ConsumerismEnergy Systems

A Solar Powered Life – Part II

In case you hadn’t realised it, I’m a big fan of renewable energy systems. In the article A Solar Powered Life – Part I I gave an introduction to both grid connected solar power systems and off-grid (or standalone) solar power systems and described some of the differences between the two.

In this article I will cover some of the common questions that I am asked by people and look at how the off-grid solar power system at PRI’s Zaytuna Farm conforms with the three ethics of permaculture.

One of the questions I am often asked by people is:

How many solar panels do I need to buy and install in order to cover my daily electricity usage?

This depends on how much electricity the household uses on average every day. In Australia, as I covered in my last article, various sources state that the average electricity used per household varies from around 15kWh (kilowatt hours) per day to about 20kWh per day (Wikipedia gives a figure of 24kWh per day for US average daily household consumption (1)).

This is the equivalent of a household having 10 x 100W (Watt) incandescent light bulbs switched on for between 15 and 20 hours per day every day of the year.

Being an optimist, I’ll use the best case average electricity usage of 15kWh per day, to determine the number of solar panels that you would require.

With solar power, the system generates power only when there is sunlight. This means that the system is limited by the amount of sunlight received each day. The further south you are in the Southern hemisphere or north in the Northern hemisphere then the greater the extremes will be between the available winter and summer sunlight.

For example: My house is located at about 37 ½ degrees latitude south of the equator. If you were in the US, according to Wikipedia the equivalent distance north from the equator would be the southernmost borders of Utah, Colorado and Kansas, and the northernmost borders of Arizona, New Mexico and Oklahoma.

The Rainbow Power Company in Nimbin, Australia provides an excellent calculator for peak sun in Australia (2). According to the calculator, during summer my house would receive at best about 6.5 hours of peak sun and during winter at best about 3.13 hours of peak sun.

If you want to generate enough solar power to cover the daily electricity usage for an average household over a year, you could probably calculate an average of the Summer and Winter amounts of daily peak sun that you receive. At my house this would be around 4.8 hours of peak sunlight per day (3).

Given that solar panels only really produce power when strong sunlight is available, you can divide the 15kWh per day by the average amount of peak sun available at 4.8 hours to determine the capacity system that you require being 3.125kWh.

This means that if you had a house at my location and you wanted to use 15kWh per day of solar generated electricity you would need to have a system that could generate 3.125kWh to cover your total electricity usage over an annual period. Note that there would be periods with greater generation and other periods with lesser generation.

Using the same calculation shown above, if you wanted to go feral and use an average of 40kWh per day of electricity (this would be the equivalent of having 20 x 100 watt incandescent light globes switched on for 20 hours per day every day), you would require a system that generated 8.33kWh at my location in order to cover your total annual electricity usage.

So how many solar panels does it take to produce 3.125kWh?

Solar panels are commercially available that can generate anywhere between less than 1Wh and 260Wh. If we assume that I wanted to buy a system based on 260Wh solar panels you would require about 12 x 260Wh solar panels (to produce 3.12kWh). You could get onto eBay and have a look at how much these size solar panels will cost (as well as other size solar panels too).

With a grid connected solar power system you need an appropriate generation capacity for your usage!

You can quickly see that it takes quite a lot of expensive solar panels to produce a large amount of solar electricity. You can also see that if a household has a 1kWh grid tied solar panel system installed at my longitude, yet they use 15kWh per day, then they are never going to cover their total electricity usage in any given year. At best, they will cover about a third of the annual electricity consumption. Not to get discouraged though as it is great that the particular household is doing something and it is to be respected, however it would be far better if that household could reduce it’s average daily electricity usage.

You may recall that if a household is not generating electricity through the installed solar panels, then any excess required is drawn from the electricity grid. In Australia this is a bit of a disaster because most electricity is generated from the burning of either black or brown coal and not only are they non renewable resources, they also produce huge quantities of carbon dioxide unless that household opts with their supplier for electricity sourced from renewable sources.

With an off-grid solar power system you need an appropriate generation capacity for your usage based on a worst case scenario!

With an off-grid (or standalone) solar power system, you have to have generating capacity based on a worst case scenario which is the available Winter sunlight. The reason for this is because if you continually use more energy than you generate, the off grid solar power system will eventually fail and you may even permanently damage the batteries.

Many off grid solar power systems try to get around this limitation by including other methods of generating electricity. These include: Wind turbine generators, hydro turbine generators, petrol and diesel generators, steam engine generators — and some may even have a battery charger connected to the electricity grid.

