Friday, May 22, 2009

CO2 emissions of electric cars

Often, when speaking of electric drive vehicles, one wonders whether the transfer of petroleum fuel emissions to emissions from power plants will actually make things better on greenhouse gases.

To answer this question, we must first consider the CO2 emissions of the various grids, expressed in grams of CO2 per kilowatt-hour of electricity produced. These values can be obtained from the statistics of ministries or departments of energy or environment in different countries or states, or through the electricity companies.

However, emissions of greenhouse gases by these organizations or corporations are often those resulting from the combustion of fossil fuels in power plants themselves. It lacks the emissions from mining coal or uranium and drilling for oil and gas. These data do not include either the transformation of raw materials and their transport, or the construction of power plants. Also missing are the emissions resulting from the decomposition of trees submerged in the reservoirs of hydroelectric dams. To account for these aspects, we must conduct a study of the life cycle of a kilowatt-hour of electricity, from the earth at the socket. Various studies have taught us, basically, to add 15% of emissions for oil and coal and 25% for natural gas. Regarding nuclear power, the emissions are usually 15 gCO2/kWh, and we must add 18 gCO2/kWh for hydroelectric dams. In doing so, we get for California, the United States, France, Canada and Québec the emission intensities in the table below.

Now, an intermediate electric car (1,500 kg), built in 2009 with the best commercially available technology, consumes approximately 17 kWh/100 km of electricity stored in its battery. In addition, with wheel-motors, a reduction in the car weight and improved aerodynamics, consumption should be reduced in the future to about 12 kWh/100 km, say around 2020. So, to assess the CO2 emissions we assume an electricity consumption of 15 kWh/100 km from the battery. We add 6% for the losses from the outlet to the battery while recharging, bringing the actual consumption to 16 kWh/100 km, from the power plant to the wheels. For CO2 emissions of the electric car, simply multiply the actual electric consumption by emissions from the various grids, as given in the previous table.

The results are presented on the chart at the beginning of this post. On this chart, there is also the CO2 emissions of various gasoline cars of different sizes for comparison purposes. The intermediate 1500 kg gasoline car (thick blue line) is equivalent to the intermediate electric car for which we've done the emissions calculations.

For CO2 emissions from conventional cars, we assume that gasoline is burned completely, which releases 2.36 kg of CO2 per liter. To take into account the CO2 released from oil well to the tank of the car, we add 15%, which corresponds to the assessments of various studies on the subject.

It is particularly interesting to note that in the United States with power stations that burn fossil fuels to produce 70% of electricity (50% from coal and 20% from natural gas), CO2 emissions of an electric car is still better than a gasoline car that consumes 5 liters per 100 km, as a Prius. In France and Québec, electric cars emit significantly less CO2 than a Prius, as can be seen.

Québec appears, in fact, a fourfold privileged place to implement the electrical mobility, due to

- the substantial reduction in greenhouse gases that will result,

- the abundance of electricity thereon,

- to its low cost (0.07 $ / kWh)

- and to the important savings in oil imports (100% of import)

To better see the difference between various types of power plants, the following graph presents CO2 emissions by an intermediate electric car whose battery is recharged with electricity from different power plants.

The method of calculation is identical to the previous graph, except the intensity of emissions that are not those of the grids as a whole, in different places, but the GHG intensity of various types of power plants, from the earth to the outlet. The following table summarizes the results obtained using the computer lifecycle analysis software GHGenius developed for Natural Resources Canada (

So, as you can see, CO2 emissions from electric drive vehicles are still considerably lower than those of traditional vehicles using petroleum fuels. The last graph also shows the importance of using renewable energy to reduce our emissions drastically.

Tuesday, April 07, 2009

Underground pumped hydro storage to increase renewables and the efficiency of thermal power plants

Illustration - Principle of the underground pumped hydro storage proposed by Pierre Couture. It can store power and regulate variations in renewable energy, among others, and is an essential component of intelligent electricity networks of tomorrow. (Illustration: Paul Berryman, from my book Driving Without Oil)

On 5 March 2009, Steven Chu, the United States Secretary of State for Energy, stated before a Senate committee his government's priorities in research and development. Five areas were identified and the storage of energy on a large scale is one of them. Storage units of appropriate size would compensate for daily variations of solar and wind, and increase the efficiency of thermal power plants. Energy storage is a key element to reduce greenhouse gas emissions as well of toxic emissions associated with electricity production.

