Archive for May, 2012


Low Enthalpy Geothermal Resources

A leading renewable energy site recently posted a news item  “Low-Temperature Geothermal: Digging for Its Vast Opportunity”

A few of the geothermal experts commented thus:

“We need to have better exploration and drilling technologies because that’s one of the biggest hurdles to geothermal prospects.”

“We must look at new technologies on all fronts – both exploring for new resources and for developing and operating those new resources — so we would like to see additional funding from the DOE [U.S. Department of Energy] in the geothermal technologies program.”

“a continued focus and expansion of trying to utilize lower-temperature resources  so that we can continue to bring what was once thought uneconomical and unattractive for geothermal, but often more abundant. These low-temperature resources actually can produce utility-scale power production.”

The need and the available low enthalpy geothermal resources, especially in the non OECD  countries  has already been brought to focus in a book way a back in 2008 in a book entitled ‘Low Enthalpy Geothermal Resources for Power Generation” ( by D Chandrasekharam and J Bundschuh, CRC Press, 149 pages).

The main aim of this book is to bring to the geothermal community, the huge quantity of available low enthalpy geothermal energy resources lying untapped in all the developing countries, the method to tap this energy sources and the advantages it will have in mitigating global climate change, reduction in carbon dioxide emissions and uplifting the socio-economic status of the rural population.

The greatest development is expected in the  non-OECD Asia where the electricity generation is expected to be of the order of 10,186 TWh in 2030 from the current 3518 TWh. This correspond to an annual average increase of 4.2 %. In non OECD Asia India and China have the highest absolute national electricity generation growths.

Low enthalpy geothermal resources occur in a wide range of geological and tectonic regime. Some time they are close to a high enthalpy domain or occur as large exploitable  independent resource. They also occur as geopressured systems within large sedimentary basins and or petroleferous formations. With the developments taking place in drilling technology and heat exchanger technology, EGS may also be able to provide low enthalpy fluids that can be utilized for power generation using carbon dioxide as working fluid. Such low enthalpy EGS resources occur in large areas in developing countries.

Although they were considered economically not viable in the past, considering the constant build-up of CO2 in the atmosphere, CO2 reduction strategies countries have to adopt and compelling situation for a constant industrial growth by developing countries, policy makers are and planners are encouraging development of low enthalpy geothermal resources. Now it is possible to generate power from geothermal fluids with temperatures as low as 82 °C.  According to estimates  use of geothermal fluids with temperature of about 100 C will increase the energy available for electricity generation from 11200 TWh per year to 22400 TWH per year with the advancement taking place in binary power generation technology.  Thus the potential of low enthalpy geothermal resources has been underestimated worldwide. Compared to other low CO2 emission sources like wind and solar, geothermal supplies base load power, does not require storage systems and back-up power facility. Once commissioned, the system runs for several years with proper maintenance. In fact for many countries are using low enthalpy geothermal resources for recreation, balneology, space heating, dehydration etc (direct applications). Now these countries can evaluate their low enthalpy resources for power generation. 400 000 TJ/y of geothermal energy is in use for direct application world over according to a recent publication by the World Geothermal Congress, 2010 held at Bali in April 2010. Countries such as those like the Caribbean islands ( Nevis, st.Kitts,Montserrat, St. Lucia etc) according the book mentioned above import oil and gas for electrification even though these countries have large low enthalpy geothermal resources.  This is true even with countries inEastern Africa. Those located within the rift environment with plenty of geothermal energy sources, depend on imported oil  to support their electricity demand and increase the GDP of the country as well as that of rural regions.



Geothermal Space Heating and Cooling is an Established Technology!

Recently a news item hit the geothermal magazines stating that some school in Boston will be using  a new energy source from groundwater for space heating and cooling.

Heat pumps are being in use for several decades in refrigerators and air conditioning units.  It is a well insulated unit that move heat from one “space A” to ” space B. When heat is removed from space ‘A’ and space ‘ A’  becomes cool and ‘B’ becomes hot.   Based on the need and space ‘A’ can be made cool or hot. This concept is in use since 1850 when James Harrison made the first refrigerator.  The ground source heat pump works on the same principle.  The ground source heat pumps (GSHP) are also known under several names: Ground Heat Pumps-GHP, Ground Coupled Heat Pump-GCHP,  Groundwater Heat Pump-GWHP.

