In Part I we had a brief look at the question of intermittency – renewable energy is mostly not “dispatchable”, that is, you can’t choose when it is available. Sometimes wind energy is there at the right time, but sometimes when energy demand is the highest, wind energy is not available.
The statistical availability depends on the renewable source and the country using it. For example, solar is a pretty bad solution for England where the sun is a marvel to behold on those few blessed days it comes out (we all still remember 1976 when it was more than one day in a row), but not such a bad solution in Texas or Arizona where the peak solar output often arrives on days when peak electricity demand hits – hot summer days when everyone turns on their air-conditioning.
The question of how often the renewable source is available is an important one, but is a statistical question.
Lots of confusion surrounds the topic. A brief summary of reality:
- The wind does always blow “somewhere”, but if we consider places connected to the grid of the country in question the wind will often not be blowing anywhere, or if it is “blowing” the output of the wind turbines will be a fraction of what is needed. The same applies to solar. (We will look at details of the statistics in later articles).
- The fact that at some times of peak demand there will be little or no wind or solar power doesn’t mean it provides no benefit – you simply need to “backup” the wind / solar with a “dispatchable” plant, i.e. currently a conventional plant. If you are running on wind “some of the time” you are displacing a conventional plant and saving GHG emissions, even if “other times” you are running with conventional power. A wind farm doesn’t need “a dedicated backup”, that is the wrong way to think about it, instead there needs to be sufficient “dispatchable” resources somewhere in the grid available for use when intermittent sources are not running.
- The costs and benefits are the key and need to be calculated.
However, the problem of intermittency depends on many factors including the penetration of renewables. That is, if you produce 1% of the region’s electricity from renewables the intermittency problem is insignificant. If you produce 20% it is significant and needs attention. If you produce 40% from renewables you might have a difficult problem. (We’ll have a look at Denmark at some stage).
Remember (or learn) that grid operators already have to deal with intermittency – power plants have planned and, even worse, unplanned outages. Demand moves around, sometimes in unexpected ways. Grid operators have to match supply and demand otherwise it is a bad outcome. So – to some extent – they have to deal with this conundrum.
What do grid operators think about the problem of integrating intermittent renewables, i.e., wind and solar into the grid? It’s always instructive to get the perspectives of people who do the actual work – in this case, of balancing supply and demand every day.
Here’s an interesting (free) paper: The intermittency of wind, solar, and renewable electricity generators: Technical barrier or rhetorical excuse? Benjamin K. Sovacool. As always I recommend reading the paper for yourself. Here is the abstract:
A consensus has long existed within the electric utility sector of the United States that renewable electricity generators such as wind and solar are unreliable and intermittent to a degree that they will never be able to contribute significantly to electric utility supply or provide baseload power. This paper asks three interconnected questions:
- What do energy experts really think about renewables in the United States?
- To what degree are conventional baseload units reliable?
- Is intermittency a justifiable reason to reject renewable electricity resources?
To provide at least a few answers, the author conducted 62 formal, semi-structured interviews at 45 different institutions including electric utilities, regulatory agencies, interest groups, energy systems manufacturers, nonprofit organizations, energy consulting firms, universities, national laboratories, and state institutions in the United States.
In addition, an extensive literature review of government reports, technical briefs, and journal articles was conducted to understand how other countries have dealt with (or failed to deal with) the intermittent nature of renewable resources around the world. It was concluded that the intermittency of renewables can be predicted, managed, and mitigated, and that the current technical barriers are mainly due to the social, political, and practical inertia of the traditional electricity generation system.
Many comments and opinions from grid operators are provided in this interesting paper. Here is one from California:
Some system operators state that the intermittence of some renewable technologies greatly complicates forecasting. David Hawkins of the California Independent Systems Operator (ISO) notes that:
“Wind, for instance, can be forecasted and has predictable patterns during some periods of the year. California uses wind as an energy resource but it has a low capacity factor for meeting summer peak-loads. The total summer peak-load is 45,000 MW of load, but in January daily peak-loads are 29,000 MW, meaning that 16,000 MW of our system load is weather sensitive. In the winter and spring months, big storms come into California which creates dramatic changes in wind. We have seen ramps as large as 800 MW of wind energy increases in 30 min, which can be quite challenging“.
..A report from the California ISO found that relying on wind energy excessively complicated each of the five types of forecasts. As the study concluded, ‘‘although wind generator output can be forecast a day in advance, forecast errors of 20–50% are not uncommon’’
And a little later:
For instance, California Energy Commissioner Arthur Rosenfeld comments that:
“Germany had to build a huge reserve margin (close to 50 percent) to back up its wind. People show lots of pictures of wind turbines in Germany, yet you never see the standby power plants in the picture. This is precisely why utilities fear wind: the cost per kWh of wind on the grid looks good only without the provision of large margins of standby power“.
Thomas Grahame, a senior researcher at the U.S. Department of Energy’s Office of Fossil Fuels, comments that:
‘‘when intermittent sources become a substantial part of the electricity generated in a region, the ability to integrate the resource into the grid becomes considerably more complex and expensive. It might require the use of electricity storage technologies, which will add to cost. Additionally, new transmission lines will also be needed to bring the new power to market. Both of these add to the cost’’
The author looks at issues surrounding conventional unplanned outages, at the risks and costs involved in the long cycle of building a new plant plus getting it online – versus the rapid deployment opportunities with wind and solar.
I’m aware of various studies that show that up to 20% wind is manageable on a grid, but above that issues may arise (e.g. Gross et al., 2006). There are, of course, large numbers of studies with many different findings – my recommendation for placing any study in context is first ask “what percentage of renewable penetration was this study considering”. (There are many other questions as well – change the circumstances and assumptions and your answers are different).
