Hybrid generation/storage for microgrids3 July 2018
Traditionally a provider of Jenbacher gas engine based power plants, Clarke Energy is increasingly finding itself involved in microgrid and ‘hybrid’ projects, where piston engines
are deployed in conjunction with distributed renewables and energy storage. By Alex Marshall, Clarke Energy, UK.
Economics and technology developments are changing the landscape of the power generation sector. Over the last 20 years, there has been a movement away from large centralised power stations towards decentralised generation close to the site of use. The price of solar photovoltaic panels has dropped dramatically and is set to continue on this path. Gas-engine-based combined heat and power technology is also now well established, and cost effective.
The global weighted average levelised cost of electricity (LCOE) for utility scale solar PV is forecast to drop by a further 40% by 2020, to $60/MWh, according to a new report from the International Renewable Energy Agency (IRENA). This follows a 73% drop in the LCOE of utility-scale solar PV between 2010 and 2017 (see graph). Other renewables are also achieving declining costs.
Battery storage technology costs are following a similar trend, with cost reductions of 50-60% projected by IRENA to 2030 across lead acid, high temperature, flow and lithium ion batteries.
These cost reductions mean that decarbonisation of electricity supply is becoming much more practical and cost effective. However, the intermittency of renewables such as solar and wind remains a challenge, with battery storage technology only suitable for relatively short releases of electrical power. Embedded generation, particularly that within island mode microgrids, is sensitive to supply and demand challenges along with frequency and loading rate changes.
This means a number of different power generation technology types are becoming more frequently deployed within microgrids, drawing upon the benefits of renewable generation, storage technologies and gas or diesel engines. This combination and synchronisation of different types of power generation technologies, typically in conjunction with energy storage, can be referred to as ‘hybrid power generation’.
Microgrids typically fall into three distinct types: grid connected; island mode; or grid connected microgrids that can be disconnected and operate in island mode.
There are also a number of distinct applications, including: microgrids linked to an unstable power generation network, such as that commonly found in Africa; microgrids linked to a stable power grid that can be affected by natural disasters, such as in the United States; and microgrids in remote areas, such as in the Australian mining sector.
At Clarke Energy (now part of Kohler) we are seeing benefits in deploying our gas engine power plant engineering experience in hybrid power generation projects. One recent example is the OK Plast microgrid in Nigeria.
Here, the industrial captive power plant user had elected to use pipeline natural gas for power generation with three GE J420 Jenbacher gas engines. The OK Plast manufacturing plant operates in island mode, isolated from the unstable Nigerian power grid. The gas engines have further back up provided by diesel gensets. A particular challenge here is that the OK Plast facility is involved in the manufacture of plastic products with machinery that imposes frequent ‘relentless’ power demand swings of 20-200 kW.
The solution proposed and delivered by Clarke Energy’s engineering team was deployment of an ultra-capacitor system. This energy storage system is able to charge and discharge power rapidly to support the stable operation of the microgrid. It also avoided the need for a third gas engine, and hence improved fuel efficiency and reduced carbon dioxide emissions.
Australia is another place where we are seeing growing interest in the potential of microgrids with hybrid generation/storage. Remote areas of Australia are of course known for their prolific levels of sun and many mines are located significant distances from electricity distribution networks. Whilst pipeline gas is a cost effective and low carbon emission solution for localised power, there are also benefits in combining gas engines with solar energy. Clarke Energy is now offering gas engines with solar photovoltaics and storage systems to meet the needs of mines in remote areas.
There is however no one-size-fits-all solution for microgrids. An understanding of the end users’ needs, the site location and local environmental considerations are of course essential in matching appropriate generation and storage technologies to what is required and providing an engineered solution.
 IRENA (2017) Electricity storage and renewables costs and markets http://www.irena.org/publications/2017/Oct/Electricity-storage-and-renewables-costs-and-markets
 Clarke Energy (2018) OK Plast Hybrid Power Plant Solution https://www.clarke-energy.com/2018/ok-plast-hybrid-power-plant-solution/