Smart Grid Fundamentals Coursework Assignment

Part 1 - Microgrid design

This part of the coursework consists of the design of a large microgrid that can supply a DC load. Your goal is to design a microgrid that can operate exclusively on renewable energy.

To do so you will need the following information:

• Assume that all days in the year are the same, and within each day there are four time periods, with the properties shown in Table 1.1.
• Solar PV can be built for a capital cost of £2000/kW (all costs included)
• Wind can be built for a capital cost of £1500/kW (all costs included)
• Battery storage can be built for £400/kWh + £100/kW. For example, the capital cost to build a 10 kW storage plant that can store 20 kWh, will be: 20kWh x £500/kWh + 10kW x £100/kW = £11, 000

Assume that battery storage system will have a round trip efficiency of 85%.

The allowed depth of discharge of the battery is 80%. This means that the state of charge of the battery should not be allowed to go below 20%.

Assume that the operating costs for the resulting system are negligible, that the system will last for 25 years, and that you can obtain a 25 year loan at 5% interest for this project.

Table 1.1: Load, wind and solar data

Note that in Table 1.1, kW/kW refers to generated output (in kW) per unit of installed capacity (in kW).

Given these assumptions, you are required to:

a) Give an expression for the total initial cost of the microgrid.

b) Calculate a suitable value of the battery capacity and power rating considering its efficiency and allowed depth of discharge. Use manufacturer's data for actual lead acid batteries to select a battery bank that can be purchased in the market and that is reasonably close to your calculations.

c) Provide a charge/discharge schedule for the battery. Note that in order for the schedule to be a feasible solution, the amount of energy in the battery will need to be the same at the beginning and the end of each day (since this pattern repeats day after day).

d) Calculate a suitable power rating of the wind generator. Use manufacturer's data for actual DC wind generators to select a power rating that can be purchased in the market and that is reasonably close to your calculations.

e) Calculate a suitable power rating of the solar PV system. Use manufacturer's data for actual PV panels to select a power rating that can be purchased in the market and that is reasonably close to your calculations. Specify how many panels would be required.

f) What would be the total initial cost of the microgrid? Can this cost be reduced to a minimum? If so, explain how and provide calculations to support your answer.

g) Calculate the annual loan repayment amount, given the total initial cost, the loan period of 20 years and the annual interest rate of 5% for the configuration that you found to give the minimum initial cost.

h) What would be the minimum price in £/kWh at which the generated energy can be sold to the customer to recover the annual loan repayment amount given the total annual load in kWh?

i) Discuss your solution. What factors might have changed your answer?

In the report, please ensure that you:

1. Clearly explain your method (including computer code, if appropriate). Explain your equations.

2. Clearly describe your solution, paying particular attention to ensure that your solution is feasible. Use tables and, if appropriate, graphics to present your results. Show what each resource is doing during each of the four time periods.

Part 2 - Economic dispatch and optimal power flow analysis

2.1 - Power system data

Consider that in a simple power system there are four power plants. The generating plants capacity, type and marginal costs are:

1. 1100 MW nuclear plant with marginal cost of £10/MWh, connected to bus 1.

2. 600 MW coal plant with marginal cost of £20/MWh, connected to bus 2.

3. 400 MW natural gas plant with marginal cost of £30/MWh, connected to bus 3.

4. 100 MW of diesel units marginal cost of £150/MWh, connected to bus 5.

Every day there are four 6-hour periods of demand:

• 12am-6am: 800 MW
• 6am-12pm: 1200 MW
• 12pm-6pm: 1920 MW
• 6pm-12am: 1600 MW

The system consists of a network with 5 buses. The load above is distributed evenly among the five buses. The transmission lines (branches) have the data shown in Table 2.1.

Table 2.1: Transmission line data

Given this information, do the following.

2.2 - Economic dispatch / power flow problem

a) Solve the simple economic dispatch problem for each time period. Report the system marginal price.

b) Solve the DC power flow problem for this system at each time period.

c) For each time period report (in a table) the flows on the transmission lines for your solution.

2.3 - Optimal power flow

a) Solve the optimal power flow problem for this system at each time period.

b) For each time period report (in a table) the flows on the transmission lines for your solution.

c) For each time period report (in a table) the locational marginal prices (LMPs).

2.4 - Discussion

a) What is the impact on this power system of having transmission line constraints?

b) How might smart grid technology impact this power system?

c) How should this system be upgraded to improve its operation?