E&T on solar thermal cooling and the world's first solar thermal winery.
It's a hot, steamy, summer day in the Styrian hill country of southern Austria. A 45-minute drive along narrow, winding roads from the provincial capital of Graz takes me deep into the heart of the Styrian wine country - rolling hills covered with every conceivable shade of green, from dark-olive pine and hardwood forests to bright green pasturelands, with patchwork fields of hops and vineyards. I emerge from the air-conditioned sanctuary of the car, the summer humidity hitting me like a warm, wet blanket, and am met by the vintner, Johannes Peitler, who, after a brief introduction, ushers me into the cool retreat of the Weingut Peitler cellar - not really a cellar at all, but a 450 sq metre building that serves as both a fermentation hall and wine storage. Aaahh yes… The fermentation hall maintains a constant temperature of about 15C year round - and all thanks to solar energy. In fact, the solar 'cooler' works best precisely when one needs the energy most - during the peak heat of the summer day.
Solar thermal primer
Solar energy for heating water has been around for centuries, but solar 'cooling'? There is something counter-intuitive to it - a sort of energy alchemy seemingly at odds with physics, but solar thermal cooling is indeed the hottest new twist in the rapidly expanding field of solar energy applications. Worldwide there have been several attempts at solar chillers dating back to the mid-1800s, but these were not developed further because oil and coal energy was so cheap.
Solar thermal arrays look like photovoltaic panels, but are essentially comprised of water-and-glycol-filled tubes that absorb heat energy from the sun. The heated fluid is circulated to a storage tank, where the heat is transferred via a heat exchanger to warm water for domestic use - solar thermal for hot water production.
It is not a great stretch to see how solar thermal can also be used for heating the home or building. Most people are familiar with solar water heaters. These have been commercially produced for decades - simple and relatively low-tech. This is most efficiently achieved by transferring the solar thermal energy to a radiant heating system (fluid-filled pipes/tubes in the flooring or walls) or by heating air or steam via an air-handling unit. Larger solar thermal applications can take this a step further by conveying the heat/steam through a district heating system.
Enter the Austrian firm SOLID (Solar Installation and Design). SOLID specialises in designing and building large-scale solar thermal projects. You may have seen one of its recent installations at the Olympic Village at Qingdao, China. Two large solar thermal collector arrays (666 and 631 sq m) produce temperatures of up to 100C with a storage capacity of 20m3. One installation is designed to supply hot water to the Olympic Village and heat the swimming pools. The solar collector panels form a striking blue wave-shaped architectural feature, while the other installation provides cooling and heating for the logistic centre, including a restaurant, shops and office facilities, with a combined heating and cooling load between the two installations of about 1MW of thermal energy.
Weingut Peitler, under the direction of SOLID, installed 100 sq metres of solar thermal panels in 2003. Even on the somewhat overcast day I visited, with thunder showers and only patchy sunshine, the array was producing 70kW, with a typical annual production of 400-500kWh/sq metre. On a clear sunny summer day, the thermal fluid coming from the panel array is about 110C. The water-glycol fluid in the panels passes through a heat exchanger in which the heat is transferred from the thermal-heated fluid to regular domestic hot water (DHW), product water coming into the storage tank at around 95C (accumulating heat from the exchanger), where the hot water is drawn from the top of the tank for DHW use, while the cooler water is drawn from the bottom of the tank and recycled back through the heat exchanger. The hot water is used throughout the Peitler's facility and for domestic use too.
Heat energy is used to warm the fermentation tanks to 20C at the beginning of the fermentation process to stimulate the yeast. Then the tanks are cooled to 15-18C to maintain a constant temperature during the rest of the fermentation cycle. Temperatures in the tanks - together with other aspects of the fermentation process, including sugar and alcohol content, CO2 release and other variables - are carefully controlled on an interface, provided by Schneid Controllers.
The basics of air conditioning are as follows: Air contains water vapour. The water vapour contains latent heat energy - solar energy that was absorbed by evaporation from water bodies in the first place when liquid water was converted to water vapour by heat and sunlight. When the air is cooled, it releases its latent heat energy as heat through condensation. In a standard open-cycle dessicative and evaporative air conditioner (DEC system), water vapour in the room is removed, condensed and released (usually via a drip spout) to the outside to dehumidify and cool the room. Thus, latent heat energy (via water vapour) is removed from the room and released to the outdoors as a heat sink.
