By Richard D. Patton
Statements implying that wind and solar can provide 50% of the power to the grid are not difficult to find on the internet. For example, Andrew Cuomo announced that
“The Clean Energy Standard will require 50 percent of New York’s electricity to come from renewable energy sources like wind and solar by 2030…”
Considering that the wind is erratic, and the solar cells only put out full power 6 hours per day, it seems a remarkable statement. Can intermittent energy actually supply that much power?
For some answers, we turn to Germany, which has some of the highest electric bills in the world as well as a high proportion of its electric power produced by wind and solar (19%). Let’s take a look at German consumption and generation.
As you can see, the power generation (black line), especially after 2011, has been rising, but the power consumption (blue line) has been falling slightly. The red line denotes dispatchable generation, i.e. all power generated except wind and solar. This includes nuclear, fossil, biomass, hydro and geothermal power.
The table below shows what happened more clearly.
Between 2001 and 2011, wind and solar generation rose 57.7 billion kwh. The difference of dispatchable minus consumption fell by 58.7 billion kwh. In this period, solar and wind were displacing dispatchable power. Germany chose to reduce its nuclear fleet in this period, so fossil fuel use (mostly coal) remained strong and Germany’s carbon footprint was not significantly reduced.
In the period from 2011-2016, Germany’s wind and solar generation increased by another 48 billion kwh, but the difference between dispatchable generation and consumption was essentially flat at around 40 billion kwh. Losses+export increased by 47.6 billion kwh to 76.1 billion kwh in 2016. This increase is due to exports of 49 billion kwh to other countries in 2016.
While nuclear power fell 20% from 2011 to 2016, the dispatchable non-fossil fuel (nuclear, hydro, biomass and geothermal) portion of power generation remained almost constant, as can be seen on this graph.
This left the German fossil fuel and the intermittent (wind + solar) portion of power generation.
In this period, wind and solar rose from 68 to 116 billion kwh, yet this rise of 48 billion kwh had no effect on the use of fossil fuels to generate power in Germany. During the period of 2011 to 2016, consumption fell by 10 billion kwh. Fossil fuel generation fell by 5 billion kwh, and non-fossil fuel dispatchable generation (nuclear, hydro, biomass and geothermal) also fell by 5 billion kwh. The increase in wind and solar (48 billion kwh) had no effect on fossil fuel use.
Stability Problems, an example
To the problems caused by intermittent power, let us examine German power usage on January 7-9, 2016.
This graph begins at start of January 7, which is a Thursday. The load line (black) shows low power usage. The spot price (orange, right-hand scale) is 25€/Mwh. The blue line is the sum of wind and solar power, and the red line is how much power is being exported.
The day starts and the load increases as people head to work. The spot price rises to 42 €/Mwh because the load is increasing. The wind picks up and the wind+solar line rises. It keeps rising throughout the day. As people go home and the work day ends, the spot price plummets to 12 €/Mwh because there are too many producers of electricity. To cushion the system, more power is exported.
The next day, the price rises in the morning but is still low (25€/Mwh) during the day due to high wind output. Around noon (hour 37) the wind power plummets. This is in the middle of the work day on Friday, so the load is high. Wind+solar was producing almost one-half of the power, but within four hours, approximately 15,000 Mw of power are taken out of the system while the system is near peak load. The spot price rises quickly to 47€/Mwh as the wind+solar power falls. The exports of power are reduced to cushion the system.
Notice that the exports move with the wind+solar power (positive correlation) and the spot price moves opposite to wind+solar power (negative correlation). The correlation coefficient of Germany’s wind and solar energy output and the exchanges with other countries in 2016 was r=0.503. The correlation between the spot price and the wind and solar generation is -.411.
Wind+solar underwent a nearly 6-fold increase in power over 30 hours, and the system must accommodate that power. Wind+solar then fell by 50% (25% of the load) in 4 hours. Exporting some of that power out of the system helps stabilize it. The spot price movements attract or repel other power producers to balance the system and prevent blackouts.
Despite these efforts, Germany is now plagued by blackouts. According to the (German) Federal Grid Agency (the Bundesnetzagentur), there are 172,000 power outages in Germany annually. This was reported by Hessen Public TV (HR). Previously, the German grid was impeccable.
After all of this effort, including patience are the part of the public in accepting these continual blackouts, Germany’s carbon footprint has barely budged. The CO2 emissions from coal and coke have only fallen 2% between 2011 and 2016, due to decreased consumption of electricity. The extra 48 billion kwh produced from wind and solar plants built between 2011 and 2016 was balanced by exports of 49 billion kwh in 2016. In terms of reducing Germany’s carbon footprint, the entire effort is a failure.
Apparently, there is a limit to how much intermittent power a grid can use before it becomes unstable. German wind and solar use maxed out in 2011 at around 68 billion kwh, or 12.5% of consumption. Back in the 90’s, engineering textbooks on wind were saying that people used to believe that wind could only supply about 10% of the power to the grid due to stability problems, but further studies showed that it could actually supply 30%. The real-life example of Germany shows that the engineers who said wind could only supply 10% of the power had a point.
It has not been proven that the NY Clean Energy Mandate (or similar mandates elsewhere) can be met by relying on wind and solar power. Given the example of Germany, doubts are in order. As advertised by its politicians, Germany gets 19% of its energy from wind and solar. What they do not say is that it also exports 1/3 of that energy out of country, leaving its carbon footprint unchanged since 2011. Some small countries, notably Denmark, have advertised that they get 50% or more of their energy from sun and wind. What they really mean is that they have a large country (in the case of Denmark, Germany) next to them absorbing that power and selling them power when the wind stops blowing and the sun goes down. Because it is a small country selling into a big market, its energy sales do not disturb the grid stability of the bigger market. It is a much different case when the larger country (Germany) tries it. Germany’s attempt, the Energiewende (energy transition), is widely judged to have been a failure. If New York goes down that path, it is not likely to do much better.
Andrew Cuomo 50% announcement
Data for graphs were sourced from the US Energy Information Administration (EIA). Unfortunately, this is a beta site, but there was no other link to international data.
The EIA website has generation and consumption figures for every country for the years 1980-2016.
The link for German electricity generation (including different sources – wind, fossil fuel, etc.) is:
The link for German electricity consumption is:
The correlation coefficients were calculated from hourly European data compiled by P. F. Bach. He did those same calculations and sent them to me in a personal communication; the numbers matched. Here is the download link to his website.
He got the data from Entso-e, a platform showing power genraton, consumption and transmission in Europe. Its website is here, and registration is free:
The power outages data are from no tricks zone. Pierre Gosslin, who runs it, usually has interesting facts about Germany. Here is the link to that:
The links to German TV from that article do not work.
Also, from no tricks zone, a report form ARD TV in Germany.
The link from that article to ARD TV is available below
My German is very poor, but the show said 473/day or 172,645/year. Also, the show linked the stability problems to storms and wind power. In other words, wind power was specifically called out for Germany’s stability problems.