# MIET2131 Electrical Energy Storage Systems Assignment

1- A small electrical energy storage system is based on a 50-W PEM fuel cell (mass 320 g, efficiency operating at an average efficiency of 45%) and a number of metal hydride hydrogen storage canisters each capable of storing up to 1.6 wt% hydrogen with an uncharged mass of 120 g (a 100% full canister includes the mass of canister, the miniature regulator connected to that, and the hydrogen stored). At what minimum total
electrical energy delivery capacity would this system have a system gravimetric energy density advantage over a battery bank based on a number of lithium polymer batteries, each weighing 80 g and rated at 1800 mAh with a nominal voltage of 7.4 V. Assume an 75% depth of discharge for each battery and a 10% drop in voltage, linear with usage, during discharge. Consider just whole numbers of MH canisters and batteries. At the gravimetric energy density crossover point, how many MH canisters would the hydrogen fuel system employ and how many batteries (rounded to the nearest whole numbers)?(4 points) 2- Compare the fueling/charging costs and GHG emissions of an electric car, a hydrogen fuel cell car, and an ICE (running on petrol) car per km of range by using the following assumptions:
• The high-pressure hydrogen is produced using a medium pressure electrolyser with
0.6 efficiency followed by and an external compressor with 80% efficiency.
• The average round-trip energy efficiency of the battery is 70% • The battery is charged in a cold wintertime in Melbourne for which equivalent to 5% of the energy content of batteries is used for their thermal management during charging.
• The energy content of hydrogen (HHV) is 142 MJ/kg (~40 kWh/kg) • The energy content of unleaded petrol is 34.2 MJ/litre
• The overall efficiency of the petrol car in converting the chemical energy of the fuel to mechanical energy delivered to the wheels is 20%
• The average energy efficiency of the fuel cells used is 45% (based on HHV), and that of the electric motors 85%
• The batteries are charged up by using grid electricity in Victoria
• The electrolyser and compressor are powered by electricity supplied by the Victorian grid
• The following document can be used for estimating greenhouse gas emissions required for answering this question:
3- An investment company intends to run a preliminary feasibility analysis for a closed loop pumped hydro storage plant in Victoria. They have specified that the plant must have 30 hours of storage and a generation power capacity of 1200 MW. You are required to find three different locations that suit this project. These locations should be in Victoria. To do so, use the Pumped Hydro Atlas that is available at the AustralianRenewable Energy Mapping Infrastructure (AREMI) website in the following link:
https://nationalmap.prod.saas.terria.io/#share=s-tPEnZ4T5NRAYIiLS0E3ftvcAzb
a. the overall generation efficiency of the plant is 83%, and
b. the overall pumping efficiency of the plant is 86%.
List the latitude and longitude of three sites that allow for storing the quantity of energy that you calculated in the previous question. To minimise the cost of constructing the penstock, the separation distance between the upper and lower reservoirs must be less than 4 km. List the separation distance of the reservoirs for each site. List the available head in each location.
Calculate the volume of the upper reservoir to store the amount of energy that you have calculated above.
Assuming that the overall generation efficiency during generation cycle is 83%, calculate the required water flow rate to deliver the rated electric power of 1200 MW during discharge.
Assuming that the overall pumping cycle efficiency is 86% and the maximum pumping power is 1200MW, calculate the time required (in hours) for filling the upper reservoir after it is fully discharged. List your assumptions if there is any.
What should the electric power of the pumping cycle (in MW) be to enable the plant to fill the upper reservoir in 30 hours?
Calculate the overall round-trip efficiency of the plant