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components. This can allow flexibility in
installation and component selection, but it
requires greater installation space and effort.
The Tesla system is one example of such a
system. What’s interesting is that most Tesla
marketing material doesn’t show the critical
inverter/charger and other components needed
to make the battery work.
Other offerings involve a completely
integrated ‘energy storage system’, in which
the batteries, inverter charger and other
components are in one box. Such systems
have a simpler appearance and easier
installation, but they can limit flexibility.
Challenges
There are still some important issues that
need to be tackled.
Prices have come down, yet the
systems remain expensive. Today, a typical
battery and solar PV system costs about
$17,000 installed.
Such systems are economic in certain
deployments, but the number of households
with the necessary electricity load and
consumption patterns are relatively limited.
Careful analysis and modelling should be
carried out to decide whether a battery is
economic for a given installation.
Experience with laptop fires, or even the
lithium battery issues that caused Boeing’s
787 aircraft to be grounded for long periods,
suggests that great care must be taken to
design safe and reliable battery systems.
Fire risk is actually relatively low if the
system is designed and installed correctly –
perhaps even less risky than storing a gas
bottle or petrol tank in the house.
However, installation and operation
Standards for battery systems, particularly
technologies other than lead-acid,
have not kept up with the pace of
technological change.
We rely on the knowledge and experience
of the installer to underpin the safety of many
modern battery systems. Poorly implemented
battery systems will represent a significant
safety issue until the Standards catch up.
Considering the two most common uses
for batteries – energy arbitrage and solar
storage – the economic benefits depend
heavily on the intelligence of the controller that
manages battery charge and discharge.
For example, if a controller cycles a
battery excessively, or operates it at too
high a temperature, this will dramatically
reduce battery life. An intelligent battery
management system would adapt to the
ambient temperature and aim to reduce
battery cycling.
Even more advanced systems would
adapt to local weather forecasts, ensuring the
battery can reduce a property’s dependence
on expensive grid electricity (by charging late
the night before) even if clouds reduce the
availability of solar on a particular day.
Battery cells must be operated within tight
temperature constraints if they are to realise
their full life.
For example, most lithium batteries can be
operated only up to 40°. Such temperature
constraints pose a substantial limit on where a
battery system can be installed and operated.
One key question as large battery systems
become commonplace is what to do when
the battery reaches the end of its life –
typically after 10 years of operation.
Lead-acid batteries are relatively easy
to recycle (the technology has been in car
batteries for almost a century), but lithium-
based batteries are much harder, with no
large-scale recycling facilities in Australia.
However, for electrical and communications
professionals the installation and maintenance
of grid-connected battery systems in homes
and businesses will become regular practice.
A future article will review the key
technologies and some of the installation
issues to be wary of.
Figure 1. Power flows in a solar storing scenario. The blue line shows a typical residential
household load profile, with the power generated by the solar system (green line) far exceeding
the load in the middle of the day. Without a battery, this energy is essentially wasted for the
householder. A battery changes this situation. With a battery, the excess energy (the area above
the orange shading) is charged into the battery during the middle of the day. This stored energy
(the red shaded area) is then used to run house loads during peak electricity prices, later in the
day when household demand is greatest.