Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
1 · 2 · 3 · 4
Spring 2011
14 solar thermal collectors on the rooftop at Williams Selyem Estate Winery face due south on tilt racking to catch maximum solar exposure. Inside the collectors is copper piping filled with glycol to collect the heat, and send it down into the building’s hot water system.
heat-transport fluid (glycol) flowing through copper tubes to accept heat from the absorber, and 4) a heat insulating backing.
The collector consists of a thin sheet of thermally stable copper to which a black or selective coating is applied, and a grid or coil of copper tubing held in an insulated casing with a glass or polycarbonate cover. Fluid is circulated through the tubing to transfer heat from the absorber to an insulated water tank.
Heat transfer to the hot water tank may be achieved directly, or though a heat exchanger. In the latter system, pumps circulate fluid through the copper tubes inside the collectors. This heated fluid then moves through a heat exchanger (either internal or external) to an insulated tank, where the fluid’s heat is transferred to potable water. This solar pre-heated water is then fed into the building’s regular water heater, reducing the amount of fuel (natural gas, electricity, or propane) typically used to heat water.
Some advantages of solar thermal systems are:
  • Very high liquid temperatures may be achieved;
  • By concentrating sunlight, these systems can get better energy efficiency than simple solar PV cells;
  • During cloudy conditions and overnight, insulated tanks can store fluids heated by the collectors;
  • Materials and installation time are less expensive than solar PV;
Tina Vierra
olar hot water systems are a relatively low-cost way for wineries to use the power of the sun to reduce energy costs. Kunde Family Estate (Kenwood, CA) installed a solar thermal system in 2010, and Williams Selyem Estate Winery (Healdsburg, CA) built a new facility with barrel storage, a bottling line, and visitor center with a solar photovoltaic (PV) energygenerating system for electricity, and a solar thermal system for hot water generation.
Solar thermal systems
Solar photovoltaic (PV) panels (see PWV, January/February 2004, July/August 2005, January/ February 2008) collect energy from direct daylight ultraviolet rays and send it to an inverter, which converts the energy to DC current that powers winery and vineyard electrical needs. Collected energy is most often stored in the existing utility energy grid until it is needed.
Solar thermal collectors are different from solar PV collectors in that they do not generate electricity — they transfer the sun’s energy into heated liquid (glycol) that is then used to heat water. Solar thermal collectors are much less costly to install (on residential systems, about half the cost of solar PV), and they are four to five times as efficient — an 80% efficiency rating versus about 15% for photovoltaic.
50 flat-plate solar thermal collectors on Kunde Family Estate’s south-facing roof send hot glycol to a 1,040-gallon water storage tank inside the winery, heating enough water to cut the winery’s annual bill for natural gas by half.
The efficiency of solar thermal collectors varies using this equation:
Temperature of liquid in collector
– temperature of ambient air
= efficiency of the collector
The greater the difference between the two temperatures, the lower the efficiency of the collector.
Flat-plate solar thermal collectors (such as the ones installed at Kunde and Williams Selyem) consist of: 1) a dark flat-plate absorber of solar energy, 2) a transparent cover that allows solar energy to pass through but reduces heat losses, 3) a