Car Park Lighting Sensors

So if you’re designing an apartment building and you’re stuck with an underground car park things can get pretty nasty with energy consumption.  With no natural light and a clear safety requirement to keep the area lit all things point to an energy hungry lighting solution.   Even the most efficient lamps will still burn a lot of power running 24 hours a day, 365 days a year.

The most obvious solution to drop run time is lighting controls.  Specifically motion sensors.  But how should these be set up, and how does the set up (number of lamps per sensor and lamp shutoff delay) actually effect the energy savings the controls will achieve?  The short answer is, make sure they turn off really quickly after the car or person is out of the area.  The long answer is below:

It’s Complex…

The interplay between the car park layout, vehicle traffic, pedestrian traffic, simultaneous use of certain areas of the car park, probability of a specific car bay being accessed, the shut-off delay timing and the distribution of sensors means calculating light run time is very complex.  Pondering the possibilities got the better of me and I ended up running a simulation to determine effect of some key parameters.

A Conceptual Car Park

The conceptual car park looked like the below pick.  Effectively 150 bays with one pedestrian access and a main vehicle exit point at one end.

Car Park Map

I used some basic lighting design to work out how many lights would be needed (single globe T5s) to achieve an adequate light levels (50lx).  The calcs indicated a requirement of about 80 lamps.  I just placed these in the road ways and walk ways in my conceptual design.  These are the numbers with the x in front of them.  In reality they’d be probably be spaced more evenly but this satisfies the requirements of the model which is just to see how many lights would be triggered when each bay was accessed.

Which Car Bay Triggers which Lamp?

That was a manual process of thinking about how a person will walk from the lift to the car, and then how they will drive out (or vice versa).  The below diagram shows that if car bay 125 is accessed the blue line will be traversed by the car driver and passengers, whilst the red line will be travelled by the car.  All the lamps highlighted in red will subsequently need to fire.

Car Park Map - Lights Triggered By Bay 125


I got some stats on how many trips and average household does from here and here.  The Sydney data also gave these neat graphs on when the trips occur as well.  This enabled me to put a probability on a given car being accessed at a certain time of the day.  The sensors are obviously going to give the most benefit during lower trip frequency times.  But depending on the set up, you can even get a reduced run time during the peak times in this car park (not every day, but some days there’ll be savings due to the random nature of when people take a car trip).

Screen Shot 2015-05-24 at 2.59.53 pm

After some sense checking I ran the simulation for different combinations of motion sensor parameters.  The focus was on:

  • The delay before the lamp is shut down after the motion sensor is activated (or re-activated)
  • The number of lamps per sensor (if you whole car park is wired to one sensor, you’re not going to get as much benefit)

The below chart shows the results.  It looks pretty clear that the most important attribute is the delay before the lights are shut down again.  Amazingly, with 10 lamps per sensor a 90% run time reduction could be achieved if the lamps only fired for a minute.  10 lamps per sensor is probably as sparsely as you’d want to space the sensors to make sure they fired when there was movement

Simulated Car Park Lighting Energy with Sensors

Pit Falls

The simulation is obviously not a real live thing so I want to note some possible pit falls.

  • I got lazy and didn’t model weekend days separately.  So the actual savings are probably greater than what I’ve reported above.
  • If you car park is full or big rodents that trigger motion sensors 24 hours a day, the savings won’t be achieved.
  • My “Shut off delay time (mins)” is actually the lamp run time from when the motion sensor is first fired during a particular event, not from when it was last fired during that event.  So for you to achieve the 1 minute shut-off delay, you’ll probably want the light to go down 5 or 10 seconds after there was no motion in an area.  Perhaps this would cancel out the additional savings you’d get from lower weekend trips.

Other Car Park Lighting Ideas

Although motion sensors in car parks are an absolute no-brainer, there are also other things that can be done to make car park lighting smarter, a few of which I’ll include below.

Lux sensors may also be utilised with dimmable lamps to ensure light levels over the requirements are not delivered and hence energy savings may be achieved due to lower average lamp power.  The benefit of lux sensors in underground car parks is limited however due to a lack of natural light.

A better coefficient of utilisation can be achieved with light coloured rooms (more reflectance, so better light utilisation from your lamps which means you’ll need less lamps).

The lamp itself should be considered carefully and in conjunction with the lighting controls.  The most efficient globe in the world may be the wrong choice if you need more of them than necessary.  Similarly, if it won’t handle being turned on and off all the time, that’s going to be a problem.

The light housing can also help if it’s got a nice reflective backing to disperse the light where it’s needed (down and sideways) instead of where it’s not (up).


LCAs For Buildings Now a No-Brainer

Leading LCA Software eToolLCD further brings LCA into the mainstream by offering innovative software subscriptions for easy access

eToolLCD, a global leader in life cycle design and assessment of the built form, is further bringing Life Cycle Assessment into the mainstream by offering a new range of subscription packages designed to further increase accessibility of eToolLCD, making it the most powerful, cost-effective and easy-to-use built form LCA software in the world.

