nergy storage and iesel generator run time...
TRANSCRIPT
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Energy Storage and Diesel Generator Run-Time
Reduction
Remote Area Power Supply (RAPS) Trial
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Summary
The aim of installing Remote Area Power Supply (RAPS) systems for the Energy Safe Victoria (ESV)
project was to determine if it is feasible to install backup power supplies to enable selective and
occasional de-energisation of high risk power lines on catastrophic fire risk days without
compromising power supplies to affected users.
In summary, this project has shown that it is technically feasible to take residential customers who
are currently connected to the grid and provide their electricity needs from an off-grid renewable
energy-based system. This allows parts of the electricity network to be de-energised and thus reduce
the risk of bush fires in remote areas.
Each of the ten households who participated in the trial were provided with a RedFlow RAPS system
that included a diesel generator, a 3.2kW or 4.8kW PV solar panel array and a RedFlow hybrid zinc-
bromide module (ZBM) flow battery and lead acid Power+BOS energy storage system (ESS). These
elements are shown below.
This report provides an overview of the proven use over this trial of RedFlow’s ZBM technology in
the significant reduction of diesel generator run-time in off-grid residential applications. It has been
shown that with the use of RedFlow’s hybrid ZBM and lead acid energy storage systems (ESS),
diesel generator run-time can be reduced to less than 33% of the time for each of the ten trial sites
of the ESV project, with the vast majority of sites operating their generators for approximately
15% of the time or less. This is a significant reduction compared to a system that does not utilize
energy storage, which would require diesel generators to run for the vast majority of the time to
ensure a steady and reliable supply of electricity to the loads.
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Background
As a result of the Victorian bushfires of Saturday 7th February 2009, the 2009 Victorian Bushfires
Royal Commission was established to investigate the causes and responses to the bushfires.
The Government, through Energy Safe Victoria (ESV), established a Powerline Bushfire Safety
Taskforce. The taskforce examined a range of options for reducing the risk of bushfires being caused
by electricity infrastructure. These included:
1. Targeted replacement of SWER and 22kV lines in highest bushfire risk areas with other
network and alternative technologies that deliver reduced bushfire risk, including aerial
bundled cable, underground cable and remote area power supplies;
2. Enhanced fault protection systems to minimise fire starts from fault currents;
3. Faster identification and location of faults to enable more rapid fire-fighting response;
4. Installation of backup power supplies to enable selective and occasional de-energisation of
high risk power lines on catastrophic fire risk days without compromising power supplies to
affected users.
RedFlow was selected to supply and install the backup power supplies (RAPS) required to trial the 4th
option. The energy storage component of the RAPS systems was aimed at reducing the diesel
generator run-time, thereby increasing diesel generator efficiency, saving costs on diesel fuel and
reducing the need for maintenance.
Ten households, each with one RAPS system, were selected as sites for the ESV trial. Five of these
systems were installed during late 2010, with the other five following in March 2011. All systems
were online by 28 March 2011. The trial officially ended on 31 December 2011, but many
households opted to keep their RAPS systems instead of connecting back to the grid. The RedFlow
RAPS were designed to the specification of an average daily load of 15kWh.
RedFlow Remote Area Power Supply (RAPS) installed at ESV 8
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Results
1. Energy Storage System
There was one RedFlow RAPS system installed at each trial household. These systems provided a
time-shifting capability to store energy generated by the solar panels for use at times of peak
demands (typically mornings and evenings). The energy storage also allowed the diesel generators to
operate at more efficient outputs by storing any energy not immediately used by the household
load. The image below shows the layout of the ESS which contains both lead-acid and zinc-bromine
batteries. Due to the nature of the SMA inverter, there is more data available for the LA batteries
than for the ZB batteries.
ESV 7
ESV 4 – LA Batteries ZB Battery
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The use of the ZB battery results in a smoothing in the LA state of charge (SOC) curve. This reduces
stress on the LA batteries, which do not react well to regular deep discharging. This is shown in the
graph below, which shows the effect of the ZB batteries over the month of July for ESV 10 as an
example. Also shown in the graph is the solar exposure for the ESV trial area over the course of the
month. The effect of high solar exposure over a period of more than one day shows a noticeable
reduction in diesel generator operation, a deeper charge of the ZB batteries and a smoothed LA
charge curve.
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LA SOC ZB SOC Diesel Generator Operation (High = On, Low = Off) Solar Exposure (MJ/m2)
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2. Diesel Generation
Each household’s RAPS system included a RedFlow-designed housing with a 7kVA diesel generator
unit to use as a back-up to the solar panels for the houses’ electricity generation. The diesel
generator was brought into operation when there was insufficient solar generation to power the
household, and the energy storage was also depleted.
