Decarbonisation Technology - May 2024 Issue

project. On-site renewable assets such as solar are inherently inflexible or intermittent, given that they are dependent on weather conditions. A BESS enables the purchase of grid energy when prices are lowest, generally overnight, and at the times when grid power is produced with lowest emissions. Where organisations are increasing electrification to a site, a BESS can be critical in allowing for high-demand technologies such as EV charging by circumventing the need to rely solely on grid supply. If the BESS also includes an uninterruptible power supply (UPS) element, this offers additional benefits, including power resilience and potential cost-savings, both crucial as we shift to an increasingly electrified world. Many organisations rely on UPS to mitigate power disruption to critical equipment. However, the traditional solution is increasingly untenable. Based on lead-acid battery technology, the UPS will be idle for much of the time, yet it will be continuously switching between AC and DC, losing up to 15% capacity. For a typical 1MW system, this represents a wasted energy spend of approximately £200,000 per annum. By contrast, a modern BESS with UPS can offer cost-effective, site-wide protection. Rotherham General Hospital in the UK needed a modern solution to its demand for a secure power supply. The proposed system was a 500kW/500kWh BESS with UPS, with the new battery cycled daily to ensure it meets the NHS minimum requirement of 20 minutes’ load supply in the event of disruption (see Figure 3 ). In one instance, the system was called upon twice in one day when grid power failed. Each time the BESS supported the full load, first for 15 seconds and, in the second instance, for 23 seconds. The greater energy efficiency of modern BESS with

Figure 2 Inside a battery energy storage system

UPS is currently saving the hospital an average of £225,000 on its annual energy spend while reducing emissions by 190 tonnes of CO2 e. Additionally, the Hospital Trust is able to access approximately £100,000 in revenue through engaging with Grid Services. Voltage optimisation assets A second and equally valuable technology, as part of a microgrid and as part of a cost-saving and emission-reduction strategy, is VO. A transformer-based technology, VO stabilises the incoming voltage to a site (see Figure 4 ). The National Grid is legally obliged to supply mains voltage at 230V +10%/-6%, which means that while supply is anticipated at 230V, it can be anywhere between 216V and 253V. To maintain the allowable range, the grid supply is generally higher than 230V, averaging at about 242V, significantly higher than the 220V operating voltage of most equipment. Operating at a higher voltage than required wastes energy, creates unnecessary emissions, and can damage equipment, leading to increased maintenance costs while reducing lifespan. Implementing

Normal voltage

Voltage interruptions

Voltage sag

Undervoltage

Overvoltage

Voltage uctuation

Frequency variation

Figure 3 Examples of power disruption