Thursday, 29 March
The Bright Future of Deep Geothermal Energy (also known as EGS)
My posting two weeks ago was from Napa Valley attending the Hedberg Geothermal
Research Conference organised by American Association of Petroleum Geologists(AAPG),
Society of Exploration Geophysicists(SEG) and Society of Petroleum Engineers(SPE).
Hedberg Conferences are organised by the AAPG. According to the AAPG web site,
from time to time the AAPG Research Committee selects a topic for critical examination.
They invite scientists from various disciplines (geology, geophysics, reservoir
engineering, etc.) to discuss state-of-the-art concepts, methodologies, case
histories, and future directions relating to this subject. The conferences are
held in informal settings with a maximum of 80-100 attendees. This particular
one fit that mold.
Overall, it was a good Conference and was worth the trip. My presentation was
on how increased power plant productivity would help EGS commercial viability.
This is summarised in the following two charts. For both of these charts, the
y-axis is my estimate for the levelised busbar cost of electricity ($/MWh) and
the x-axis is the geothermal fluid production flow rate. Three curves correspond
to the three different well preparation costs, $10m/well, $15m/well and $30m/well.
 |
 |
| Figure 1 - Levelised EGS Electricity Cost at Present Power Plant Productivity |
Figure 2 - Levelised EGS Electricity Cost at 50% Higher Present Power
Plant Productivity |
The chart on the left plots the costs at the typical present power plant productivity
and the chart on the right plots the situation that would arise if the current
QGECE project on supercritical turbines succeed. The goal of this project is
to achieve a 50% increase in power plant productivity. Other parameters are
listed in Table 1 below. The main lesson to draw from these charts is that a
concerted effort is required to make EGS viable and advances are required on
at least three fronts: drilling costs; production flow rate; and power plant
productivity. The pleasing outcome of the Hedberg Geothermal Conference was
that this was generally acknowledged by the participants. Joel Renner in his
presentation expressed the DoE expectations that the following was required
to make EGS commercially viable: (a) 20% reduction in driling costs; doubling
the flow rate from 40 l/s to 80 l/s; and 20% increase in power plant productivity.
Gary Isaaksen of Exon Mobil in his presentation listed the same three requirements
as the preconditions which in his view needed to be satisfied before Exon Mobil
would become interested in the technology.
| Parameter |
Value for Chart 1 |
Value for Chart 2 |
| Plant productivity in terms of the generator output shaft kwe per kg/s
of brine flow (after accounting for the pump) |
84 |
126 |
| Life of plant, years |
25 |
25 |
| Parasitic losses (cooling circuit and reinjection), % of generator output |
16% |
16% |
| Capacity factor |
90% |
90% |
| Unit plant cost, $/kWe |
$3500 |
$3500 |
| Number of wells |
2 |
2 |
| Discount rate (not meant to be realistic) |
0% |
0% |
We in the QGECE have good reasons to believe that we could do much better than
20% increase in power plant productivity. In fact our supercritical turbine
project is aiming to increase the binary plant productivity from a 250-oC
resource by 50%. The following two charts compare the expected productivity
of a supercritical CO2 cycle against a conventional steam Rankine
cycle.
 |
 |
| Figure 3. Binary power plant using supercritical CO2 cycle |
Figure 4. Binary power plant using steam Rankine cycle |
We know other research teams are working towards the first two criteria stated
by Joel Renner above, namely the drilling cost and the flow rate and they have
good reasons to believe that they will succeed too. In other words, the next
five years may be the period which will make it possible for the EGS to fulfill
its potential promise of cheap virtually unlimited and energy without emissions
nor significant environmental hazards.
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