Inverter Building Cooling Study and Design for 2MW Photovoltaic Array

First Solar

Boulder City, NV

EI Associates was retained by First Solar to perform an Energy Usage Analysis and recommendations for proposed HVAC systems to cool a photovoltaic system inverter building. The inverters take the DC power provided by the solar panels and convert it into AC power.  The installation comprises a 2MW array located outside of Boulder City, Nevada.  Temperature swings are extreme at this location and provided a unique challenge.

Our analysis covered solutions to the air conditioning of the inverter building utilizing as little energy as possible to minimize the parasitic load on the output of the inverters. Based on manufacture information provided by First Solar the waste heat spilled into the inverter building is 60,000 MBTUH per each inverter.  Basic information provided by First Solar is as follows and forms the parameters for this report:

*Inverter based on Xantrex 500 KW inverter technical information.  60,000 MBTUH per inverter as waste heat, 2 inverters per building. Inverter fans are 3,500 CFM each. Environmental conditions require that air enter ant 104F (40C) and would correspond to a exit temperature of 115F.  Calculations will be performed at maximum room temperature conditions of 75F, 95F, and 104F.

*If temperature requirements exceed recommended maximum the inverter will turn itself off, no output.

*Weather design conditions are115F (5 year event), 117F(10 year event), 119F (20 year event), and 121F(50 year event).  117F will be the basis of calculations.

*Inverters require a low dust environment.  Filtration required.

*The solar panels output decreases as outside air temperature increases.  During July and August the output may fall to 80% of maximum as peak outdoor air temperatures are reached.  Our analysis was based on 100% output with no decrease.

*Inverter output will vary during the day based on sun position.

Our analysis considered various mechanical equipment selections, including various efficiencies, as well as water versus air-cooled equipment.