Solar thermal cooling takes place by running the heated circulation fluid, coming out of the storage tank at about 83C, through a 'chiller'. There are two basic thermo-chemical strategies to achieve solar thermal cooling: adsorption and absorption. Adsorption chillers remove heat by 'adding' or attaching the heat to a solid, highly porous material, like silica, and then removing that material and transferring the heat off of the material in another chamber; while absorption chillers take up the heat by direct absorption into the chemistry of a liquid or solid material itself, as in the water/lithium-bromine water chiller used at Weingut Peitler.
To summarise the basic solar thermal cooling process, sunlight heats the solar thermal fluid in the rooftop panels to 75-80C. The heated fluid is circulated through a heat exchanger, transferring the heat to hot water in a storage tank, producing temperatures between 80-100C. Water can be drawn from the storage tank for domestic hot water, or the hot water can be directed to the 'chiller', where it works its magic, converting solar heat into summer-cooled water and air conditioning. Thermal 'cooled' energy is stored in a cooling tower for use in the chiller during low-sun or no-sun periods, or for other domestic cooling purposes, as needed.
Chilled fluid is circulated through an air-handling unit to keep the cellar room temperature at a constant temperature of 15C, while slightly warmer temperatures of 18C are maintained in the fermentation tanks.
Through yet another step involving an ammonia-circulating chiller, even lower temperatures, as low as -10 to -12C can be achieved. In the case of Peitler's wines, the wine is briefly subjected to temperatures of 2C to 5C, causing the 'Weinstein' (literally, 'wine stones') to crystallise and precipitate out of the wine prior to bottling. These tartaric acid crystals (potassium hydrogentartrate) are a natural product of the finer white wines, particularly the German and Austrian late harvests - the 'spätlese, auslese, beerenauslese and trockenbeerenausleses' - which obtain top prices in wine auctions around the world. Weingut Peitler's Ausbruch, a late-harvest made from Welschriesling grapes, is a fine example. The observant oenophile may notice tartaric acid crystals in the bottle, but tartaric acid occurs naturally in grapes, bananas, tamarinds and other fruits, and is an antioxidant associated with good aromas and bouquet of high quality wines.
Other solar thermal beverages
In keeping with the solar thermal libation theme, SOLID has designed and installed a large process heat installation in Arizona for one of the largest soft drink producers in America. Industrial process heat is the term for energy used to supply heat during the manufacture of basic materials and goods. Many processes, such as those in the food or textile industry, need temperatures between 50C and 100C, the ideal range for solar thermal. In this installation, an 893 sq m solar array preheats incoming fresh water for the production of sports drinks, generating 625kW of thermal power. This facility recently set a new world record for specific energy gains, producing more than 1,200kWh/sq m per year in the clear Arizona desert sun.
Meanwhile, back at the Weingut Peitler Keller, I take my seats in a solar-cooled tasting room overlooking the six-hectare estate and vineyards. Founded by Johannes's great-grandfather in 1902, Weingut Peitler produces about 40,000 bottles per year. One by one, Johannes pours a sample of each of their wines, derived from five white grape varieties: Welchriesling, Weisburgunder (Pinot Blanc), Morillon (Chardonnay), Sauvignon Blanc, and Muskateller; and the smooth, distinctive Austrian red, a barrel-aged Zweigelt. The painstakingly hand-crafted results are impressive. From the fresh and fruity Welchriesling, to the mineral, butterscotch of the oaked Pinot Blanc; from the delectable Frizzante - a sparkling wine of Muskateller grapes, to the complex Zweigelt barrique (barrel-aged), we sample the data of Johannes's labours, culminating in the rich honeyed-apricot of the late-harvest Ausbruch. Nine testers later (thanks to my designated driver and SOLID guide, Harald Blazek), I emerged to the most magnificent afternoon sunset, shining through the scattered thunderclouds draped across the Styrian hills around me. Sunlight, rain and green vineyards yield some of the very best of Austria's fine wines; and using solar energy once again to heat and cool the wine production itself.