Small-scale Energy Production in Remote Areas relies on Ni-Cd

Battery storage systems help compensate for the fluctuating output of large solar or wind power plants, but also make it possible to operate critical equipment in remote locations without connecting it to the grid.

Coupled with large solar power plants or vast wind farms, battery systems are used to store excess energy production during peak hours of sunshine or the wind blowing, and release the accumulated energy when the opposite is the case. This is done to ensure that the installation is providing a constant output according to what the operator is obliged to deliver to the transmission network, but also to prevent the local grid from overloading, known as the ramp-rate control application. 

Such storage systems have to cope with large fluctuations in energy production, and as they are delivering energy to HV grid infrastructure, they operate in a high voltage - low current mode. Conversely, small renewables installations generate electricity at a much lower voltage, typically under 50 V, while their batteries must handle currents in the thousands of amperes. Facilities such as base stations of telecommunications infrastructure do not need to quickly compensate for fluctuations in electricity generation, but instead rely on receiving constant voltage. 

Remote areas also tend to be either too cold or too hot, or also high moisture salty sea environments. As Li-ion cells are particularly susceptible to temperature, they can’t do without sophisticated temperature control, as well as other auxiliary systems. This electronics suffers in dusty or salt-moisture conditions, and requires significant maintenance. It also consumes electricity, ranging up to 5-7 percent of the system’s rated power.

Beyond the Arctic Circle or in the Desert

Because of all this, at remote unmanned industrial installations, nickel-cadmium batteries are preferred over Li-ion technology. Ni-Cd cells tolerate both very high and very low temperatures. In fact, while they are usually designed for ranges between -20 and +50 °C, they can as well withstand temperatures of -50 or +70 °C, at least for short periods of time. 

Dust, moisture or salt does not affect Ni-Cd cells, which are typically placed inside a battery box with just sufficient louvers for air ventilation, without any air-conditioning. They do not require any other supporting systems, thus requiring minimum maintenance. Ni-Cd cells can be discharged  autonomously over a long period of time, even for 10 days of insufficient or no solar irradiation, which is also advantageous for critical, must-run applications.

Particularly in extreme climatic conditions, Ni-Cd  batteries tend to be the only choice. For example oil pipelines going  through deserts need to have boosting stations every 50 or 100 km to  ensure that the oil flows constantly through the pipe. Alongside steel  pipelines, there are also Impressed Current Cathodic Protection (ICCP)  stations applying an electrical potential along the pipeline in order to  prevent corrosion in both underground and over the surface metal parts  of the pipeline. Additionally, the communication and control of the  distant site through Remote Terminal Units (RTU) must run in a fail-safe  mode, never running out of power.

This equipment comes  in different sizes, but the most common design is about the size of a  smaller lorry. They consist of several dozens of Ni-Cd cells connected  in parallel, with a total nominal capacity of thousands of Ampere-hours.  The installation is covered by a photovoltaic panel doubling as a roof.  Similar devices featuring Ni-Cd batteries are also used for  anti-corrosion protection of steel constructions in the completely  different environment of off-shore oil rigs.

In this  type of applications, Ni-Cd are useful for their reliability, as they do  not require constant monitoring nor a controlled environment. A Ni-Cd  battery storage can be installed even in very remote and inaccessible  locations, and can operate almost without maintenance for 20 or even 30  years. This contributes to another of the major benefits of Ni-Cd  technology: a significantly lower total cost of ownership, even when  compared to lead batteries.