NOT PART OF CLIMATE GUP-SHUP: ANY THOUGHTS ON STEADY BACK UP SOURCES FOR INTERMITTENT RENEWABLES?

This article is a sequel to yesterday's write up and it is originated in response to the comment from Rajat: Any thoughts on the steady backup sources for the intermittent renewables?

Here are my thoughts:

Fortunately we are nearing the end of the wait for a couple of newer zero-emission technologies (that can potentially be used as backup for intermittent renewables) that are currently very promising. They are in the development and demonstration phase at the moment (kind of like vaccine trials!). One of these, a small modular zero emission natural gas plant, is about a year away from actually becoming commercialized and competitive. I have included details near the end of this article. A 50MW demonstration plant has been built and is up and running in the US.

In the meantime it looks like in most countries traditional natural gas plants (with all the emissions) are still most often being used today to back up intermittent renewables. Even with the decision to use natural gas plants as steady backups for renewables, there are still important tradeoffs to be made among what types of gas plants to use as balancers. I go into this in more detail further below.

There is a really good part of the story, on what is actually happening on the ground in terms of advances in the "steady backup" side of renewables: Interestingly, solar-wind hybrid plants are another balancing option, with the added benefit of no emissions. Countries such as the US and others attempted this several years ago, but developers in teh US have run into bureaucratic tangles (for example, can you get an investment tax credit twice for the same plant, once for the solar and once for the wind that are standing on the same site? What about permitting? There are no written rules for putting solar and wind in the same location. And so on). These are the administrative obstacles that have slowed the growth of hybrid plants in the US, which explains why there have been so few wind-solar hybrids in commercial operation there.

It is great to see that India is now very much in the forefront of the solar-wind hybrid strategy, using these as complementary renewables for both generation and balancing. India is prominent in the group of global leaders on wind-solar hybrids.

India is also one of the few countries that has gained valuable experience in tendering for such wind-solar hybrid plants (in other countries the hybrid plants are put up at the initiative of the developer, usually on private property, and the plants are funded through a bilateral contract with the off-taker, which limits the scope for price discovery). India’s track record of multiple solar-wind hybrid tenders (firming one renewable through another intermittent renewable) is innovative, given the limited global experience available in this area.

The solar-wind hybrid is where solar panels and wind turbines are co-located in the same area (care is taken for the wind masts not to cast shadows onto the solar panels). The rationale for this hybrid is the assumption based on observed weather data, that solar and wind will mostly balance each other and rarely fade out at exactly the same times. At night the wind continues to generate; energy demand on the grid is lower and the solar energy is not needed.

The wind-solar hybrid design is also expected to reduce the size requirement and the cost of investment required in the additional “firm backup source”—and thereby also minimizes emissions overall. Often the wind-solar hybrid then becomes a wind-solar-battery hybrid, but with a smaller battery requirement since wind and solar are doing most of the firming for each other. This design takes advantage of the sharper fall in costs that has happened for wind and solar, relative to batteries which are also declining in cost but not yet as much as the other two. So it loads up on more of the elements whose costs have really come down, and economizes on the battery whose costs are not yet down far enough. This allows the bid tariff to remain as low as possible, for a unit of clean energy coming out of this plant.

I was really pleased to find multiple variations of the India story online, so it appears to have really caught the attention of the global renewable energy community; the Indian experience with tendering and seeking solutions from the private sector to provide hybrid power with storage seems to be unique (in the first SECI tender, the choice of which storage technology to use, was left up to the bidder). For example, this is how one online article puts it:

Emerging markets, India

Siemens Gamesa claims to have completed the world’s first commercial solar and wind hybrid on-grid plant at Kavital in India in 2018, with the installation of 50MW wind power to an existing 28.8MW solar PV plant. Subsequent to its completion, this plant was reported to be including lithium battery storage to improve the operation of the plant. This solar/wind/battery project will be used to review such hybrid systems with a view to further implementation in other Indian projects. The Solar Energy Corporation of India issued a request for 2.5GW of hybrid solar and wind projects to be connected to the Interstate Transmission System.

Renewable plus storage combinations are becoming competitive with coal in Indian tenders

A recent oversubscribed 1.2GW hybrid tender for firm power supply has shaken up the Indian energy sector as it is competitive with coal power. The results of the competitive bid led to 900MW from Greenko ($US0.086/kWh peak tariff; $US0.040/kWh off-peak tariff, with weighted average $US0.0561/kWh) and 300MW from ReNew Power ($US0.096/kWh peak tariff; $US0.040/kWh off-peak tariff) for 6 hours/day during peak and off-peak hours on a day-ahead demand basis. To achieve the firm power requirements, storage capacity of at least 3GWh was needed. This tender is a first in India for firm power from renewables and it provides a viable alternative to peaker plants on the grid.

