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Tag: geothermal electricity

Aquifer Thermal Energy Storage for Renewables

Posted on by dishanth
Aquifer Thermal Energy Storage for Renewables

It’s Not All About Energy Generation

When the topic of decarbonization comes up, oftentimes, we think of transportation or energy generation. These issues are important, as vehicle emissions are a major problem, as well as emissions from fossil fuel power generation. However, while important, these issues only partially show the roadblocks to moving towards a green future.

Another component that needs to be addressed in the conversation is energy storage and efficiency in renewable energy.

Wind and solar energy are important and rapidly developing technologies but are dependent on weather conditions that vary from month to month and from year to year. In colder months, when houses need to heat, that is when significantly less sunlight is present, thus driving down the available energy to heat them.

This is why energy storage is crucial to the conversation regarding renewable energy, but other solutions might mitigate this problem if properly implemented. This is how aquifer thermal energy storage (ATES) could help assist in cooling and heating buildings, reducing the reliance on other renewable energy sources.

How About Aquifer Thermal Energy Storage?

Energy storage is a difficult topic to address, as the technologies required to implement large-scale grid energy storage require, ironically, a lot of energy. This isn’t helped by the fact that hydrogen energy storage systems right now lose a significant amount of the energy stored.

This is why reducing the grid energy demand is important to implement renewable energy systems successfully. Aquifer thermal energy storage is an interesting form of renewable energy specific to the heating and cooling of buildings because it ties in directly with the seasons that affect solar energy so much.

It works by utilizing two wells connected to the same groundwater reservoir. Cold groundwater is pumped up to cool the building during the summer, then stored. The same process happens in winter but in reverse. Warm groundwater is pumped up into the building, then stored.

Aquifer thermal energy storage systems can also store excess heat from industrial operations, similar to the geothermal systems being deployed in decommissioned oil wells. This process can help bridge the gap between the seasonal availability of renewable energy while at the same time decarbonizing the heating and cooling sector.

This system is also useful because it can make energy infrastructure more resilient by reducing the demand currently placed upon it by heating and cooling. According to a study in Science Direct, Aquifer thermal energy storage systems could reduce reliance on fossil fuels for energy by up to 40%.

New Tech can Help but not Solve Inherent Limits

The importance of renewable energy in the transition to a greener world cannot be understated. However, it is also important to recognize that there are limitations to the technology currently available.

Going forward, there are certainly ways that renewable energy, specifically solar, can become more efficient; the issue of seasonal availability will always be there. This is why alternative methods of addressing needs like heating and cooling are as important.

The issue of energy storage is also important because bridging the gap between availability and need is necessary for making renewable energy a viable alternative to our current fossil fuel energy generation system.

 

 

 

 

 

 

Source Happy Eco News

 

Climate explained: Why does geothermal electricity count as renewable?

Posted on by dishanth
Climate explained: Why does geothermal electricity count as renewable?

Geothermal electricity produces emissions but is categorised with wind and solar power as a renewable source of power. Why? Can we reduce the emissions geothermal plants produce?

Geothermal resources occur where magma has come up through the Earth’s crust at some point in the distant past and created large reservoirs of hot rock and water.

 In New Zealand, the Taupo Volcanic Zone has 23 known geothermal reservoirs. Seven of these are currently used to generate more than 15 per cent of New Zealand’s electricity supply.

Continuous but finite energy source

The geothermal reservoirs are vast in both size and stored energy. For example, the Ngatamariki reservoir extends over seven square kilometres and is more than a kilometre thick.

The geothermal resource is more consistent than hydro, solar and wind, as it doesn’t depend on the weather, but the geothermal heat in a reservoir is finite. Environment Waikato estimates that if the thermal energy in New Zealand were extracted to generate 420MW of electricity, the resource would likely last for 300 years. The current generation is more than twice this rate, so the reservoirs will last about half as long.

Geothermal energy is extracted by drilling up to 3km down into these hot zones of mineral-laden brine at 180-350 degrees Celsius. The engineering involves drilling a number of wells for extraction and re-injection of the brine, and the big pipes that connect the wells to the power plant.

The power plant converts the thermal energy into electricity using steam turbines. These plants generate nearly continuously and can last for more than 50 years.

 

(Source: https://en.wikipedia.org/wiki/Wairakei_Power_Station)

 

Greenhouse gas emissions

The brine contains dissolved gases and minerals, depending on the minerals in the rocks the water was exposed to. Some of these are harmless, like silica which is basically sand. But some are toxic like stibnite, which is antimony and sulphur.

Some gases like carbon dioxide and methane are not poisonous, but are greenhouse gases. But some are toxic. For example, hydrogen sulfide gives geothermal features their distinctive smell. The carbon dioxide dissolved in geothermal brine normally comes from limestone, which is fossilised shells of sea creatures that lived millions of years ago.

The amount of greenhouse gas produced per kWh of electricity generated varies, depending on the reservoir characteristics. It is not well known until the wells are in production.

The New Zealand Geothermal Association reports the greenhouse gas emissions for power generation range from 21 grams CO2 equivalent per kWh to 341gCO2(equiv)/kWh. The average is 76gCO2(equiv)/kWh. For comparison, fossil fuel generation emissions range from 970 to 390gCO2(equiv)/kWh for coal and gas combined cycle plants.

The gases have to be removed from the brine to use it in the plant, so they are released to the atmosphere. The toxic gases are either diluted and released into the atmosphere, or scrubbed with other substances for disposal. The Mokai power plant supplies carbon dioxide to commercial growers who use it in glasshouses to increase the growth rate of vegetables.

 

Finding ways to use less energy

All energy-conversion systems can be made better by employing engineering expertise, investing in research and enforcing regulations, and through due diligence in the management of the waste products. All energy-conversion technology has costs and consequences. No energy resource should be thought of as unlimited or free unless we use very small quantities.

New Zealand is in a period of energy transition, with a goal of reducing greenhouse gas emissions to net zero by 2050. The production and use of coal is already in decline globally and oil and gas are expected to follow.

We tend to think about energy transition in terms of technologies to substitute “bad” energy with “green” energy. But the transition of how energy is produced and consumed will require a massively complex re-engineering of nearly everything.

The installed capacity for wind and solar has been growing over the past decade. In 2018, however, New Zealand consumption of electricity generated by wind and solar was 7.72PJ, while oil, diesel and LPG consumption was 283PJ and geothermal electricity was 27PJ. Another consideration is lifetime; wind turbines and solar panels need to be replaced at least three times during the lifetime of a geothermal power plant.

A successful energy transition will require much more R&D and due diligence on products, buildings and lifestyles that need only about 10 per cent of the energy we use today. An energy transition to build sustainable future systems is not only possible, it is the only option.

Susan Krumdieck is professor and director at the Advanced Energy and Material Systems Lab at the University of Canterbury.

This article was originally published on The Conversation.

 

 

Source: Stuff