It will take a masterful blend of renewable energy sources to slowly replace fossil fuels. Luckily, there are plenty of mature projects that show how technologies can work together to produce reliable supply. EcoGeneration looks at some recent success stories and at what’s in the pipeline, including a towering new entrant making its way to our shores.
It sounds very simple to talk about “hybrid systems” but there are many, many configurations of generation and storage. What can you say about the long route between taking a brief and designing a solution? How many pretty-good solutions fall by the wayside until the best one is found?
Windlab executive chairman Roger Price: Designing a hybrid solution is an optimisation task. You need to ask yourself what are you optimising for. Lowest cost of generation? Matching demand? Reliability? Ancillary services? In the case of the Kennedy Energy Park [project in Queensland, which will include 41MW of wind, 15MW of solar and 4MWh of storage] our design objective was to match demand. But as we are connecting to the National Electricity Market we also needed to make sure we were ultimately price competitive.
It was straightforward to produce an optimised design but the challenge for Kennedy was more in the connection process. The grid that Kennedy is connecting to is limited in capacity and quite weak. This placed constraints on the design of the system which ultimately required a number of iterations to optimise the solution for demand-matching at a competitive price.
SolarReserve vice-president global communications Mary Grikas: Our hybrid systems are comprised of solar thermal energy collection and conventional steam power generation combined with integrated molten salt energy storage technology. The molten salt serves as both a heat transfer fluid and thermal energy storage medium.
The journey to commercialization began nearly three decades ago. Back in the 1990s, a group of scientists at Pratt & Whitney Rocketdyne, a top supplier of rocket engines into NASA, worked with the US Department of Energy [DOE] to develop technology to collect the sun’s thermal energy and then store it in molten salt, eliminating the operational problems caused by intermittent generation. From 1994 to 1999, Rocketdyne and DOE’s Solar Energy Technologies Office built and studied a pilot project to validate the technology, a 10MW test facility in the Mojave Desert called Solar Two. One challenge remained: how to cost-effectively scale up and commercialize the technology at the utility-scale. This is the stage where many good solutions fall by the wayside.
SolarReserve was formed in 2008 to commercialize the technology and until 2011 worked closely with Rocketdyne to design a commercial-scale molten salt receiver assembly and an advanced heliostat control system that significantly reduced costs and had 10 times more capacity than the Solar Two pilot project.
In 2011, SolarReserve began building Crescent Dunes in Tonopah, Nevada, a solar receiver that sits atop a tower and absorbs sunlight from over 10,000 mirrors. These mirrors follow the sun over the course of a day and magnify its power 1,200 times, heating molten salt to high temperatures. This molten salt circulates through the tower, is stored, and is then used to create steam to power a conventional steam cycle that generates electricity whenever it’s needed, day and night.
In late 2015, Crescent Dunes reached commercial operation. It delivers 110MW of electricity, plus a massive 1.1GWh of storage under a 25-year power purchase agreement with NV Energy, the largest utility in Nevada.
Hydro Tasmania hybrid off-grid solutions development manager Ray Massie: There is never a one-size-fits-all solution. It is more the case that there are a range of solution elements that can be brought to bear to a project with the mix determined on a case by case basis. The journey starts with understanding the user’s goals and investigating options. What renewable resources are there? What are the community’s expectations? What is the existing energy use and what are the future needs? Is there opportunity to manage the demand side rather than a purely supply side driven solution?
Inevitably in developing new hybrid solution technologies there will be failures and sub-optimal outcomes. Hydro Tasmania experienced an example in early battery technologies in 2004. This trial system was undertaken on our own isolated hybrid system rather than deployed to a customer that may not be aware of the degree of experimentation. Having been in the industry for decades I’ve seen many projects fail within the first few years as often suppliers have been aiming at deploying immature technologies or just getting the sale and considering the project ends at the ribbon cutting.
Critical to a successful solution is looking at the whole of life of the project. We have seen projects lose all their benefits because the utility operators of the completed system have not been adequately trained or supported and reverted to manual operation. Engagement with all levels of stakeholders through the development, delivery and operation phase of projects is crucial to a successful outcome.
Senvion project manager Dale Wiessner: I agree there are so many possible configurations for generation and storage. For the Coober Pedy Renewable Hybrid Project, Senvion was able to deploy an established, familiar product to meet the requirements of our customer, Energy Developments Limited. Our 2MW, MM92 [2.05MW] turbine is established in Australia and our team is familiar with it. However, to cope with the specific demands of the off-grid system, we needed to deploy a system that allowed greater over-voltage ride through capability. Our turbines already have this capability, which we use frequently in Europe but hadn’t applied in Australia. By accessing the existing capabilities of our technology we were able to avoid the disappointment of solutions falling by the wayside.
