Xcel Energy fires up hybrid coal-solar power plant
Xcel Energy has fired up its hybrid coal-solar experimental plant at its Cameo power plant in Colorado.
I have already written a blog post on the subject of hybrid power plants.
The reason such facilities make sense is because the solar plant gives the fossil-fuel boilers a "head start" by initially producing low-grade hot water/steam before superheating in the fossil fuel boiler and therefore reduce fossil fuel consumption.
At the Cameo plant, 6.4 acres (2.6 hectares) of land with solar trough collectors aid in heating the feed water for the existing coal boilers. The solar plant is said to be able to produce 900 tons of coal equivalent per year (7.327 million kilowatt-hours thermal). 2.6 hectares of land in Grand Junction, CO with average solar insolation of 5.5 kWh/m2/day would receive around:
2.6 ha * 10,000 m2/ha * 5.5 kWh/m2/day * 365 days/year = 52.195 million kWh/year
...representing a land-use/collection/usage efficiency of 7.327/52.195 = 0.14, or 14%. Not bad for a prototype.
Most hybrid power plant proposals have opted to use natural gas as fuel but Xcel Energy's Cameo plant uses coal. Addition of solar collectors to coal-fired power plants in sunny regions will likely be a strategy used to maintain the use of coal while reducing carbon dioxide emissions, though considering the shale gas finds and what appears to be extreme excitement regarding shale gas resources, natural gas will likely be fueling most hybrid fossil-solar plants. That is not necessarily a bad thing, considering the lifecycle costs (green-paper costs as well as social and environmental costs) of coal compared with gas.
Hopefully as fossil-solar technology progresses, we will see solar-fossil plants coming online using concentrated solar energy as the primary energy source.
"Pumped Heat" Electricity Storage
Harnessing energy from natural forces (wind, sun) has proven difficult in part due to the fact that production and consumption of electricity are rarely synchronized, requiring some kind of energy storage system.
A UK company known as Isentropic has developed a technology known as Pumped Heat Electricity Storage for the storage of electrical energy in the form of a temperature difference. The company and idea appear to have been around for a few years, though the concept is not yet commercialized.
How it appears to operate
The core of the system is two large insulated silos or tanks containing common gravel or stone through which a gas such as air can be moved.
Air (or maybe a more inert gas) is compressed inside of one of the tanks using electricity to drive the compressor.
The hot compressed gas heats the gravel in the tank to a high temperature - 550 degrees Celsius is stated in articles on the concept.
Once the gas has given up most of its heat to the gravel, it is allowed to expand into the other tank. The expansion process removes heat from the gravel in that tank, cooling it to a low temperature.
When the time comes to recover the electricity, a compressor moves the gas (the "working gas" ) into the hot tank where it is heated. The gas then flows through the engine (which, in the case of the Isentropic system, is reciprocating) where it produces mechanical work and subsequently electricity.
The engine exhausts the working gas to the cold tank, which increases the Carnot Efficiency. The compressor then recycles the cold working gas back through the hot tank and engine and maybe past a regenerator/heat exchanger for efficiency.
Because the incoming electricity drives a heat pump to provide the thermal gradient, the efficiency of the system can be much higher than the typical heat engine efficiency such as a power plant where fuel is burned and the heat exhausted at atmospheric temperature. Comments on the popular news articles regarding the system noted the work->heat->work conversion inefficiency but assumed that the electricity would be heating the gravel with resistance (heating elements), resulting in an extremely serious round-trip efficiency hit.
Losses
- As the temperature difference between the hot and cold tanks decreases, the efficiency of the electricity-producing engine decreases.
- As the temperature difference between the hot and cold tanks increases, the efficiency of the electricity-consuming compression-expansion (heat pump) cycle decreases.
- Loss of energy results due to imperfections in machinery and work required to move the working fluid through the gravel bed. We don't get this work back upon reversal of the cycle because both the "charging" and "discharging" of the system requires work to move the gas through the gravel beds, pipes, etc.
- Despite the name (Isentropic), it is not possible to have a 100% reversible process, but it may be possible to have a round-trip efficiency similar to that of battery systems which store electricity directly - 70% and higher. The use of a heat pump in combination with a heat engine makes the process as reversible (efficient) as possible.
- There is also heat loss/gain through the tank walls, piping, etc. which can be minimized with good insulation and timely cycling of the system.
Possible Scenario
An electricity storage system would allow the supply of electricity from less-predictable forces of nature to be matched with the demands of society.
AN IDEAL STORAGE SYSTEM MATCHES SUPPLY WITH DEMAND. THE AMOUNT OF ENERGY PRODUCED IS EQUAL TO THAT CONSUMED (LESS INEFFICIENCIES) BUT THE POWER LEVELS ARE DIFFERENT WITH TIME.
Gasification Experimenter's Kit
The ALL Power Labs web site contains some interesting information: A "gasification experimenter's kit", plans for various gasifier designs made from common parts and results of gasifier tests. Very interesting technology and material.
Small-scale gasification of biomass waste and coal for operating cogeneration units (gas/diesel engines connected to generators with exhaust and coolant heat recovery), vehicles, and other purposes is a technology in-line with sustainable development, localization, and decentralized control of resources. Developing countries which inefficiently use firewood for heating and cooking may gasify this wood to produce heat and electricity, getting more out of the resource and reducing deforestation.
