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WindTech: Gamesa goes offgrid with hybrid system

SPAIN: A new wind-solar-storage system aims to provide reliable and competitively priced grid-independent power.

Offgrid prototype… Gamesa chose the well-proven G52-850kW turbine
Offgrid prototype… Gamesa chose the well-proven G52-850kW turbine

On 10 May Gamesa inaugurated its offgrid system prototype in La Meula, near Zaragosa in north-east Spain.

Its primary purpose is to provide clean energy for regions that lack centralised grid access, but Gamesa's engineers are also aiming for a decisive reduction in the levelised cost of energy (LCOE), even in conditions where there is a high penetration of renewable energy.

The integrated system comprises power-generation and power-storage modules, together with advanced control systems and capabilities that were developed in-house. The development fits into Gamesa's interests in exploring fresh business opportunities to complement its traditional wind activities.

At the opening ceremony, Gamesa executive chairman Ignacio Martin said that from starting development of the system to commissioning the first prototype had taken only about six months.

"Our commercial future offgrid systems will have a minimum installed capacity of 2MW and will enable the ad-hoc combination of all incorporated technologies, depending on specific project requirements," he said.

"They will further guarantee reliable, long-term power generation with minimised fuel consumption. Our main market focus will be on remote regions in the world lacking access to a centralised electricity network."

Remote locations

More than 1.2 billion people in Africa, India and island states, such as Haiti, Indonesia and the Philippines, stand to benefit most from offgrid solutions, not just to meet their growing need for electricity, but also to generate less expensive and more environment-friendly energy, said Martin. In addition, there are thousands of small islands and remote mines around the world that are well-suited to Gamesa's offgrid system.

"Many such remote places today depend heavily on diesel generators, characterised by expensive fuel and high operating cost. This is typically due to long sea or road transport routes, poor infrastructure and inadequate distribution networks," said Martin.

"Our customised offgrid systems will become a real alternative for a wide variety of these and other specific market needs, including in emerging economies with growing demand for energy. Gamesa will make offgrid solutions available as turnkey packages, together with multiple options for long-term upkeep service support."

Hybrid experience

The Offgrid prototype builds on Gamesa's experiences with its first hybrid wind-diesel installation at the Galapagos islands off the coast of Equador, which has been operating successfully since 2007.

This is a "classic" layout comprising three 800kW wind turbines and three 600kW diesel-generator sets. Wind-diesel management control is achieved by an in-house developed control system plus the "standard" Gamesa Scada system.

Over the past eight years, the plant has achieved an average wind-power electricity share of 30%, representing 8 million litres of diesel fuel saving while avoiding the release of 20,300 tonnes in CO2 emission.

The offgrid system built inside the boundaries of Gamesa's existing La Plana wind turbine testing facility is destined as an R&D and testing and validation project. The range of turbines tested over the years includes models of various size and ages, but it is the well-proven 15-year-old variable-speed G52-850kW that was selected as an integral part of the offgrid prototype.

Standing next to this unit, modestly sized by today's standards, project manager Enrique Las explained that for its new function, the turbine was electrically isolated from the facility's centralised electrical infrastructure.

"This G52-850kW is also a standard product now via a new cable network reconnected to two additional power-generating modules - 10,000 square metres of 816 photovoltaic modules for 245kWp with a Gamesa-designed DC/AC inverter, and three 222kW diesel-generator sets," said Las.

"The remaining modules are two different power storage systems that will be installed later this summer, comprising two complementary technologies. The first is a lithium-ion type of 143kWh/429kW with key characteristics of high power and low energy. The second is a HydraRedox fluid battery of 400kWh/120kW for low power and high energy."

"High power" for lithium-ion refers to its comparatively rapid charge and discharge capacity for its stored energy capacity. HydraRedox batteries need more time to discharge, but more energy can be stored at lower costs due to the large tanks containing the electrolyte.

The fluid battery contains two separate 12,000-litre tanks, individually acting respectively as a positiveand a negative-charged battery electrode.

Load banks

In any electricity network situation, loads are typically made up by a combination of residential, industrial and utility power uses. Such systems must be capable of coping with a wide variety of use-specific demand variations. These fluctuations occur during the days, weeks, months and seasons throughout a year. Additional main-demand variations are caused by 24-hour day and night cycles.

Because the offgrid prototype lacks such traditional loads, it can simulate various loads and load patterns through two load banks. The first is a resistance type for simulating demand, and the second an induction type for simulating grid power factor variation.

"Smooth operation and swift, continuous interaction between the offgrid modules and other system elements is functionally managed by our in-house developed hybrid power controller, which is the brain of the system," said Las. "Its main function is to continuously maintain a balance between all system loads, and the combined interconnected power generation and storage supply of the five modules.

This includes rapid response to peak power demand, but also coping with the control system's main challenges, like those caused by PV system 'cloud passing' under zero-diesel operation conditions."

Elaborating on specific features of the offgrid system, Las explained Gamesa's choice of three diesel generators rather than one. "Island communities using diesel generators for their power supply often choose a minimum of three individual units to provide redundancy in the event of a unit failure.

We further chose an engine make and type capable of operating at load levels down to 20% of rated output. Most engine suppliers can only go down to 30%"

Wind and PV

Regarding offgrid's general characteristics, and comparing wind and PV, Las noted that wind's capacity factor is typically in the 23% range versus about 15% for PV because there is no sunshine during night hours. For this reason, the batteries will be charged by wind power at night when demand is low, he added.

Also important for the comparison is that PV's capital expenditure (Capex) has fallen by a factor of five since 2006 to about €1.2 million/MW today. These and other variables explain why onshore wind's LCOE is currently in the €80/MWh range against €100/MWh for PV. For islands with only diesel generation,Las quoted capacity factors of 31-36%.

Las pointed out that lithium-ion batteries are widely used in applications that range from laptop computers to electric vehicles. "They are well-suited for fast charging and discharge cycles and 50Hz/60Hz frequency control. But two disadvantages are a still high LCOE level of around €600/MWh and a maximum of about 3,000 loading and unloading cycles, which corresponds to an operating life of roughly nine years," he said.

Rising renewables ratio

According to experts, 40% of electricity generated from wind is about the maximum achievable from a "classic" wind-diesel system.

Gamesa's offgrid system graph (below) with LCOE plotted at the vertical axis and renewable electricity at the horizontal, shows a curvature with the lowest LCOE at an optimum mix of 45-60% renewables. With higher renewable energy percentages, the LCOE curvature rises sharply, reflecting the need for growing storage and pushing up battery cost.

"This is where the HydraRedox fluid battery can make a real difference, because its main benefit is up to 200,000 loading and unloading cycles, or about a 40-year operating life," said Las. "Our comparative calculations show a very favourable battery LCOE of about €77/MWh, about one-eighth of the lithium-ion type."

The HydraRedox technology is not yet ready to become a viable commercial product, but it will be developed further by Gamesa and dedicated battery partners into a fully integrated offgrid system module.

Many experts are convinced that this battery technology has the full potential to at least flatten the Gamesa offgrid LCOE curvature for renewable energy percentages in excess of 55-60%. This, in turn, will give a huge commercial boost to offgrid system commercialisation and market reach.

"Gamesa's entry into the offgrid sector represents a fresh technological challenge and a new market niche opportunity, and implementation is expected to reach 1,200MW of installed offgrid systems in the coming years," David Mesonero, Gamesa's director of business development, said at the launch.

"Our system benefits are based on concept layout and design flexibility, enabling it to be tailored for any customer need by increasing, reducing or even eliminating capacity in any incorporated technology module."

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