Storage is an important consideration in some hybrid systems. What have you learnt about using this rapidly-changing technology? What are some surprising outcomes? How do consumers feel about storage?
Hydro Tasmania: Energy storage should not be just thought of as batteries. Energy storage can be in the form of a few seconds of power injection such as from a flywheel at one end of the scale out to many days of energy shifting in, for example, large pumped hydro systems. These other options, along with wider renewable enabling technologies, can be overlooked as it is human nature to want an easy fix for a given need and battery systems are seen and promoted in this way. The truth is they will form part of the solution but not wholly be the solution to increasing renewable energy use.
In using a number of utility-scale battery systems across a range of chemistries over the last decade or more we have learnt that neither the end users nor suppliers fully understand the specific application of batteries in hybrid systems. This is evolving over time but still has a way to go before batteries are fully mature and understood in the market.
Modern battery systems have often been developed from the EV industry or research streams and adapted to the utility industry, adding to the integration challenges of a hybrid system. Many battery suppliers run into issues along the way by not appreciating the required response and performance characteristics needed in a hybrid system. This not only relates to the battery chemistry but also the power conversion system, typically the inverter. Inverters themselves have had considerable development in recent years and are an equally important part of the battery systems beside the cell chemistry.
SolarReserve: We have been developing our global pipeline of hybrid solar thermal with storage projects because we are a believer in the technology; we knew the day would come that energy storage would be valued, and we knew that we would be able to optimize pricing to be competitive globally with conventional energy.
Inexpensive but variable PV and wind seemed to be the easy selection over the last five years for utilities and large energy consumers to put renewable energy onto their systems. But now with greater and greater implementation of renewable energy the intermittency issue and generation of power during the wrong (off peak) time periods has become a greater problem.
In areas around the world with high penetrations of variable renewables, such as California, too much PV generation in the afternoon has rendered the power valueless, requiring the power to be dumped for free or even at negative prices. Consequently, the issue of energy storage has taken on a much greater importance.
From a cost perspective, solar thermal with storage is more expensive than simple PV projects which provide variable generation, but is proving to be much more cost effective than PV with batteries, and provides more “bulk storage” allowing utilities to shift power from off peak periods to peak periods.
Windlab: The key point with regards Lithium-ion storage is that it is rapidly reducing in price. It is following the same technology price experience curve as solar. It is today already as cheap as diesel generation and will halve again over the next 18 to 24 months. This will mean that much more storage can be economically and competitively deployed.
Some of you are working with complementary sources of generation, such as wind with solar. How does colocation of different generation types reduce risk in a project? And what do you have to say about weather forecasting technology and its importance in delivering results?
Windlab: The key to colocation in many parts of Australia is all about the wind resource. In many parts, like Queensland, solar is almost ubiquitous. It is everywhere and all the same. But where is the wind? And where is the wind that has a long-term diurnal generation pattern that complements solar? This is not an issue of weather forecasting but instead long-term wind prediction. Windlab has a competitive advantage in this regard, using our WindScape technology to identify the best and most complementary wind resources anywhere in the world from our technical centre in Canberra. This is why Kennedy Energy Park is located 300km inland from Townsville. This location has the most complementary wind resource to solar of any location in Australia.
Hydro Tasmania: One of the first steps of developing a hybrid project is looking at the available renewable resources: typically wind, solar or hydro. More broadly a modern hybrid control system should be capable of incorporating any future resource as it may become available, such as wave, tidal, biomass, etc. We look at the site variability of the resource and the overall interplay with the load use to examine how well or otherwise the resources complement the load and each other. Economic-based energy modelling will then help determine the optimal mix of renewable energy generation types and sizes.
In our experience, systems that have a diversity of generation sources can generally achieve higher levels of renewable energy contribution at a more economic cost. For example, trying to shift solar generation across the day, say, to an evening peak involves charging and discharging energy storage – and at the current battery price points and the round trip losses it is cheaper if there is some wind available in the system that can generally cover or offset the non-solar parts of the day.
With the inherent variability of renewables, knowing ahead of time what the output is likely to be in the next “time step” can help the decision making of a responsive hybrid control system. That would enable the system to adapt such that stability of supply is maintained while maximising the renewable content of the supply. Weather forecasting systems such as skyward-looking cameras that detect the approaching cloud cover can provide this input to the control system and will form an increasingly important and common part of a hybrid system as they increase in maturity and uptake.