With a standalone system you need to be committed to being conscious about your levels of electricity consumption, rather than the typical mindless consumption of electricity by households that are connected to the electricity grid. I have had to change the way that I consume electricity, by understanding what appliances use large quantities of electricity and using them when I know the solar system is generating large amounts of power, rather than just when it’s convenient. Using solar makes you think about your energy usage and consider ways to to reduce it.

How does an off grid-solar power system align itself with the three permaculture ethics if the surplus electricity is not shared with the mainstream electricity grid?

The article Advanced Solar, and Independence, at PRI’s Zaytuna Farm received several comments, and the gist of one of them was "how can an off-grid solar power system comply with the three permaculture ethics?" I thought that this was a fair concern that required addressing.

The three permaculture ethics are People Care, Earth Care, and Return of Surplus to the first two ethics.

The concern of the commenter was really based on the third ethic, which focuses on the return of surplus — in this case surplus electricity for the benefit of both other people and the Earth.

The answer to this is that the system installed at PRI’s Zaytuna Farm is unlikely to have much surplus electricity. If you have a second look at the example above about covering average daily electricity usage and how many solar panels are required to do so, you will notice that it takes a very large solar power system to generate an average households electricity needs. In addition to this, with an off grid solar power system you have to change the way that you use electricity (ie: reduce and minimise your usage). This can be as simple as running the washing machine at noon rather than at night, or holding off a welding job until the next sunny day. It’s not dissimilar from obtaining your heating needs from a wood stove where you have to plan your fuel requirements years in advance as trees need to be planted and cut firewood needs to be seasoned for up to 2 years before use. Contrast this concept to simply switching on a 2,400 watt fan heater!

The other thing to consider is that in a rural situation the electricity grid may be 100s of metres away from your household. To connect up to the electricity grid via underground cables may cost upwards of AU$10,000 per 100 metres. The resources spent on achieving this may be better spent elsewhere.

Finally, disconnecting an inhabited property from the electricity grid has the benefit of making the electricity available to other households. If you’ve ever looked at a housing development, you’ll see lots of new houses being built and occupied. Well, each of those households will consume electricity, so over time electricity consumption rises, of course. What we are not doing as a society in Australia, is increasing our generating capacity in any meaningful way (and I am not advocating that we should do so). With rising electricity consumption and a finite supply, we end up in a situation where (in Australia) on hot days, sections of the electricity grid are shut off until the conditions creating the huge demand change.

What happens with an off-grid solar power system when the electricity grid fails and your household still has power?

Another commenter from the Advanced Solar, and Independence, at PRI’s Zaytuna Farm article suggested that if the electricity grid failed for a period of time and your household, having an off grid electricity system still had power, you may be in trouble. This is what I call the zombie argument. It’s a false argument, because I have been in this situation where the electricity grid has failed for just under a day and although I have good relations with the neighbours who are also lovely people and I had previously offered help in these circumstances, they did not take up the offer. They preferred to tough it out on their own.

In the next Article I’ll look at how solar panels operate in the real world.

Continue to read Part III


  1. – There is a reference to the average daily consumption of electricity for a US household as being 8,900 kilowatt-hours. Divide this amount by 365 days to get an average daily usage of 24.38kWh per day.
  2. – The site provides a calculator for Australian Solar Radiation Figures originally sourced from the Australian Solar Radiation Handbook, April 1995 (Energy Research and Development Corporation)
  3. You get an average of 4.815 hours of sunlight per day by adding summer peak sun hours 6.5 + winter peak sun hours 3.13 and dividing it by 2.


  1. Thanks for the article Chris.
    In June – July solar panels using sliver technology will be available to households through Origin Energy. These panels can produce up to 7 times more than the current ones. This means that it will able to produce more than 15kW per day. Thus if connected to the grid one can “return the surplus”.
    I am unaware of the cost of these panels. However I am holding off from going solar until sliver solar panels are available. As they will produce all my electricity needs and more. Thus really reducing my carbon emissions and hopefully that of others. And no more electricity bills – only cheques.
    For more information of sliver solar panels follow the link and then hit transform solar.

    The panels are produced in Australia (SA) which is another bonus (on various levels) as current panels are made in Germany or China.

  2. Another way to lower the cost is deciding what you can do without. We only use electricity for our netbooks, lighting, heating(on extremely cold days only), and power tool usage(sporadic). We have no air conditioning, refrigerator, microwave, or washing machine which are all HUGE energy hogs. It isn’t easy to go about getting rid of modern conveniences, but we found it was best to take it one step at a time.

