21 October, 2020

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Technology Simplified For The Layman

By Kumar David

Prof Kumar David

Technology simplified for the layman:Too much wind and solar!

We have been brought up to believe that renewable or green energy, such as wind and solar generated electricity, is more expensive than natural gas, coal power or nuclear power, but it is good for the environment, and reduces health concerns and fears of catastrophic nuclear accidents. This is broadly true with some caveats that I will touch on anon, and this is why the Dutch, Danes, Germans and other rich countries are willing to pay more for electricity so that the wind generated component in their energy mix can be increased. However, except for the technical cognoscenti, few are aware that the electricity supply system itself could encounter hiccups if the amount of wind and solar energy incorporated therein became large; for example if it exceeded 20%. There are two types of concerns and I will touch on, both in language that a layman can follow.

It is important to appreciate that there is nothing in technology that is so complex that the elements essential for the public to make informed decisions have to be excluded; I refer to matters that have policy implications. As one of my friends put it, “make the political and administrative system people cantered and participatory”.  One does not need to be acquainted with cutting-edge medical science to understand the choice between treatment options if the implications are clearly explained by an able physician. Similarly, one does not need to be able to solve hard equations or write avant-garde software to get a grip on what I will explain here.

This topic was thrown into the limelight by a story in the Island (9 September) that upset many people; the headline alone was traumatising, “CEB blocks clean energy generation”! The gist of the matter was contained in a few sentences:-

“The Island learns that the Ceylon Electricity Board sent a confidential letter signed by General Manager F. K. Mohideen to the Sustainable Energy Authority ordering the immediate suspension of all upcoming renewable energy projects. When contacted, SEA Director General Dr. Thusitha Sugathapala told The Island that his institution had been instructed to limit solar power to 80 MW and wind power to 220 MW due to technical issues. Authoritative sources said that the shocking decision was based on a study done by the Asian Development Bank, and CEB management would review the matter after April, 2014”. 

I certainly am not suggesting that the ADB-CEB decision is correct or in error; that can be decided only when the report is made public and the community at large has an opportunity to study it, and researchers in universities and consulting houses have replicated the studies. This is what I mean by participatory decision making, and it is the duty of the CEB and the Power Ministry to make the report public, if indeed such instructions have been sent to the SEA. There are, however, certain known technical problems and it is good for the public to learn about them without needing to agree or disagree with the ADB-CEB in advance. This is my sole purpose today.

Stochastic or intermittent energy sources

I will focus on wind power though the arguments, mutatis mutandis, are applicable to solar. With the exception of places like Arabia, Sahara and Mojave Desert, wind is more important than solar. The land needed for a solar station producing as much energy as Norochcholi when all three stages are completed (and assuming they work properly!) would be about 5000 acres located in the dry zone. Hence more than 5% solar penetration in the CEB system is unlikely because of land constraints.  Wind has greater scope, especially if off-shore capacity (turbines out at sea and power brought in by cables) is included. Both wind and solar power plant are stochastic or intermittent. Intermittent is a simple word, stochastic emphasises that in studying these types of plant, engineers must use probability mathematics. Let me stick with the layman’s word intermittent.

There are two headaches that intermittent power plant create; a long term planning (or capacity) problem and a short-term operational (or spinning reserve) problem. The first is easier to explain. If one has a 100MW wind farm and the wind does not blow for a month; what the heck! The system is stuck without power for a month! True, wind farms are installed at windy locations after careful surveys, but there is still a possibility of reduced wind for periods of time. Will consumers accept power cuts because it is the slack season in Kalpitiya? Therefore large wind farms have to be backed up by large conventional power stations which run when the wind farm is becalmed. Germany’s E.ON Netz, one of the largest wind power suppliers in the world, says:

Wind energy is only able to replace traditional power stations to a limited extent. Their dependence on the prevailing wind conditions means that wind power has a limited load factor even when technically available. It is not possible to guarantee its use for the continual cover of electricity consumption. Consequently, traditional power stations with capacities equal to 90% of the installed wind power capacity must be permanently online in order to guarantee power supply at all times”. 

In concrete terms, this means that in 2020, with a forecast wind power capacity of over 48,000MW, only 2,000MW of traditional power production can be replaced by these wind farms”. 

