Intermittence of renewables

Composed by Galina Vitkova

Everybody knows that renewables are expensive, sometimes very expensive and make electricity price go up. For example, in the Czech Republic the expansion of building solar photovoltaic installations, donated from the state budget, caused increasing electricity price over 12 %. Another example of increasing the costs is given in the table below.

Increase in system operation costs (Euros per MW·h) for 10% and 20% wind share^[7]

	Germany	Denmark	Finland	Norway	Sweden
10%	2.5	0.4	0.3	0.1	0.3
20%	3.2	0.8	1.5	0.3	0.7

Nevertheless, only few people are aware of great intermittence of renewables, which excludes their usage as a main source of electricity generation not only nowadays, but in the future too. Actually no technical and industrial society can exist and develop using unreliable and intermittent power supplies. Nothing in our integrated and automated world works without electricity, this life-blood of technical civilisation. Just imagine what would happen to a society where electricity supply is turned off only for a short time, possibly every week, or if the power is cut for a whole fortnight or more. Life stops, production ceases, chaos sets in. And this is exactly what could arise if we bank on renewables. Thus let us take notice of features specific for wind and solar (photovoltaic) power installations, which are typically built in Europe. 

Image via Wikipedia

The entire problem with renewables is that they are perilously intermittent power sources. The electricity produced using them is not harmonized with the electrical demand cycle. Renewable based installations generate electricity when the wind blows or the sun shines. Since the energy produced earlier in the day cannot be stored extra generating capacity will have to be brought on-line to cover the deficiency. This means that for every renewable based system installed, a conventional power station will have to be either built or retained to ensure continuity of energy supply. But this power station will have to be up and running all the time (i.e. to be a ’spinning-reserve’) because it takes up to 12 hours to put a power station on-line from a cold start-up. Thusly if we want to keep up continuity of supply the renewable sources result in twice the cost and save very little of fossil fuels.

Wind power is extremely variable. Building thousands of wind turbines still does not resolve the fundamental problem of the enormous wind variability. When days without significant winds occur, it doesn’t matter how many wind turbines are installed as they all go off-line. So, it is extremely difficult to integrate wind power stations into a normal generating grid.  

Solar energy is not available at night and cloudy days, which makes energy storage the most important issue in providing the continuous availability of energy. Off-grid photovoltaic systems traditionally use rechargeable batteries to store excess electricity. With grid-tied systems excess electricity can be sent to the transmission grid and later be settled.

Renewable energy supporters declare that renewable power can somehow be stored to cope with power outages. The first of these energy storage facilities, which comes to aid the thousands of wind-turbines motionless when winds do not blow and solar installations without generating when the sun does not shine, is the pumped water storage system. However, this claim is not well-founded for the following reasons:

• In most countries of Europe pumped storage systems are already fully used for overpowering variability in electrical demand, and so as a rule they have no extra capacity for overcoming variability in supply due to the unreliable wind and solar generation systems.
• Pumped storage systems have limited capacity, which can be used for electricity generating  for just a few hours, while wind or solar generation systems can go off-line for days or weeks at a time.
• Pumped storage systems are not only hugely expensive to construct, the topography of european countries ensure that very few sites are available.

As for flywheel energy storage, compressed air storage, battery storage and hydrogen storage each of these systems is highly complicated, very expensive, hugely inefficient and limited in capacity. The hydrogen storage is especially popular and hyped among proponents of renewables. The hydrogen, produced and stored when renewables generate more electricity than it could be used, is supposed to propel vehicles and generators. Unfortunately these hydrogen powered vehicles and generators are only about 5% efficient. In addition, hydrogen storage vessels are highly flammable and potentially explosive. Practically nowadays there is no energy system available that can remotely be expected to replace renewable energy resources in a large scale, while they are out of functioning.

In numerous publications about renewables we are chiefly informed about expanding and increasing investments in renewables, multiplying their installed capacity and volumes of produced electricity, everything in absolute values, without comparing these indicators with values of other resources, especially when they speak about volumes of production. In the table below you find comparable values of volumes electricity produced by nuclear power plants and renewable installations. Look it through and have your own opinion of the problem.

Comparison of nuclear and renewable electricity producing by top nuclear electricity producers (TW·h-year/% of total electricity production in the country)

	Country	Year	Nuclear  2007	Wind Power	Solar Power
1	USA	2009	837/19.4%	70.8/1.64%	0.808/0.019%
2	Japan	2008	264/23.5%	1.754/0.156%	0.002/0.000%
3	Russia	2008	160/15.8%	0.007/0.0007%
4	Germany	2010	141/22.3%	36.5/5.499%	12.0/1.898%
5	Canada	2008	93/14.6%	2.5/0.392%	0.017/0.003%

Conclusion: Common people must know and must interest about situation in producing and supplying electricity. Only then they will be able to enforce on the governments to make rightdecisions in order to ensure stable supplying electricity, without which modern civilisation cannot exist and improve.

 References:

• Wikipedia, the free encyclopedia, Wind Power, Solar Power
• Renewable energy – our downfall?   By Ralph Ellis
• Key World Energy Statistics – International Energy Agency (IEA)
• Comparative costs of electricity from different sources |April 26, 2010

Related articles

• Environmentalists vs. Renewable Energy (papundits.wordpress.com)
• Renewables and efficiency cannot fix the energy and climate crises (part 2) (buildeco.wordpress.com)

Advertisements

---

Posted in education, electrical engineering, Tech Comm, technical English
Tags: Electricity generation, English for engineers, English for technical students, English for technicians, Nuclear power, Renewable energy, Solar power, studying technical English, Tech Comm, technical texts for English studying, Wind power