Over the last two decades Life Cycle Design (LCD) and Assessment has evolved significantly and demand for LCD continues to grow exponentially. Life Cycle Design is now the premier decision-making tool for improving environmental performance and has been incorporated into green building rating schemes all over the world[1].

The LCA industry has met this demand with the introduction and alignment of international standards (ISO 14040, ISO 14044, EN 15978), improved background data sources and better software. Once strictly the domain of expert researchers and consultants, front line professionals now have the ability to harness the power of LCA to dramatically inform and improve their projects with modern streamlined tools. In particular, the building profession can now harness the renowned strengths of LCA through an intuitive and easy to access platform – eToolLCD.

Originating in Perth, Western Australia, eTool has now opened up offices in Canberra, Australia and Brighton, United Kingdom as the demand for life cycle assessment and design of the built form continues to soar. eTool has conducted the most built form LCAs in Australia and is quickly establishing themselves as built form LCA leaders around the world.

“We have seen LCD become a standard part of good design all around the world and we felt that making eToolLCD even more accessible was the next move. Everything we do with eToolLCD is designed to make it easy for anyone, located anyone in the world, to login to eToolLCD and be guided through a life cycle design approach to higher performing buildings and infrastructure. eToolLCD is the first built form LCA software in the world to adopt this open-use model, and this will always be a crucial element of our business because our goal and passion is to reduce global carbon emissions from buildings. We believe that educating people about LCD/LCA and putting an LCA software into the hands of as many people as possible will help us achieve that goal,” said Henrique Mendonça, eTool Regional Business Development Manager.

The new subscriptions can now be tailored to meet users unique requirements and they experience a range of additional functionalities associated with each of the subscriptions. Some of the benefits associated include reduced certification costs and accessibility to comprehensive built form LCA training.

“As LCD continues to take the sustainable building industry by storm, the availability of accessible and affordable tools such as eToolLCD is a crucial element to ensuring the highest performance outcome of projects around the world. We’re ecstatic to be at the forefront of the next evolution of sustainable design,” said Alex Bruce, eTool Co-Founder and Business Development Director.

< ENDS >

[1] Countries who have adopted LCA into green building standards: Australia, Germany, UK, France, USA, Netherlands, Switzerland & Japan.


Media contact:

Portia Odell
eTool Marketing Communications Manager
+61 08 9467 1664

About eTool

eTool is a world leading life cycle assessment and design consultancy that optimises building design for lower environmental impact and high performance. Utilising our unique software eToolLCD®, we work with architects, engineers and developers to measure and improve the life cycle impacts of buildings, surpassing industry standards. eToolLCD® makes sustainable development easy to achieve and cost-effective for all size projects, from residential and commercial building to land development and infrastructure.


Grid-tied VS Off-grid Solar PV systems


With the tremendous uptake of residential solar PV installations all around the world, the next question that often comes to mind is: to stay grid connected or go off-grid? For most people who are concerned about environmental issues, they might be led to believe that completely weaning off our fossil fuel powered grid is the truest form of sustainable living. However, here at eTool we like to challenge people’s beliefs based on data from life-cycle analysis.

To start, let’s quickly look at the difference between the two systems.


Grid-tied PV system


A grid-tied system is connected to the utility grid. In new systems, there is only one meter that measures both in-coming and out-going power to the house. Power generated from the solar panels goes through the inverter which converts DC to AC which then used throughout the house. Any left-over power that is not used goes out to the meter where it is measured then fed into the grid to be consumed elsewhere. This system has no on-site battery storage so any solar power that is not used at the time it is generated will be fed directly out to the grid. When no energy is generated by the solar panels such as at night or on overcast days, power will be drawn back from the grid to supply the house.


Off-grid PV system


An off-grid system means that the system has no connection to the grid at all. In this situation, battery storage is necessary in order to provide power to the house when there is no power generated by the PV system. An additional on-site generator may also be required as a backup in case the stored power runs out. In this system, the power from the solar panels goes through a charge controller or battery regulator then into the battery bank for storage. On demand, the power is drawn from the batteries through an inverter then to the house to be used. If the power stored in the batteries run out, a generator can be started to produce backup energy.


LCA Comparison

Carbon Intensive Grids


AU Standard Structure – timber + double brick
Cooking – Electric
HWS – Gas storage
HVAC – Airsource heat pump (MEPS ave)
Lighting – CFL
Refrigeration – AU average
Water – AU average

In order to compare the systems, we will use LCA to quantify the impacts in CO2e. We assume that all other factors are constant such as water, gas and the carbon intensity of the grid. The table above shows the building structure and appliance specifications for a standard Australian detached home. Only the PV systems will change in order to better compare the difference between grid-tied and off-grid.


The graphs above shows the life-cycle carbon impact of a standard Australian home with no PV system installed. We can see that the life-cycle energy of the building takes up the largest portion of the overall impacts of the building. The graph on the right shows the end-use breakdown of the standard Australian household’s energy use.


