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Q1.a) i) In your own words, discuss the different types of hydro turbines available and under what flow and site conditions they can be used. (6)

ii) A hydroelectric generating set operates at a rated head of 15 m, a rated flow of 0.65 m3/s and 1200 rpm. Determine the rated output power and its Capacity Factor, if it has an overall efficiency of 85% and produces an energy output of 520,000 kWh per year. Also select the most appropriate turbine(s) for these conditions. (4)

b) Consider a grid integrated PV system as presented below:

Figure 1

On a particular day, the system is operating at a condition given below:

Charge Controller with MPPT |
Efficiency=90% |

Battery Bank |
Status= Charging. Voltage=24 V, current=13 A Charging efficiency=96% |

Inverter |
Efficiency=85% |

AC Load |
250 VA with power factor 0.9 |

Grid |
Receiving power 900 W |

Each PV module is providing the maximum possible power of 180 W. To support this operation requirement, how many PV modules are required? (5)

(c) Discuss the effect of connecting PV and wind based renewable energy sources to the grid from a stability perspective based on the conditions below:

(i) Solar irradiance changes throughout the day

(ii) Wind velocity variation throughout the day

(iii) What actions can be taken to mitigate the instability caused by these conditions (5)

Q2. a) One of the main limitations to hydrogen vehicles currently is the hydrogen infrastructure. In your own words, discuss two of the infrastructural issues /requirements to enable hydrogen vehicles to be viable on British roads. (10)

b) In your own words, discuss the process of undertaking an LCA on a renewable energy system. You should mention the key steps involved (goal and scope definition, inventory analysis, allocation, etc.), as well as guidance on how an LCA report should be interpreted. What would be the expected main sources of carbon emissions for such systems and how could the environmental impact be reduced? (10)

Q3. A potential client is considering installing a biomass boiler in a property at a remote highland location. The existing kerosene boiler is rated at 17 kW and quoted as having an efficiency of 86%. The client is presently paying £2242/yr for fuel, at a price of £0.06 p/kWh. You have undertaken a survey of the property and have determined that through additional insulation and draft proofing, the building Design Specific Heat Loss is currently 380 W/K. The biomass boiler supplier can provide units rated at 10 kW, 12 kW, and 15 kW.

i) Determine the annual heat purchased, and the annual heat delivered to the property before any insulation upgrading and improvement. (2)

ii) For a design internal temperature of 20C, and an external minimum temperature of -10C, specify which of the three boiler options you would recommend. Also, given the same temperature rating, estimate the DSHL for the house prior to renovation. (4)

iii) Building glazing, occupancy patterns and appliance use provide a useful annual gain of 9100 kWh. To a base internal temperature of 18C, the annual Degree Days figure for the location is 4192 DD. Determine the building annual heat input required for the biomass boiler. (3)

iv) Considering the RHI Tier payment scheme (Tier 1 = £0.076/kWh), determine the annual RHI income for the biomass system. (2)

v) The manufacturers quote an efficiency of 93% for the wood pellet boiler. Determine the annual running cost (accounting for RHI payments), and hence the fuel cost saving if the pellet purchase price is £0.04/kWh. (3)

vi) What is the difference between a “Passivhaus” and a “zero carbon” home? What are the advantages and disadvantages of such buildings? Also, briefly ways of correcting these issues. (6)

Q4. a) Discuss, in your own words, the benefits of public transport in relation to reducing carbon emissions. What are the limitations of public transport, i.e. will it always produce a reduction in carbon emissions? You may consider economic factors as part of your answer as well as other alternatives to motor vehicles and how to encourage them. (10)

b) Briefly define the following:

- Downcycling
- Upcycling
- Fermentation
- Non-woody biomass
- EROI

Q5. a) Figure 2 below shows the results of the analysis for the key months driving the design and selection of the appropriate components for an autonomous hybrid Wind/PV system. As can be seen, any design selected needs only to meet the maxima criteria specified by considering solely the August and February system specification lines. Satisfying these conditions will satisfy all other months.

Figure 2

The design line for August is represented by the equation, WT = (-0.61 x PV) + 2.4, where WT is the size of the wind turbine in kW, and PV is the peak output of the PV array (kWp). The design line for February is given by WT = (-0.15 x PV) + 1.7.

i) Using a 2.5 KW wind turbine alone is one option, however this would require 5 days autonomy from the battery, while it is desired to limit this to 3 days autonomy. Wind turbines of 2kW, 1.5kW and 1 kW ranges are available. Assuming dependance on the PV or wind less than 75% of total installed capacity will allow 3 day’s autonomy, and assuming installation costs of £3 per Wp for the wind turbine and £1.5 per Wp for the PV array, find a suitable combination of Wind and solar that will meet the design requirements. (5)

ii) The power consumption for the property runs at an average of 5/kWh’s per day for 3 days, with a depth of Discharge of 60%. The preferred battery cells have a C20 rating of 750 Ah at 2V. Assuming an operating voltage of 12V determine the number of battery cells required to meet the battery requirements (5)

b) i) A 60 kW wind turbine has a cut in wind speed of 3 m/s, and an output power characteristic defined by the equation:

P = -0.1066x3 + 2.4018x2 - 7.6362x + 3.2209

where P is the power output in kW, and x is the wind speed.

The local measured average annual wind speed at 10m above ground level is 5.9 m/s. The turbine is mounted on a 30m tower. From consideration of the local topography, a Hellman coefficient of 0.14 is deemed appropriate for wind speed correction. Calculate the average annual wind speed at the turbine hub height. (3)

ii) It is proposed to install a turbine similar to the above unit at a site 1850m above sea level to help power a mountain lodge in Spain, where the average air temperature is 14°C at this location. Using the appropriate equations, determine the average air density for this location. (4)

iii) If the average wind speed for the proposed site, in respect of power generation, can be taken as the answer to part i), calculate the average power output for this location. (3)

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