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A detailed overview of Solar Power Applications

Solar electricity can be used in virtually any application where electricity is required, from powering watch batteries to running entire cities. However, because solar electricity is generated only when the sun shines it is typically either stored in batteries or used to supplement other forms of electricity, such as grid power or generator power.

The way these different solar electricity applications operate and the way solar electricity performs are described below.

Solar generation performance

Excellent data is available which enable us to predict how much solar irradiation will be available throughout the year across the entire planet and thus, predicting what you can power is simply a matter of matching the predicted available energy to the load.

By using good data and taking into account location, seasons and geography we can predict with great certainty the average annual energy that will be produced, although the day to day levels may vary slightly. From year to year there is some variation but generally sunlight intensity and therefore annual energy production is relatively predictable.

A number of factors can affect how much energy your solar system will generate.We have separated these into primary effects (the things that make a big difference) and secondary effects (the things that make a smaller difference). These include the following:

Primary effects on generation

  1. Ratings
  2. Location
  3. Season
  4. Time of Day
  5. Shading

Secondary effects on generation

  1. Angle & Orientation
  2. Annual variation
  3. Product and system efficiency
  4. Air flow
  5. Dirt build up

However, we can use some averages to give you a good idea of what to expect.

Ratings

An important thing to remember is that whilst we can accurately predict how much energy a solar system will generate, solar panels are rated under a set of very specific and Internationally standardised set of conditions for the purposes of uniformity.

For example, 1000 Watts of solar panels will only generate 1000 Watts at what is referred to as Standard Test Conditions (STC). STC’s are used by all manufacturers to rate their panels and are equivalent to 1000W m2 of solar radiation, an Air Mass Density of 1.5 and 25 degress Celsius. However, in reality you will rarely see a 1000 Watt solar array generating 1000 Watts.

Although this might appear misleading it is not intended that way. These standards were developed to reflect typical manufacturing equipment and testing conditions– much like the way motor car engines have a maximum power rating but only deliver maximum power under certain conditions.

The important thing to remember here is that it is energy generated over an average day that counts, and this takes into account de-ratings for real world conditions.

Location

In Australia, across the year you will generate on average 3.9 ~4.17kWh per day for every 1kW of solar you install (assuming average weather conditions and ideal mounting). Of course, where you live will influence how much energy is available because some locations are sunnier and clearer on average, than others.

Depending on your latitude, a different amount of energy will be available because your location effect’s how perpendicular the sun is and also, how much atmosphere the sunlight needs to travel through to reach you. Australia happens to have one of the best latitudes in the world for solar energy.

A secondary effect of location is local geography, which can affect how much cloud cover or smog is typical. Although solar panels still produce electricity in cloudy or smoggy conditions, the clearer the sky the better the energy production will be. As a rule of thumb, on a really cloudy day a solar system will produce around 20% of the energy it would produce under ideal conditions.

The following graph shows how much energy you will generate on average, each day, in various locations according to Clean Energy Council design data.

Average kWh per day per kW installed

Seasons

Average monthly kWh/kW

Average annual generation is a good guide to how much energy you can expect in total each year but of course, this varies with the seasons too. During the changing seasons the earth rotates on its axis changing the perpendicularity of the sun and thus the intensity of the energy reaching us. Logically, generation is strongest in summer and weakest in winter and this will affect the performance of solar systems.

Cloud, heavy smog and rain will reduce your energy generation, although it is important to note that average generation predictions take these weather impacts into account. On a really cloudy day you should expect around an 80% drop in the amount of energy you will generate.

The following graph shows how the generation of energy varies each month on a typical 1kW system in Adelaide which is a good representation of National average conditions. Note of course that this does vary by location.

Time of day

Intuitively, as the strength and angle of the sun varies throughout the day, so too does the strength of the sun and this affects the amount of solar energy you will generate. Days are longer in summer and shorter in winter and correspondingly, the available “window” of generation changes with the seasons.

A sample of 5 different system sizes and how their energy generation varies throughout the day based on data from real customers in NSW is provided in the graph below to illustrate how generation changes throughout a typical day.

Shading

In the simplest of terms simple terms,solar panels need to be in the sun to generate electricity so any shading will reduce their output. Although some shading does not rule out the use of solar power, the effects can be significant and therefore having a shading analysis done before you buy is a good idea if the area where you will install your panels is affected by shading. The impact of shading varies by season too, as shadows get longer and can affect larger areas in the winter months.

