Sustainable Energy NZ #13 – making light work of savings at home

Welcome to the thirteenth post in the Sustainable Energy without the Hot Air – A New Zealand Perspective series. After our previous posts on hydro power, geothermal and wind (and a summary on the big three), solarbiofuelsmarine and waste energy, we’re now looking at answering the question:

How can we achieve a BIG reduction in our personal and national energy consumption?

We covered the breakdown of where we use this energy in the last post. Today we’re dealing with commercial and residential building energy use. Be sure to check out our treatment on road and air transport from the last few days.

A few notes before we begin: as before, the units are in kWh/day/person – ie. if you ran a 40W lightbulb for 24 hours, it’d take ~1 kWh over the space of a day. We then divide it by person to give you a sense of the scale of the resource proportionate to the size of the population. Be sure to check out the methodology. For reference – we’ve been looking to replace around 55 kWh/d/p of energy currently generated by fossil fuels.

Commercial and Residential Energy Use

Making sense of the commercial and residential energy use in the Energy File is more complicated. All the commercial energy to light, heat, and power our gadgets both at home and at work amounts to 21.2kWh/d/p. Compare this with a UK usage of 37kWh/d/p for heating and cooling. A couple of caveats about these figures though. First, “industrial” energy use almost certainly includes some workplace heating, lighting and gadgets, so the real number is certainly higher. The number includes 5kWh/d/p of firewood but excludes firewood obtained from non-commercial sources. Using MacKay’s estimates as a rough guide, we would break this down as follows.


The UK estimate is 4kWh/d/p for all lighting – work, home, and street. NZ is not so dark in winter.  Assuming 5 hours of lighting in mid-winter, 0 in mid-summer, and 30% of days at work needing fluorescent lights on, then 2kWh/d/p looks realistic.

Gadgets (including work and school computers)

We are guessing our houses and work have pretty much the same list of gadgets that MacKay uses, but on a per person basis (using 2.6 persons per household from the census), I suggest 4kWh instead of 5kWh.The University of Otago’s Home Energy Web Project estimates gadgets use at 19% power = 2.4kWh. [8p45wmp] Add a similar number for work and 4kWh/d/p appears realistic.

Heating and Cooling

Subtracting lights and gadgets from the total residential and commercial energy leaves a total of 15kWh/d/p. Add in another 2 for industrial sources (e.g. factory heating) and 1 for private firewood and this gives an estimate of 18kWh/d/p — less than half the UK usage. While it certainly helps to live closer to the equator, it is also confirmation of what Europeans complain about — our houses are cold. Other studies (see below) would put home heating/cooling energy at 8kWh/d/p. If we use the same again for work, then this is 16kWh/d/p for heating, which in turn implies that gadgets (at work especially) and lighting might be more than estimated above.

Potential savings in commercial and residential energy use

So what efficiencies can realistically be made here? The lighting figures already include some use of compact fluorescent bulbs (CFLs). In future, LED lights might reduce energy for lighting from 2 to 0.2kWh/d/p.

More and more, modern gadgets have advanced power management, but then we keep buying more of them.  We strongly doubt that any significant saving will be made in this area.

Water heating is one place where significant savings can be made. As noted under the solar section, we have good solar water heating potential for many homes. A 50% take-up of solar hot water heating could close to 2kWh/d/p.

Refrigeration has room for improvement too. Fridges running on 0.1kWh/d/p have been achieved although at some cost in convenience. Nonetheless it seems realistic to expect that savings of 0.5kWh/d/p could be achieved with better design and placement.

Home heating is a more complex issue. A new house meeting the German Passivhaus [kWzrkz] standard requires less than 2kWh/d/p to heat, but the existing NZ housing stock will take hundreds of years to replace. Retrofitting to improve the heat retention of existing houses can be done, but I suspect that this will allow us to live with healthier temperatures rather than saving much energy. Finally, we can use air-source heat pumps to heat more efficiently. Saving even 2kWh/d/p for houses is probably optimistic.

There is quite possibly more potential for saving in the commercial and industrial sectors. Because of building density, the cost per person of putting in more efficient heating, lighting and power management systems is cheaper than doing the same thing to individual residences – but nowhere near as popular politically. Perhaps 4kWh/d/p could be gained.

In total, efficiency improvements from lighting, gadgets and heating might save 10kWh/d/p, much of it from workplace efficiency gains.

Just for people interested in what they have personal control over, here is the breakdown of average house energy use in NZ, again from the Otago Home Energy Web project [8p45wmp]. (Note that the cost of this average energy use comes to about $2000 per annum, per household).

Lights 0.9kWh/d/p
Refrigeration 1.1
Gadgets 2.1
Water heating 3.2
Heating/Air conditioning 3.8
TOTAL 11.1

The Royal Society of New Zealand has produced a teaching resource on energy use in New Zealand homes, which can be found at [8rxkn29]

One very important point to note here, if you want to make a difference – we tend to concentrate a lot on saving at home but this is only looking at 11kWh/d/p, and much of this is electricity already sourced from renewables. Per capita fuel use is 31kWh/d/p, which thus provides opportunities for far bigger savings.

Further Reading:

Tom Murphy at Do The Math has a whole section on home energy use for his residence in San Diego. Many of the findings are very applicable for NZ. From his Guide to Posts:

“Treating energy as precious across the board, we can make gigantic changes to the amount we use without dropping out of society.  Tracing my own path, we first look at pilot lights, and the dramatic impact this led to in home heating practices (now using a fifth of the gas I used to).  Likewise, I have trimmed my utility electricity use by a factor of five—thanks in part to an off-grid solar installation (efficiency report here).  I have cut back on use of gasoline as well.  Dietary choices can also have a big impact on personal energy: especially meat vs. veggie choices.

I recap the various avenues of personal energy savings and compare this to the national average, musing also about ways to make this a more widely practiced endeavor.

In my quest to measure and understand energy use, I have detailed the maximum efficiency achievable by lighting, and have measured the efficiency of heating/boiling water by a variety of methods.  I am also a compulsive collector of data, and offer glimpses of electrical activities/devices in my home.”

4 thoughts on “Sustainable Energy NZ #13 – making light work of savings at home”

  1. I have been using fluorescent bulbs for about 20 years and recently a handful of M16 12v LEDs but Jaycar are getting in shortly, maybe next week, a line of LED 230V retrofit bulbs, both bayonet and edison screw in “warm white” and “natural white” (i.e. cold white with significant blue) with 270° illumination which is an achievement with LEDs. Price per unit for the 5W is $18.90, while their 3+ price is $16.70 and their 6+ price is $14.70; price per unit for the 10W is $37.50, while their 3+ price is $33.90 and their 6+ price is $29.90 – Warm White and Natural White are the same price. Hopefully they are rated for 25000 hours like my M12 lights in which case the 6+ price is low enough to tip me toward replacing the CFCs.


  2. Well the biggest Jaycar outlet in Auckland only got 3 of each kind of bulb in (bayonet/edison screww – warm white – natural, 5w 10w) The warehouse is already out of stock. At only half the price of competitors they could have been bolder. As it was only possible therefore to buy one off over the counter we restricted ourselves to a one of each as a sampler., yet to test them. Confirm the life is rated at 25000 hours (I tend to be sceptical of any larger figure).

    5 watt 2800K lumens are 300 – 60 l/w
    5 watt 4000K lumens 360 = 72 l/w
    10 watt 2800K dimable 820 lumens = 82 l/w equiv 82 watt tungsten they say
    10 watt 4000K dimmable 900 lumens = 90 l/w


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