The most recent thermal power tenders in India produced tariffs in the range $US0.0694-0.0972/kWh. The peak hybrid tenders described above were also competitive with international markets (e.g., USA $US0.1111-0.1250/kWh). (https://seekingalpha.com/article/4333896-hybrid-renewable-systems-storage-makes-for-revolution)

Let's Get Back to Looking at Various Options for using Natural Gas Technologies as Steady Backup on Intermittent Renewables:

First, there are two qualifications for any good backup or balancing generation source. One is the ramp rate, i.e how fast it can kick into action (if you only need a second or two to come to life from a cold start, you are the favorite and best qualified technology to offer backup. But if you need 20 minutes to get started and get going, that doesn’t make you a great candidate to offer backup services. You might still be a good follow-on candidate, though, after the first backup has already balanced the grid for 20 minutes and we find that the windspeed is not back yet. More on this further below).

The other qualification for being a good candidate for backup, apart from quick-start, is the duration of the backup service that can be delivered. Many backup technologies with very fast ramp rate, like batteries and flywheels, can only provide backup service for a limited duration, as they discharge whatever stored energy they are holding. Then they need to be taken offline and recharged again. So, after your battery or flywheel are fully discharged, usually your wind or sunshine would be back and you would be fine. But if for some reason they are both not back yet, then you would need to keep another backup balancing technology waiting in reserve to take the baton, on the very rare and unexpected occasions that your balancing service requirement continues for longer.

For example, say you have a 6MW/2MWh battery; it can deliver 6MW continuously for 20 minutes. You always get signals from the grid every two seconds on how much energy they need. If your solar or wind plant is still not working, even after your 6MW/2MWh battery runs out in 20 minutes, then you need to have another fast-ramping, steady generation source that can kick in after that.

(Costs are an important determinant of battery size at this stage. We might daydream that it would be really ideal to have a 10MW battery that could keep going all night, for 8 hours. It would be delivering firm power of 10MW continuously during the night while the sun was not shining, and folks were mostly asleep, offices closed, and electricity demand on the grid was low…but such a 10MW/80MWh battery is not yet cost-competitive as part of a low-cost solar or wind generation picture. You might be happy to generate but no one would pay for it!)

Battery costs will still need to come down further before large grid-scale batteries become good candidates for long-duration backup. I have heard that at present, lithium-ion batteries are already competitive for up to 3-4 hour storage services—but I am not exactly sure what size of battery capacity that 3-4 hour discharge period refers to).

Bottom line: Everyone loves to say that if you have pumped storage hydro, that’s the best as a (zero emission) balancing source for your intermittent renewables, but we know that such facilities are only rarely available, in limited locations, and it is not practical or fast to construct new ones. (That's why I will not go into what it is, for those who are not familiar). So it's great if you happen to have that, but there are other options for steady sources of balancing if you don't.

If, as is common, there is no pumped storage hydro, then your best choice is a battery and/or a flywheel, but this will depend on the duration and frequency of backup needed (do you have enough time to fully recharge your battery for another round of play? in the above example (6MW/2MWh) needs to be charged again to be ready for its second 20-minute showtime. Can you leave the balancing to something else while you charge the battery again between appearances? What will you charge it with, if your generation happens to be low? Same with the flywheel.

If the intermittency of your renewable generation sources is too high in the particular location where the plant is, and the battery is not yet ready for its second act, by the time it is needed again, then an additional or larger battery is needed. Cost economics will be important. The firming cost (whatever technology you use for firming) gets loaded onto the unit cost of the power that the solar or wind or hybrid plant is selling. We can't go overboard in trying to make it super-firm, but at the same time so expensive that no one buys it.

The good thing (for the economics of the battery investment) about having a battery as the steady backup, is that sometimes the solar or wind plant is producing more electricity than the grid can absorb (maybe because demand is low at that time period). Let me try to explain this:

Overproduction of the renewable energy relative to demand at that moment, normally results in “curtailment”, i.e the grid operator asks the solar or wind plant to “back down”. Of course, the solar panels still keep on generating as long as the sun is shining, but curtailment means that the excess solar energy being generated is “spilled” or wasted, and will not be paid for by the grid operator.

At times like this, it is ideal for the solar plant owner if there is a nice battery standing by, as part of the solar plant, so that the curtailed excess energy, unwanted by the grid, can actually be fed into the battery by the solar plant operator, for sale later on, when it is wanted by the grid operator. This can keep the battery ready and fully charged, to offer balancing services to the solar or wind plant itself, when needed. It firms up the electricity offered by that solar plant (or hybrid plant).