  3. Incidentally, our own last electricity bill was fairly high, for exceptional reasons. Even so, we presently (3-person household) stand at about 4 kWh/day, which would translate to about 1500 kWh/year or so. A more normal present rate of electricity consumption for us is about half that value. (And we are bringing it down.) If I am on my own, I can very easily get by with 1 kWh/day with practically no impact on my lifestyle. I know one guy in the UK, in Nottingham, who became self sufficient in electricity with his family of four on 0.7 kWp of installed PV power (amorphous cells, as they do better in the often overcast conditions in the UK).

    I think average UK single person electricity consumption is somewhat above 3000 kWh/year, while a four person household of people most of the time not at home (at work/school) seems to have an electricity consumption of about 5500 kWh/year, which would translate to 15 kWh/day.

    Seriously… what the hell? I would actually have to try very very hard to use that much electricity, if I wanted to. What on earth are people doing with all that power?

  4. Hi all,

    Joshua – Thanks for the positive comment

    Fernanda – It’s great to see some local manufacturing of panels.

    Strongarmzz – You are spot on about the types of appliances that use lots of energy. It’s the refrigerator and pumps that kill my daily useage and they’re both pretty efficient. I’d be interested to see how you get by without a refrigerator, as people may forget that in the greater scheme of things they’re a reasonably new invention and there are plenty of ways to get around having one. Good work!

    Thomas – Top marks too! 4kWh per day is pretty good and to be commended for a family of 3. It’s great to hear about the guy on 0.7kWh per day too, what an achievement in this day and age. Unfortunately for me, the individual components in the off grid system use up around 0.5kWh per day by themselves, which I’ll talk about in a later article. Mind you, a basic off grid system doesn’t use anywhere near this amount of power and I’ll talk about this as well too. Much respect.

  5. Chris,

    Considering that 0.7 kWp installation, that’s Nigel Lowthrop’s private power system – he’s the director of Hill Holt Wood in UK.

    Here’s one article:

    There even was one in the Sun:

    Unfortunately, I can’t find the article in which I found a description of their power set-up. There are some interesting design aspects – for example, I think I remember Nigel told me they had put in cold cathode lighting a long time ago.

  6. Fernanda,

    “These panels can produce up to 7 times more than the current ones. This means that it will able to produce more than 15kW per day”

    Ultimately it’s the amount of panels x generating capacity x average generation in your area that will determine what’s appropriate for your situation. Whether or not the panel is type A that has a low generating capacity or type B that has a much higher generating capacity – the only difference is you’ll need more or less panels. Sometimes restricted (roof) space is an issue for people so this can be important.

    I think what you’re really hoping for here is that on a cost per Watt basis these panels are much cheaper – and lets hope it is :)

  7. I should point out two things:

    1.: In the present situation, it might be imprudent to focus too strongly on pie-in-the-sky tech which will not be produced in any relevant quantity for a number of years to come.

    2.: Having 1 kWp of installed PV power vs. having 0 kWp makes much more of a difference than 2 kWp vs. 1 kWp. And even if a “let’s put up PV that can cover average household consumption” is quite expensive, small systems are affordable and can make a lot of a difference.

    I find that William Kempp’s “Renewable Energy Handbook” is quite useful – it documents a number of installations with a wide range of price tags and capabilities that manages to give one a good idea about what is achievable at what cost.

  8. Becoming more common (or requested) are grid connect systems with battery backup – very important if you are connected and can’t live with/work without power. This is usually suitable for those with regular brown/black outs.

    Strictly From a financial point of view, as prices of electricity increase we’re seeing more customers interested in running their daytime use from batteries whilst exporting their solar (for those with feed-in tariffs) and charging them at night when “mains” prices are lower.

    Having said that I still advocate going off-grid when feasible.

    @ Fernanda – don’t hold your breath. I’ve been in the solar industry for 11 years and for the last 8 Origin have been spruiking their Sliver cells and on numerous occaisions they have come out saying that the product will be available soon. The theory is great, the commercialisation has been a problem due to the intricacies of sliver cells – meanwhile they have taken millions from the Australian government and unfortunately all of us for a ride.

  9. Hi all,

    Thomas – Thanks for the link. The Hill Holt Wood is an impressive venture with positive community outcomes. I’m not sure that my lady could do 10 years in a caravan though! We rented for 2 years in a outer suburban housing development whilst we built this place here and it was hard enough after having lived in eco friendly low energy requiring houses for years before that. To his credit too he used some very eco friendly tech, we’ve done exactly the same, but are a bit more high tech. Thanks again, I’m often humbled when I see the works of others.