Senvion: It was a pleasure to be a part of the hybrid puzzle at Coober Pedy. Like any renewable project, the natural environment determines generation. Colocation of wind with solar and storage offers the beautiful complement to enable increased renewable penetration with decreased reliance on individual sources. On a “pub test” level, this helps respond to the often asked question: “Yeah, but what happens when the wind doesn’t blow?” Weather forecasting technology is very important to us as it influences our construction process, for example planning when we can use cranes to install turbines.
In Coober Pedy, due to the remote location, we didn’t have ready access to the highly accurate weather forecasting systems that we would refer to for other projects. This meant we were confronted with high temperatures (no great surprise in Coober Pedy), significant wind shears with high average and gust speeds, and storm and lightning events. To overcome the lack of reliable local data, we engaged a specialist consultant to develop accurate forecasting data plots specific to our location. This enabled us to plan our installation in discreet timeslots that addressed weather-related health and safety challenges.
What are some of the difficulties of replacing good old reliable diesel with intermittent renewables in hybrid systems?
Hydro Tasmania: Synchronous diesel generators are a well proven technology over 100 years old and are capable of delivering all of the requirements of a power system: voltage and frequency control, real (kW) power, reactive (kVAR) power, inertia, fault currents and spinning reserve.
While renewable energy generators can provide cheaper real (kW) power, they may not provide all of the basic system reliability requirements alone. Reliable hybrid system operation relies on the careful integration of renewable energy with autonomous control and enabling technologies. These are the key elements to building high renewable penetration power systems. These smooth the output of renewable energy and maintain power system stability, security and ensure safety of operation.
Depending on the size of a power system, including the size and strength of the distribution system, different levels of complexity and technologies are required to achieve power system safety and stability while using little or at times no diesel generation. 
Typically, however, a comparison of what each component can provide is shown in the table at the right. For example, on a pure energy balance, a battery system may be able to meet the energy deficit of variable renewable energy supply with no diesels running. But battery systems are not capable of injecting the large fault currents required to clear a fault in any reasonably sized distribution system, leading to an inherent safety issue. The addition of enablers, such as flywheels, in such a scenario facilitate the use of high levels of renewable energy in the system while at the same time enhance safety and stability.
In the hybrid systems we have designed to be capable of periods of stable 100% renewable energy – including those that have been constructed on King Island, Flinders Island and Coober Pedy – there is still the need for some diesel generation but this is driven purely by economics, not because of any notions of base load or stability requirements of diesels. As the prices of renewable energy generation and enablers continue to decrease over time this diesel portion will decrease further.
The potential of demand management is slowly being taken seriously as a way of turning energy consumers into energy suppliers. Is demand management a simple consideration to design into hybrid systems or too much of an unknowable?
Senvion: Demand side management has an important role to play in facilitating a greater uptake of naturally variable renewables. Personally, I am very interested in residential systems. Driven by power price concerns, and I hope a broader growing awareness of the importance of renewable self-sufficiency, this will be an increasing force for consideration in demand management.
Hydro Tasmania: Demand side management as part of a hybrid system, embedded network or larger grid will be an important part of the future energy management mix. The challenge in deploying systems is more likely to be faced in the customer involvement. The greatest challenges will be identifying suitable schedulable load, persuading customers to take on the demand side management technologies and ensuring that a commercial return is available to customers and the market entrant.
In our own demand side management trials involving aggregating loads of around 100 households on King Island considerable community engagement was undertaken to not only allow the system to be deployed but understand the way the customers preferred to engage, what they wanted to know about and have control over and what they preferred to be have done automatically. This type of approach is what will help unlock the potential of demand side management, but it will take time.
Though approaching demand side management through aggregating a large number of small loads such as households is attractive, managing fewer relatively larger loads can have advantages in having fewer counterparties. For example, Hydro Tasmania has undertaken a project on Rottnest Island in Western Australia in which one of the elements was incorporating the desalination plant into the hybrid control system, enabling more water to be desalinated and stored in tanks when there is excess renewable energy. With the desalination plant owned and operated by the power utility, the integration and outcomes where much easier to achieve.
SolarReserve: While our technology doesn’t specifically address demand side management, one of the benefits of solar thermal with energy storage is its flexibility to adapt to changes in demand profiles. Solar thermal with storage will maintain its value over the long term, even as demand profiles change.
Windlab: Demand management will play a role in NEM demand management, but I think it has little effect on hybrid systems, particularly off-grid solutions.
Finally, as we transition to replacing coal and gas with clean energy sources, are you confident that stable systems can be designed with renewables?
SolarReserve: Yes, we’re confident that stable systems can be designed with renewables but, as we deploy more and more renewables, energy storage will be even more critical to maintain system stability – without contributing to carbon emissions.
