Shade management for production loss
If you notice that your solar system is not performing as well as it should, the first check you should make is for production loss due to shade or dirty panels. See our panel maintenance article if you'd like to read more about managing dirty panels and we'll deal with shade management here.
If you have trees shading any part of your system, you will certainly be experiencing a power production loss. The amount of loss will depend on the configuration of your solar panels and the type of solar inverter you have. By knowing a few basics, you can quickly identify how much solar savings you are potentially loosing.
HOW DOES SHADE CAUSE PRODUCTION LOSS?
Inverter type
String inverter - The majority of inverters sold in Australia are string inverters. This means that you will have one or two 'strings' of solar panels cabled to the inverter as a group. For example, if on a system with 12panels, there may be 6 panels on one string facing north and 6 panels on another string facing west.
If a tree is casting shade on 50% of just one panel, it will be creating a 50% loss on that entire string. Because the other string is unaffected, the overall system loss is 25%. (Each string is 50% of the system, therefore one string with a 50% production loss = 25% total system loss)
The common comparison for shade loss on a string inverter is water flowing through a hose. When the hose has a bend or kink, it will slow the rate of water flow.
So - do you have a string inverter? Unless you discussed this at the time of purchase, you probably have string inverter. Other alternatives are more expensive and generally not required unless you have obvious shading issues.
Micro Inverters or panels with optimisers
Micro inverters and panel optimisers allow each panel to work independently. This means shade on one panel will not affect any other panel on the system. Because of the additional cost, these systems are generally only used if there are shading issues. There are also marginal production benefits with these options and some clients have decided that the additional annual cost savings would mean the higher upfront cost is worthwhile. There certainly can be additional cost benefits, however it is worth noting that you may also multiplying the possibility of hardware faults by increasing the number of devices (micro inverters or optimisers) that could potentially fault.
CALCULATING THE FINANCIAL LOSS OF SHADING
Calculating the shade loss and the financial loss due to shading is a complex task. If you begin to read the information below and find it far too much, the next section is a simple guide. If you love the maths, then feel free to read on.
An easy guide to shade loss
Firstly, scroll down and take a quick look at the chart labeled 'solar production - daily breakdown'. If you notice shade occurring after 3pm - your worst case scenario is going to be 12.5% loss. It will almost certainly be a lot less than this if your have two strings facing in different directions.
An alternative way of understanding production loss is to view your solar monitoring. If may see a visual reduction during shady periods. For example, if your production drops suddenly after 3pm, you can almost guarantee that there is a shade source to the west of your solar panels.
The final step is to calculate the financial loss. If you've purchased a system from us recently - this can be worked out by looking at the savings estimates provided on the quote and subtracting the loss you have estimated.
If you have had your system running for some time, you should have a reasonable understanding of the savings your solar system is providing. If you usually see $500 per quarter saving - then simply remove the estimated loss. (for example, if you've estimated a 25% loss - you would be loosing $125 per quarter or $500 per year)
If you are able to remove the shade issue by trimming or removing the tree - they your savings will increase. It's important to remember to check for shading issues a few times a year to make sure you stay on top of your trimming. The easiest way to do this is by being familiar with shading signs in your solar monitoring, otherwise, a visual inspection in the mornings and evenings is recommended.
A detailed guide to shade loss
Solar production varies depending on where you are in Australia and what time of year it is. Shading from trees will be greater in winter than they are in Summer. The height, position and distance of trees in relation to the solar panels will also be key factors.
There are industry tools that use special lenses to take 360 degree photos from the roof, they provide a shade analysis. This sort of tool is very accurate in predicting year round shade loss, however they would generally be too expensive for most consumers to consider. In reality, if you work out a 'worst case scenario' with a reasonable degree of understanding - you can provide yourself with reliable guide to the production and savings loss that you might be facing. The following details will give you a good understanding of how to calculate these figures.
Summer
In Summer, the sun moves high in the sky and has an early sunrise with a late sunset. The peak of summer will provide the highest solar production because the days are long and the sun is high in the sky to create a stronger solar path to your panels.
In summer, shade issues are lower because the sun is overhead for most of the day. Trees to the east of the system may cast shade on eastern facing panels until 9-10am depending on the height, size and position of the tree. As long as the tree is not directly over the panels, by late morning the shade issues are reducing.
Winter
In winter the sun travels lower in the sky throughout the day and has a later sunrise and earlier sunset. This means less hours to produce solar, and less solar energy from the sun due to its lower position in the sky.
