Environmental Engineering Reference
In-Depth Information
developing technology that will help realize a smart community network, and to
provide various next-generation services, such as visualized portal sites, car sharing
services and energy accommodation between buildings (GSES
2012
).
The system developed for local production and consumption of renewable en-
ergy, uses a combination of solar power and large lithium-ion secondary batteries,
and is supported by the standard commercial power supply to meet demand which
exceeds the local supply (Fig.
7.1
). This is combined with DC-driven LED lighting,
which is supplied directly from the PV solar supply, thus improving the power utili-
zation efficiency. Furthermore, in the rooms supplied by DC, we are able to explore
the optimum configurations for an energy-saving environment, through combina-
tions of DC and AC power with digital household appliances. By using IT, we have
also developed control systems to automatically deal with DC and AC load varia-
tions. This system has the additional critical advantage that it can use both accumu-
lated electricity and renewable energy during disasters and emergencies to ensure
stability in supply for as long as possible. The system also has resilience because,
even after the energy has been completely consumed, the IT system automatically
restores each part of the system when renewable energy is restored.
7.2.2
Renewable Energy Supply
The basic renewable supply is a 392 m
2
area of solar panels on the building roof
which provides a maximum of 60 kW output providing a DC 300 V supply. The
specifications of this solar panel are the followings. This photovoltaic system pro-
vides electricity to the main building of the Graduate School through the lithium ion
secondary batteries, and reduces the need for commercial power by around at least
10 % on the annual average consumption.
7.2.3
Battery Storage and Management
This is a large-scale power storage system of approximately 50 kWh that efficiently
stores power generated in the solar power system. It serves to reuse all outlets (ex-
cept those used for connecting experimental equipment) by the DC 300 V wiring
used in the building. LED lights installed in the main building can be powered
without DC/AC and AC/DC conversion losses. The selected battery was an olivine-
type iron phosphate lithium ion battery connected with 240 sheets in 30 columns
comprising a photovoltaic solar cell with a maximum output of 250 W. Specifica-
tions are in Table
7.1
and the system was one of the first mass-produced secondary
battery cells and packs for sale to the public. We use 1.2 kWh modules and this
stationary power storage system is characterized by its long life and high safety,
making it ideal for a large-scale power storage system. It has a quick charge and dis-
charge performance and can charge over 90 % of its capacity in 1 h. It also has the
resource efficiency advantage of using iron instead of rare metals for its electrodes.