These percentages can vary from place to place depending on the consistency of wind 24/7 and 364 days of the year, but clearly this is a problem. For example, if 800MW of wind power were installed at the best locations in Lanka, it would be possible to reduce conventional power plant installation by no more than about 100 or 200MW. You may say, “Why not, when the wind blows the turbines turn and we get free power, at other times run the say 600MW of backup conventional plant?” OK, but what about the capital commitment? Capital for 800MW of wind and for 600MW of gas turbines! The investment needed is almost doubled.

Megawatts versus Megawatt-hours

Newspaper reporters and sensationalists get the power-energy issue wrong; Megawatt (MW) refers to the size (power) of the wind-turbines; Megawatt-hour (MWh) refers to the energy output. It’s similar to the power of your car’s engine and the amount of petrol in your tank. OK you may have a V-6 engine that can churn out 380hp and wow the girls, but dear boy, if your tank (I mean petrol tank) is empty, what’s the use?

Sufficient spinning capacity has to be kept on-line to meet the collapse of wind power

Anyone who quotes the MW capacity of a wind or solar installation, but does say how many MWh of energy to expect in an average year, is a joker. The electricity output depends not on the size of the plant alone, but also on the reliability and quantity of wind blowing (or solar insolation). Solar energy varies diurnally (at night the sun goes down but the lights come on), is affected by cloud cover, and season (monsoon; length of day). To use a technical term, the ‘capacity credit’ of an intermittent power source is much below its nameplate MW rating.

Storage can help. Since the wind blows when it wills and the sun shines bright on your old Kehelwatte home, energy can be stored and used later, when demand comes on. Yes, but storage facilities cost money; batteries, compressed air, or on a large system scale, pumped-storage plant. Hence the gross MWh output and the overall cost economics (wind/solar equipment plus storage) have to be evaluated together in reviewing project viability. Simple megawatts, the journalistic profession notwithstanding, is the least relevant of the parameters. A finely filigreed case by case study is needed before project decisions are made.

Spinning Reserve

A family keeps some money in its current account at the bank, or under the pillow at home, to meet unexpected eventualities like having to rush a kid to hospital. The larger part of its savings, to buy a house or send a kid to university, is allowed to mature in time-deposits or such slow maturing instruments. Controllers operating the CEBs power system will call the former ‘spinning reserve’ and the latter load carrying plant cum long and medium term reserves. The need for spinning reserve arises from the possibility of unexpected happenings; the demand for electricity may suddenly increase due to unforeseen events, or a big generator or transmission line may trip-out (get disconnected due to a fault) increasing the strain on the plant that remains operational.

The problem with intermittent sources like wind and solar is that by their intermittent nature they add to this headache. Nature is an unpredictable woman; the wind may suddenly turn frigid like an unreasonable wench. The graph accompanying this article is taken from a report of the same German company that I quoted from before. It illustrates what happened during the Christmas period in 2004. Between noon on Christmas Eve and noon on Boxing Day the wind power being injected into the system collapsed by 6000MW (more than twice all Lanka’s generators combined). Worse was the operator’s panic when wind power was declining at 16MW per minute on the afternoon of 24 December. This is not as nightmarish as the catastrophic collapse that precedes a total black-out, but it is problem enough. Operators have to guard against instability by keeping sufficient spare capacity spinning on other generators.

Not so green

The case I have made so far is that it is true that there are certain planning and operating constraints to keep in mind regarding the maximum amount of wind and solar power that can be comfortably incorporated in a system. This is not to endorse or contradict the reported ADB-CEB figures and I repeat my call for the publication of the technical report in full with elucidation of methodology and assumptions. Then the results can be reviewed by others.

There is however another point that is of interest to the public at large; green energy is not altogether green. As discussed before, if each MW of wind or solar has to be backed up by installing 0.8MW (or whatever) of conventional plant, and if each MW of intermittent power in operation needs to have 0.3MW of conventional plant running as spinning reserve, well plenty of carbon dioxide and particulate matter are getting into the atmosphere.

Apart from this there is the energy used in the construction of plant whatever the technology. Compare a 2000MW coal fired or nuclear power station to 2000 units of 1MW each wind turbines. Compare again with the great dam to support a 2000MW hydroelectric project – which of the three uses more energy in construction and materials processing? There is no one answer that fits all cases.

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