Cross-posted from Climate Progress.
Intermittent renewables at high penetrations will bring new challenges for the grid. But how big will they be? And is it true that wind and solar will necessarily need storage or natural gas back-up at high levels?
The International Energy Agency (IEA) wanted to know, so it modeled a variety of high-penetration scenarios in eight geographic regions around the world. Hugo Chandler, a senior policy analyst with the IEA, explains the organization’s findings to Climate Progress:
Variability is not just some new phenomenon in grid management. What we found is that renewable energy is not fundamentally different. The criticisms of renewables often neglect the complementarities between different technologies and the way they can balance each other out if spread over certain regions and energy types.
Grid operators are constantly working to balance available supply with demand — it’s what they do. There are always natural variations that cause spikes in demand, reductions in supply, or create disturbances in frequency and voltage. Once you see there are a variety of ways to properly manage that variability, you start whittling away at the argument that you always need storage or a megawatt of natural gas backup for every megawatt of renewable energy.
Theoretical modeling is important. But what companies are doing in reality?
Here are five of the top methods for integrating renewable energy into the grid — proving that intermittency isn’t the showstopper that critics make it out to be. Explanations of each of these with videos are below.
- Intelligent demand response
- Microinverters and maximum power point trackers
- Wind energy management tools
- The virtual power plant
- The hybrid solar-gas power plant
Intelligent demand response
Intelligent demand response is often called the “killer app” of the smart grid. Demand response is not a new concept — but the “intelligent” part is still somewhat new.
The demand-response leader, EnerNOC, is now applying this concept to renewable energy. The company announced earlier this year that it would work with a Northwestern transmission operator to help manage demand to meet the fluctuating output of wind electricity in the system. EnerNOC President David Brewster calls it “the perfect dancing partner for wind.” By ramping up demand at facilities during times of peak supply and lowering demand when supply drops off, the grid can respond to changing conditions in real time without the need for storage.
Microinverters and maximum power point trackers
Inverters are the gateway to the grid — turning direct current electricity from solar photovoltaic (PV) systems to grid-friendly alternating current. Over the past several years, there has been a revolution in inverter technologies that allows project owners to more effectively regulate system performance. One technology, the microinverter, is installed on the back of individual panels, turning each module into its own unit and providing real-time data on how each is operating. Therefore, if clouds roll over a PV system, the “Christmas tree light effect” is avoided, and each panel still functions normally, maximizing the output of a system — sometimes by 20 percent or more.
Speaking of maximizing output, that’s where maximum power point trackers come in. These pieces of power electronics are also installed on the back of individual panels. But they’re not microinverters; instead, they boost voltage to an optimal range for a central inverter, thus allowing the device to run more efficiently. By allowing a system owner to control a PV plant at the module level, you can boost performance on the module level and regulate voltage even as weather patterns change.
Wind energy management tools
Supervisory control and data acquisition systems that remotely monitor wind farm performance have been around for years — but there are a host of new applications being developed that allow grid operators and utilities to monitor system-wide performance in an easier, more compelling way.
The Wind Energy Management System (WEMS) from the Portuguese company Logica is a great example. The company manages over three gigawatts of wind farms in the U.S. and Europe using its WEMS, which allows for real-time monitoring of a set of geographically dispersed wind plants — providing the tools to balance voltage, ramp wind farms up and down quickly, and plan for maintenance.
A company like EnerNOC provides the tools for better management on the demand side; a company like Logica provides the tools for better integration on the supply side.
The virtual power plant
Virtual power plants combine intelligent demand response with supply-side management software, bringing distributed renewable energy plants together to form a “virtual” centralized resource.
We previously wrote about Germany’s regenerative combined power plant, a project that proved existing renewable energy technologies could provide 100 percent of the country’s electricity. The project blended three wind farms worth 12.6 megawatts, 20 solar PV plants totaling 5.5 megawatts, four biogas systems equaling four megawatts, and a pumped-storage system with 8.4 gigawatt-hours of storage. By using geographically dispersed renewable resources that complement one another, the plant operators were able to meet needs on the grid as supply and demand shifted. The project shows that with better information technologies and a balanced set of resources, the intermittency issue can be dealt with.
The hybrid power plant
While innovative grid management tools will allow us to scale wind and solar without an equivalent megawatt-to-megawatt backup, there will definitely be a need to better integrate renewables and fossil energies to boost output and maximize current infrastructure.
Concentrating Solar Power (CSP) can be a great way to increase efficiencies of newer fossil fuel-based infrastructure that may be around for a while. A number of companies are integrating direct-steam CSP technologies into coal or natural-gas plants. Florida Power & Light recently finished a 75-megawatt combined CSP/natural gas plant in Florida, with plans to add 500 more megawatts of hybrid plants in the coming years; Areva Solar is building a 44-megawatt plant at a coal facility in Australia; and GE, which recently invested in e-Solar, plans to integrate CSP technology into its natural-gas plants, boosting power-plant efficiencies substantially.
In an ideal world, CSP would be developed on its own to phase out fossil-based plants. And that is happening. But in order to scale these technologies, drop costs, and better utilize power plants that are in operation (or switch from burning coal to far more efficient natural gas), the hybrid approach is a very attractive option. Here’s how one type of direct-steam CSP plant works:
To categorically claim that intermittent renewables can’t scale without hurting the grid ig
nores the very real innovations that are evolving today.
As the IEA’s Hugo Chandler explains: “We want to explode the myth that there’s a technological limit.”
