Photo: / Norayr Chilingarian CC BY-NC

Wind and solar can be integrated into the grid

There are strategies to manage variablity in electricity generation. A succesful example is Denmark, which somtimes produces more than half of its electricity from wind and solar.

Wind and solar can be integrated into the grid much more effectively than at present. This is not just theory. Denmark got 53 per cent of its electricity from wind and solar in 2017. It is one of the real-world examples in a new study by the Energy Economics and Financial Analysis (IEEFA).

Solar and wind are growing fast and will continue to do so. The International Energy Agency has consistently underestimated renewables in its forecasts. But in its latest World Energy Outlook it says renewables will make up two-thirds of total global investment in new power plants.

Others believe wind and solar will grow even faster. But how can they be integrated. This question is examined in some detail in a new study from the IEEFA think-tank: Power-Industry Transition, Here and Now. Wind and Solar

Won’t Break the Grid: Nine Case Studies It shows how nine countries or states have coped with a high percentage of variable renewable electricity (VRE). The countries or regions studied are: Denmark (52.8% VRE); South Australia (48.4%); Uruguay (32.2%); Germany (26%); Ireland (24.6%); Spain (23.2%); Texas (18%); California (15%); and the state of Tamil Nadu, India (14.3%).

It works.

The average annual duration of blackouts is generally lower in high-VRE countries than in comparable countries.

One way to manage variability is to “curtail” when VRE is too much for the grid or greater than demand. In Texas, the curtailment rate was unacceptable, at 17 per cent in 2009, but then dropped to below 2 per cent from 2013 on. Irish and German curtailment has also dropped in recent years. In Denmark it simply doesn’t happen.

The ways to balance VREs are many and varied.

Denmark is well connected to neighbouring countries, of which Sweden and Norway have a lot of hydro, which can swallow a lot of variation. So Denmark exports when winds are high, and imports when they are not.

A well-functioning electricity market has helped VRE integration in Denmark. It allows for “negative prices”. Denmark has a lot of district heating, where heat is normally co-generated with electricity, as or biomass plants. When winds are strong and electricity prices negative or low, turbines are turned off, and boilers are turned down. Wind is stored as heat, produced from cheap electricity. Fuel is saved for later use.
Improved weather forecasting has made it easier to match supply with demand.

South Australia has had other problems and found other solutions. A big blackout in 2016 was blamed on renewables, and showed too great a dependence on one interconnector. The government has since reduced vulnerability. Three gas power stations, seeing VRE undermining electricity prices, sold their gas elsewhere instead of producing power, but under some pressure they resumed power production. In order to preserve grid stability, frequency control and active power control have been mandated on wind turbines, so grid operators can modulate their output by altering the pitch of the turbine blades. A 5-minute market has been introduced. South Australia also has the biggest storage battery in the world, 100 MWh, alongside a 315 MW wind power plant, with more to come.

1000 MW of demand reduction has been negotiated. A concentrated solar power station of 150 MW will be in place by 2020. Unlike PV, this can deliver dispatchable power, with 8–10 hours of storage.

More interconnection to other states is under construction or planned.

In Uruguay, VRE grew from 1.3% of electricity in 2013 to 32% in 2017, which mainly replaced oil power. Hydro power provides more than half of electricity, so Uruguayan electricity is now more than 90% renewable, and the country exports electricity to its neighbours. Hydro, and exports, are perfect for balancing VRE. The grid needs to be modernized to reduce the blackouts, however.

Germany has only modest hydro resources, though it can export/import some of its flexibility from the north and south. Bio-power, which is dispatchable, helps to stabilize and enjoys a flexibility premium. Germany, which started its road to renewables some 20 years ago, has fine-tuned a large number of policies to go even further.

Texas may not have a very green image, but it is the #1 state for wind power in the US, with 62 TWh in 2017, providing 18 per cent of its electricity. Solar came late, but is now growing fast. The Texas grid is essentially an island, so import/export is no option. Reinforcement of power lines within Texas from west to east in 2014 reduced curtailment dramatically. More reinforcement will be needed, as much of the best resources for more wind and solar are in West Texas.

Fredrik Lundberg



In this issue