IEEE Power Electronics Magazine - December 2016 - 45

Electricity Cost/Day in INR ( )

of a UPS during its lifetime and an
interest rate of 12%, the electricity
costs would have tripled if there
7%
10%
were 4-hour load shedding. Instead,
4%
Air-Conditioning
the school opted for a solar PV dc
Fans
system with Inverterless-2500 and
Evaporative Cooler
1 . 2 -kW pe a k s o l a r P V p a n e l s
mounted on the rooftop with a batRefrigeration
34%
tery of 9.6 kWh at a total investment
28%
Lighting
of INR 200,000, as shown in FigTV
ure 3. The school changed all lights
and fans to dc-powered appliances.
Other
Costs of these dc appliances was
4%
13%
another INR 180,000, with the costs
for dc fans being 20% higher than
that of ac fans and the costs of dcpowered LED lights being three FIG 2 The typical energy consumption in the residential sector in India in 2010 [4].
times that of CFL lights today (the
additional costs due to dc appliances
worked out to be INR 50,000). Wiring
Solar Panels
changes were not required, as the
1.2-kW Peak
1.5-mm copper wire, used for ac,
could be used for 48 Vdc because the
Wired/Wireless Interface for Power
power consumption for dc appliances
Management and Remote Monitoring
Inverterless
is lower. The cable loss for the farthest ac appliance with ac wiring was
Grid
Classroom
assumed to be 2%, which went up to
One
Corridors
5% for the farthest dc appliance. This
Classroom
Cloud
was found to be acceptable, as most
Two
Battery
Four Tube Lights,
appliances were closer to the dc solar
48 V/9.6 kWh
14 LED Bulbs
Classroom 12
PV system, where the losses did not
exceed 2%, even for dc appliances.
Each Classroom with
Six Tube Lights and Four Fans
The system has been operational
since March 2016.
Figure 4 compares the costs FIG 3 A solar-powered 48-Vdc power distribution system implemented in a school
(including depreciation and finance in India.
costs) per day, when the school is
fully operational, for the ac and dc systems, without
considering the costs of appliances. The grid-power
1,142
1,200
cost was assumed to be INR 5 per unit of power, the
ac
dc
943
1,000
solar dc power cost was a bit over INR 4 per unit when
751
800
a battery was not involved, and a battery added INR
12 per unit cost. The advantage is greater for the
549
600
dc system, which keeps increasing as the number of
341
400
301
265
hours of load shedding increases. The additional costs
248
181
200
107
for dc appliances could be recovered in fewer than 18
months (considering 225 school days in a year), even
0
0
2
4
6
8
if there were no power cut; but in case of 4-hour power
Load Shedding in Hours/Day
cuts, the additional costs could be recovered in about
six months.

Powering a low-Income
apartment Building
The Inverterless-2500 was also deployed for a new building
with 24 apartments meant for low-income families. Each apartment has a load and corresponding usage hours as shown in

FIG 4 The comparison of electricity costs per day for ac and dc
power systems in an Indian school.

Table 3. Only dc-powered appliances were chosen. The corridors have 36 tube lights and 36 bulbs, each operating for 8
hours. Apartments have to share the costs of common areas.
December 2016

z IEEE PowEr ElEctronIcs MagazInE

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2016