IEEE Electrification Magazine - June 2016 - 15

costs low. The ac-GtoL losses in this system are 6%, and
StoL losses come down to 3%. GtoB losses are still 15%,
but StoB and BtoL losses are down to 5% and 10%,
respectively. The loss values are confirmed using extensive measurements.
These losses will amount to a decrease in efficiency, as
power is delivered from a source (at the inlet of a home) to
the load. Table 3 presents these efficiency numbers. Thus, if
an ac home is powered 30% through the grid without a battery, 20% through a battery, 25% from a solar panel without
a battery, and 25% through a battery, the total power efficiency will be 77%, whereas that for a dc home will be 89%.
As the available grid power decreases (more load shedding),
the efficiency of the ac home will become worse, whereas,
that for the dc home will improve.
a) In the case of off-grid homes, it was assumed that the
battery is consumed only when the available solar
power is not enough to drive the load. For on-grid
homes with load shedding, the priority of source consumption assumed was a solar panel, the grid, and a
battery in that order.
b) The battery used here is a special valve-regulated
lead-acid (VRLA) high-performance battery developed
by Amararaja (see http://www.quanta.in/products.asp
for product-related information) in technical collaboration with IITM. The VRLA are low-cost batteries used
widely in India. A typical 1-kWh battery, priced at
around ₹6,000 per kWh, can be charged and discharged 800 times at 0.1 C and at a depth of discharge
of 50% at 30 °C. The high-performance VRLA 1-kWh
48-V battery was especially designed to double its life
and the number of charge-discharge cycles. The cost
is about 15% higher than the conventional batteries.
c) Per unit costs of power are assumed as per Table 4.
The corresponding solar-ac and solar-dc costs
include the costs of deployment and balance of
systems. [Depreciation of 20 years for solar panels
and interest rate of 7% are assumed in computations of costs. A 500-W solar system including rooftop deployment and cables is assumed to be at
₹50 per watt. The cost of the balance of systems for
a 500-W solar panel is assumed to be ₹3,000 for
inverterless (solar-dc system) and ₹10,000 for the
solar-ac system but with a life (depreciation) of five
years only. The costs for a lower wattage system
may be slightly higher.]

Solar Panel

125-500 W
48 V dc

Grid

dc
Bluetooth Home
Low-Energy
Interface
Cloud

230 V ac
Battery

Figure 5. A solar-dc inverterless system for a dc home.

power is delivered to a load (directly and through a battery) at 91% efficiency in dc homes as compared to 65% in
ac homes. As a result, the per day cost of power was found
to be around ₹12.6 for the solar-dc home, which is significantly lower than ₹50.6 for a solar-ac home. More interestingly, as shown in the section "Economics of On-Grid
Homes Without Load Shedding," the per day cost of power
in a grid-connected ac home with zero load shedding is
₹16.3 for the same load, implying that for an efficient offgrid solar-dc home the power costs are lower than even
the current grid-connected ac homes.
Recognizing that solar-dc technology has the potential to revolutionize and transition India's power sector
to a more sustainable one, the Government of India
recently started supporting its deployment in 4,000 offgrid homes in Rajasthan. In December 2015, deployments started in Bhomji ka Gaon, a village in Rajasthan
located in a region where the terrain conditions are
harsh with no road connectivity, marked by frequent
sandstorms and lack of resources. Each home is powered by a 125-Wp solar panel supported by a 1-kWh

TABLE 4. Per unit costs of power

from different sources.

Source of Power

Per Unit Cost (₹)

Grid

5

Solar-dc system

4

Battery

12

Solar-ac system

5

Results and Discussions
Economics of Off-Grid Homes
To begin with, an off-grid ac home and a dc home with the
same load and solar profile were considered. The simulation results obtained are presented in Table 5. As shown,
the per day load requirement in the dc home was about
37% of that of an ac home due to lower consumption of dc
appliances in comparison to ac appliances. Further solar

TABLE 5. Per day cost of power in off-grid
ac and dc homes.
Type of
Home

Load/Day
(W H)

Cost/Per
Day (₹)

Efficiency
(%)

ac home

3,266

50.6

65.1

dc home

1,212

12.6

91.4

IEEE Electrific ation Magazine / j unE 2 0 1 6

15


http://www.quanta.in/products.asp

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