Dugga 2:) Flashcards
flex. thermal generation(check), linkages to DH (check), hydropower(check), system interaction, actors (check) & environment (check)
Explain why a heat pump greatly benefits from thermal energy storage in a system with high levels of vRE.
What is the case for electric boilers?
HP: has a high investment cost and is operating most of the time. With heat storage, the heat pump can avoid operation during high electricity prices while the storage meets the heat demand.
EB: has a low investment cost and is only used to act opportunistically during low net load events and therefore does not benefit as much from storage.
(2)
Give three heat storage options and one main advantage and disadvantage for each option
- Tank heat storages: +fast discharging -expensive
- Pit storage: +low cost -requires a large area
- Bore-hole storage: +low cost -slow discharging
(4)
Provide two explanations each for how thermal energy storage can help manage variations in
a) the district heating and
b) the electricity system?
a) the storage can be charged when heat demand is low using base load heat generation such as CHP or HP and discharged when heat demand is high to replace peaking units such as HOB.
b) the storage can be charged by running the HP even if heat demand is low when electricity prices are low and then discharge the storage when electricity prices are high and heat demand is high to avoid HP operation
(4)
Give two ways in which linkages between the electricity and district heating system can increase the value of wind power
- Electric boilers can consume electricity during low net load hours
- CHP with thermal storage can reduce production during low net load hours
(3)
Give three properties which define the flexibility of thermal generation.
Start-up time, start-up cost and minimum load level
(3)
List three differences between a thermal powerplant with a steam cycle compared to a thermal power plant with a gas cycle
Explain how these differences impact their respective role in the electricity system
Working media, cost structure, size, combustion (single-phase or multi-phase)
With single phase combustion and gas as working media the plant can be smaller and heated and cooled faster. This gives shorter start-up time and lower start-up cost and lower investment cost. However, the fuel deployed is expensive. This plant is thus preferably used for mid-merit or peaking operation. With multi-phase combustion and steam as working media the plant is larger and heated and cooled slower which gives high investment cost and high start-up cost. However, cheap fuels can be used. This plant is thus good for base load operation.
If thermal generation is operated flexibly the cost of operation increases for two main reasons, which?
- Start-up costs from fuel consumption during start-up and 2. increased maintenance cost and/or shorter lifetime
Give one technical and one non-technical limitation on hydropower flexibility (explain the reasons for the limitations)
Dynamic loading of turbine at deep part load (less than 60%)
Environmental court restrictions on minimum flow (see lec 8 for more options)
A cost-minimizing actor is building two hydropower stations with storage in two different electricity systems; system A in which 10% of the electricity demand is supplied by wind power and 50 % by nuclear power and system B in which 40% of the demand is supplied by wind power and 20% by nuclear power. The new hydropower stations will supply the remaining 40%. Which hydropower station (the one in system A or B) will have the highest full load hours? Why?
System A has highest full load hours since system B will be wanting more hydropower capacity to compensate for wind variations.
Give one technical and one non-technical limitation on hydropower flexibility
many options, e.g.Technical: Cannot operate the turbine on deep part load or overload. Then there is a risk that vortices create cavitation on the turbine baldes. Non-technical: Have to stay within environmental legislation on water level in reservoirs.
State the hydropower storage equation and explain how the limitations relate to the equation.
s(t+1)=s(t)+I(t)-g(t) Where s is the storage level of the hydropower reservoir at time t, I is the water inflow to the reservoir and g is electricity generation. Environmental legislation gives upper and lower values of s. Risk of cavitation give an upper and lower limit on g.
List three types of variations in the electricity system and explain on which geographical scale they best are tackled. (weekly wind variations, hourly solar and minute wind)
“There are more than 3, see learning activity for Actors & Scales
weekly wind variations: best tackled with hydropower or hydrogen production for industry, these are concentrated to few locations so interaction takes place on national/international level
hourly solar: not a lot of energy in these variations, can be managed locally and by prosumers with small modular battery storage
minute wind: on-site, very little energy volume to even out but frequent activation and close integration with generating technology beneficial”
(6)
On which geographical scale(s) do you recommend managing solar PV variations (solar park/household, city, national, international)? Motivate your answer.
Diurnal variations can be managed by batteries which are modular and can thus be placed on solar park/houshold level. Seasonal variations can be managed with heat storages in district heating systems on city level.
(3)
On which geographical scale(s) do you recommend managing wind variations (wind farm, city, national, international)? Motivate your answer.
Wind variations can have long duration and require VMS with low cost of energy storage such as hydropower with storage and strategic hydrogen production. These VMS are concentrated to few places on national level and trade on national level is often required. Trade internationally enables geographical smoothing.
(3)
Pick a shifting VMS and explain one positive and one negative impact it has on the environment
Batteries + increrase the share of solar PV (fossil thermal power displaced) - mining of metals such as cobolt and lithium
(2)
Pick a complementing VMS and explain one positive and one negative impact it has on the environment. (Hydrogen production w storage)
“lots of options here
E.g. Hydrogen production with storage:
- use of critical materials in electrolyser
+ can increase penetration of wind power and thus lower environmental impact of power generation (fossil thermal power displaced) “