    Jason – I’m a bit dubious too about claims relating to increased energy output when comparing one type of solar panel to another. I’m going to cover this very issue in part 3. Good point, it would be nice to see cheaper solar panels on the market.

    Thomas – Again you are correct, in that doing something is much better than doing nothing. I keep coming back to the point that reducing your (by this I mean everybody) energy use is the most effective thing that you can do.

  10. Hi all,

    Haydn – It would be a good situation for the batteries to be able to be regularly charged from the grid too as it would extend their life considerably. Do they run a separate inverter to send power to the grid as well as power the household, or is it simply a battery charger hooked up to the grid?

  11. Hi Guys,

    In my own situation described better in this link,, I have a smal pv panel of up 375 Watt/h mounted on a smal tracker which is connected to a MPPT solar charge regulator to a battery bank of 840 Amps/h and an inverter of up to 1200 watts nominal usage, to drive up to a washing machine.(in this case the resistor for heating the water was removed and the machine is filled with hot water from the sun. So a two inlet washing machine for both cool and hot water is a good aproach)
    All gear which is resistive like, toasters, hair dryers and stuff like that which are driven on a Reistence to produce heat or alike ara BANNED from my system. This way the system is able to produce all the energy required for a house that normally powers up, a small refrigerator class A+, CFL lights bulbes, up to two computers daily, a (3/4 hp) 750 watt water poump and all sorts of power tools if required.
    Worse case scaenario is winter time to my location 38º North. Rarely my battery bank goes down do under 80% charge and actually I do not impose any more restrictions than those refered.
    Hope to give a help to this article readers.

    Good decisions are based on two things: learn how to spend less energy by changing the way you do stuff and buy stuff considering the best ratio Price/Performance having in mind an island of power.

  12. You’ve mixed kW and kWh up all through this article. It’s not hard to get right: kW is like speed, kWh is like distance. You would not say Sydney is 100km/hour from Nimbin, nor would you say I drove at 100km down the freeway.

  13. Thanks mate – this is gold for people in my situation and i am passing it round to others – appreciate the insight into your experience.

    John Banks – get over yourself.

  14. Hi all,

    Jorge – I agree with you totally about the resistive loads, anything that heats or cools sucks tons of power. I haven’t been able to convince my partner about the hairdryer yet… How do you run a refrigerator, if you have one at all? There are plenty of ways around not using a refrigerator and it would make for interesting reading. Top work on the system too.

    John – Fair enough. I’m more of a generalist than a tech head so if my incorrect useage of terminology offends then I apologise. It hasn’t stopped me specifying and wiring up my own system though…

    Denis – Thanks I really appreciate your comments. I hope you enjoy the photo’s in part 3.



  15. Chris,
    I normally wouldn’t jump in and be picky, but your readers are here because they want to learn about domestic solar power systems. If your goal is to make such a system more accessible to more people, rather than confuse them even further, then – please – use the correct units of measure. I think the calculations are baffling to people only because of the prevalence of explanations in which the writer has not taken care to use the correct terminology and units. Once it’s explained properly most people find it really easy.

    So, I’m with John Banks – It’s *important*. Please use the correct language. You’re writing about something which can help someone to escape being dependent on others. Please make it as easy as you can.

    ‘kWh’ (and Joules) is a measure of an *amount* of energy, like the petrol sitting in your car’s tank.
    ‘kW’ (and Joules per second) is a measure of a *rate* of energy use, like how fast your car’s engine converts that petrol into acceleration.

    Solar panels deliver a certain peak *rate* in full sunlight, measured in kW.
    Over the course of a day, a system can produce a given *amount* of energy, measured in kWh. That’s kilowatts multiplied by hours.

    I want to read your series of articles, as it seems very interesting, but I keep wanting to stomp off. :-)

    I’m not trying to be mean. Please help people to understand!

  16. Hi Matt L,

    Dude, you need to relax. I am not an electrician or a physicist but rather a dedicated and interested amateur who specified, obtained and installed the system myself. If I get some terminology incorrect, who cares. I am trying to pass on some of the bigger picture ideas so that people can have a bash themselves.

    The whole terminonolgy thing is a pretty minor gripe in the big scheme of things, and I suspect people are raising this issue to bignote themselves, however, it also has the effect of detracting from the big picture. Please try to focus on the big picture rather than worrying about small details.

    In addition to this, mentioning joules as a unit of energy is a waste of time because most people can’t even imagine what a joule is. I certainly have no idea and don’t intend to find out, it is at best an irrelevance.



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