Wednesday, 22 May 2013

Diesel Generator loading and renewable systems integration


Diesel Generators are widely used in India and most of the developing countries where the grid is unstable. The cost of diesel fuel has been growing rapidly in the past few years. The demand for diesel is only expected to raise day by day and can no way come down. How equipped and aware is the Indian/developing community regarding their dependency on such a fuel? Should we think about conservation and smart usage of these non-renewable fuel like Diesel, as these are the primary source of fuel for automobile industry?

In this article I will be focusing on DG sets loading profiles, effects of low loading and how to make your DG more efficient. As discussed in my previous article on smart power management, regarding synchronization of DG with solar inverters, I will be adding more flavor to this article by also discussing on integration of renewable energy systems to the existing DG systems to make it economically viable option.

"Any creative comments or ideas from the readers are welcome, since this is just a platform for me and peers in the same field to make people aware of these technologies"

Diesel cost has doubled in the last decade: 

The cost of diesel was INR 23.29 per liter in 2002. Now the cost has doubled to INR 52.45 (Check graph below). Can the cost of diesel increase more? I leave the answer to the experts!

I have the following questions in my mind.

In this current situation what must be the steps taken by the Indian central and state governments? Is there any restriction in fuel consumption or purchase by a individual.? Do we have any restrictions on DG sets purchase or usage? The DG usage increase the burden on a common man indirectly? should the government think about imposing special prices on diesel for DG usage.? 

Lastly,  how do we act smart in this scenario and contribute as individuals and also benefit financially?

Diesel Generator working and Loading profile: 

In actual practice the diesel fuel consumption (kWh/litre) is never in exact proportion to the load and reduces non-linearly with reducing load. Figure below indicates maximum energy production occurring at the rated capacity and the production rate reducing with the load.

While selecting a diesel generator it is always better to understand its loading profile. If loading can vary drastically over a limited time period, it is always better to consider two or more DG's synchronized in modular fashion. The savings can be considerably high on the long run, please find some calculations below under Economics heading.

At idling conditions, ie., at no load, the diesel engine consumes approximately 2.5 times more fuel to produce a unit of energy (or generates only 40% of the energy for a litre of diesel) than when operating at the rated capacity. At a loading of 40%, the fuel consumption is 23% higher than at full load or the energy generation is 19% less than at the rated capacity. Thus efficiency of diesel generator always reduces with the decrease in load.[2]

DG with renewable energy technologies: 
As discussed in my previous articles and blogs, it is possible to run renewable energy technologies like solar and wind synchronized with diesel generators. Usually in developing countries like India diesel generators are used in almost all commercial and industrial buildings, this is due to the unstable grid.

The following are the options to be considered

1. Have 2 or more DGs based on load requirements (sync one by one based on load - in modular fashion) this can help in fuel reduction

2. Have solar PV or wind 20-30% of the load requirements

Economics or Cost savings:  
  1. Cost of 100kVA diesel generator - 12lakhs (supply+installation) 
  2. Cost of 100kW (Solar grid tie system) - 100 lakhs (Supply+installation) 
The payback from solar is completely dependent on generation and the FiT or savings from conventional electricity tariff. If generation or usage (load) is not optimized the payback can be prolonged. These is a misconception that running DG under idle condition just for solar operation is profitable.

The design engineer or project developer should understand that loading DG below 40-50% can always make the system consume more fuel. Here is a example,

Here is a cost comparison (using simulation): (please check reference 2 for more details)

As per the research paper published [2] at Murdoch University, WA., the comparison has been generated using Hybrid2 simulation.

Here two scenario's have been considered

  • Under Normal Load conditions 
  • Under Modified load conditions 

Obeservation from above table: 

Under Normal Loading condition - 
  • Using a single 60kW diesel with a additional 20kW wind can increase the dump load % upto 10% (this is too high) and the % of fuel saving is 9.3%. This leads to a average cost/kWh as 14.30 $cents. 
  • Whereas under the same loading condition but with two generators (40+20kW) with 20kW turbines can bring down the overall average cost upto 13.36 $cents. This is due to the modular fashion generators and reduction in dump %

Under variable loading condition -
  • Under this condition the with 40+20kW DG in modular fashion and 20kW wind turbine, the system seems to perform much economical fashion (12.87 $cents)
Potential in Micro grids: 
Lots of isolated grid installations have happened in the past and the potential is huge. For example islands like Maldives after being affected by Tsunami in December 2004, have been completely dependent on micro grid systems with renewable energies. 

Similarly many developing countries like India, countries in south America and Africa can greatly benefit using these systems. In my future blogs/articles I will be discussing a case study on these micro grid systems.

The above results show the commercial advantage on using two diesel generators instead of a single big diesel generator. In a two-diesel generator modular system the flexibility in choosing the diesels to meet the load has resulted in better operational efficiencies. Thus the smaller diesel along with the wind generator can take care of the low load situations leading to reduced fuel use and lower operating costs. The load management strategy resulted in better overall cost savings and reduced generation cost in the dual diesel scenario.


2.  Effect of load management and optimal sizing on the economics of a wind-diesel hybrid power system. P. S. Panickar*, S. M. Islam** and T. L. Pryor* * Murdoch University Energy Research Institute, Murdoch University, WA.