Geothermal energy facilities – how do they work

This post looks at three main methods of harnessing geothermal energy; a) to use the heat directly to serve a heating function, b) to use the geology as a heat source or sink and c) to use the heat to generate electricity.

a) Direct use of geothermal (heat) energy

Heat from the geothermal springs is used to provide heat as a service where needed.  This could be for heating buildings, drying food or for other applications that require heat.

This is fairly easy to understand, and is not dissimilar to applications of solar thermal energy.

b) Geothermal heat pumps

The earth’s crust temperature remains fairly constant, regardless of atmospheric temperatures.  This means that on hot days the earth can be used to deposit unwanted heat and on cold days, it can be a source of heat.

The ground then becomes the sink or source of the heat exchanger in geothermal facilities.  Water (or other fluid) can be directed through a series of pipes underground.  There needs to be a difference in the temperatures between the fluid and the ground.  If the fluid is warmer (i.e. on a hot day), the ground will act as a sink.  If the temperature is cooler (i.e. on a cold day) the ground will act as a source, and heat will move from the ground to the fluid.  This fluid can then be integrated into, say, a building’s air conditioning system.

c) Geothermal electricity generation

1. Flash and double flash

Flash (39%) and double flash (19%) accounted for nearly 60% of all installed geothermal electrical generation capacity in 2013, so I’ll cover this first.

This facility type uses pressurised hot water (>180ºC).  The water is delivered to a steam separation chamber.  Here, the high temp water is separated rapidly (‘flashed’) into steam and water.  The steam is used to power a turbine, and the water (called brine as it will be a solution of water and various minerals) is returned to a reservoir.  If it’s returned to the same geothermal source, it will heat up to repeat the cycle once more.

If this brine is still at a high enough temperature, the same process can take place again, effectively re-flashing the water, separating once more into steam (to power a turbine) and a more concentrated brine (to be returned to the reservoir).

Here’s a schematic showing the basic layout, from Energy Almanac, that I pinched:


2. Dry steam

This one is the simplest to understand, and accounted for 25% of all geothermal electrical facilities in 2013.

Underground water is heated to such an extent that it exits the reservoir as steam, and this steam goes directly to the turbine to generate electricity.  ‘Spent’/condensed steam (aka water) is returned to the reservoir as with flash systems.

There would be heat recovery systems in place to increase the overall system facility.

Here’s another pinched diagram:


3. Binary systems

These systems, making up 14% of global installed capacity in 2013, are better at making use of water at a lower temperature.  They also keep the ground water in a closed system.

Moderate temperature water enters a heat exchanger, where energy is transferred to a substance with a lower evaporation temperature.  This substance vapour is then used to drive a turbine to generate electricity.  Two different types of fluid are used (i.e. binary systems).

It’s good to know that this system can be integrated with the flash and dry systems above, as the condensed water from the high temperature systems still has usable energy available, and, when integrated with a binary system, two different turbines can be powered in different loops.

In for a penny, in for a pound – another knicked pic:


4. Enhanced geothermal systems (EGS)

This is similar to the CCS technology post that I did, which looks at injecting CO2 into depleting oil reserves to maximise output.  Like that, water can be injected into a geothermal reservoir where there may not be any water reservoir (dry rock), or where there may not be much permeability in the rock.

Once the water is heated and then delivered to the plant, the same technologies as listed above would apply.

Global geothermal capacity trends

Edit: I’ve replaced the pie chart below as the version I posted yesterday had a glaring error (flash type had been totally left out).  Apologies.  Fixed now…

This is the first of a series of posts that will be focusing on geothermal energy. This is of interest to me as I’m travelling through the Philippines, and, as you can see from the graphs below, Philippines is second on the list in terms of installed capacity.

I’d been to an energy conference in Johannesburg a year or so ago focusing on energy security in Africa and geothermal in Kenya and Ethiopia came up a lot. The interest of these countries to pursue geothermal is, I think, demonstrated by the sudden increase in capacity in Kenya between 2013 and 2014, where they go from 237MW to 600MW; they’ve also got a number 22 projects in the pipeline, totalling nearly 1GW.  Ethiopia has plans to increase their capacity to over 1GW in the early 2020’s.  Tanzania is also looking to get in on the action.

All of the data below have been taken from Geothermal Energy Association’s Annual reports which you can find here.

Geothermal_Developed Geothermal_Developing Geothermal_New


As with all projects making use of naturally occurring resources, developers are tending towards locations with abundant thermal resources, preferably with underground water sources, proximity to demand and suitably regulatory arrangements.

Over the next few posts I’ll be having a look at some of the different technologies that are used, to try and sum up some of the key technical aspects/considerations and possibly challenges that exist around this technology, but what is clear is that geothermal capacity is increasing, year on year.

Renewable Energy projects and targets in the Philippines

The Philippines has developed a roadmap or National Renewable Energy Program (NREP) to nearly triple their renewable energy installed capacity from its 2010 value of 5,438MW by 2030.  This will mean an installed capacity of 15,304MW by 2030.  To do this, they will focus on the following 6 steps:

  1. Increase geothermal capacity by 75%
  2. Increase hydropower capacity by 160%
  3. Deliver an addition 277MW of biomass power capacity
  4. Attain wind power grid parity through the commissioning of 2,345MW of additional wind capacity
  5. Mainstream solar through the addition of 284MW of solar capacity, and aim for an aspirational target of 1,528MW
  6. Develop the first ocean energy facility for the country
[SOURCE: NREP Renewable Energy Plans and Programs (2011-2030)]

The Department of Energy releases a summary of awarded projects every two months on their site.  I’ve taken some of this data to make the graphs below.

The four different categories that I’ve pulled out are only for grid connected projects.  There are some projects that have been awarded or that are pending for own-use, but I’ve left these out for the minute.  My reading of the reports that go along with the summary tables are that projects that have been ‘awarded’ still need to demonstrate compliance with various obligations.  Those that are listed as ‘awarded’ and ‘potential’ are not fully compliant with these obligations.  Obligations relate to the work programme, posting of performance bonds and something called “RESHERR,” which I can’t find an explanation for, but am guessing it relates to Health & Safety and Environmental obligations.  This is a total shot-in-the-dark guess.

Projects that have not been ‘awarded’ and are listed as ‘pending’ are still to have their status finalised under the Renewable Energy Law.  It seems that some of these projects awaiting this have been constructed.
Awarded installedAwarded potential
Pending installed
Pending potential













[Source: Department of Energy]

What also interests me is how this looks compared to the same time the previous year.  What jumps out at me from the below is that they seem to have some difficulty converting potential projects to installed projects, even when awarded.  The greatest movement seems to be in hydropower and solar, with wind and biomass projects moving in the wrong direction; possibly from a failure to comply with the above-mentioned obligations.

Change in awarded capacity