Electricity is one of those things which tends to bring about massive increases in quality of life, enabling clean water, food preservation, lighting, etc. Problems will only begin to arise when we begin using firewood to power 52-inch screens and hot tubs in every household. That is when the world's forests are in trouble!
Cooling Water for Desert Solar Thermal may be scarce
Electricity companies are coming out with plans to build large solar-thermal power plants in the deserts of the Southwest United States. Solar thermal technology promises lower construction costs and higher thermodynamic efficiency compared with the more familiar photovoltaic panels, and also offers the possibility for storage and hybrid operation with natural gas. There is only one catch which some developers are finding: water. It takes water to cool the plants, billions of gallons of it per year, in a place where there is already fierce competition for water resources.
Most thermal power plants, whether solar, coal, nuclear, gas, or geothermal, utilize wet cooling. Evaporating water carries the waste heat away from the plant in an extremely efficient manner and allows the temperature of the plant's heat sink to be lower than the ambient air temperature, especially in dry desert regions. In a water-starved area, however, sending all of this pristine water into the sky is not an option.
Dry cooling towers use mechanical draft (electrically-driven fans) to blow air over a heat exchanger carrying the hot water from the condenser. The problem is that the temperature to which the condenser can be cooled is limited to the ambient air temperature (which in the desert reaches above 100°F during prime power production periods), and requires electricity to drive the fans. The lower temperature difference between the boiler and heat sink results in an efficiency hit as does the need to send electricity to the cooling fans instead of the grid. Lower thermodynamic efficiency increases the economic cost of electricity production.
It is a serious setback, and another example of the interconnection of ecological issues and how technology has limits. Shop-till-ya'-Drop throwaway culture isn't going to find its salvation in renewable energy or any form of energy production for that matter, including $8000/kW nuclear power plants for those free market capitalists pushing nuclear energy and its "affordability". The same goes for IGCC coal with front groups (e.g. America's Power) putting the "Affordable Clean Coal" fossil fuel techno-fix in our faces with little idea of how much it will really cost.
Solar photovoltaic systems do not require water at all (besides for periodic panel washing), and may have an advantage in desert areas despite the higher cost and lower efficiency. Where water is available, the thermal option is superior. Solar thermal on homes and other buildings to replace electric water heating should also be highly promoted in national and state energy policies.
Pizza Delivery Taxi Service
In college towns there is a high incidence of both late-night debauchery and pizza consumption. There are also issues with drunk driving and transportation home from a night of drinking. It is quite obvious that telling people not to party does not work (they only party harder). Equally ineffective is making transportation from parties/bars difficult - that only exacerbates the problem of drunk driving. Shutting bus lines, ticketing cars parked between odd hours such as 2:00 to 6:00 AM, and "fishing" for DUI cases while other serious crimes are being committed just doesn't seem to work. People still do it. While it is important to understand that especially if one must drive they should limit their drinking, a safe alternative to driving is necessary as well. Taxi services are the obvious choice but dedicated taxi fleets are energy-intensive, expensive, and sometimes prone to overload.
Based upon some observations of friends in the delivery pizza business, I've come up with one hypothetical answer: Take advantage of the massive power of late-night pizza establishments. Pizza shops are continuously sending cars out to various areas, with the delivery load often peaking slightly after the closing of bars or events. The cars are already running, the gas is already burning.
Intoxicated partygoers could call a pizza shop and tell them the general area in which they need to go. Even if it is not a direct drop-off, a drop-off a few blocks away would most often be sufficient - the 18-23 year old patrons are usually physically fit and can handle a walk. Most people in these situations are capable of functioning - they simply lack the motor skills and reaction times require to safely operate a vehicle and would peg a Breathalyzer if one were issued. Once a delivery has been called to the general area, the partygoer is picked up at a predefined location (maybe at the store, or at a street corner, building, etc. negotiated with the driver). A flat fare can be charged, but it must be much less than that imposed by the regular taxi companies. A tip to the driver is also expected, being based upon the distance driven. The rider must be able to tolerate sitting through pizza drop-offs which may occur along the way. As the desired product is the pizza delivery, this must take priority over the taxi service in order to keep the pizza business reputable with short delivery times.
Such a service would add practically no cost to delivery drivers - the fuel burn in the cars would increase by an insignificant amount (hauling more mass around), delivery times may be extended by 1-2 minutes. The fares and tips received would far exceed any costs, safety would be increased far above the level of drunk driving, and gasoline consumption as a whole would be decreased.
The concept is similar to cogeneration in the energy world where the already-running car is being used to deliver an extra service, just as the already-burning fuel for electricity generation is used to produce useful heat as well.
The users of such a service would go into it knowing that they will pay a lower fare than a traditional taxi cab, but sacrifice convenience (waiting for a delivery to their destination, or the risk that there may not be one).
Of course, in this age of lawsuits, government and insurance industry concern, taxi companies possibly speaking of "unfair competition", and possibility for violence, such a service could never exist legally. It is, however, a very interesting solution to several problems (drunk driving, energy consumption, cost of taxi cabs, etc.) which doesn't require fancy technology and has no huge economic debt to be bestowed upon taxpayers and ratepayers.