Currently, the most used technology for large-scale storage of energy is pumped hydro. In its traditional version, there are two water tanks located one above the other, connected by an underground tunnel which houses a turbine that can operate in both directions. During periods of low electricity demand (eg at night) the electric motor-generator coupled to the turbine pump water from the lower reservoir to upper reservoir. In periods of high demand, we let the water flow from upper to the lower reservoir, which causes the turbine to generate electricity. In a well designed power plant, the movements of water between the two reservoirs cause a loss of about 20% of stored energy.

But to regulate the daily fluctuations of wind and solar power or to control the variations in demand throughout the day, we do not need to store more than 25% of the energy produced. Hence, regulation leads to a loss of only 5% of the total energy produced.

Illustration - Principle of a traditional pumped hydro storage facility. (source: Wikimedia Commons)

There are currently about 200 pumped storage facilities on the planet, totaling 90 GW of power, or about 3% of the installed capacity at the global level, according to the ESA (Electricity Storage Association).

The obligation to have a significant height difference between the two water tanks has brought many people to say that pumped hydro storage is a technology that could not operate on a large scale. As proof, the following statement

"Expanded use of this technology depends on the availability of suitable geography"

found in the "National Energy Policy Recommendations" of the IEEE-USA (Institute of Electrical and Electronics Engineers), dated 15 January 2009 (download HERE under the heading Energy and Environment).

But it seems that such an assertion is a lack of imagination, because one can very well build pumped hydro storage in the midst of vast plains or in the heart of a city. Just dig a deep well in the rock and build galleries at the bottom to get the second tank.

This is the concept which was proposed by Pierre Couture, a researcher for Hydro-Quebec and inventor of the modern wheel motor (previous post). Louis-Gilles Francoeur, journalist at Le Devoir has unveiled the project in an article dated 22 January 2004.

To avoid too large excavation for the galleries, it is expedient to settle at a greater depth. Pierre Couture recommended digging a well about 2 meters in diameter and three kilometers deep. Turbines that can be reversed and also act as pumps are placed at every kilometer going down, with a buffer cave behind each group of turbine-generators assembly (see illustration at the top of the post).

Calculations show that for a 1 GW of power lasting 10 hours, one must have 3 kilometers (1.9 miles) of galleries with a 20 meters x 20 meters (65 feet x 65 feet) opening, that is 1.2 million cubic meters, to store water at the bottom. The cost of such a plant would be in the range of $ 700 million to $1,000 million, and could regulate power plants with nameplate power of 3 to 4 GW.

If the facility lasts 50 years, we arrive ultimately at a cost below 0.2 cents / kWh of energy produced and regulated, which is only a few percent of the production cost.

Such pumped hydro storage facilities can be used in multiple ways. One can, of course, increase the percentage of renewable energies on a grid by regulating their inherent fluctuations. To reduce the need for too large storage facilities, we need to set up power lines to connect wind farms over thousands of kilometers, because there is always wind somewhere. The high voltage DC power lines are particularly interesting in this regard since they generate only 3% loss per 1000 km (600 miles). As for the solar power plants, they follow quite well the daily demand for electricity (more sun at noon). By placing them in desert areas, one ensures a minimum of cloud cover, which requires less storage of energy for the fluctuations. Most of the storage would be used to postpone to the night a part of the energy produced in the day.

Furthermore, pumped hydro is also interesting to increase the efficiency of thermal power plants. We know, for example, that gas-fired combined cycle plants can achieve an efficiency of 60%. Unfortunately we can not vary significantly the power of such plants to follow daily demand. We must use for that gas power plants whose efficiency is less than 40%. Thus we see all the benefits of coupling a pumped hydro storage to one or more gas-fired power plants. We could then use the most efficient combined cycle gas-fired power plants operating at constant optimal conditions. The daily fluctuations would be managed by the pumped hydro facility. In doing so, we would obtain 50% more electricity with the same natural gas!

With the additional electricity recovered one could close much dirtier coal power plants, waiting to close also, over time, the gas power plants and replace them with renewable energy.

Pumped hydro storage is an essential element of any smart energy policy! And with the underground concept proposed by Pierre Couture, it will become more and more interesting.

Monday, April 06, 2009

How much water to produce biofuels?

Illustration - Fresh water, a resource to preserve. (photo: Wikimedia Commons)

One of the main arguments put forward against biofuels is the high consumption of fresh water to produce them, at least with current technologies. But, as you will see, advanced plug-in hybrid of tomorrow will consume less than one liter of water per day.

