One company which decided to take this precaution is Eaton. Energize interviewed Eugen Ranft, Eaton’s operations manager, who explained how the system works, as well as the benefits companies derive from installing a private microgrid.
In Eaton’s case, the company experiences, on average, four outages per year which last for about four hours at a time. The company has two large sites in Wadeville, Germiston and, faced with every-increasing electricity tariffs and being supplied from an ageing distribution infrastructure, the company decided to invest in a microgrid system which would provide reliable power to the factory.
Ranft says that the company installed a renewable-energy plus battery-storage type of microgrid at its factory. This system enables the company to isolate itself from the power utility’s supply should it need to do so – or during an outage – without loss of electricity to the facility. The microgrid consists of rooftop PV panels which provide 233 kW of electricity on a sunny day, a battery storage system which is rated at 275 kVA and a 400 kW diesel generator.
The whole system is managed by a computer-based controller. Apparently, the microgrid’s controller automatically selects the appropriate power source according to prevailing requirements. For example, during the day, when the utility’s electricity tariffs are high, the system draws power from the PV panels as well as from the batteries if necessary. At night, when the tariffs are lower, the utility’s supply is used to recharge the batteries. Should more power be required than what can be supplied by the PV-battery combination, the diesel generator will provide the difference.
According to Ranft, although a 400 kW diesel generator may seem large, it is smaller than would have been required by the factory during a power outage, if the microgrid did not have a battery storage system. Buying a smaller-than-needed generator saved the company money and the unused diesel fuel saves it even more.
The PV panels are mounted onto the factory’s roof and require no additional space on the site.
The batteries are “second-life” electric vehicle (EV) batteries. These batteries were previously fitted to EVs and although they still have plenty of life in them, they are deemed to be unsuitable for continued use in an EV. Ranft pointed out that the idea of extending the life of EV batteries by using them in stationary instead of mobile applications offers a number of advantages.
Firstly, he says, extending the life of these batteries has an environmental benefit. It removes the problem of disposing batteries which are no longer suitable for use in EVs, and secondly, the availability of these “second-life” batteries removes the need for more material to be mined for the manufacture of additional batteries for use in stationary applications.
Furthermore, the price of second-life batteries is about 30% lower than similar new ones. This helps to keep the overall cost of a microgrid down. Also, in Eaton’s application, the pay-back period is expected to be between four and five years.
According to Ranft, these second-life batteries still have an expected life of between seven and ten years depending on load and how they are recharged. There are, apparently, enough second-life batteries in the market to support this purpose, and as EVs become more popular the number of them will continue to increase.
Ranft says that to ensure that the microgrid system would meet the factory’s current and future needs, the company implemented an energy-efficiency programme which included replacing certain pieces of equipment and lighting with more modern energy-efficient types. Furthermore, to reduce its overall electricity demand, the company replaced its electric furnaces with gas-fired ones.
In Eaton’s case, the installation of this microgrid resulted in a reduction of 40% in the company’s electricity bill in June 2018. Savings during peak tariff periods could be as high as 65%, Ranft says.
Eaton manufactures most of the equipment used at the company’s factory. The installation is therefore useful as a demonstration site for those companies which are interested in investing in a microgrid for their facilities too. To run a factory efficiently, Ranft says, a reliable supply of electricity with high power quality specifications is essential. This can be assured from the microgrid system which has been installed at his site, he says.