Energy Costs and Energy Efficiency, PETMAF Can Help
Energy efficiency projects on a ship are much more cost-effective than those carried out on land-based facilities. This is mainly due to the higher energy costs incurred on a ship: $0.25/kWh compared to $0.10/kWh. Despite this reality, the industrial processes on ships are often more energy intensive than those in industry.
Why is this so?
Normally, there are three types of energy used in maritime transport:
Each of these forms of energy is produced from fossil fuel. It is well known that energy efficiency is measured by dividing the amount of energy used by the amount of energy contained in the fuel. The greater the energy efficiency, the more effective is the process.
A diesel engine transforms the thermal energy contained in fuel oil into mechanical energy. Normally, the bigger the engine, the more effective it is. The main engine is more efficient than a diesel-electric group, for example.
In the world of diesel engines, thermal performance is defined as the number of grams of fuel used for each kilowatt-hour of energy produced (g/kWh). It is the engine’s specific fuel consumption (SFC). This number can easily be transformed into a unit of thermal efficiency expressed as a percentage. This is what we prefer doing in order to be able to compare different heat engines with each other.
For the purpose of this article, let’s use the following values:
- 200 g/kWh for a diesel generator running on MDO
- 190 g/kWh for a main engine running on HFO
In this particular case, our small engine has a thermal efficiency of 42% while our main engine achieves approximately 46%.
In the case of our diesel generator, the performance of the alternator must be taken into account. Let’s use 90%. The thermal efficiency of the diesel generator then declines to 37.7% and its specific fuel consumption rises to 222 g/kWh.
If we produce electricity through the shaft alternator, what will be the performance of the electricity produced?
Using the same alternator at 90% efficiency, the specific fuel consumption will drop to 211 g/kWh. However, if other components are taken into account such as a reduction gear which has a 98% efficiency rating and a power converter at 95%, the specific fuel consumption rises quickly and can easily reach 220 g/kWh. In the end, there is relatively little difference from the point of view of thermal performance between a small diesel generator and a shaft alternator. It’s through avoiding maintenance on the diesel generator that gains are made. Very little is gained in terms of energy and fuel consumption.
For a marine boiler, the thermal efficiency is normally around 75-80%. If thermal heat is needed, it’s better to use the boiler instead of electric block heaters. Energy consumption will thus be reduced by half (37.5% vs 80%).
The least expensive energy is the one that costs nothing. Heat recovery on a diesel engine offers good opportunities. Every effort must be made to recover the free heat from the stack economizers and from the engine cooling systems. Doing so increases its performance and reduces the production of GHG.
On a ship, everything that must be heated should be done so with recovered heat.
Today, the price of MDO oscillates around $750/ton and HFO around $350/ton.
The price of a kilowatt-hour of electricity produced on a ship varies between $0.10/kWh and $0.19/kWh. This is not much and the exceptional situation surrounding the price of oil price will not last forever. Besides, adopting good practices and implementing energy-efficient projects are still very cost-effective in several cases. Moreover, reducing GHG continues to be a pressing issue.
Let do a simple exercise: reducing electrical by 50 kW.
50 kW * 24 hrs/day * 250 days/year = 300,000 kWh
300,000 kW * 220 g/kWh = 83 tons of fuel per year, or between $29,000 and $62,000 in savings per year.
This represents 211 tons of reduced GHG. With the help of the ministère des Transports du Québec’s PETMAF Program, you could receive a subsidy that will reduce the period of return on your investment to such a point that you will quickly become convinced that the right time to invest is now.
We can help find projects that are cost-effective for you and the environment.