In winter, the morning and evening shade from trees often lasts longer because the sun sits much lower in the sky. Our satellite reporting tools often highlights trees that only cause a small shade issue in summer, creating an impossible shade situation in winter.
If you are able to spend time observing when shade stops in the morning, or starts in the evening you can then use the guide chart below to calculate savings loss.
This chart is a general guide to the amount of solar energy your system is making at different times of the day.
Calculating the shade loss
Calculations can be complex depending on how your solar panels are positioned. These calculations will also change between summer and winter. We suggest working out the winter (worse case) first and then look at summer.
Below are two examples to provide further clarity. In both examples I will use a tree that is positioned on the west of the property and casts a shadow over 1 panel at 2pm. This means we are reviewing the last 25% of the solar production period.
Example 1: 20 solar panels in one string facing north
Because all panels are on a single string, as soon as one solar panel is in full shade, the system will no longer be producing energy. Therefore if this is occurring at 2pm the loss calculation is 25%.
Example 2: 10 solar panels on one string facing north and 10 solar panels on a second string facing west
The red line below shows solar production from north facing panels. The yellow line shows production from west facing panels.
The position of the tree here might be casting a shadow on the western panels by 2pm, but the northern panels may not see that shadow at all depending on the position of the tree and the panel locations. This might mean the northern panels continue to produce energy until the end of the day. If this is the case, the Northern panels, being 50% of the system will continue with its 12.5% share of the evening solar production.
The western facing panels won't start generating energy until later in the morning. You'll also note that they produce the bulk of their energy in the evening. At 2pm, it appears that the western facing panels still have approx 30% of their production potential available, meaning that this string will have a 30% loss.
Because the western string is 50% of the total system production, the total system loss is 15%.
Calculating the financial loss
There are a few individual calculations required to come to a final result. You'll need to know your systems daily average production, your energy tariff cost and then you'll need to calculate how your system is affected by shade.
Average daily production estimate
This formula helps you calculate your average daily production estimate: System size X expected daily production
The expected daily production hour figures are provided by the Clean Energy Regulator as an industry standard figure. It is based on 20+ years of solar data and varies from area to area. Here are a few area examples. You can reasonably use the closest location to you to calculate your systems average daily production.
3.6 hours per day - Melbourne and surrounds
3.9 hours per day - Sydney & surrounds
4.2 hours per day - Cairns - Brisbane, Northern NSW, Adelaide
4.4 hours per day - Perth & Mt Isa
Here is an example for South East QLD*
This shows an annual average of 27.7kWh per day. Please note the graph below provides a monthly estimate of the average daily production.
Please note that these figures are only every an estimate. Annual weather changes directly alter the actual results.
Calculating your systems shade loss
Note: If you have solar monitoring, you can probably use it to work out general system loss. The information will then just provide context for understanding shade loss.
Step 1 - work out the percentage split between panel strings.
If you know your system size, and how many panels you have, you can calculate the percentage of each string.
For example, a 5kW system with 8 panels panels facing west and 12 panels facing north will have these figures
West - 40% (2kW)
North - 60% (3kW)
Calculate each string separately for the next step.
Step 2 - estimate you shade loss on each string.
The following charts are taken from Desert Knowledge Australia - a solar test site in Alice springs. I am highlighting that solar production patterns are similar in summer and winter, however the start and finish times of solar production and the maximum power production varies. This can also be reflected in the monthly breakdown example above. You can certainly add complexity to your calculation by trying to work out summer and winter loss figures, however if you work out winter first - you'll have a worse-case-scenario as a baseline figure for losses.
Blue - North
Red - East
Yellow - West
Summer
Winter
The information above is there to provide you with a guide for each panel orientation.
You can now either rely on visual inspection of shade on each string. This will require visually recording when your panels start to experience full shade on each string.
Once you know when your panels are affected - use either the graphs above or your solar monitoring to estimate the shade loss percentage for each string.
When you've worked out what the percentage loss is for each string, you should be able to work out the total system loss by adding the two percentages together and dividing by 2.
For example: String 1 loss may be 20% and string 2 may be 10%. Therefore the system loss will be 15% (10+20 divided by 2).
Calculating your energy cost per kWh
The final step is to take a look at your energy bill and work out your tariff cost per kWh. Once you know this, you can easily work out the financial loss.
For example, if your system produces a daily average of 25kWh and you have a 20% loss, you have lost 5kWh per day. 5kWh per day x 30c per kWh is $1.50 per day or $547.50 per year.
As always, if you are concerned with your system performance and are unsure about anything, please contact us and we'll work it out with you.
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