Compared to other firming technologies like natural gas etc, the battery is a bit of a Swiss Army Knife! Notice in the earlier case we were talking about the battery DIS-CHARGING and supplying electricity to the grid, acting like a little balancing generator.

In this case, on the other hand, when grid demand for the solar plant's output is low, and there is excess energy generation, the same battery is now CHARGING and taking in surplus electricity that would otherwise be wasted and would not earn any revenue for the renewable plant operator.

This curtailed electricity is effectively being “parked” in the battery for a later time when it can be supplied to the grid. At that future time, when the sun is behind a cloud and solar generation has dropped off, the electricity that has been previously stored in the battery WILL be able to earn revenue from the grid operator. So, apart from providing a valuable balancing service when needed, the battery has also helped the solar plant to avoid a revenue loss. This is a further justification for shortening the payback of the investment in the battery as part of the hybrid plant, and helps in quantifying the return on the battery investment.

(Incidentally, there is a whole new topic lurking behind all this (a topic much beloved by economists), on “energy markets of the future”). There is a range of services called “ancillary services” which include the balancing services that are being discussed here.  

The key point in an ancillary services market is that ownership of assets is dispersed in the market, but that owners of these decentralized assets can efficiently and transparently transact with each other to meet their needs on a platform (e.g. I happen to have an idle battery today; you are looking for a battery today during your maximum sunshine hours when you will generate more than you can sell to the grid, so let's make a deal).

SIDE COMMENT: For people who have used the Task Rabbit app in the US, the ancillary services market is like the Task Rabbit of the energy sector! :) (there must be something like that everywhere, but Task Rabbit is the one I am familiar with--instead of doing difficult things yourself, like assembling an IKEA furniture piece, it lets you easily find and hire someone who is an expert, has better skills than you, and enjoys doing it. This means the assembly gets done in two hours instead of twelve. You pay them whatever they quoted you, but it is far less than the ten hours of your time that they saved you. You also dare to happily buy more furniture if you have an expert to assemble it for you!) So if you need a spare battery or flywheel, or a range of other services, you can go to the ancillary market and look at who is bidding the service you need, and find your Task Rabbit over there. But alas, this is only happening in very few countries at the moment, because the energy regulators are not comfortable with it.

In countries where there is an ancillary services market, the solar plant need not be the owner of that battery which was just discussed in the above example when we were talking about how to justify the cost economics of this battery.

The "just in time" access to a battery through the market is even better, because the full investment cost of the battery does not have to be loaded into his energy selling price. The solar or wind or hybrid plant owner can instead pay a third party owner of a battery whatever is a competitively discovered price, in order to “rent” that battery capacity. He pays the battery owner to keep that battery available on stand-by for him to use at the times he estimates he will need it. THIS IS ANOTHER WAY TO TACKLE THE INVESTMENT IN A FIRMING ASSET.

Third party owners of assets like batteries, small stand-by plants, flywheels, even pumped storage etc, also benefit instead of having their equipment sitting idle when it is not in use by them. They want to be able to monetize their assets by bidding to provide these balancing services to the grid or to owners of intermittent generation sources, in order to help them to firm up their offering. That’s all for now on ancillary services markets, I will stop here—I am just mentioning it since we are talking of balancing in this article.

Regulators need to wake up and allow these markets to happen in certain places like India. I am not 100% sure, but I believe that in India at the moment only government owned assets on the grid are allowed to offer ancillary services. More on this in another future article, when I get around to the series on Solar Energy).

Now let’s get back to the steady backups and move on to the natural gas plants, of various technologies:

Many transmission grids around the world today have a lot of peaker natural gas plants sitting around idle for many hours of the day or week. These plants are deliberately kept on standby, ready to go at any time, but are intended to be switched on only during times of peak demand. (Think of them as the “reserve bench” of basketball players who will jump onto the court if a player on the team is injured or removed by the referee). Remember, we have shifted gears from talking about balancing intermittent renewables and are now briefly talking about peaking plants (because there is a connection). Peakers are the small electricity generating plants that you as a system operator need to turn on when your electricity demand on the grid suddenly jumps up and your baseload generation is not enough to meet that higher demand.

The peaker plants were acquired as “load-following assets”, long before wind and solar came along needing firming, when no one was thinking of balancing. But when balancing became a “thing” in the last few years, as renewable energy penetration on the grid went up, naturally the existing reserve bench of peakers looked like an obvious asset to tap into, for the firming requirement.

In many countries these peakers include dirty natural gas plants, meaning they are built with the older, single cycle technology.

