When it comes to hybrid microgrids, writes Fabian Baretzky, senior business development and sales manager for Dhybrid Power Systems, the incorporation of various sources of energy and complex requirements for long-term stability of the energy supply requires expertise and an effective energy management system.

The Cheetah Plains Lodge, located in South Africa’s Kruger National Park
Image: Dhybrid

When we think of a microgrid, we typically think of an installation which relies on a few sources of energy and supplies relatively few consumers with electricity. We automatically think of isolated regions – in fact, microgrids are typically equated with fully grid-independent standalone systems.

By contrast, hybrid microgrids can be connected to small public, regional or even national power grids. At the same time, they do need to be able to operate in complete self-sufficiency in order to supply consumers with electricity as needed. The power output of such hybrid microgrids ranges from a few kilowatts to several megawatts.

The customary purpose of conventional microgrids is to supply power to off-grid regions and facilities. However, the main goal of hybrid microgrids is to reduce the costs of energy provision and move more in the direction of complete independence from fossil fuels by raising the proportion of renewable energy in the energy mix. In some particular applications, there is a grid connection, but the grid is not sufficiently stable. Then the hybrid microgrid is intended to secure the supply of energy, even in the event of a blackout.

Complex requirements

Their various functions and modes of operation mean that hybrid power plants – and in particular, their energy management systems – face complex requirements. They must be able to incorporate local energy sources such as solar energy or small hydro stations, ensuring that the proportion of renewables is as great as possible, particularly with regard to the reduction of carbon emissions. The different energy generators must also be monitored and controlled accordingly in real-time. This is the job of the energy management system (EMS). Acting in a manner similar to that of an orchestral conductor, the EMS monitors and optimizes all the important parameters, such as frequency and voltage, as well as active, reactive and apparent power.

As proven by the approximate 70 projects brought to fruition worldwide, electricity consumption rises as soon as a stable power supply becomes available, and this increase in consumption can range anywhere from 7 to 24%. A hybrid microgrid must also be able to keep up with and adjust to the rising demand for energy.

Since power plants are designed to operate for at least 20 years, advancements in technology and components must be taken into account. Hybrid microgrids should be made ready to incorporate new developments and amended technologies – ideally regardless of the manufacturer since market change is a given. Existing companies could disappear from the market or new suppliers could enter it and introduce innovative new technologies. Therefore, the EMS should be able to monitor and control the technology of any origin.

Since these power plants are typically installed in remote areas, a supplementary web-based cloud solution, such as the one offered by Qos Energy, is practical for the energy management system. The software is intended to analyze all of the data received from components such as the PV inverter, power generator and storage system. If an operator is in charge of multiple power plants, the EMS should assist them in comparing the data coming from the various sources, in order to identify optimization potential.

A hybrid power plant must be carefully modelled in its entirety prior to installation. Taking the modelling software and also using it both for simulation and as an EMS under normal operating conditions makes the entire project more time-efficient, reduces costs and avoids technical difficulties such as power outages.

Kruger National Park

The Cheetah Plains Lodge in South Africa’s Kruger National Park showcases the benefits of an EMS optimized for hybrid power plants – in this case, Dhybrid’s Universal Power Platform (UPP). The luxury resort had been connected to the local energy company’s single-phase auxiliary feed (max. 64 kVA). In addition, demand for electricity in the region was higher than the supply, leading to continual power outages.

In the course of upgrading the building complex, a self-sufficient hybrid power plant was installed, with PV on rooftops, carports and trackers working together to provide 300 kW of generation capacity.

The installations are connected to a tailor-made lithium-ion storage system with a storage capacity of 1,027 kWh. A diesel generator with a power output of 150 kVA replaces the old generator but is only intended as a back-up to charge the energy storage system in periods of low sunlight.

