preston Mill moved several miles to the north to Clayton where it is still in existence and has been restored and is now a listed building known as "Jill".  Towards the end of the 19th century the windmills came under the combined pressure of demand of building land and competition from steam and motor mills and their numbers dwindled.