Minor effects such as shading in the early morning or late afternoon have a much smaller impact. However, large trees, chimneys or neighbouring buildings can have a very significant impact and should be carefully analysed to ensure that an accurate assessment is made.

It is also important to understand that because of the way most solar systems are connected together, shading on (for example) one or two solar panels can impact on the output of your entire system – the effect is something like standing on a garden hose in terms of energy flow.

A good solar installer will be able to provide a shading analysis using a variety of tools, devices and models, will be able to provide an accurate assessment of whether shading will have a minor or a major impact.

Angle and Orientation

Solar panels generate the most energy when they are perfectly perpendicular to the sun, which varies throughout the year as the sun’s position in the sky moves with the seasons.

However, as a general rule, most solar systems are installed at an angle roughly equal to your latitude which produces an excellent annual average amount of energy. It also happens to match the angle of most Australian roofs which is between 20 and 30 degrees.

Most solar system owners also prefer the look of solar arrays when they are installed parallel to the roof structure and it helps to keep mounting costs down by reducing the wind loading. As a general rule, a roof angle of plus or minus 10% from the ideal angle will have a negligible effect and is widely acceptable.

Angles of less than 10 degrees are likely to create additional cleaning requirements as water will tend to pool more and collect dust and mould more readily.

The orientation of your solar panels (ie North, East, West or South) is important too. The sun travels through the Northern sky in Australia and hence, facing your solar array due North is the ideal situation. Once again however, small variations of plus or minus 10% in either direction has a negligible effect and are widely acceptable.

Less than optimal angles or orientation are increasingly common, and particularly so where angling solar panels might (for example) avoid shading or maximise your energy production in the afternoon when electricity prices are highest. The key here is to ensure that your solar designer has calculated the impact on energy production and financial returns and accurately taken into account the loss of energy production versus any positive benefits.

One important point to note is that unless you are using micro inverters, all the solar panels in your solar array should be at the same angle and orientation.

The following diagram provides an indication of the impacts of angle and orientation on annual energy generation in Australia.

Angle and orientation of solar panels

Annual variations

Annual variation

Solar radiation data is based on historical measurement of the suns strength hitting measurement stations around the world.

This data is the basis for all solar design and is generally accurate and in most cases, solar designers apply a conservative estimate taking into account the potential for variation.

However, it is worth noting that some years will inevitably produce slightly above and or below the expected annual average amount of solar radiation.

It is not possible to predict what variation may exist in advance and by using long term averages we can get very close but it is important to understand that your solar system may generate slightly more or slightly less each year based on actual levels.

The graph below demonstrates the historical variations in solar radiation in Adelaide for the last twenty two years as an example. It demonstrates that annual radiation has varied by as much as 16% above and 12% below the long term mean radiation over the period.

Product and system efficiencies

Assuming that all other factors are equal, the efficiency of the individual products and combined losses that accumulate when they are connected together becomes a factor.

The efficiency of a solar panel (ie how many Watts it will produce per square meter) predominantly affects how much energy you will produce in a given area.

However, like virtually all manufactured products solar panels made in high volume are rated on a test machine and have a tolerance applied to their expected power. For example, a 250 Watt solar panel with a + or – 5% power tolerance will actually deliver somewhere between 240 Watts and 260 Watts depending on the particular solar panel your get. Some manufacturers specify “positive tolerances” so you are assured of a minimum power rating for example -0%, +5% power tolerance.

Inverters also have efficiency ratings, which in their case describes what percentage of the energy fed in from the solar panels is lost in converting it to from DC to AC. Most quality inverters are around 96%-98% efficient so a minimal amount is lost but without doubt, a more efficient inverter will produce more energy for you.

However it’s also important to consider other factors when it comes to inverters such as their ability to cope well with heat, their flexibility to accept a wide range of voltages from your solar panels and their ability to connect and stay connected to the grid under varying conditions. A good general rule with inverters is to consider them like any other fairly sophisticated electronic device - you generally get what you pay for.

Beyond these two main factors there are standards which apply to the losses in cabling and the types of safety and disconnection devices which you must have in place. Generally, cabling is sized so that no more than 5% of the maximum energy being generated is lost in the cables.  A good rule of thumb is to look for quality workmanship and to remember that saving a couple of dollars by sacrificing cable and safety devices is rarely worthwhile in the long term.