The basic principle on which the GHP works is “refrigeration cycle”. The refrigerant carries the heat from one “space” to another. The heat pump’s process can be reversed.  The earth is the main source and sink of heat.  In winters it provides heat and summers it takes the heat.  The heat pumps are very common in USA, Europe, E. Europe and China. The heat pumps can be adopted to any kind of building at any place.  In the United States of America, over 400 000 GHPs are working in schools, hospitals, commercial complexes and government buildings. GHPs have low carbon dioxide emissions, low energy consumption (~ 40-60 % lower than the conventional systems),  low operating cost and competitive life cycle cost compared to the conventional HVACs.

The common two types of GHPs in use are 1) earth-couple (closed loop) system that uses sealed pipes/tubes-placed vertically or horizontally, through water or a mixer of water and antifreeze circulates transferring heat to and from the earth and 2) water source (open loop) system where water from the underground aquifer pumps water to the heat exchanger. Between the two, earth coupled GHPs are very popular because they are very adoptable.

The technology is very matured and systems can be installed adopting the local temperature variations. According to the reports published in the World Geothermal Congress 2010, up to the year 2010 (ending December 2009) the installed capacity of GSHP in the world is 50583  MWt and the energy generated was 438071 TJ/year (121696 GWh/y: CF of 0.27). The country that has the highest installed capacity of GSHP is USA (12611 MWt) followed by China ( 8898 MWt).  In China the amount of utilizable geothermal energy (for space cooling and heating) at shallow depths, according to a news  published in “Renewable Energy World.com” in 2011, is equivalent to about 350 million tons of standard coal, which is equivalent to 2.8 million GWh of electricity. If this energy source is tapped, then this will reduce emission of 500 million tons of CO2 by avoiding to mine 250 million tons of coal. The extractable geothermal energy in China’s 12 major geothermal provinces is equivalent to about 853 billion tons of standard coal that could generate seven billion GWh of electric power!!

China is using its GSHP technology to adjust/ modify its energy structure to reduce CO2 and other GHG emissions. Today in China research on GSHP technology is given top priority with full government support. Thus academic institutions, industries and companies are enjoying a boom with regard to this technology and it is paying rich dividends to the country today. According a paper published in the Proceedings of the World Geothermal Congress 2010, China has proved its supremacy in GSHP technology by providing 26% of energy to the Olympic Games in 2008 from geothermal sources. Excellent examples where such GSHP technology in the Olympic games is seen from the Olympic tennis courts, the National Olympic Stadium ( Bird’s nest), National Swimming Centre and Olympic Gymnastics Hall and Badminton Hall. Besides this, the hostels for the athletes were also temperature controlled through GSHPs. For the tennis courts, 35 holes were drilled within a 7 x7m layout. This GHP unit has 138.2 kW heating capacity ( in put power 37.5 kW) and cooling capacity of 139.6 kW (in put power 32 kW). The Olympic National Stadium (Bird’s Nest) drilled 140 holes with depth of 80-100 m. With such a strong GSHP technology in hand, it is not surprising to read about China’s determination to reduce CO2 emissions and phase out HCFC by 2015 by adopting clean technology for space heating and cooling.

The performance of a heat pump is a measure of its COP ( Coefficient of performance). Commercially available HVAC systems have COP of 3 to 4 while GHPs have greater than 6. The COP also depends on the temperature difference.  When the temperature difference is small then the COP will be large.  Similarly the cooling performance, measured as energy efficiency ratio (EER). The GHPs EER, depending on the seasonal temperature variation is about 80% and above.

In the case of HVAC systems, the heat is transferred between the inside and out side air to cool or heat the space. The COP of such systems vary drastically since air temperature variation is  diurnal and as well as seasonal.  This problem does not arise in the case of GHP system. The heat transfer takes place in the ground/soil that maintains more or less constant temperature. This is a very great advantage where GHPs score its COP. The GHPs can be installed vertically/horizontally, before the construction of the building or after the construction of the building. It is cost effective if the design of the system goes along with the building plan. The builder and the architect should work in collaboration in the installation of GHPs for cooling and heating.   Besides heating and cooling the space, GHPs can also provide hot water to the house hold at no cost.

The GHP technology is very well matured and can be bought off-the-shelf. Countries in Europe have installed GHPs at district level and residential spaces, office buildings and commercial establishments have been put under GHP technology. This is  why Europe is able to earn carbon credits and  trade with countries like India and other develoing countries. Buying carbon credits is not good to any country, especially those that are on the development path. China is ahead among all the non-OECD countries in controlling carbon dioxide emissions without compromising the industrial and commercial growth. India, with its large geographical spread and with a large temperature variation, GHP technology will bring a sea change to Indian economy, GDP growth and provide carbon free environment to the future generations.