The blue column on the left in Graph 2 above is a standard Australian home with no PV. The red column is an off-grid system sized to provide 100% solar power throughout the year. This is a 15kW PV with about 100kWh of battery storage to provide backup power for 3 days while the green column is the grid-tied version with 15kW of PV without battery storage. The orange& dotted columns show the impact of a smaller off-grid 8.5kW PV system with 60kWh of battery storage. The dotted orange column has an additional backup diesel generator that provides 10% of the energy demand. The teal column on the right is the grid-tied equivalent with 8.5kW PV and no diesel backup or battery storage.

We can see that installing a PV system alone has a significant effect at reducing the CO2e impact of the building. Note that despite a near two-fold increase in the amount of PV, the life-cycle carbon savings in the off-grid system only has marginal improvement when compared to the grid-tied system. This is due to the high embodied impacts of the larger PV system which are underutilized in the off-grid system whereas in the grid-tied system all extra power generated by the over-sized system is fed into the grid.


In the graph above, we compare the category breakdown of the 15kW PV systems versus the AU standard home, we can see that while the life-cycle energy use of the solar powered homes have dropped significantly, the recurring impacts on the other hand have increased due to the impacts related to replacing PV panels and batteries.

Low Carbon Intensity Grids

In areas with cleaner grids, in this example I’ve used the Tasmanian grid (even though it is still connected to the NEM) – is a grid-tied PV system still relevant?



The graph above shows that although the proportion of savings is much less in a low-carbon grid, a grid-tied PV system still has a lower life-cycle CO2e impact compared to an off-grid system. In areas with cleaner grids, the embodied energy impact of the building becomes proportionately more important than the operational energy as shown in the graph below.



Best Practice Design

How about a house that is designed by someone who knows what sustainability is about? Let say they designed using low-embodied energy materials and didn’t install any air-conditioners – how would such a house compare? The low-impact or ‘best practice’ design building assumes that the occupants are more sustainably conscious and try to reduce electricity demand as much as possible in the choice of appliances they will use and are more likely to build with low embodied impact materials such mud brick. A detailed list of specifications in the ‘best practice’ house are listed below while still assuming Australian averages for water and refrigeration energy use. Based on these specifications, the off-grid ‘best practice’ home will need 4kW of PV and 48kWh of battery storage assuming 10% of the energy demand to be provided by a diesel generator.


Best Practice Structure – mud brick
Cooking – Wood
HWS – biomass
HVAC – ceiling fans+wood pellet heater
Lighting – LED
Refrigeration – AU average
Water – AU average
PV – 4kW
Off-grid Backup –  48kWh battery storage + diesel generator

The graphs below show the global warming impact of a ‘best practice’ home on an Australian average grid the embodied and operation energy breakdown and the carbon impacts on a low-carbon grid. Even though the overall life-cycle carbon impacts of the building has dropped significantly due to the ‘best practice’ design, the results still indicate that being grid-connected is better for the environment in both grid situations.
Graph6 Graph5 Graph4




In areas with carbon intensive grids such as Australia, it is important to help ‘clean up’ the grid by staying grid-connected with our PV systems. This is due to the fact that all the excess potential energy from off-grid PV panels is ‘wasted’ instead of captured to be used elsewhere. An off-grid setup will usually have a PV system that is large enough to meet most of the energy demand of the household throughout the year. This means that the system will be sized to produce enough power in winter but in summer when there is more daylight, the extra electricity generated by the system will be wasted.

A grid-tied system on the other hand is able to take advantage of an existing energy network and maximise the energy generation potential of their PV systems as any excess energy is fed back into the grid to be utilised elsewhere. This means that the embodied energy of the building can also be offset when the building produces more renewable energy than it consumes throughout its life.

A cleaner grid also means that other homes, offices and industries such as water desalination plants and manufacturers that use this cleaner electricity will be less carbon intensive. We all benefit from the knock-on effects of staying grid-connected.

For areas where the grid is already ‘clean’, the operational energy impacts become less significant from a carbon perspective but you’re still better to have grid-tied PV. Staying connected in a green-grid also helps avoid the additional embodied impacts from an oversized PV & battery storage system.



Bear in mind that there are other resources and technologies that haven’t been modelled here which may provide better solutions by taking the best of both systems. For example, hybrid systems combine the advantages of grid connection with battery storage to help moderate grid loads. To provide an efficient solution to large scale energy distribution, ‘Smart Grid’ systems that monitor and control the grid’s energy distribution and production is the way to go. Combine smart grids with hybrid solar systems and the economics and efficiency of renewable energy distribution and supply grid will be greatly improved. Nevertheless, the underlying message still points to the fact that staying grid-tied is the key in order to stay most sustainably relevant today and in the future.

Tesla most recently announced their low-cost ‘Powerwall’ battery storage system which will affect the current PV market.