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A Solar Powered Life – Part III

When the band Bananarama penned the ditty, “A cruel summer” back in 1983, I’m sure they must have been singing about solar power. Well, upon reflection, they probably weren’t. Anyway, it is an appropriate metaphor for solar power generation in the Macedon Ranges in Victoria and indeed elsewhere across the country for this summer given the La Nina influence on our weather. In the article A Solar Powered Life – part II, I wrote about how many solar panels you would need in order to generate your average electricity requirements. These were all based on a best case scenario which is rarely achieved in the real world. Not to fear though, as solar power has plenty to offer people even in less than perfect conditions.

Solar panels are affected by all sorts of factors in the real world. Usually, anything that affects the performance of a solar panel will tend to reduce its electrical output, so it’s worth understanding these factors so that you can set-up your solar panels so that they provide the best possible output.

There are various things that affect the output of solar panels and they include:

  • Heat. Generally, as the air temperature increases the electrical output of solar panels decreases. At an air temperature over 25 degrees Celsius, you’ll find that the electrical output begins to decrease. By around 30 degrees Celsius I’ve noticed electrical output can drop by around 15%, and by 35 degrees Celsius it can be reduced by as much as 33%. It’s worth noting that some types of solar panels are better adapted to warmer environments than others (for example the type of solar panels installed at Zaytuna Farm). People tend to confuse the optimal conditions for electricity generation with that of the production of solar hot water where you require the heat from the sun to warm the water. Solar panels simply require strong direct sunlight, without the heat.
  • Shading. Any shading across a solar panel will reduce its electrical output. Sunlight is a diffuse form of energy and the trees are also competing with your solar panels for the same available sunlight. If you have large trees shading the area where you are considering installing a solar panel array, then it’s probably worth installing the solar panels in a less shaded area. There are panels that perform slightly better in shaded conditions, however no solar panel will produce maximum output without strong direct sunlight available across the entire solar panel. A solar panel in shade will probably only produce about 15% of its rated output.
  • Available sunlight, summer versus winter. In the previous article I explained that where you are located on the planet will affect how much peak sunlight you receive over summer and winter. I’m at 37 ½ degrees latitude south (for the technically minded) so receive 6.5 hours of peak sunlight over summer and 3.13 hours of peak sunlight over winter. As you move closer to the equator, the difference between available summer and winter peak sunlight will be less, although it will also become much hotter.
  • The optimal angle of solar panels differs between summer and winter. For solar panels to receive the greatest amount of sunlight possible at any time of the year, then they need to directly face the sun. As previously mentioned, over winter the sun is low in the sky. For the solar panels to directly face the sun, you can imagine that they’d need to be on quite a steep angle which can sometimes be close to vertical. Over summer, with the sun high overhead you need to have the solar panels angled more or less flat to receive the greatest amount of sunlight. In the real world, you can achieve an average (between vertical in winter and horizontal in summer) by angling the solar panels at the same angle as the latitude of your house. This is a general rule applied to most well installed fixed solar panel installations. I’m at 37 ½ degrees latitude south, so the panels themselves are mounted at about a 37 ½ degree angle from horizontal. Fortunately for me, the angle of the roof of my house roughly matches this. You never really get the maximum electrical output, but it’s a good compromise for both winter and summer.
  • Trackers. With some installations, where the budget exceeds my meagre resources, people install their solar panels with a solar tracker, rather than just at a fixed angle. A solar tracker is usually a pole mounted in the ground with a frame at the top of the pole which can hold a number of solar panels. The wonderful thing is that the frame can change angles and directions so that it can always face the sun at the best possible angle. The adjustment can be either manual or for the really well resourced, automatic. These tracker systems are the single most effective thing you can do to increase the electrical output of your solar power system. The tracker system can increase output by approximately 20% to 30%.
  • Panels facing towards the equator are preferable in fixed installations. Most fixed solar panels face roughly north in the southern hemisphere or south if you’re in the northern hemisphere. The reason for this is that the sun rises in the east and sets in the west, so a panel facing towards the equator will on average face the sun for the longest amount of time each day of the year. If a solar panel is facing slightly north west (or south west in the northern hemisphere) output won’t be noticeably reduced. If you live on an easterly facing sloping block, you’ll probably find that you have predominantly morning sun. If on the other hand, you live on a westerly facing block, you’ll probably find that you have predominantly afternoon sun. As a general rule west facing slopes tend to receive more sunlight than easterly facing slopes so they are more suitable for the generation of solar power.
  • Maximum output is usually around the summer equinox. In the southern hemisphere the summer equinox is usually around the 21st December. The summer equinox is literally the day of the year with the longest available sunlight. What a lovely Christmas present for those in the southern hemisphere who have warm to hot Christmases, in that you also receive the maximum output from your solar power system! The simple reason for this is that the sun is high overhead and in the sky for a longer number of hours than at other times of the year, both of which increase the amount of electricity generated.
  • The cloud edge effect can be quite substantial. The cloud edge effect is where the sky is predominantly sunny with some dispersed clouds. What happens is that the sunlight literally bounces off the edge of the clouds so that you can receive more than the normal quantity of sunlight on the face of your solar panel. I’ve seen around the summer equinox and on a cool, partly cloudy day, that electrical output can exceed the rated output of the solar power system. I’ve also had anecdotal evidence of this effect from other people with solar power systems.
  • Rain has a greater effect than cloudy days. Rainy days tend to also be days where the cloud layer is quite dense and relative humidity is quite high. This heavy cloud has the effect of reducing the available sunlight. A rainy, cloudy or misty day can reduce output to about 15% of the rated capacity of the system. Generally, days with a higher layer of cloud can reduce the output to about 40% of the rated capacity of the system.

