Jason Yates, Technical Services Manager at Riello UPS, explains how rethinking the role of uninterruptible power supplies can transform them into ‘virtual power plants’ that aid the ongoing energy transition.
With soaring energy costs never too far from the headlines in recent months, electrical systems throughout the world continue to evolve. The shift from fossil fuels to renewables is a necessary one on the journey to zero carbon. But a consequence of this ongoing energy transition is that system operators such as National Grid now face a much trickier task to balance supply with demand and ensure a stable grid frequency.
Rather than simply controlling power generation to meet demand, as we’ve done in the past, the power grids of the future will be smarter and more flexible, with demand controlled to meet supply in real-time.
Energy users will become producers too, with electricity flowing in both directions as they not only draw power from the grid but also feed stored energy back into it.
Concepts such as demand side response, which incentivise customers to store power and shift energy use from busy to off-peak times, also offer organisations the opportunity to reduce their eye-watering electricity bills.
But it will require a significant shift in mindset to take full advantage.
From underutilised asset to virtual power plant
From the data centres that are crucial to our digitally-driven lives, through to factories, shopping centres, and processing plants, virtually any facility with a critical electrical load will have uninterruptible power supplies (UPS) and batteries installed to protect against damaging downtime.
Fortunately though, major power cuts in the UK are relatively rare. So, while a UPS is undoubtedly an essential insurance policy against the worst-case scenario, in some ways they’re an underutilised and expensive asset. And if the batteries aren’t being used regularly, can you be 100% sure they’ll actually work if and when you really need them to?
Thanks to advances in communications software and protocols, along with the development of premium cycle-proof batteries, many modern UPS systems are now smart grid-ready. They can communicate with local power networks and either draw electricity from the grid or push stored energy back into it, depending on the real-time requirements.
These characteristics have the potential to transform your UPS from a reactive piece of hardware into a dynamic ‘virtual power plant’ that can contribute to the ongoing energy transition and profit from the energy markets, whilst also benefiting from enhanced reliability.
Putting theory into practice
As an example, we teamed up with RWE Supply & Trading, one of Europe’s leading energy trading companies, to develop Master+, a smart grid solution specifically for data centres and other large-scale energy users.
It comprises a highly efficient, smart grid-ready UPS backed with cycle-proof premium lead-acid batteries (NB lithium-ion batteries are a viable option too). Thanks to a compact battery arrangement, the system is able to provide up to four times the usable capacity but with only a 20% increase in footprint, so enough battery capacity for both emergency backup and for commercialisation.
The solution also has an integrated, highly-secure control and monitoring system that enables two-way communication with the grid and aids with predictive maintenance.
The battery system is split virtually into two separate parts. There’s a backup segment representing around 30% of the total usable capacity. This element is configured and controlled by the UPS and is preserved only to support the critical load in the event of a mains failure.
The remaining 70% of the battery capacity is the ‘commercial’ segment, which RWE can deploy to participate in grid balancing schemes such as Firm Frequency Response (FFR). This is a demand side response mechanism National Grid operates to help maintain a consistent and safe grid frequency within one hertz of 50 Hz.
So in practice, if the frequency increases above 50 Hz, the UPS effectively draws power from the grid into the battery system to help pull the frequency back down. On the other hand, when the frequency falls below 50 Hz, we push the power stored in the commercial segment of the batteries back into the grid.
The typical state of charge during system operation fluctuates between 60-70%. Therefore, if there is a mains failure, the site would benefit from extended backup autonomy because whatever energy is left in the commercial segment tops up what’s already in the guaranteed backup segment.
So in return for RWE gaining the usage rights for the commercial segment of the battery, the site owner benefits from a significantly discounted battery system, extended backup time, 24/7 monitoring, lower ongoing maintenance costs, and reduced grid tariff charges, which depending on the site can potentially be worth up to £6,000 per MW per year.
Potential of peak shaving
Peak shaving is another potential function of a smart grid-ready UPS. In practice, this is using the UPS batteries to effectively limit how much power is taken from the mains supply. If the load on the UPS output goes beyond a set level, then the UPS takes a proportion of the load from the mains, with the remainder coming from the batteries.
There are four main types of peak shaving. Firstly, there’s static, where the UPS has a fixed setting and peak shaves to that defined limit. There’s also user-controlled, where the facility can reduce the input power ad-hoc by pushing commands to the UPS using volt-free contacts or protocols such as Modbus.
There’s also impact load buffering, which is predominantly for sites with a weak power source or generator and sees the UPS in effect slow down the incoming mains supply. Finally, and probably the most commonly used, is dynamic peak shaving, which as the name suggests, works according to the real-time on-site conditions.
How does this work in practice? Say you’ve got a site that is contractually limited to 1 MW of mains supply. Its typical load ranges between 500-900 kW, while they have a critical load of another 300 kW. Potentially, that’s a maximum load of 1.2 MW, which would be in breach of their contract.
During these peak load periods, the UPS automatically pushes the energy stored in its batteries to reduce the power required from the mains. And of course, when loads are lower, the UPS recharges the batteries for future use.
In addition to frequency response and peak shaving, smart grid-ready UPS can also carry out other valuable functions, including voltage optimisation, which guarantees a stable voltage (i.e. 400Vac + or -1%) no matter the incoming mains supply, and waveform correction, which reduces the harmonic distortion on the load and improves the overall power factor.
Unlocking the value of battery power
It’s clear that modern UPS have much more to offer than just sitting and waiting to provide emergency backup power.
Just a few weeks ago, tech giant Microsoft announced its data centre UPS across Ireland would start using lithium-ion batteries to feed power back into the grid by the end of the year. This battery power will reduce the reliance on coal and gas-fired plants to maintain spinning reserves, helping to significantly reduce the Irish energy sector’s CO2 emissions.
As smart grid technology continues to improve, there are similar opportunities for other facilities to follow suit and harness the true power of their UPS systems and batteries. Not only do you reap the financial and performance rewards, but it’ll also help with the security of supplies for society as a whole.