Page 110 - Zero Net Energy Case Study Buildings-Volume 3

CASE STUDY NO. 15
BUTTE COLLEGE CHICO CENTER
Energy Production versus Energy Use: Zero Net Energy Performance
Energy production for 2016 is shown in the chart on the top of the opposite page. The chart also includes the energy used by both the building and the electrical vehicle charging stations in the same year. This annual total energy use was 50,000 kWh more than the annual energy produced by the Chico Center’s solar PV arrays. (See the chart on the bottom of the opposite page, the Cumulative Net Energy Performance, which shows this net-negative total of 50,000 kWh at the end of the year.)
The building would be exactly ZNE if this 50,000 kWh shortfall were due entirely to the electric vehicle charging stations. The charging stations are not separately metered, but it is not unrea- sonable that this could be the case. The 50,000 kWh annual total translates to 190 kWh per day when the Chico Center is open. Electric vehicle batteries currently range in capacity from roughly 20 kWh to 85 kWh (Tesla Model S) and there are currently five electric charging stations at the Chico Center. Some pattern of intermittent use could therefore account for this daily total electric energy consumption. In this case, the building alone would be achieving ZNE performance.
At present, Butte College is providing use of the charging stations at no charge and is not meter- ing the electrical energy consumption due to intermittent use. It will be interesting to evaluate the metered data at a later time if conditions of use are changed and meters are installed.
Post Occupancy: Observations and Conclusions
This is an unusual case study since the building was not designed with a mandate or project goal of ZNE performance and the solar PV system was added six years later. In addition, the PV system is providing energy for electric vehicles in addition to the building. Therefore, obser- vations about “lessons learned” do not apply in any but a general way.
Simply put, the basic observation is that solar PV systems can be added at a later time to an energy-efficient, conventionally-designed building and ZNE performance will still be technically possible and cost-feasible. In the case of the Chico Center, the significant decrease in cost of solar PV systems and the continuing rebates only made such a “retrofit” more attractive as an investment for the District.
96 Z 96
Z
e
er
r
o
oN
Ne
e
t
tE
En
ne
er
r
g
gy
yC
C
a
as
se
e
S
S
t
t
u
ud
d
y
yB
Bu
ui
i
l
ld
di
i
n
n
g
gs
s
:
:V
V
o
ol
lu
um
m
e
e3
3