To begin, let us look at a midsize car that normally consumes 8 liters of gasoline per 100 kilometers (60 miles) (fuel efficiency of 29 mpg). If we run it with 85% ethanol (E85), the largest commercial concentration, then we will need 11.2 liters of E85 (including 9.6 liters of ethanol) to travel 100 km. The highest amount is required due to the fact that ethanol contains only 2/3 of the chemical energy of gasoline, for a given volume.

Now, if to produce this E85 biofuel we use corn grains from Nebraska, we know that this corn requires 780 liters of irrigation water per liter of ethanol produced (see my book Driving Without Oil for more details). In addition, about 4 to 5 liters of water per liter of ethanol is needed for the manufacturing plant. In total, 785 liters of water are required for each liter of ethanol produced.

Thus, our traditional midsize car running on E85 ethanol in Nebraska consumes 7500 liters (1980 gallons) per 100 km (60 miles). This represents about 4,100 liters (1,082 US gallons) of water a day for someone who will travel 20,000 km (12,420 miles) per year. It is therefore understandable why many environmentalists are not warm to the idea!

But before you throw out the baby with the bathwater, let's see how we can achieve a consumption of less than one liter of water per day!

This requires, of course, the use of energy crops that do not involve watering, which is the case for wild prairie grasses, such as switchgrass. We have seen in a previous post that these perennial plants have roots 3 meters deep that are very effective in capturing soil moisture.

Furthermore, we have also seen in another post that advanced plug-in hybrid cars will consume 4 times less fuel than conventional cars when running on fuel, after their battery is discharged. But as these cars of tomorrow will run 80% of their mileage on electricity, they will actually consume 20 times less fuel.

But we have mentioned earlier that a traditionnal midsize car running with E85 ethanol mixt requires about 10 liters of ethanol per 100 km. The plug-in hybrid cars of tomorrow will therefore need only 0.5 litres/100 km on average (20 times less), which corresponds to 0.28 liters (0.6 pint) of ethanol per day for an annual mileage of 20,000 km (12,420 miles).

Finally, new ethanol plants will reduce their water consumption to about 3 liters of water per liter of ethanol produced, thanks to new technologies such as the one developed by the company Vaperma. This innovative company has developed molecular filters used to separate very efficiently water from ethanol without using distillation. They can save up to 45% of the energy normally used in an ethanol plant, while consuming less water. The decrease in CO2 emissions is also considerable.

Illustration – Vaperma molecular filter used to separate water from ethanol without distillation. The filters are made of polymeric membranes in the form of hollow fibers that are gathered to form the filter cartridge.

Furthermore, for thermochemical biofuel fabrication technologies (pyrolysis, gasification) manufacturing plants consume less than 2 liters of water per liter of biofuel produced.

There is also a new thermo-biological hybrid technology put forward by the company Coskata, which uses microorganisms to convert the syngas (mixture of CO, H2 and CO2) from a thermal process (gasification) into ethanol. According to Coskata, the process consumes less than one liter of water per liter of ethanol produced! This is less than for gasoline. To achieve such performance, Coskata does not use distillation but a molecular filtration process to separate water from ethanol, probably similar to Vaperma filters. In addition, the Coskata process does not include drying of tailings, as is found in the traditional corn ethanol plants, to make the solid protein supplement sold to the livestock industry. The distillation of the beer (fermentation mixture) and drying of tailings are the two processes that consume most water, by evaporation.

Illustration - Coskata thermobiologic process of making ethanol (Source: Coskata).

Ultimately, our advanced plug-in hybrid car traveling 20,000 km (12,420 miles) per year from which 16,000 km (10,000 miles) on electricity, will consume less than one liter (2 pints) of water per day, using biofuels based on tall wild grasses that do not require watering, and manufactured with the best technologies!

To put this water consumption of our future cars into perspective, it is interesting to know the consumption of water per kilogram for different food products. The table below summarizes the results found in the book by David Pimentel and MH Pimentel, Food Energy and Society, CRC Press, 2008. It shows that we need 43,000 liters (11,360 gallons) of water to produce 1 kg (2,2 lbs) of beef, which means more than 6,000 liters (6,000 quarts) of water for a steak of 150 grams (5,3 ounces)! So it is not the 1 liter (1 quart) of water per day consumed by our car that will endanger our freshwater resources. Too large portion of meat in our diet, particularly red meat, is much more worrying in this respect ...

Illustration - Number of liters (1 US gallon = 3.785 liters) of water required to produce one kilogram (2.2 lbs) of different foods, according to the work of David Pimentel, professor of ecology and agriculture at Cornell University.