In A Solar Powered Life – part II I wrote about a 260Wh solar panel and how it related to the electricity requirements in a household. How do the above factors affect that 260Wh solar panel?

It means that you will only ever generate 260Wh on a cool partly cloudy day around the middle of summer, and only then if that solar panel is exactly facing the sun! For the remaining part of the year in different conditions, it will be less than this.

What type of panel should I buy?

There are different types of solar panels commercially available, made of differing materials. If you look at some sales blurbs for solar panels they may include specifications like: advanced mono-crystalline, polycrystalline, thin film, flexible, HIT etc. These different materials and technologies may mean that some panels may be more efficient or better constructed than other panels, or perform slightly better under certain conditions, but they all ultimately perform the same function. All solar panels take light from the sun and then output electrical energy which we can then use. It’s that simple.

I run two separate solar power systems at my house, one based on mono-crystalline and the other on polycrystalline solar panels and they both perform equally well. The differences aren’t as great as you may be lead to believe, so I am very dubious of claims of massively increased outputs from a particular panel relative to other types of solar panels. It is also worth noting that under laboratory conditions with exotic materials very high conversions of sunlight to electricity have been achieved, but these are not commercially available.

For my house, I have a system that is rated to generate 1.44kWh. It includes 8 x 180Wh mono-crystalline solar panels of dubious parentage (ie. no name brand). The solar panels are fixed at an appropriate angle for the latitude and they face approximately north-north-west which is quite acceptable. I’m also surrounded by quite tall trees but with no over shadowing on a westerly sloping block. I’m pretty happy with the system and can’t afford to increase or optimise it’s performance.

Getting back to Bananarama though (or was it La Nina?) the system has been challenged by excessive rainfall in recent times. Over January and February this year (2011) I received about 437.2mm (about 17 inches). In the previous calendar year (2010) I received in total a record breaking 1,420mm (about 56 inches) of rainfall spread throughout the year (rainfall has been recorded in this area from about 1870 onwards). All of this intense weather means that what buffer I had between my usage and my generation capacity has been tested at times.

So, you can get an idea of the current end of summer / early autumn sky conditions and how they affect the output of the solar power system, below you’ll see photo’s which are representative of each day this week and the respective power output per day of the system (remember that the maximum potential output.