The author of this paper is more convinced that any issues are minor and the evidence all points in one direction:
Perhaps incongruously, no less than nine studies show that the variability of renewables becomes easier to manage the more they are deployed (not the other way around, as some utilities suggest). In one study conducted by the Imperial College of London, researchers assessed the impact that large penetration rates (i.e., above 20 percent) of renewable energy would have on the power system in the United Kingdom. The study found that the benefits of integrating renewables would far exceed their costs, and that ‘‘intermittent generation need not compromise electricity system reliability at any level of penetration foreseeable in Britain over the next 20 years.’’ Let me repeat this conclusion for emphasis: renewable energy technologies can be integrated at any level of foreseeable penetration without compromising grid stability or system reliability.
Unfortunately, there was no reference provided for this.
Claiming that the variability of renewable energy technologies means that the costs of managing them are too great has no factual basis in light of the operating experience of renewables in Denmark, Germany, the United Kingdom, Canada, and a host of renewable energy sites in the United States.
As I commented earlier I recommend readers interested in the subject to read the whole paper instead of just my extracts. It’s an interesting and easy read.
I can’t agree that the author has conclusively, or even tentatively, demonstrated that wind & solar (intermittent renewables) can be integrated into a grid to any arbitrary penetration level.
In fact most of the evidence cited in his paper is at penetration levels of 20% or less. Germany is cited because the country “is seeking to generate 100 percent of its electricity from renewables by 2030”, which doesn’t quite stand as evidence (and it would be uncharitable to comment on the current coal-fired power station boom in Germany). Denmark I would like to look at in a later article – is it a special case, or has it demonstrated the naysayers all to be wrong? We will see.
The penetration level is the key, combined with the technology and the country in question. It’s a statistical question. Conceptually it is not very difficult. Analyze meteorological data and/or actuals for wind and solar power generation in the region in question over a sufficiently long time and produce data in the format required for different penetration levels:
- minimums at times of peak demand
- length of time power from X MW capacity is below Y% of X MW capacity & how often this occurs & as a function of peak demand times
- ..and so on
This does mean – it should be obvious – that each region and country will get different answers with different technologies. Linking together different regions with sufficient redundant transmission capacity is also not trivial, neither is “adding sufficient storage”.
If the solution to the problem is an un-costed redundant transmission line, we need to ask how much it will cost. The answer might be surprisingly high to many readers. If the solution to the problem is “next-generation storage” then the question is “will your solution work without this next-generation storage and what specification & cost are required?”
Of course, I would like to suggest another perspective to keep in mind with the discussion on renewables: the sunk cost of the existing power generation, transmission and distribution network is extremely high, and more than a century of incremental improvement and dispersion of knowledge and practical experience has led us to today – with obviously much lower marginal costs of using and expanding conventional power. But, we are where we are. What I hope to shed some light on in this series is what renewables actually cost, what benefits they bring and what practical difficulties exist in expanding renewables.
The author concludes:
Conventional power systems suffer variability and reliability problems, just to a different degree than renewables. Conventional power plants operating on coal, natural gas, and uranium are subject to an immense amount of variability related to construction costs, short-term supply and demand imbalances, long term supply and demand fluctuations, growing volatility in the price of fuels, and unplanned outages.
Contrary to proclamations stating otherwise, the more renewables that get deployed, the more – not less – stable the system becomes. Wind- and solar-produced power is very effective when used in large numbers in geographically spaced locations (so the law of averages yields a relative constant supply).
The issue, therefore, is not one of variability or intermittency per se, but how such variability and intermittency can best be managed, predicted, and mitigated.
Given the preponderance of evidence referenced here in favor of integrating renewables, utility and operator objections to them may be less about technical limitations and more about tradition, familiarity, and arranging social and political order.
The work and culture of people employed in the electricity industry promote ‘‘business as usual’’ and tend to culminate in dedicated constituencies that may resist change.
Managers of the system obviously prefer to maintain their domain and, while they may seek increased efficiencies and profits, they do not want to see the introduction of new and disruptive ‘‘radical’’ technologies that may reduce their control over the system.
In essence, the current ‘‘technical’’ barriers to large-scale integration of wind, solar, and other renewables may not be technical at all, and more about the social, political, and practical inertia of the traditional electricity generation system.
I’ve never met a grid operator, but I have worked with many people in technical disciplines in a variety of fields – in operations, production, maintenance, technical support, engineering and design. This includes critical infrastructure and the fields include process plants, energy, telecommunications networks, as well as private and municipal. You get a mix of personality types. Faced with a new challenge some relish the opportunity (more skills, more employable, promotion & pay opportunities, just the chance to learn and do something new). Others are reluctant and resist.
The author of the paper didn’t have so many doubts about this subject – other studies have concluded it will all work fine so the current grid operators are trapped in the past.
If I was asking lots of people in the field doing the actual job about the technical feasibility of a new idea and they unanimously said it would be a real problem, I would be concerned.
I would be interested to know why grid operators in the US that the author interviewed are resistant to intermittent renewables. Perhaps they understand the problem better than the author. Perhaps they don’t. It’s hard to know. The evidence Sovacool brings forward includes the fact that grid operators currently have to deal with unplanned outages. I suspect they are aware of this problem more keenly than Sovacool because it is their current challenge.
Perhaps US grid operators think there are no real technical challenges but expect that no one will pay for the standby generation required. Or they have an idea what the system upgrade costs are and just expect that this is a cost too high to bear. It’s not clear from this paper. I did peruse his PhD thesis that this paper was drawn from but didn’t get a lot more enlightenment.
However, it’s an interesting paper to get some background on the US grid.
The intermittency of wind, solar, and renewable electricity generators: Technical barrier or rhetorical excuse? Benjamin K. Sovacool, Utilities Policy (2009)