The pictures below show the generator unit manufactured by RedFlow with a weatherproof
enclosure, a larger fuel tank with remote fuel level monitoring and a 7kVA Yanmar diesel generator.
There were large discrepancies between the percentages of time that the generators were
operating. As can be seen below, while the majority of generators were operating for under 15% of
the total trial time, ESV 1 and ESV 2 in particular had generators that ran for over one quarter of the
time. The reasons for this include high load usage and low solar generation, which is discussed in
further detail below.
ESV 9 ESV 3
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Ultimately, this meant that the energy storage in the RAPS system enabled a significant reduction in
diesel run time, compared to a system with no storage. Such a system would have required the
diesel generators to operate during most of the day, with the possible exception of times of the
highest solar exposure, when the solar panels produced an adequate output to power the household
load.
The weather also had a direct effect on the operation of the diesel generators. This can be seen in
the graph below, which shows the seasonal variation in the average generator run time for all ten
households (reduced to nine households once ESV 1 had withdrawn from the trial), compared to the
average monthly solar exposure (data taken from Bureau of Meteorology) for the area. There is a
clear inverse relationship displayed in the graph. The need for diesel generation increases during
the winter months due to the reduced solar exposure that limits the output of the solar panels.
From the data presented above, it is clear that there were great differences between the ten
households in terms of diesel generator operation. This is primarily due to significant variations in
individual household electricity use compared with the amount of electricity generated from the PV
solar array. However, the RAPS systems were still successful in reducing diesel generator run-time
to less than 33% in all cases.
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Average Weekly Diesel Generator Run Time vs. Solar Exposure
Average Diesel Generator Run Time (hrs/week) Solar Exposure (MJ/m2)
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3. Solar As can be seen below, the average daily solar generation also varied greatly between trial
households. When compared to the diesel generator run-time, it can be seen that there is an
inverse correlation: high levels of solar generation generally resulted in low percentages of diesel
generator run-time.
The fluctuations in solar generator were not only due to the different sized panels installed at the
trial households, but were also influenced by the sub-optimum installation positions of many of the
panels. This included issues such as sub-optimum solar panel angles, installations behind hills and
installations behind fast-growing vegetation
In summary, increasing the size of the PV solar panels and installing them in the correct location and
orientation resulted in significantly higher solar panel outputs. This in turn resulted in reduced
diesel generator runtime, as shown above. It is important to note, however, that a generator will
always be required as a backup.
4. Household Usage The graph below shows the average daily load used by each household over the course of the trial.
As can be seen, there were significant variations between household loads. When compared to
diesel generator run-time, a correlation can be identified between high load diesel generator usages.
It is thus clear that most households remained at an average daily consumption of about 15kWh or
less, as the RAPS systems were designed for. However, ESV 2 significantly exceeded this figure,
contributing to its high diesel generation totals.
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Average Daily Load Usage by Household
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Conclusions
Overall, this project has shown that it is technically feasible to use an off-grid renewable energy-
based system to take residential customers off their normally-connected grid electricity supply. This
allows parts of the electricity network to be de-energised and thus reduce the risk of bush fires in
remote areas. In particular, it has been shown that RedFlow’s hybrid ZBM and lead acid ESS are
effective at reducing the diesel generator run-time of these RAPS systems.
Overall, RedFlow has learnt many valuable lessons over the course of the ESV trial, and will use these
to improve upon their technology for future RAPS applications. These have included:
The effectiveness of the RAPS system in greatly reducing the diesel runtime of each
generator.
o All households that kept true to the 15kWh per day load usage design specification
were able to limit their diesel generator run time to less than 15% of the time.
Furthermore, had the solar panels been installed in more favourable locations, and
their outputs been higher, this could have been reduced even further.
o In the most favourable circumstances, the RAPS system was successful in reducing
the generator run-time at ESV 9 to less than 4% of the trial time.
o Most households would have required diesel generators to run for almost 100% of
the time without the use of the RAPS system, and in particular, without the ESS.
This means that the RAPS systems were able to reduce diesel generator run-time by
approximately 95% in the case of ESV 9.
The significant effect that large household loads had on the reduction of diesel generator
run-time.
o Load profiles with higher usage during the middle of the day reduce the need to
start generators since this is the time of highest solar output. While the RAPS
system can time-shift this energy from the solar panels, there are losses associated
with storage and inverters etcetera. Large demand at peak times also increases the
need to operate diesel generators.
The significant effect that reduced solar exposure during winter, as well as poor locations of
solar panels during installation, can have on the reduction of diesel generator run-time.
o Diesel generators need to run more in winter than in summer due to the reduced
output from the solar panels during months of low solar exposure.
o Higher solar exposure reduces the need for diesel generators to operate to supply
loads when the energy storage is depleted.