Sunday 27th February – Output 0.6kWh

Monday 28th February – Output 0.84kWh

Tuesday 1st March – Output 3.6kWh

Wednesday 2nd March – Output 5.2kWh

Thursday 3rd March – Output 3.6kWh

Friday 4th March – Output 2.3kWh

Saturday 5th March – Output 6.1kWh

Total Output from the solar panels for the week is 22.24kWh (or an average of 3.18kWh). I use about 2.9kWh per day and the system itself uses about 0.4kWh per day so have had to draw on the batteries to be able to sustain my usage

In part 2, I wrote about the differences between a grid tied solar power system and an off grid solar power system, but it’s useful reiterating those differences again. Aside from the technology and cost differences, the main difference is where a household obtains their electricity from when the renewable energy sources are not generating power. With a grid tied system, the excess requirements comes the electricity grid and with an off grid system, it comes from a battery (or other source) connected to the system.

In the next article I’ll look at batteries and how they perform in the real world.

Continue on to read Part IV


  1. Thanks for sharing more info Chris.

    One of the beautiful things about solar power is it has no moving parts, therefore regular maintenance is kept to cleaning the glass as needed. Once a tracker is introduced, regular monitoring, maintenance and oiling of the tracker is required to ensure smooth tracking.

    Also, depending on the tracker technology used, trackers are notorious for either chasing the wrong sun (ie, bright clouds) and resetting back to start (east) when the sun goes behind a dark enough cloud. If you are getting a tracker, make sure it uses a GPS or timer to follow the sun.

    For similar costs as a tracker, spend the money on another panel or two for the same output of power.

    Despite what I have said above, trackers are useful for solar pumping where you need to get as much water as possible. In this situation trackers can start the pump earlier in the morning and run a little longer in the evening. They are also used in commercial grid tied systems where the benefits will outweigh the cost.

  2. Thank you very much. Your pictorial diary is a wonderful way to show and tell the realities of solar. It will help simplify ones calculation needs for us less solar knowledgeable.
    You state: All of this intense weather means that what buffer I had between my usage and my generation capacity has been tested at times.
    So I gather that you do not have a generator automatically starting a battery ‘top up’? So running a vacuum cleaner and washing machine when there is least capacity in the batteries could damage them. Large farms without grid connection always have large generators; meaning diesel costs and noise. As some added Solar PV systems there was a learning curve. Hence The Land country newspaper published; that stand alone solar power systems meant that the generator only runs half the time. As apposed to farms running generators for 100% of the time.
    So if the system is enlarged (without generator back up) to cope with the ‘least capacity’ period, there will be much over capacity at other times. Hence some have a large array of lights to dump the energy…
    Rather like the coal power stations world wide will ‘dump’ the excess energy into the cooling lakes when folks do the Earth Hour!!!!!
    For me personally the generator backup seems the compromise, the next step is to use biogas as the fuel.
    People starting with Solar PV will get used to checking the readings on the Inverter Screen to judge the systems capacity for that day. So the washing machine and welder can be used during that day.
    It is a strange feeling of elation to use power tools, welders and white goods knowing the no coal was hurt in the exercise…..

  3. Pietro – Thanks

    Haydn – I reckon you are spot on about the tracker as it’s just another thing to go wrong in an already complex arrangement. Although if they’re setup right, they really do earn their keep. The same thing can be said about pumps as I have 3 separate (and different) pumps in the house and it’s only a matter of time before one of them packs it in – probably at the worst possible moment too!

    Louise – Thanks for mentioning the photo’s. It’s amazing how a bit of blue sky makes all the difference and the photo’s say it all.

  4. Hi all,

    Coevicman – Thanks for the comments. You’ve hit on the topic of batteries which I’ll cover in part 4. I do have a petrol powered battery charger (generator), but have only ever used it twice for a couple of hours. Each time was a waste of time too, because after an hour or two with the charger running, the clouds broke and the sun came out! I’m starting to think that maybe the charger is actually a magic sun generator! I had a week a while back where it rained solidly for 5 days (250mm in total). Stay tuned for part 4 and all will be explained. Good question.

