{"id":222450,"date":"2021-09-12T00:00:14","date_gmt":"2021-09-11T18:30:14","guid":{"rendered":"https:\/\/www.colombotelegraph.com\/?p=222450"},"modified":"2021-09-15T23:24:25","modified_gmt":"2021-09-15T17:54:25","slug":"stochastic-interruptible-electricity-sources","status":"publish","type":"post","link":"https:\/\/www.colombotelegraph.com\/index.php\/stochastic-interruptible-electricity-sources\/","title":{"rendered":"Stochastic & Interruptible Electricity Sources"},"content":{"rendered":"

By Kumar David<\/a> –<\/span><\/strong><\/span><\/p>\n

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Prof. Kumar David<\/p><\/div>\n

As the country moves towards increased generation from renewable sources the public will need to learn a little bit about some peculiar aspects of wind and solar power. I will call them the stochastic (S-word) and the interruptible (I-word) nature of both. They are related but for the engineer the implications are different. The S-word says the wind may blow like crazy all night but come morning it\u2019s becalmed and may not pick up again till god knows when. (\u201cThe wind bloweth where it listeth, but thou canst not tell whence it cometh and whither it goeth\u201d: John 3.8). More troublesome is the I-word, quick and intermittent fluctuations between furious force and stately calm. The chaps in the Control Room tear their hair out when a large quantum of wind power freaks out suddenly. Imagine if one Vitoria-equivalent of wind power splutters on and off like a car with a petrol block. I will explain how the control people deal with it. <\/span><\/p>\n

Similar things happen with solar; it\u2019s a beautiful sunny day but quickly darkens with rain. It\u2019s clear morning but clouds drift across and cut the insolation on the panels. Oh hell!<\/span><\/p>\n

Shall I compare thee to a summer\u2019s day?<\/span><\/p>\n

Thou art more lovely and more temperate:<\/span><\/p>\n

Fresh winds do shake the darling buds of May,<\/span><\/p>\n

And summer\u2019s lease has all too short a date:<\/span><\/p>\n

And often is his gold complexion dimm\u2019d;<\/span><\/p>\n

By chance, or nature\u2019s changing course untrimmed:<\/span><\/p>\n

~ Lines from Sonnet XVIII<\/i><\/span><\/p>\n

The S-word (stochastic is a fancy way to say probabilistic) is used to emphasise the headaches of the planner not the operator. Planners don\u2019t tear their hair in panic as operators do, they go bald slowly; Buddhika\u2019s hairless pate shimmers like a polished egg. Look at it in a simple way. Say we have two 100 MW wind farms, one in Mannar, the other Pooneryn. Take Mannar first: Full power output is 100 MW when wind blows with force. Say the mean is 60, hence between zero and 100 it is distributed with a probability like a bell-shaped curve with a peak at 60 and cuts off completely at 100. Pooneryn will be similar but here\u2019s the jinx. The two may not be correlated (occur simultaneously) or only partly correlated. As the apostle John perceptively pointed out, the wind listeth as it wishes.<\/span><\/p>\n

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Proposed gigantic 10 GW array covering 30,000 acres in Australia\u2019s
Northern Territory; expected to yield over 20 TWh<\/p><\/div>\n

Planner have a good idea how much energy to expect each year from each farm but cannot hope for a steady 120 MW all the time. True they mostly think of the energy availability per annum but they must also tell management to give operators the right tools at each location to ride over severe fluctuations. If there are a large number of wind-farms distributed across the island, planners can estimate how much energy to expect each year or season, but riding through large fluctuations is a different story. I worked on this topic 40 years ago but those braincells are all dead. But don\u2019t panic, there are bright young lads and lasses in CEB planning who know how to tackle these ambiguities.<\/span><\/p>\n

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The 140 MW Luz del Norte solar plant in ever cloudless Atacama occupies 1200 acres<\/p><\/div>\n

Operational concerns \u2013 the I-word – seem to agitate the CEB these days as more windfarms are slated to come on grid in the next three or four decades (unless the economic debacle of a penniless government shrivels up money for food, medicine, electrification and renewables). The wind that shakes the darling buds of May, and the lovely sun of a summer\u2019s day, are as fickle as my lady\u2019s changing countenance untrimmed. \u00a0 <\/span>Imagine you are the control engineer leaning back in your dispatcher\u2019s chair sipping your well-earned morning coffee after a busy night reading Tom Mix comic books. You are gloating over 600 MW of wind and solar that you are dispatching, and then the gods strike! A large part of it goes up in metaphorical smoke at a moment\u2019s notice.\u00a0 <\/span>If wind or solar output fall quickly by a hefty amount it is the same as the forced outage of a big unit like Victoria or Norochcholi and the shock to the system is similar. <\/span><\/p>\n

Germany suffers horrendous outages of power whenever the wind gods go on a lightning strike (no pun intended) and the system not only in Germany but throughout the interconnected Northern European grid experiences severe stability problems. Now wind farms are being shredded; see for example:<\/span><\/p>\n

\u201cThousands of wind turbines in Germany will be shredded next year\u201d<\/span><\/p>\n