Providing baseload power from renewable sources to further increase renewable energy is challenging but it can be achieved. This is how.
A common criticism of renewable energy is that because it is intermittent it requires backup power from conventional energy technologies based on fossil fuels such as natural gas. A recent critic posting a comment on another article on Interesting Engineering asked how the UK could cover the baseload demand in winter, citing a figure of about 32 GW and peak demand of about 47 GW, when the wind isn’t blowing and the sun isn’t shining.
To begin with, this assumption is based on a number of fallacies, one of them being that we already have a perfectly reliable power system. Actually, we don’t, for the simple reason that there is no such thing. Furthermore, some renewable energy technologies, such as biogas and geothermal, can indeed supply baseload power already.
Malte Jansen is an energy expert working with Germany’s Fraunhofer Institute. Mr Jansen spoke at an event in July this year organised by the Energy & Climate Intelligence Unit (ECIU), a non-profit organisation that supports informed debate on energy and climate issues in the UK. Jansen runs a project in Germany called Kombikraftwerk which models the implementation of a 100 percent renewable energy network. In this German scenario, the most important renewable generators are wind, solar and biomass. The most important form of energy storage is assumed to be the conversion of renewable electricity to methane, alongside pumped storage power stations, batteries and power to gas. Decentralized CHP stations and centralized gas power stations using biogas (methane) can convert biogas to electricity thereby acting as reserve power stations for times when there is little wind or sunshine. In a high-load hour, with little generation from wind and solar, the methane power stations generate a maximum value of 43 GW.
Two different mechanisms were modeled for frequency stabilization. One of these concerns the main short term frequency change resulting from a sudden failure of a large generator. In this case, the missing energy is taken from the rotating masses of thermal and hydroelectric power stations. After this passive stabilization mechanism, the primary balancing power comes from intended power stations, supplied within a few seconds. These provide more power thus stabilizing the frequency again. However, if the period to full provision of balancing power remains at 30 seconds, the frequency after such a failure is too low for high renewable energy feed in, given that the wind and solar energy plants cannot provide rotating mass for the grid. For this reason, the model simulates far faster reaction times for the system incorporating solar and wind energy, power to gas and batteries, thus solving the problem.
Such rapid draws from these systems are already possible, thereby allowing renewables to compensate for the lack of rotating mass. The system requires large storage capacities for full supply and the various decentralized systems must be networked in order to compensate for frequency and local voltage fluctuations.
Field tests were also conducted alongside the simulations in order to prove the ability of such a system to provide control reserve. The various renewable energy systems – wind, solar, biomass, geothermal, hydro, energy storage and backup power stations - can be combined to form a virtual power plant which can not only generate electricity but also provide balancing power. Geographic balance with regard to wind power is a major advantage, in that there is rarely a situation when there is ‘no wind anywhere’. Wind farms across various regions therefore have to be networked. Furthermore, weather forecasting for larger regions is more accurate. The forecasting used to predict generated power from wind and solar energy systems is improving steadily and that means that the energy from these systems is becoming increasingly more predictable, thereby enabling them to contribute to frequency stabilization.
The main problem at the moment is that the framework conditions of the balancing market prevent renewable energy sources from providing these services. This means that the transformation of the energy system which is already being implemented should also include the balancing market, offering opportunities for renewable energy sources to participate. This can be achieved by providing shorter tender announcement periods and lead times. This would also allow renewable energy systems based on the conversion of renewable gas into electricity to access the market.
“When demand exceeds supply, non-essential demand is reduced and backup storage systems activated” explains Director Richard Black explains on the ECIU website. “When supply exceeds demand, the spare power is used for things like producing hydrogen for use later on or for heating, or is exported. The exact solution for any given situation is largely worked out by the market: wind and solar power take precedence when they're generating because they produce basically free electricity, and other supply- or demand-side measures come in depending on price. Smart technology oils the decision-making wheels.”
“But the wind doesn’t blow and the Sun doesn't shine all the time”
“Sure” says Richard Black, “but there isn’t peak demand all the time either, which is why it’s called ‘peak’ demand.”
In order to make this work, the grid has to be flexible. In other words, it has to be modified in order to be adaptable to the new renewable energy systems coming in. According to another ECIU speaker, Exeter University’s Professor Catherine Mitchell, overall demand needs to be reduced by making energy use more efficient. The peak load then needs to be shifted to other times of the day, using energy storage. Finally, there needs to be short-term flexibility in order to catch random fluctuations.
Using biogas to generate electricity
Another solution is to burn biogas. This can be produced through anaerobic digestion from farms and from processing of food waste, which is a major problem in many countries, a lot of it currently being disposed of in landfill. The gas can be stored underground. Unfortunately, the AD sector in the UK is much less well developed than Germany at present, but on closer examination it actually has enormous potential.
According to the Anaerobic Digestion and Bioresources Association (ADBA) biogas from anaerobic digestion (AD) plants can meet up to 30 percent of the UK’s domestic gas or electricity demand or in excess of 80 Terrawatt hours (TWh). In 2014, according to a report by the Parliamentary Office of Science and Technology (POST), biogas represented 7 percent of the UK’s indigenous gas supply, provided by AD plants and landfill gas. Figures have shown that Scotland’s AD sector could grow by 200 percent over the next two years while biogas produced by the UK farming sector has led to a 40 percent surge in electricity from biogas. According to UK bioeconomy consultants NNFCC on their AD portal, 1 tonne of food waste can generate about 300 kWh of energy. The Renewable Energy Association (REA) believes that if all the UK’s domestic food waste it could generate enough electricity for 350,000 households.
Another possibility is biogas from human feces. The UN has just released a report claiming that, globally, biogas from human waste could supply electricity for 138 million households.
There is also the option of importing renewable energy from abroad via interconnectors, HVDC subsea cables, from places such as Denmark, Germany and Norway. The UK already has such interconnectors running from Ireland, France and the Netherlands and moves to develop an interconnector between the UK and Norway were initiated by an agreement in May this year. Furthermore, the EU is progressing rapidly with its plans to develop a Europe-wide Energy Union. If this is successful, Europe as a whole will have moved even further towards the goal of 100 percent renewable electricity, silencing the critics.
There are numerous reports in existence which really goes into the nitty gritty detail of how countries around the world can run entirely or almost entirely on renewable energy by 2050. For example, earlier this year Demand Energy Equality was commissioned by Greenpeace to examine this question as it applies to the UK and found that the country could reach 90 percent renewable energy provision, including more than 80 percent of its electricity from wind, solar and tidal.
So the baseload power is not an issue at all really, given the political will to achieve it. The real problem therefore is all the vested interests who want to cling on to an outdated, and dirty, fossil fueled energy system, despite the fact that this outmoded way of doing things is rapidly endangering the Earth itself, and everything that lives on it.
Written by Robin Whitlock