Hydrogen – A Blooming Welcome Component in a Power Grid
- Aug 8, 2021 3:18 am GMT
Just as a lotus blooms in a pond of filth, Hydrogen is set to bloom in a pool of excess renewable energy. Solar and Wind are now producing so much renewable energy that most grids are not able to cope with the excess. Since, Solar and Wind follow Mother Nature’s orders and not the wishful thinking of humans, there is a significant disconnect between renewable power generated and its utilization
Engineers, smart as they are, have found a solution to this problem. Excess renewable energy is to be diverted into Hydrogen production (or batteries) for use at a time of their choice, thus solving a problem which is only going to get worse if left unattended
In this article, Part III in a series of articles on Hydrogen by Numbers, we attempt to understand how Hydrogen presents itself as a very viable solution for grid balancing
Distributed Energy Resources – A Boon for most, Bane for some
Mother Nature has made renewables inherently variable. Distributed Energy Resources (DERs) or Variable Renewable Energy sources (VREs) or Inverter Based Resources (IBRs), all of which essentially mean the same thing and include Solar and Wind power plants, ranging from a few KWs to MWs and now GWs, have grown by leaps and bounds over the last decade. These variable, decentralized power sources are behind a massive energy transformation that is challenging the fundamental grid goal of supply-demand balance
Earlier grids were designed to manage fluctuating loads. Now, even supplies are fluctuating. This will get worse as the looming energy demand from EVs comes to the fore. EVs will not only tap into multiple charging points at homes at times of their choice, but will also expect to tap into high-power rapid charging infrastructure in public places and office towers. Not just that, EVs, batteries and all, will look to sell their power to the highest bidder when called to do so. In short, EVs are one more challenge the grid has to cope with
As this energy marathon unfolds, where can the grid operators expect to get relief from?
The answer is HYDROGEN. Let us see how Hydrogen can help by first understanding the challenges in more detail
What are the Challenges from DERs?
There are three broad challenges to the grid from DERs:
- Two-way flows of energy
Universally, power grids have been designed like a royal decree ie top-down – where power literally flows from the top of grid down to the masses ie consumers. But now vox populi want it their way. Consumers till yesterday have turned prosumers today – producers as well as consumers rolled into one. Rooftop Solar PV began this phenomenon when spare energy was exported into the grid. This was fine till local distribution networks’ base capacity for edge exports was not breached (essentially the nearest distribution transformer capacity). Now, energy exports from prosumers is approaching the limit of the distribution networks. As a result, the ability of networks to transport and deliver electricity safely, securely and reliably is being challenged
- Amount of energy flow
Over time, volume of Solar and Wind has increased so much that almost all major economies of the world report >20% penetration of respective national production from renewables! Such large scale renewables export, and intermittently, can cause voltage and frequency changes in the grid due to see-sawing oversupply and undersupply of electricity in the grid. This rocks the permanent equilibrium between electricity production and consumption central to maintain the power frequency around its nominal value (50 Hz or 60 Hz) and power voltage around (220V or 110V). If frequency is allowed to deviate far from this value it leads to dirty power, brownouts and blackouts. If voltage is allowed to deviate far from this value, as in voltage spikes, it could damage consumer equipment and the network. Therefore, new balancing adjustments must be made by entities to quickly adjust their power injection or power consumption
- Lack of dispatchability
Due to the inherent variability of renewables, there is lack of “dispatchability” of power. By definition, dispatchable energy sources are those sources that can be ramped up or shut down in a relatively short amount of time. This could refer to time intervals of a few seconds up to a couple of hours. Renewable energy sources do not fit this characteristic. For this reason, grid operators have to resort to curtailment. Curtailment is defined as a reduction in the output of a power generator from what it could otherwise produce given available resources (eg sunlight and wind), typically on an involuntary basis. In a study undertaken by NREL (National Renewable Energy Laboratory, USA), curtailment levels reached 4% on average in Western States and up to 17% in peak situations in Texas. This was till 2013 and with mostly Wind. Situation has significantly changed since. Similar figures of around 2-3.5% were reported in Germany till 2015, again mostly with Wind. Recently in India also curtailment was witnessed, as power demand dropped due to Covid19, when a solar park was subject to curtailment
It is clear grid operators have their work cut out. As the renewable energy revolution gathers momentum, curtailment will not suffice. Curtailment may appear as an act of utilitarianism – greatest good for the greatest number – yet the party that suffers most – the renewable energy generator – is the one who is actually doing the world of good by offering non-fossil-fuel based power. Shutting off revenue for such generator(s), whether a large Wind Farm or a Solar Park or a Solar prosumer, sends a wrong signal for the government of the day
How Hydrogen fits into this equation?