Windlab: Absolutely. Wind, solar and storage will replace the majority of coal generation in Australia over the next 20 years of so. This will occur at a lower cost than new thermal generation and with all the necessary reliability.
Senvion: Renewables can absolutely underpin a stable energy network. Increasingly, utility-scale renewable projects are being developed or retrofitted with more than one type of generation and/or storage. Renewable manufacturers are demonstrating frequency control and ancillary services capability that support grid stability in times of network stress. We have evolved from the days of questioning what the risks of renewable hybrid projects may be to pursuing the opportunities.
Hydro Tasmania: There is no reason that reliable, stable, low emission and economic renewable energy solutions will not dominate the future energy sector. Hydro Tasmania has already shown this is possible and at different scales. On our multi-MW scale hybrid systems on King and Flinders islands we are able to operate these systems for considerable periods with 100% renewable energy while enhancing system stability. The levels of renewable resource variability managed in the King and Flinders systems is extreme, with the enabling technologies keeping the system safe and stable through swings in renewable generation of half the system load in a few seconds. This level of variability will decrease as systems get larger, meaning the techniques we have proved on small-scale systems will transfer to larger grids relatively easily. This proves that the traditional concept of baseload generation being needed for stability is a myth.
For example, we have had the King Island hybrid system run on 100% renewable energy continuously for two and a half days with better power supply reliability, quality or stability than a traditional diesel system. At a larger scale, Tasmania has for years even prior to the connection to the NEM via the Basslink cable run on predominately renewable energy only and is currently working with ARENA on the “Battery of the Nation” project to investigate utilising the hydro system stability to benefit the wider grid.
Project profiles
SolarReserve: Aurora Solar Energy Project
The Aurora Solar Energy Project is a 150MW solar thermal power station with eight hours of storage (1,100MWh) to be located about 30km north of Port Augusta, South Australia. It will utilise SolarReserve’s solar thermal technology with integrated molten salt energy storage and deliver over 500GWh of energy annually, providing fully dispatchable power to the network when electricity is needed most. Storage will enable the solar thermal station to operate just like a conventional coal or gas power station, reliably generating electricity day and night – without any emissions.
The project is expected to create 650 construction jobs and up to 4,000 direct, indirect and induced jobs during construction and around 50 long-term jobs during the operations phase. About 60% South Australian content is targeted for construction and the solar thermal supply chain developed in the state would be leveraged for other solar thermal projects in the region.
Hydro Tasmania: King Island Renewable Energy Integration Project
The King Island Renewable Energy Integration Project was an initiative of Hydro Tasmania, with assistance of the Australian Renewable Energy Agency, which resulted in the development of a hybrid off-grid power system capable of supplying 65% of energy needs using renewable energy. The system is capable of 100% renewable operation when conditions permit, the first megawatt-class off-grid system with this capability in the world when it was developed in 2012.
While the renewable energy sources being used were well-established, the enabling and storage technologies are highly innovative. The hybrid system includes a 3MW/1.5MWh battery, two 1MVA flywheels that significantly aid system security and stability, a 1.5MW dynamic resistor to manage surplus renewable generation and an aggregated customer demand response system to provide additional reserves. The real time performance of the system can be viewed at http://www.kireip.com.au
Hydro Tasmania: Flinders Island Hybrid Energy Hub
Flinders Island has traditionally been heavily reliant on expensive diesel fuel from the 3MW power station, serving 6.7GWh of annual customer demand. Hydro Tasmania developed the Flinders Island Hybrid Energy Hub which is capable of displacing 60% of diesel used on the island. The system is capable of diesel-off operation, allowing 100% renewable penetration when conditions allow.
The system includes a 900kW wind turbine, a 200kW solar array and the enabling systems including a 750kW/300kWh battery, 850kVA flywheel and 1.5MW dynamic resistor. Building on the technology from our King Island project the system for this project was designed as a series of scalable modular units to house and ship the enabling technologies. These modular units provide a lower cost and scalable solution that allows easy and rapid deployment and installation for hybrid energy projects.
Windlab: Kennedy Energy Park
Located in Flinders Shire, Queensland, about 290km south-west of Townsville, the Kennedy Energy Park will include up to 1GW of wind, single-axis tracking solar and a battery storage system. The site was chosen for high levels of solar irradiance world class complementary wind resource. The project is jointly owned by Windlab and Eurus Energy.
Senvion: Coober Pedy
The Coober Pedy Renewable Hybrid Project developed by Energy Developments Limited includes 4MW of wind, 1MW of solar and 1MW of battery storage. The wind component was managed by Senvion, which provided two MM92 turbines. The units produce 2.05MW each, with 92-metre blade diameter and 80-metre hub height.