Based on *Geothermal Handbook (ESMAP 2012)*
## Geothermal Energy
### High Temperature Field
- Heat source
- magma or hot rock
- Convective system
- heat convects down from sides, upwards over heat source
### Location
**High-temperature** geothermal found near:
- volcanic areas
- often close to tectonic plate boundaries
- may not be easily accessible, populated area
### Types and Uses
| Resource Type | Goegraphical/Geological Location | Use/Technology |
| --------------------- | ---------------------------------------------------------- | --------------------------------------------------------------------------------- |
| High: &g;200°C | Boundaries of tectonic plates, hot spots, volcanic areas | Power generation: conventional steam, flash, double flash, dry steam technology |
| Medium: 150-200°C | Sedimentary geology or adjacent to high temp. resources | Power gen. w/ binary power plants |
| Low: &l;150°C | Exist in most countries, 150°C found at depth of ~5 km | Direct use (space and process heating), limited power gen. w/ binary power plants | | | |
### Pros and Cons
| Advantage | Challenge |
| ------------------------------------------------------------- | ------------------------------------------------------- |
| Globally inexhaustible | Locally exhaustible |
| Low CO<sub>2</sub>, air pollutant emissions | Hydrogen sulfide (H<sub>2</sub>S) content can be high |
| Low land requirement | Often in inaccessible areas |
| Isolated from fuel price volatility, no need for fuel imports | Geothermal "fuel" is non-tradable, location constrained |
| Non-intermittent (strong base-load resource) | Limited ability to follow/respond to demand |
| Relatively low cost per kWh | High risk, investment cost, long development cycle |
| Proven/mature technology | Require sophisticated maintenance |
| Scalable to utility size without much land use | Requires extensive drilling |
### Geothermal Development in Iceland
| Plant | Electric Capacity |
| --------------- | ----------------- |
| 1. Bjaranarflag | 3.2 MW |
| 2. Svartsengi | 76.4 MW |
| 3. Krafla | 60 MW |
| 4. Nesjavellir | 120 MW |
| 5. Husavik | 2 MW |
| 6. Reykjanes | 100 MW |
| 7. Hellishedi | 213 MW |
### Power Generation Technologies
| Technology | % of 67 TWh total |
| ------------- | ----------------- |
| Single flash | 42 |
| Dry steam | 24 |
| Double flash | 21 |
| Binary | 8 |
| Back pressure | 4 |
#### Single Flash
- flash - drop pressure of geothermal fluid
- increases steam content
- done twice for double flash
- separate geothermal fluid from steam before entering turbine
### Multiple Uses
Energy and waste can be used for other processes:
- fish farming
- greenhouses
- swimming pools
- crop drying
### Costs
- Power plant 35%
- Drilling 34%
- Steam collection system
Further depends on:
- Ease of business
- Availability of skilled labor
- Geology and geography
### System demand
- Total geothermal capacity should not exceed minimum demand
- Typically not equipped to follow demand, provide base load power
- Often given priority dispatch
- High capacity factor, want to save resources that can be stored (hydro)
- Workarounds
- Interconnections (increase minimum demand)
- Turbine bypass (wastes steam)
### Reservoir Potential and Plant Size
Build in steps:
- based on preliminary surveys and test drillings
- 30-60 MW steps, minimizes risks of
- pressure drops
- reservoir depletion
- Operate just initial unit at first
- provides information about "dependable potential"
- production that can be sustained for 100-300 years
- overuse in short term leads to loss in future capacity
### Profit Maximization Strategy
- initially invest in capacity that exceeds "long-term sustainable" production
- allow production to taper to recharge rate if drilling extra capacity too expensive
### Modified Hotelling Model
Maximize:
$\underbrace{\Pi}_\text{profit}=\sum_{i=1}^n(\underbrace{I(P_i,E_i)}_\text{income}-\underbrace{C_w(N_i,N_{i-1}-C_{\text{om}}(E_i,N_i))}_\text{variable costs}e^{-r(i-1)\Delta t}-\sum_{j=1}^m\underbrace{C_p(E_{pj})}_\text{construction cost}e^{-r(j-1)\Delta t_p}$
Constraints:
$\underbrace{S_i}_\text{current stock} = \underbrace{S_{i-1}}_\text{stock from previous time period}-\underbrace{E_i\Delta t}_\text{energy used}+\underbrace{R(S_{i-1})\Delta t}_\text{energy recharged}$