Wonderfully well. Hydrogen rises to meet the challenges in both situations - when there is oversupply as well as undersupply of electricity in a power grid
Here we look at 4 distinct ways renewable Hydrogen can be used, at grid-scale (there may be more),
- When Oversupply of electricity - Hydrogen Storage - This is akin to battery storage. When renewable energy produced by Solar and Wind exceeds demand, then excess renewable energy is diverted to Electrolyzers to produce Hydrogen. In other words, when curtailment strikes, Electrolyzers get into action. Produced Hydrogen is stored away locally. This can offer GWh storage over a very long duration (in terms of months and even seasons). Note, batter lose energy over time. Hydrogen thus produced is green Hydrogen and a prized commodity in a world chasing COP21 Paris Accord Climate targets. It can be stored locally in tanks, cylinders or salt caverns or injected into the gas grid for cooking and heating purposes or compressed and shipped away for miscellaneous uses in industry or converted into Ammonia or MHC and exported to needy markets
- When Undersupply of electricity - Co-firing Natural Gas Power Plants – In an undersupply situation, rapid reserves (usually gas-fired stations) quickly come online. Today, these use natural-gas turbines to generate electricity. Blending into this natural gas of Green Hydrogen eg as in Siemens and Mitsubishi turbines already shows acceptability of 30% blend and GE up to 20% pointing to an important role for Hydrogen in the power grid in near future and in reducing GHG emissions. Soon it will be possible to run industrial scale MW-level turbines 100% on Hydrogen (Siemens, Mitsubishi, GE, etc have 2023+ targets)
- When Undersupply of electricity - Co-firing Coal Power Plants – Similar to point 2 above, rather than green Hydrogen, green Ammonia, a Hydrogen-related fuel is used for co-firing with coal. Acceptability of up to 20% ammonia mix with pulverized coal in combustion is reported. Even this small measure, is a step in the right direction and a mitigant for a vast number of coal power stations still in their early years of life, in order to reduce GHG emissions
- When Undersupply of electricity - Hydrogen Fuel Cells as a Power Source – This is an exciting area of Hydrogen application and is covered in detail in the next section
The most exciting application of Hydrogen in power generation is its use in a Fuel Cell. A Fuel Cell by providing electrons can bestow balancing services to the network by participating in primary frequency and voltage regulation, whether at distribution level (kW) or at grid level (MW). Fuel Cells can be stacked together to achieve a bigger power capacity. Currently the largest Fuel Cell Plant of 59 MW is in South Korea.
The role of Electrolyzers / Fuel Cells combination in frequency control is going to be crucial. Rapid deviations of primary frequency have in the past caused massive grid disruptions like the South Australia blackout in 2017 and the North American blackout in 2003 in extreme cases and loss of primary generation in many other cases. PEM technology is most interesting and suitable here as it provides fast response times (quickly turn on power supply) and high power density (more power in smaller size). As a combination, the capability of PEM electrolyzers to rapidly change the power consumption and the fast power injection of PEM fuel cells into the power grid emerges as a very attractive feature for frequency stability
However, how does a Fuel Cell know when it is required to produce energy for the grid? And if we have a live Electrolyzer-to-Fuel Cell configuration how does the Electrolyzer know when to start feeding Hydrogen to the Fuel Cell, instead of routing it to local storage? Latter is not relevant if Fuel Cell feeds off Hydrogen from local storage. This is a call the smart grid needs to make
Enter Virtual Power Plant
A Virtual Power Plant is a network of decentralized, medium-scale power generating units such as wind farms, solar parks, and Combined Heat and Power (CHP) units, Electrolyzers/Fuel Cells, as well as flexible power consumers and storage systems. The objective of a Virtual Power Plant is to relieve the load on the grid by smartly distributing the power generated by the individual units during periods of peak load
VPPs are becoming increasingly common in the main grid, particularly in South Australia where the share of rooftop solar is the highest and can sometimes deliver the equivalent of all the consumer demand in the state
Using intelligent algorithms, the control system in a VPP can command flexible power generators such as Electrolyzers to ramp up and down precisely, say to the quarter of an hour. As the order is received at the Electrolyzer, it responds promptly within agreed SLAs to produce Hydrogen that drives the Fuel Cell which will feed electricity into the grid. Thus, the central control system helps in stabilizing the power grid even before the use of balancing services further upstream becomes necessary
From firming renewable generation capacity to participating in frequency and voltage control and grid balancing services, we see the role of Hydrogen is set to bloom. In this way, the renewable energy generators who suffer loss of revenue during curtailment get an opportunity to recoup losses by offering grid support services as mentioned above.
However, this is still not the biggest claim of Hydrogen. Rather, the claim is that this is achievable in a decarbonized way, in a renewable way using green Hydrogen and for that primary reason one can expect an even bigger role for green Hydrogen in the future
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