ON THE HORIZON

Cooling Off With The Sun

Although it sounds counter-intuitive, the heat of the sun can be used to cool off a building with the help of an absorption chiller. The technology is not yet commercialized, but in a few real-life settings solar-powered absorption chillers are already providing air conditioning cost-effectively.

Absorption chillers, which use heat to drive a thermodynamic cycle that produces cool air, are flexible enough to take in heat from solar or fossil fuel heat sources. They require little or no modification to utilize heat collected from flat plate or parabolic trough collectors, and are the most common approach to solar cooling. Recently, solar-powered absorption chillers have been integrated into complete heating, ventilation, and cooling systems (HVACs). Heating and cooling are powered by the sun while the fans run on electricity.


CASE STUDY: A COMMERCIAL BUILDING IN SACRAMENTO, CALIFORNIA

In 1990, a hybrid solar HVAC system was installed in an 8,000 square foot, single-story commercial building in Sacramento, California. According to its designer and maintainer, the solar thermal system annually saves $6,080 in cooling costs and about $3,344 in space and water heating costs compared to using a combination of grid electricity (at $.10/kWh in Sacramento) and natural gas. The total cost of the system including installation was $107,900 -- about $80,000 more than the installed cost of a conventional system. By annually saving a total of $9,424, the solar system will pay for itself in 8.5 years using simple-payback calculations.

The system uses 2,400 square feet of roof-mounted, double-glazed, flat plate solar collectors to capture solar thermal energy. The collectors provide energy for a (nominal) 10-ton absorption chiller, a heat-exchanger coil and storage tanks which together supply up to 80 percent of the building's water heating needs, 50 percent of its space heating needs, and 80 percent of the air

conditioning load. A thermal energy storage system, acting as backup, is charged during off-peak hours by a conventional compression chiller. The solar system is designed so that the hotter the outside temperature, the better the absorption chiller works. It also uses water as a refrigerant rather than an ozone-depleting refrigerant such as freon. In the six years since installation, the solar HVAC system has not had any failures or shown any problems, according to Michael Proulx of Solar Depot, a building tenant.

For More Info: Pramod Kulkarni, Manager for Technical Assistance, California Energy Commission, 1516 9th Street, MS 43, Sacramento, CA 95814; (916) 654-4637; Fax: (916) 653-6010.


Grid-Connected PVs: No More Blackouts

Has your area suffered from power outages recently? Many areas this summer have had blackouts, most notably in the west, due to both poor weather and a power overload on the electrical grid. In response, many areas are developing grid-connected PVs to provide uninterrupted power, especially to facilities such as hospitals. Unfortunately, these systems are generally prohibitively expensive compared with utility-supplied electricity due to the high installation costs and inequitable market value. But a growing number of "net metering" laws (California and Minnesota) and regulations (11 at last count) are helping to close this gap by more fairly crediting a PV user for PV generated electricity. This helps encourage utility customers to own and operate small PV systems.

Net metering laws and regulations require utilities to value all PV power produced at the full, retail rate -- as opposed to the lower avoided-cost rate --up to the total amount of power the facility consumes. In California, net metering works simply: the meter runs forward to measure utility electricity supplied to a home from the grid, and backward when the PV system generates more electricity than the home consumes. At the end of the monthly billing period, the meter registers either the net energy consumed or produced. The customer pays the bill, at the regular retail rate, for net energy consumed. If the customer is a net producer of electricity, the utility may purchase the excess at a substantially lower "avoided cost" rate, rather than the retail rate. Other states are considering implementing similar legislation and/or regulations. The main drawback to the California law is that it only applies to residential customers. The other 12 states with regulations (with the exception of New Hampshire) allow all customer classes to benefit from the regulation.

Les Nelson, Technical Director of the California Solar Energy Industries Association (CAL SEIA), argues that "net metering encourages private investment in [PV] technology, advancing the day when PV systems will be affordable to all. All stakeholders agree that only by increasing production will PV prices decrease. Net metering removes a significant impediment to those willing to invest today." (Solar Today, March/April 1996, p.54).

For More Info: Les Nelson, CAL SEIA, 2391 Arden Way, Suite 212, Sacramento, CA 95825; (916) 649-9858. Jay Morse, Regulatory Analyst, California Public Utility Commission, 505 Van Ness Avenue, San Francisco, CA 94102; (415) 703-1587; Fax: (415) 703-1981; E-mail: jmx@primeu.cpuc.ca.gov.