This document describes an approach to rural electrification using solar DC nano-grids. The nano-grids are sized to provide electricity to small clusters of 20-50 houses located close together through a central solar array and battery storage. Electricity is distributed via low-voltage DC cables to avoid inverter costs. Households pay membership fees to connect efficient LED lights and other appliances. The nano-grid approach aims to provide basic energy access at lowest cost while allowing for future expansion through interconnectivity between clusters. Initial tests in Bangladesh have shown the technical and economic feasibility of the solar DC nano-grid model.

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Solar DC Grids for Rural Electrification
Conference Paper · January 2015
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Sebastian Groh
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2. Solar DC nano-grids – A promising low-cost approach to village electrification
Timothy Walsh1
, Sebastian Groh2
, Shahriar Chowdhury3
, Hannes Kirchhoff4
, Daniel Ciganovic2
, and
Peter Adelmann5
1. Solar Energy Research Institute of Singapore (SERIS), National University of Singapore (NUS), 7 Engineering Drive 1,
Block E3A, #06-01, Singapore 117574, Phone: +65 6601 1148, Fax: +65 6775 1943, Email: tim.walsh@nus.edu.sg 2. ME
Solshare, Dhaka, Bangladesh, 3. United International University (UIU), Dhaka, Bangladesh, 4. Technische Universität
Berlin, Berlin, Germany, 5. Hochschule Ulm, Ulm, Germany.
Abstract
More than a billion people worldwide still do not
have access to basic modern energy services such
as electric lighting in their homes. Most of these
people live in remote rural areas, which makes
extension of national electric grids to meet their
needs prohibitively expensive. Several solutions
involving solar photovoltaic electricity generation,
such as solar lanterns, solar home systems (SHS),
and solar (AC) mini-grids are being actively
pursued to address the energy requirements of these
people. These current solutions each have certain
limitations, such as high cost for the cases of mini-
grids and solar home systems, or limited
functionality and expandability in the case of solar
lanterns. This work describes an approach to rural
electrification – solar DC nano-grids – which
attempts to address these limitations by providing
basic energy services at lowest possible cost, while
using a system architecture which is expandable
and future-proof.
Background
In the rural areas of Sub-Saharan Africa as well as
in South and South-East Asia where most of the
world’s unelectrified people live, the typical
housing pattern includes small clusters of closely-
spaced houses (comprising around 20 to 50
houses). The solar DC nano-grids we are
developing are sized to suit this typical housing
arrangement. Each nano-grid comprises a main
solar photovoltaic array for electricity generation
co-located within the housing cluster with a main
battery for energy storage. The individual houses
within the cluster are connected to this main
generation and storage facility via cables and
energy meters.
Methodology
Electricity is distributed via low-voltage direct-
current (DC), thus avoiding the cost of an inverter.
Highest efficiency low-power-consumption loads
are provided along with the nano-grid
infrastructure to ensure that resistive cable losses
are kept to an acceptable level.
A central system monitoring and transmission
device sends information about the system status to
the energy meters in the individual houses which
allows for flexible tariffing depending on the state
of charge of the main battery and the solar
resource.
Any households within the cluster having existing
solar home systems may also be connected to the
nano-grid via an energy meter, meaning that
existing SHS infrastructure is not rendered obsolete
by the arrival of the nano-grid. In future, higher
voltage DC interconnection of nano-grids between
clusters may be implemented to form a wider-area
grid by a process of “swarm electrification”(Groh,
Philipp, Brian, & Kirchhoff, 2014).
Figure 1. Cable losses on thin cables with efficient loads.
Payment Model
For participation in the DC nano-grid, each
household has to sign up for a membership. The
membership fee consists of a one-time payment
that ranges between 500 BDT and 750 BDT (6.4 –
9.6 USD). After signing up for the membership the
energy meter is installed in each house and
connected to the nano-grid. The equipment stays
with each household for the time of the
membership.
Energy services are provided through energy
service packages. These service packages are based
on loads. In a first approach, there will be three
service packages for lighting, ranging from 120 lm
to 240 lm. By signing up for an energy package,
the load and required electricity to run the load are
provided to the household.
Energy service packages can be ordered by each
household on a monthly basis, giving maximum
flexibility to the end-user. Through this model, up

3. to 20 h of light can be provided to a household for
a monthly price of only 100 BDT (1.3 USD).
The described payment model ensures that only
high efficient loads are used and furthermore helps
to bridge the financing gap for the end-user. In
future, similar energy service packages for fans and
TVs will also be offered.
Results
The key concept behind the DC nano-grid structure
is the element of efficiency. The starting point of
implementation was chosen in Bangladesh due to
the high level of local technology development in
this area. PV modules, efficient lead acid battery as
well as ultra-efficient LED technology are
developed and manufactured in the country. This
results in three critical factors:
a) The overall system sizing can be much
smaller than with regular loads.
b) Cable losses are kept at a minimum even
with small cross sections that would otherwise only
be used for higher voltages (see Figure 1).
c) The cost portion that is required for the
appliances is significant, reaching 20% of the total
hardware costs (c.f. Figure 2).
Figure 2. Cost Structure of Hardware Equipment for DC
Nano-grid.
Once energy efficient loads are applied,
differentiated electricity amounts can be granted to
an individual user thanks to the smart meter. These
programmable devices can allow a user to opt for
different packages of electricity access. These
packages were designed under guidance of the
current ESMAP developments for measuring
energy access on a multi-tier framework (Muench
& Aidun, 2014; Tenenbaum, Greacen,
Siyambalapitiya, & Candelaria, 2014). Hence, the
number of lights and duration of service are
controllable by the user her/himself as well as the
ability to power a fan or TV. Due to the smart
tariffing structure, usage hours can be increased
beyond the guaranteed amount when the user
follows the demand management incentives.
Discussion
This paper demonstrates the concept and benefits
of a solar DC nano-grid for implementation in
Bangladesh, with a potential for global replication.
Although DC technology is on the top of the
agenda in international organisations, its full
benefits are not yet implemented and demonstrated
in the field. The approach detailed above fills this
gap by bringing together smart energy meters,
ultra-efficient loads and locally resourced
technology that enable a multi-tier electricity
access infrastructure that is modularly adaptable
and therefore future-proof and upwardly
compatible. This is reflected in specific in the
ability to integrate solar home system within the
existing grid. This feature is of particular relevance
for the context of Bangladesh, with more than 3.5
million solar home system already installed
(IDCOL, 2015).
The technical and economic architecture of the
approach is designed for a bottom-up electrification
approach. Our experience in the field, however
shows that such a bottom-up approach is not
always possible in practice. We would have liked
to be able to present results of the installations at
this conference, but unfortunately, and perhaps due
to the site chosen for the first installations – a
government housing project near Aricha – several
rounds of discussions with various levels of local
government were required before permission to
proceed was granted, thus delaying installation of
the hardware.
Bibliography
1. Groh, S., Philipp, D., Brian, E. L., &
Kirchhoff, H. (2014). Swarm Electrification -
Suggesting a Paradigm Shift through Building
Microgrids Bottom-up. In Proceedings of the
International Conference (pp. 69–73). University
of California, Berkeley: Universitätsverlag der TU
Berlin.
2. IDCOL. (2015, January). IDCOL SHS
installation under RE program, Map. Retrieved
March 5, 2015, from http://www.idcol.org/old/bd-
map/bangladesh_map/
3. Muench, D., & Aidun, C. (2014).
Considering Access to Energy Services. New York:
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Siyambalapitiya, T., & Candelaria, J. (2014). From

4. the bottom up: how small power producers and
mini-grids can deliver electrification and
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