    Oyvind – Thanks for the links and I always appreciate your thoughtful comments on articles. Fossil Fuel addiction is a bit of a disaster. I’m all for swapping over to renewable sources and have put my own money where my mouth is. The problem with solar though stands out in the photo’s above. I have to manage my energy consumption so that it is in sync with my energy generation exactly as you would in a vegie garden. As a contrast to this, people have become accustomed to energy on demand. If you look at the Tesla roadster on page 8 of the link, you could see that my system wouldn’t even be able to provide enough energy to run the car for 100km in a day – let alone daily on a guaranteed basis. People are also getting energy quite cheaply at the moment and are really reluctant to commit their own funds or their countries funds into installing the necessary infrastructure required to switch over to a renewable energy future. I’m not sure whether you are aware of the rhetoric going on in Australia at the moment about putting a price on Carbon. People understand instinctively that something needs to be done, but only as long as someone else pays for it. I like Permaculture, because it puts in place infrastructure which is resilient, diverse and long term. My grandfather who has now passed said to me when I was too young to appreciate the sentiment, “Only those that look ahead, get ahead”.



  5. Hi Oyvind,

    Sorry mate. My experience doesn’t extend that far north or south. I’d imagine you have special conditions because you just wouldn’t get much in the way of winter sun, so the 45 degrees is an obvious compromise between the short days of autumn and spring and the very long days that you would have over summer. As you move further south or north from the equator, solar has less to offer you over the winter period. In these conditions, it would be difficult to provide a base load power supply. In part 2 you can see that even at 37 degrees south, I receive only 3.13 hours of peak sun per day.

    In these conditions, wind, tidal, hydro (if not frozen) and wood provide more reliable energy generation opportunities. Personally I’d favour a wood lot as you are capturing the summer suns energy with simple methods for later useage in less favourable conditions – kind of like preserving fruit and veg, but with energy. I’d reckon for a small population, it would be the most sustainable resource.



  6. I am wondering if anyone has any information regarding how to solar-storm proof a solar powered electrical system? Electromagnetic radiation from solar flares will disrupt all electrical boards. Does anyone have a solar system that is solar storm ready?

  7. Hi Claire,

    I can answer this question, but can you firstly tell me more about your solar power system?



  8. Hi Chris, you are right, solar cells are only reliable here about half the year. But in the book I referred to above, which now also is published in English, see: , they describe how you can apply a stirling engine to your wood fire stove to support you with electrisity during winter time. Also Sweeden is the leading country in sterling engine technology, from my knowledge. So if you have an energy forest you can get yourself off-grid also here, using solar cells during summer time and the sterling engine during winter time.

    This book was the third book I read about building biology after I started my searching for a new way of living, and it also has a chapter about permaculture, which actually was my very first introduction to permaculture. This year it will even be published in Chinese. I recommend this book for everyone, and especially for those living far North, as it is based on the climate conditions of Sweden.

  9. Solar system: 8 or 10 PV panels, 190 watts each. Have bank of 6V lead acid batteries to make up a 1000 AH at 24 volts. outback solar controller. twin outback inverters pack total of 5000 watts turning power into 240 volts at 50 hertz. that’s the general idea.

  10. Hi Oyvind, I totally agree with you. Using a stirling engine to produce electricity is quite a good and sustainable idea in your climate. You just have to grow your own wood lot, use coppicing techniques and get quite a few leguminous trees in amoungst the wood lot to fix some much needed nitrogen in there as well – slash them for mulch or just leave them do their thing. I’ve just grown some tagaste plants from seed and will incorporate them around the chook run and orchard. Around here I also plant blackwoods (acacia melanoxylon which are a long lived, very hardy, shade giving wattle. They’re quick growing and great for firewood too.



  11. Hi Oyvind,

    Don’t stress! If you can’t find any suitable leguminous trees for your area, have a look at suitable understorey species or shrubs, even ground cover plants. All of them will contribute something. If you’re unsure have a look at an older less disturbed patch of forest near where you live and look at the support plants for the over storey and then use them. Observe what works with other peoples wood lots too. Failing that, try building up the humus in the soil through mulch which should encourage a more fungal dominated environment which will accelerate the growth in your wood lot.



  12. Hi Claire,

    Thanks for the specifications. As a general note, the twin inverters are at the higher end of their ability to suck power from your batteries than your actual battery capacity. I assume out of interest that you would have to be pretty careful at night not to draw huge loads from the batteries? I’m covering this issue in part 4 which is under production now (much re-writing is required for such a complex subject to ensure that it is accessible), so you may find it to be interesting reading.

