IEEE Electrification Magazine - June 2016 - 13

dc-powered load with losses as low as 8% (in addition to
the battery losses). Such products could make the solar-dc
microgrid very attractive for homes.

Solar Panel
dc

However, Can Solar-dc
Microgrids Break the Logjam?

Power usage and Costs in a
Solar-ac and a Solar-dc Home
In this section, the technoeconomic
viability of a dc microgrid supplemented by solar power in juxtaposition with

Available Solar Power
from One Panel (W)

A dc microgrid for a home with a solar PV, a battery, and an
incoming ac grid to drive dc loads can indeed help overcome many a problem. First, it would be highly cost effective for off-grid homes as discussed in the "Economics of
Off-Grid Homes" section. Furthermore, as and when the
power grid reaches these homes, it can be connected to the
dc home microgrid. Second, for homes that are already on
the power grid but suffer long hours of power cuts, a solardc microgrid would ensure uninterrupted power. As shown
in the "Economics of On-Grid Homes with Load Shedding"
section, the power costs would be much less as compared
to that for today's home using an ac power line along with
an inverter providing power backup. Third, as shown in the
section "Economics of On-Grid Homes Without Load Shedding," rooftop solar panels would lower the cost of power
for most homes, possibly to a level that they can afford.
This is achieved by first reducing power consumption by
use of dc-powered dc appliances in place of today's ac
appliances and second by a rooftop solar PV, which produces dc power at lower costs than the current domestic power
tariff. This is used to an advantage by keeping the conversion losses to a minimum. The key here is to use the battery
minimally. A smart controller on the dc microgrid helps prioritize the usage of the solar panel, the grid, and the battery
in that order. When this is followed and losses are kept to a
minimum, the total cost of power to home owners comes
down considerably, even though a battery is used. Finally, as
rooftop solar panels start getting used widely, DISCOMs
have to supply less and less power to homes. This would
reduce the subsidy that they need to provide to the domestic sector and will help them break even more easily.
Healthy DISCOMs can then expand their grid to most
homes faster to ensure that no home remains dark.
Thus, a solar-dc microgrid could help in breaking the
logjam that the domestic power supply currently faces in
India. Over time, the solar power cost is likely to reduce,
and better batteries will become available. The solution
will therefore become more and more
affordable. Finally, as 250 million Indian
homes start adopting energy-efficient
80
dc-powered appliances and rooftop
70
60
solar panels, India is likely to become a
50
green nation. This could alter the
40
30
debate on climate change significantly.
20
10
0

=
dc Load
dc

Grid
dc

Battery
Figure 2. A rooftop solar-powered dc microgrid for homes.

similar systems in homes running completely on ac is
assessed. We present the simulation results of power
usage in a solar-ac home and a solar-dc home backed up
by actual data obtained from deployment to show that:
1) For off-grid homes, the cost of power per day is much
lower for a solar-dc home as opposed to that for a
solar-ac home. In fact, the results obtained will show
that the per day power costs for a solar-dc home is
comparable to the per-day power costs for an on-grid
ac home today. As and when the grid is connected to
these off-grid solar-dc homes, the per-day power costs
will further reduce.
2) For an on-grid home with power cuts, the use of solardc power not only enables 24 /7 power but also makes
it available at a fairly low cost as compared to that for
a solar-ac home.
3) Even for on-grid homes with no power cuts, considerable savings are possible using solar-dc power.

Assumptions and Methodology
Consider low- and midincome homes with the above
power scenarios. To make sure that the systems are comparable, the following assumptions are made.
a) As a solar panel in India produces 4-4.5-kWh/kWp
power per day (http://www.solarmango.com/faq/5), a

2:24 a.m. 6:00 a.m. 9:36 a.m. 1:12 p.m. 4:48 p.m. 8:24 p.m. 12:00 a.m.
Time (h)

Figure 3. The available solar power from a typical 125-Wp solar panel over a day.
IEEE Electrific ation Magazine / j un E 2 0 1 6

http://www.solarmango.com/faq/5

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2016