Energy storage is something we are all familiar with, from stretching an elastic band, to pressure tanks in our water systems, to the batteries in our phones and electrical devices. Even the gas in your car is a form of energy storage.
Have you heard that energy storage is key to the success of renewable energy and wondered why?
Every system in life should be balanced. Energy storage is one method to balance our energy system, which is why we installed the Battery Energy Storage System (BESS). The BESS provides us with a cost-effective way to balance the energy demand for our customers.
Currently we have predictable, controllable and reliable engines that can be throttled up and down to balance Bermuda’s energy demand. When someone turns on an appliance such as a clothes dryer, our engines immediately react to supply that electrical energy.
Just like travelling in a car, when you start going up a hill the shaft speed (RPMs) of the car’s engine reduces and the car slows down. The driver applies more throttle to maintain speed when they notice the car has slowed down a bit.
Similarly, at BELCO, when the shaft speed reduces, the throttle is increased within a few seconds to apply more power to the engine’s shaft to bring it back up to speed and balance the energy system’s demand and supply. This is done while trying to use the most efficient and cheapest energy source available.
When we run out of power meeting a particular consumer demand, we must start another engine to match the demand. The energy stored in the BESS can be used to balance the demand for a short time, whilst another engine is primed and started.
Energy storage can be critical to secure an energy system that has fluctuating renewable energy supply. Imagine a day with cumulus cloud cover[1], passing over the island causing solar fluctuations. We are responsible for smoothing these fluctuations out.
The key to successful renewable energy adoption will be adequate storage for quick and easily dispatchable energy to deal with large fluctuations.
Energy storage for utility scale energy systems is not limited to batteries, but includes technology such as pumped hydropower storage, spinning flywheels, large capacitors, flow batteries, thermal storage and compressed air energy systems to name a few.
Energy storage can be broken down into 4 main energy groups:
- Gravitational and mechanical
- Electrical and electrochemical
- Thermal
- Chemical
Gravitational and mechanical includes systems that store potential energy such as pumped hydro and gravity-based storage systems. Mechanical systems also include flywheels, compressed air and liquid air storage.
Electrical and electrochemical systems include rechargeable batteries, supercapacitors and flow batteries. Short term solar variability such as cumulus clouds can be met by spinning flywheels and capacitors that have high power outputs for short durations, however large cloud cover can last days and requires high power storage for long durations.
Thermal energy technologies typically take advantage of the phase change of materials, for example cold energy is stored as ice, whilst hot energy is stored in molten salt energy.
Finally, chemical energy storage includes natural gas, oil, coal and hydrogen.
It is important that the lifetime cost and operability of the storage system meets the needs of the renewable energy fluctuations and demand profiles but is cost effective, safe and long lasting.
Batteries are a common form of energy storage for utilities, and the technology has developed a lot over the past century but it still needs to be developed further. There are a range of different battery chemistries, including but not limited to lead-acid, lithium-ion and sodium-sulphur. All batteries are a form of dense energy storage and require proper handling and operational safety measures. The BESS has a 10MW capacity and can output for 30min. To provide power for one average business day in Bermuda (9am to 5pm), the system would require approximately 130 BESS batteries fully charged.
Pumped hydro stores energy as gravitational potential energy by pumping water uphill. The water is then allowed to flow downhill converting the energy to kinetic energy as it turns a turbine connected to a generator. In fact, the turbines and generators are often bidirectional, meaning they are a pump/turbine connected to a motor/generator and they can either push water uphill using electrical energy, or allow water to push the turbine generating electrical energy. These systems are heavily used in larger countries with an abundance of fresh water and higher topologies. The technology is extremely well understood, Bermuda could easily do this if we had high hills and an abundance of fresh water, unfortunately we do not have either.
Compressed air energy storage (CAES) is a form of energy storage that stores high pressure air in large underground caverns or tanks. It is one of the few energy storage technologies that work for long durations. Typically, the high-pressure air is stored in salt caverns, hard rock or porous rock that is confined impervious rock. Bermuda has lots of porous rock on top of volcanic rock, but has no impervious rock on top to hold the compressed air in. So, any compressed air storage for Bermuda would require fabricated high pressure storage tanks.
In the end, energy storage can be costly and can take up a lot of physical space, which Bermuda has a limited supply of.