    As to your solar flare question though, the simple answer is: unless your entire system is under ground or in a shielded environment then you’re pretty stuffed. You’ll find that the cells in the panels will be OK, but at 190W each they’ll have diodes in them somewhere which will get fried. As to your regulator and inverter, well they’ll make an interesting sculpture in the garden perhaps? Seriously though, I know that you can buy plaster which has a lining in it which resists radiation, although I’m not sure of the actual spectrum of a solar flare. This is what they use in radiology rooms. You can buy it through commercial suppliers/distributors of plaster. Although I’m not sure how you’ll save the panels themselves which by their nature have to be exposed to the elements. Such an event anyway would bring us all back to an agrarian civilisation status pretty quickly and fry all of the electronics in your immediate area so having electricity wouldn’t be much good.

    Hope this answers your question. Regards


  13. Hi Kurt,

    Thanks. Brisbane would be awesome for the production of solar power as you get a lot more peak sun hours.



  14. Hi Chris,
    thanks for pointing to your site on some Report I happen to be following too ;-)
    I find the practical experience you are implementing very interesting, to say the least.

    Thanks also to Claire for asking the question of the impact of solar flares on PV cells. This is a question that I haven’t been thinking about before, but that prompted me to review some literature. Here is a summary of what I gathered, in case it could prove of interest to some of you. The two main points I found are

    1) The *direct* impact of cosmic rays on PV cells on the ground is small/negligible. Based on a paper studying the impact of cosmic rays on PV cells where they to be used on the moon (, a bit technical), we see that the main direct impact of cosmic rays on PV cells is to decrease slowly their efficiency. In other words, cosmic rays make PV cells age faster. Considering how slow this aging is on the Moon, PV cells on the ground have other aging effects (like temperature aging) to worry about even during large solar flares.

    2) There is an impact of large cosmic flares on the electric grid, but this is a *large scale* effect. Electric lines acting like antennas can catch up very high voltages. Similarly, a grid being grounded on very distant locations on Earth will pick up grounding voltages differences that can be very large. Those large voltages in turn create large currents in the grid that can damage it. Because of it’s scale an off grid house is quite save w.r.t these problems. Moreover, a system on lead batteries is usually *not* grounded: it works between the + and the – of the lead batteries, without a connection to the ground. In this case the PV electric system is shielded from those large grid currents that a large solar flare could create.

    Finally, note that the frequency of such flares is quite rare, and that their threat comes from the fact that our whole economy is based on lots of critical inter-connection on a global scale. But this is a much broader subject…

    Have a nice day
    Sebzefrog at hotmail dot fr

    PS: pointers to interesting articles about those large scale currents:

    Good explanation:

    Good explanation, more technical:

    A broader view of the problems caused by large solar flares on our interconnected society:

    The largest solar flare of the 2 last centuries:

  15. Hi, I’m a high school student and my research is on about developing a Solar Energy System for our school building.

    And I want to know HOW DO YOU MEASURE THE POWER OUTPUTS AT DIFFERENT WEATHER CONDITIONS? I mean Power = Voltage x Current isn’t enough, right? Can you please tell me the step-by-step process. I really need to know the method asap so we can start on our preliminary work.

    Thankyou so much!

  16. Hi Len,

    Well done.

    For the weather conditions, I have a small weather station.

    For the solar power system, I have a meter which records:
    – Battery Voltage current (as well as minimum and maximum in a 24 hour period)
    – The current Amps generated at this point in time (as well as the total amp – hours generated in a 24 hour period)
    – The current Amps being used at this point in time (as well as the total amp – hours used in a 24 hour period)
    – The % state of charge of the batteries (ie. how full are they like a cars petrol gauge, but more accurate)
    – The temperature of the batteries at that point in time (ie. as the batteries get cooler they need to be charged at higher voltages, than when they are warmer)
    – The voltage that the solar panels are generating at a point in time (this always needs to be higher than the batteries so the electrons flow towards the batteries)

    Hope that helps, it is interesting stuff!


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