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Wind and solar powered generators are weather dependent systems, the data feed for Doris is weather reports, these are in real time on the Pi and historic on the laptop. Climate is what you expect and weather is what you get. In the UK our weather is influenced in turn by the land mass of continental Europe and the water mass of the Atlantic Ocean from which come a procession of depressions. The result is a moderate, but varying climate. The yield from Agriculture is in part influenced by the weather, for example in the period 2010 to 2014, the UK wheat harvest varied from approx. 12 to 16 million tons.
When I first became interested in sustainable energy, I started to seek out data on wind speed and solar irradiance and cycle around the town and local countryside with a wind speed meter, these exercises were undeniably instructive. About the same time, I saw my house on Google Earth and became ashamed of the state of the garden. I cleared the weeds, made an attempt to improve the flower beds and created a small vegetable garden. This provides a small supply of misshaped vegetables of a quality that supermarkets refuse to stock . It also taught me the relationship between sunshine and plant growth. Beetroot grown in the partially shaded front garden are sad, weedy things, whilst those grown at the back in full sun are big enough to cook and eat, even though they are smaller than the imports from Spain and Egypt. The seasons that shape a garden, also determine the output of wind and solar energy systems. Solar panels have good and bad years, just like the harvests.
A useful piece of advice from a manager on whom I was inflicted, was "first make the code work, then make it work quickly". Doris is still in the first stage and does not run quickly, so it had only worked through five years of data before I had to move on, ideally, you would need a much bigger sample to get an understanding of year-on-year variations, so this graph which shows the %age of energy taken from conventional sources only shows that there is year-on-year variation.
Some of the variation is due to variations in wind speed as shown in the graph below. I have memories of the summer of 2013 as being sunnier than usual and this is reflected in the low dependency on conventional sources because of the increased output from solar panels under a clear sky.
Doris is intended to explore the response of a system which attempts to minimize dependency on conventional energy sources. The output of coal and gas power stations can be varied to meed demand whilst that of sustainable systems is dependent on the weather. In the 19th century, sailing ships started to be displaced by steam driven ones because they were more reliable. The design of sustainable system need to be aware that the supply may be constrained.
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