Air flow

Contrary to intuition, solar panels produce more energy when they are cooler. Therefore, ensuring that your solar mounting system allows a good flow of cooling air will assist in optimising their energy production.

Dirt build up

Much like shading from other obstructions, anything, including dirt, bird droppings or mould that builds up can shade your solar panels and this will reduce your output.

As a general rule, solar modules installed at greater than 10 degrees angle will tend to self-clean with average rainfall in Australia so little maintenance is required. However, the cleaner they are the better. Typically, installers recommend that solar panels are cleaned each time you clean your gutters which is generally recommended once a year. Some solar installers offer maintenance services where they come and check the electrical connections and clean the solar panels on a periodic basis.

On Grid

The most common use for solar electricity today is called On Grid: where solar electricity is connected to an existing grid power supply. This use for solar electricity is extremely popular because instead of using batteries for storage, electricity is imported and exported to the grid as generation and demand varies. This helps reduce the cost and complexity of solar systems.

On Grid solar systems use sophisticated electronics (called inverters) to convert the electricity produced by solar panels to the same voltage and frequency as grid power and to synchronise the systems together. Advanced safety devices are also included which allow solar systems to be isolated automatically if the grid is shut down for safety or maintenance purposes.

On Grid systems constantly monitor the voltage and frequency of the grid and specific standards exist to ensure that solar systems comply with this in Australia and around the world. This is one reason why choosing a high quality inverter is important. Lower quality inverters may suffer annoying “trip-outs” if the grid power is varying but higher quality units are better able to cope with fluctuations and keep you connected.

One implication of this type of system is that if there is a grid blackout, your solar system will not be able to supply your home with electricity, despite the fact that the solar panels may still be generating energy, unless you have an On Grid Support system.

On Grid Support

Although not widely used, On Grid Support systems are gaining popularity. They are a combination of an On Grid system, some more sophisticated electronic control equipment and storage, typically in the form of batteries.

The main feature of these systems is that in the event of a blackout or poor grid power quality, an On Grid support system can disconnect your home from the grid, then reactivate your solar system to provide power to your home without compromising the safety of grid workers. Such systems will automatically combine solar energy being generated from the solar panels and energy stored in batteries and provides energy to dedicated circuits within the home, in a similar way to Uninterruptible Power Supplies that are used on computers or other equipment.

Off Grid

Off Grid systems are used where grid power is unavailable such as remote farms or homes, telecommunications sites, water pumping or other remote industrial facilities. Off Grid systems need to be very carefully designed to match energy generation to energy demand and require a detailed energy audit and site specific assessment to work effectively.

Off Grid systems use batteries to store solar energy so it is available to be used 24 hours a day and often include a back-up generator for unusually high energy demands or long periods of low solar irradiation. It is possible to such systems without a back-up generator but great care must be taken to ensure the energy demand is matched very carefully to the amount of energy stored in your batteries, both of which will vary throughout the year.

Off Grid power has been used to great success around the world and has been particularly useful in Australia. Telstra was one of the early users of solar power in Australia using it for remote repeaters in place of generators with enormous success; thousands of systems have been deployed across Australia stretching right back to the mid 1970’s and the excellent reliability of Australia’s telephone system is even today, reliant on solar electricity.

Many remote homesteads, farms and industrial sites also use solar electricity in Australia as a cost effective and highly reliable alternative to diesel generation for household electricity, water pumping and agricultural uses. Solar electricity can significantly reduce the difficulties associated with getting fuel, maintaining complex generators and are virtually silent.

Off Grid solar systems are used in a huge variety of applications and are often life changing experiences for people in areas where little or no electricity was previously available. Millions of people around the world still have no access to electricity and rely on kerosene lanterns or candles for light which are dangerous and can cause eye disease.

Some of these applications include:

  1. Remote power for villages
  2. Water pumping
  3. Water purification
  4. Vaccine refrigeration
  5. Electric fences
  6. Telecommunications
  7. Remote farms and homes
  8. Signalling
  9. Industrial applications
  10. Disaster relief

Other uses

Solar electricity is increasingly appearing in more and more consumer devices driven by reducing cost, increasing performance and reducing energy demands in small electronic devices. Solar electricity is increasingly used in the following applications:

  1. Camping, caravaning and boating
  2. Recharging mobile phones
  3. Powering laptop computers
  4. Watches and calculators
  5. Street lighting
  6. Isolated vending machines
  7. Bill board lighting
  8. Security systems