The UPP was previously used in the planning phase to simulate the microgrid and is currently used for the fully automated monitoring and control of all the components. It ensures an uninterrupted energy supply and stabilizes the grid voltage and frequency. Thus, the electricity demand can almost completely be covered by renewable energy.

This technology has raised the lodge’s available peak power capacity fourfold to 250 kW. Moreover, the power plant is capable of reliably supplying electricity to large three-phase energy consumers such as cooling systems and motors without interruption. Even the charging stations for the lodge’s electric safari Jeeps are largely supplied with solar energy.

Source: PV-magazine

Tesla has a new Solar Roof – and Musk says this one will work

Elon Musk revealed Version 3.0 of the Solar Glass Roof, which is made of solar panels, but looks like slate.

Tesla roof

Elon Musk revealed details of the latest version of Tesla’s Solar Glass Roof, announcing that installations have begun and should ramp up in the coming weeks. This third iteration of the electricity-generating house-topper will be cheaper, easier, and faster to install than its predecessors, Musk said in a public Q&A session. That makes it a viable candidate for the kind of scale the Tesla CEO tends to target, reaching thousands of homes a week in a few months’ time. “It’ll grow like kelp on steroids,” he said. And with enough growth, it could revive Tesla’s stumbling attempt to be not just a carmaker, but an energy company.

Rather than installing solar panels on an existing roof (a service Tesla also offers), this product is the roof. It’s made of glass tiles that can turn photons into electricity. From the ground, the tiles are meant to be indistinguishable from opaque slate, assuaging concerns about a trade-off between helping the environment and hurting one’s eyes. Musk showed off the first version of the product in 2016, and never disclosed the second version until Thursday. The latest version comes with a 25-year warranty and a promise that the glass can withstand 110-mph winds and chunks of hail nearly 2 inches in diameter.

For years, Musk has said that the solar roof and Powerwall (basically a big battery that allows owners to store energy produced by solar power, instead of sending it to the grid) are important to the company’s quest to accelerate the adoption of clean energy. But in the three years since it started taking reservations for the solar roof, Tesla has struggled with the product, delaying its launch and winning relatively few installations. The second version, Musk said Friday, was so expensive to produce and install that Tesla was “basically trying not to lose money.” The edges, especially where the tiles met gutters, were “very artisanal” and often completed at the worksite, making for a complicated and time-consuming installation. In the second quarter of this year, Tesla installed just 29 megawatts of solar power—far from its quarterly high of 200.

Version 3.0, he said, uses bigger tiles and different materials (no more detail there), and cuts the number of parts and subassemblies by more than half. Work slowed while Tesla focused its resources on producing its Model 3 sedan, but now that production’s running smoothly—and profitably—it has swung its attention back to the roof.

Musk’s solar ambitions have been troubled by more than delays. The roof started as a partnership with Solar City, which Tesla acquired in 2016 for $2.6 billion. Since then, the business has lost market share, and Tesla shareholders have filed a lawsuit alleging that Tesla overpaid for the company—of which Musk was chairman and the largest stakeholder—given its financial difficulties. It’s also facing a suit from Walmart for breach of contract and gross negligence, after solar panels that Tesla installed on seven Walmart stores allegedly caught fire.

True to form, though, Musk moved on Friday to supersede past and current worries with big promises for the future. He is targeting an eight-hour installation time, about what he said it takes a crew to lay down a simple conventional roof. He promises a price similar to that of a standard roof, too. “We’re coming after you, comp shingle,” he said. Tesla plans to start with in-house crews doing installs, and to start working with other companies once it has nailed down its processes. The tiles will be built at Tesla’s Gigafactory 2 in Buffalo.

Tesla’s home market, at least, may be ready for Version 3.0. As wildfire season ignites, the California utility PG&E has repeatedly turned off electricity to hundreds of thousands of people, in an attempt to stop damaged power lines from starting fires. (That didn’t prevent the Kincade fire, which is now tearing through Sonoma County.) Musk said Tesla has seen a bump in orders in a possible response to the power outages, along with more orders for Powerwall units. The idea of a roof that turns sunshine into electricity one can bottle up at home may be strange, “but it’s just a thing that should be,” Musk said. “You can have a live roof instead of a dead one.” And Tesla might have a live energy business, instead of a dead one.

