Page 181 - Hybrid-Renewable Energy Systems in Microgrids

162 Hybrid-Renewable Energy Systems in Microgrids

was also carried out to calculate the Net present values and payback periods of the system
when presented with a fairly accurate forecasting data for the day-ahead schedule. The stud-
ies proved that each case needs to be evaluated individually to estimate the most economical
choice of hybrid renewable-storage mix.
4. Wind Smoothing in Hawaii: A Huge 11 MW/4300 kWh Lithium battery in Maui, Hawaii
to smooth ramp rates in a wind farm of capacity of 21 MW [20]. Wind power generated is
usually intermittent and disrupting due to the nature of the wind. This posed a huge issue
for grid intakers and hence smoothing it to meet local grid regulations. The installed battery
enabled the wind farm to meet the specified ramp rate limitations to ensure the local grid
stability. The battery systems were part of the wind project and hence entitled to a 30% tax
credit. Another advantage that the Lithium batteries have is the availability of commercially
available power electronics, which could be easily customized as per requirements. The bat-
tery delivered at an efficiency of about 80% with major losses coming in the ac-dc-ac con-
version. The project was well planned and supported with a well-equipped technical team.
5. Energy shifting in Yap State: Five lead acid-flooded batteries with an energy capacity of
1593 kWh with PV systems of 270 kW spreading over five islands encompassing ten mini-
grids [21]. The battery systems were selected based on their cheaper costs and to enable
replacement of diesel generators. Some issues faced by the deployment team were the high
operating temperatures, regular maintenance by adding distilled water. However, effective
management with predetermined DoD helps in extending the lifetime of the project to nearly
15 years.
6. Frequency reserve and spinning reserve in Japan: 34 MW/204 MWh Sodium sulfur bat-
teries were installed for a 51 MW wind farm in Aomori Japan in 2008 [22]. The batteries
were used for energy storage, energy shifting, frequency response and as spinning reserves.
The entire battery was housed in 2 MW NaS units and equipped with smart monitoring
systems. The operating temperatures for NaS as explained before need to be maintained at
300–350°C.
7. Energy shifting and ancillary services in China: Vanadium Redox batteries were supplied
by Prudent Energy for a hybrid wind farm and solar PV system [23]. The size of the system
was estimated to cater to applications including energy shifting, load following, and voltage
support and decided to be 500 kW/1 MWh. The wind-PV farm is of a 78 MW wind capac-
ity and 640 kW solar PV panels. The vanadium battery consists of storage tanks to hold the
electrolyte which can then be circulated into the battery packs where they absorb/discharge
power as per requirement.

8 Technological challenges for ESS

ESS market potential is much larger than the existing one and is mainly driven by
renewable and microgrid developments in current power in infrastructure [24]. Bat-
teries and SC have been available commercially and widely used for grid and electric
vehicles too. Conventional storage systems such as PHS and CAES are also imple-
mented across the world for large-scale storage. However, some of the challenges
facing development of ESS can be listed as
• Public Interest and support for ESS development
• Incentives for ESS investment and development
• Safety and flexibility in operations