The dirtiest peaker plants — combustion turbine (CT) plants — are able to ramp up in seconds, which is why they are currently used for up to the first half hour to balance intermittent renewables, while the less GHG-emitting, newer gas plants, with combined-cycle (CC) turbines, ramp up in about 20 minutes. This does not make them suitable to be peaker plants.

Even the very newest generation of CC plants need, at best, 10 minutes to ramp up, which is why they are also not able to be used as peaker plants. They are either part of baseload, always on, or they are used as needed, but they can be neither peakers nor balancers, unless they are used in sequence, after another true peaker or balancer has been deployed.

Both types of gas plants are used on the grid. The 10-minute ramp up of the newest combined cycle (CC) plants may fit well in combination with a small battery that provides the initial 10-15minute balancing service and is then followed by the new generation CC plant. (https://www.renewableenergyworld.com/storage/fast-responding-energy-storage-digs-into-frequency-regulation-market/)

Those CC gas plants can ramp as fast as 100 MW per minute. Even if batteries can take care of the first few minutes, system operators and utilities would likely still favor gas to take over after batteries, switching to CC gas the same as they now do to take over after the CT peaker plants.

So, natural gas is the main reliable and steady balancing technology we have right now, which is a fossil fuel with GHG emissions. These plants are doing the job for those short intervals of balancing when the sun and wind drop off intermittently. What to do about the fact that they lower the cleanness of the renewable energy, with their GHG emissions? (much less than coal, but emissions still).

This emissions dilemma is now being addressed through attempts to capture the carbon emissions before they are released into the atmosphere (CCS, carbon capture and sequestration). Several attempts at adding a carbon capture system onto a regular natural gas peaker plant have been unsuccessful and have not been commercialized for high cost reasons.

So, this is the big question: is it possible to operate a natural gas plant with zero emissions, then, by burning the natural gas in a different way? Yes, fortunately it is! A new and cost-competitive technology has come along just in time.

A so-called “game-changer” (by Forbes magazine) demonstration natural gas plant with zero GHG emissions and a size of 50MW has been up and running in the United States for the past two years. The cost per kWh with this new emissions-free technology for burning natural gas is only 1.9 cents whereas it is 4.3 cents for a regular CC plant.

One of the articles in the links below mentions that this new Allam-cycle technology plant has a turbine with a footprint only the size of a minivan/SUV, whereas the standard gas turbine footprint is the size of a city bus. That’s impressive.

Small, powerful and no GHG emissions, while offering the steady and reliable output of natural gas!

The only thing that was not clear to me is whether this new natural gas technology also works well as a balancing source, meaning it can be switched on and off repeatedly and at short notice. Possibly not. The articles do not really shed light on that part. Instead, they capture the excitement about having found a zero-emissions way to run a natural gas plant that is competitively priced. Maybe it does not want to be a balancing source, but a zero-emission baseload source instead.

More details about the innovative technology approach are here:

https://spectrum.ieee.org/energy/fossil-fuels/this-power-plant-runs-on-co2

and here https://www.forbes.com/sites/jamesconca/2019/07/31/net-zero-natural-gas-plant-the-game-changer/?sh=13a4694c1de2

This final article on the same topic of the Allam-cycle was my favorite https://www.vox.com/energy-and-environment/2018/6/1/17416444/net-power-natural-gas-carbon-air-pollution-allam-cycle and it did make a mention of balancing plants at the very end, but in a general sense, to say how these would be greatly needed, as solar and wind raise their profile in the generation mix.

Last but not least, there is another article called "The Benefits of Baseload Renewables: A Misunderstood Technology" https://www.sciencedirect.com/science/article/pii/S104061901500024X which echoes what I often hear from supporters of geothermal and large hydro. “Don’t bother with balancing!”

 This view says that we should be transforming our energy sector from the bottom up, by going after zero emission sources like hydropower and geothermal power for our baseload. Baseload is the always-on portion of our generation that meets the steady portion of demand for electricity from the grid. Today baseload is met by coal in most countries, including India and the US. These guys say forget that, use hydro and geothermal instead (if you happen to have a developed geothermal sector, that is! Most countries do not, and many don't have hydro either. So they can't be part of this exclusive club).

In this case the grid would be supported by always-on emission-free energy sources, and wind and solar would complement them but the importance of the balancing function would be negligible, since hydropower has a very fast ramp rate and could increase its output when required for balancing the wind and solar energy. https://www.sciencedirect.com/science/article/pii/S104061901500024X

That’s it, I’m done! Congratulations if you have managed to read this far! Probably no one actually reached here...well, at least I had some fun thinking about all this stuff, thanks to Rajat's question. ??