Source: Wired

New method analyzes which materials in next-gen solar cells harvest the most energy

NTU Singapore and Dutch scientists show how perovskite solar cells can capture more electricity (Nanyang Technological University)
NTU Singapore and Dutch scientists show how perovskite solar cells can capture more electricity (Nanyang Technological University)

Scientists from Nanyang Technological University, Singapore (NTU Singapore) in a collaboration with the University of Groningen (UG) in the Netherlands, have developed a method to analyze which pairs of materials in next-generation perovskite solar cells will harvest the most energy.

In a paper published in Science Advances this week, physicists Professor Sum Tze Chien from NTU and Professor Maxim Pshenichnikov from UG used extremely fast lasers to observe how an energy barrier forms when perovskite is joined with a material that extracts the electrical charges to make a solar cell.

Conventionally, a solar cell absorbs sunlight and converts it to an electrical charge. During this process, the light particles have more energy than needed to generate electrical charges in the solar cells.

This excess energy gives rise to what is called “hot” charges, which lose their excess energy very fast as heat (within one picosecond), leaving only “cold” charges available for electrical power generation.

This energy loss is why conventional solar cells have a theoretical limit of 33 percent for power conversion efficiency. The best perovskite solar cells so far have exhibited 25 percent efficiency, almost on a par with the best performing silicon solar cells.

Scientists believe that if “hot” charges could be extracted fast enough, then together with the harvested “cold” charges, it could lead to a “hot carrier” solar cell with a theoretical efficiency of up to 66 percent.

The key to extracting these hot charges quickly enough lies in the selection of the correct ‘extraction’ material to bond with the perovskite. Prof Sum’s team has now devised a way to measure which are the best extraction materials.

Prof Sum, the Associate Chair (Research) at NTU’s School of Physical and Mathematical Sciences, said “Our latest findings show how ‘hot’ these charges have to be, in order to cross over the energy barrier without being wasted as heat. This highlights the need for better pairing of ‘extraction’ materials with perovskites if we want to lower this energy barrier for more efficient solar cells.”

Perovskite solar cells’ primary advantage over silicon solar cells is that they are cheap and easy to manufacture using common chemistry laboratory supplies and do not need silicon’s costly and energy-intensive manufacturing processes.

Prof Sum and his collaborators previously published in Science their discovery that “hot” charges in perovskites lose their excess energies more slowly than in other semiconductors. The team subsequently slowed this energy loss further using nano-sized perovskites, making it easier to extract the hot charges as electricity.

In their latest experiments, the NTU and UG scientists ‘watched’ the solar cells at work using femtosecond pulsed lasers that can measure processes that occur roughly 100 billion times faster than a camera flash. The scientists studied the behaviour of the “hot” charges that are generated and how they moved through the perovskite into the extractor material without losing their excess energy as heat.

Prof Pshenichnikov said, “Such high-efficiency solar cells could mean the possibility of increasing the energy supply from solar panels without the need for more surface area.”

Giving an independent comment on the research, Dr. Henk Bolink from the Institut de Ciència Molecular (ICMol) of the Scientific Parc of the University of Valencia, said besides a suitable light-absorbing layer, solar cells also need charge extraction layers that selectively extract either electrons or holes to the two terminals of the cell.

“It is currently unclear what the charge extraction interface composition/property should be, to allow for the extraction of both the “hot” and “cold” charges,” said Dr. Bolink, who was not involved in the study.

“In their recent work, Prof Sum and Prof Pshenichnikov shed light on this crucial puzzle by demonstrating a method that allows for the identification of the suitability of these charge extraction layers.”

Source: PVbuzz