Lecture 3 - Renewables

Question 1

What is electricity?

Answer 1

• The flow of electrons driven by a potential difference (voltage).
• Measured in kWh
• Must be used as it is created.
• Can only be stored in specifically designed devices.
• Can be used directly off-grid
• Can be transmitted ( long distances, high voltage) and distributed (smaller scale.lower voltage) through a grid system.
• May be direct current (DC) or alternating current (AC) - grid is AC.
• Some forms of electricity generation generate AC directly, others in DC.
• Most electrical devices operate in AC but some off-grid devices are designed to operated in DC to avoid conversion.

Question 2

What is an inverter?

Answer 2

• Used to convert between DC and AC.
• Add cost to a system and lose some energy in the conversion process.
• Solar PV inverters typically cost 0.15-0.4 $/Wp and operate at efficiencies of 90-99%.

Question 3

What metrics can be used to compare technologies?

Answer 3

• Typical output - capacity factor
• Reliability of supply - capacity credit
• Cost - LCOE
• Emissions intensity
• Land use - % for each technology

Question 4

What is capacity factor?

Answer 4

• Quantifies the typical output of a generating source over a given period of time.
• Don’t generate full capacity due to: maintenance, intentional ramping down of supply to meet demand, unavailability of fuels
• May vary by geographic location and time of year
• Doesn’t tell the full story - may not be used because no demand rather than because unable to use.

Question 5

What is the formula for capacity factor?

Answer 5

Actual energy produced / Energy produced of system is running 100% of the time

Question 6

What is capacity credit?

Answer 6

• Reliability of an electricity source, or amount of output from a power source which can be statistically relied upon at peak demand.
• Defined as peak demand less peak residual demand, as a % of variable renewables installed

Question 7

What is the formula for capacity credit?

Answer 7

Reduction in capacity of conventional plant / capacity of variable plant

Question 8

What is levelised cost of electricity (LCOE)?

Answer 8

• Cost of generation of a technology over its lifetime
• NPV cost of a generating asset per unit of electricity generated over time
• Useful for comparing the costs of technologies with different characteristics

Question 9

What is the formula for levelised cost of electricity (LCOE)?

Answer 9

Sum of PV of costs over lifetime (investment, operation & maintenance, fuel) / Sum of electrical energy produced over lifetime

Sum(I + M + F) / (1+r)^t / Sum E / (1+r)^t

Question 10

What is emissions intensity?

Answer 10

Total quantity of GHG emitted over entire lifetime Including construction, installation, fuel and operation) divided by total energy produced over lifetime.

Question 11

What is the formula for emissions intensity?

Answer 11

Total GHG emissions over lifetime (gCO2e) / Total electricity produced over lifetime (kWh)

Question 12

What are the typical emissions intensities for: hydro, onshore wind, nuclear, biomass, CSP, Geothermal, solar PV, natural gas and coal?

Answer 12

Hydro = 4
Onshore wind = 12
Nuclear = 16
Biomass = 18
CSP = 22
Geothermal = 45
Solar PV = 46
Natural gas = 469
Coal = 1,001

Question 13

What will be the land use for electricity generation in the UK in 2015 under the 2DS?

Answer 13

Bioenergy - 10%
Onshore wind - 0.6%
Hydro - 67km2
Solar PV - 62km2

Question 14

Key features of world electricity generation

Answer 14

• Electricity generation accounted for approx 15% of total energy consumption in 2014 (and is rapidly growing)
• Proportion of primary energy used for electricity is significantly larger owing to relatively low efficiencies of generation (39% in 2008)

Question 15

World energy consumption stats?

Answer 15

• 78.3% fossil fuels
• 19.2% renewables: 10.3% modern renewables (biogas, geo, wind, solar, hydro etc), 8.9% traditional biomass
• 2.5% nuclear