Decide How Many Panels You Need
The number of solar panels you need ultimately depends on how much electricity you want to generate.
Most domestic systems have a capacity of between 1 kilowatt and 4 kW. Largercapacity systems are more productiveand will save you more moneyso you should get the biggest system you can for your home.
Read more about capacity and output in our guide How much energy do solar panels produce for your home?
How To Calculate Solar Panel Size Needed
If you are looking into purchasing solar panels to be installed on your roof, then you are in for a fantastic experience. They are a brilliant way to provide energy for your home and lower your annual energy bills in one go. Plus, they are environmentally friendly and require hardly any maintenance. However, before you buy, it is important to have a rough idea of the panel size and amount that you will need. Make sure you consult a professional and accredited installer about this, but this page can act as a rough guide.
Figure Out How Many Solar Panels You Need
Now that weve determined battery capacity, we can size the charging system. Normally we use solar panels, but a combination of wind and solar might make sense for areas with good wind resource, or for systems requiring more autonomy. The charging system needs to produce enough to fully replace the energy drawn out of the battery while accounting for all efficiency losses.
In our example, based on 2.5 peak sun hours and 240 Wh per day energy requirement:
240 Wh / 2.5 hours = 96 Watts PV array size
However, we need to account for real-world losses caused by inefficiencies, module soiling, aging, and voltage drop, which are generally estimated to be around 15%:
96 array watts / .85 = 112.94 W minimum size for the PV array
Note that this is the minimum size for the PV array. A larger array will make the system more reliable, especially if no other backup source of energy, such as a generator, is available.
These calculations also assume that the solar array will receive unobstructed direct sunlight from 8 AM to 4 PM during all seasons. If all or part of the solar array is shaded during the day, an adjustment to the PV array size needs to be made.
The maximum charge current for lead acid batteries is typically around 20 amps per 100 Ah and somewhere between this range is ideal .
Here are standard configurations of PV arrays with battery banks. The battery capacity calculated in the previous step can be compared against this table to find a suitably sized system:
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Why Bigger Is Better Even If You Believe You Wont Need A Larger System
Even with feed-in tariffs dropping and export limitations for single phase homes in certain states, maxing out your roof with solar panels is a smart move for two reasons:
Batteries and electric cars need lots of solar generation to reliably charge, and then you need more solar electricity to offset the energy needs of the rest of your home.
Im about to install more solar panels on my south-facing roof because my home now has two electric cars and a Tesla Powerwall battery. My existing 6 kW system struggles to generate enough energy for them all.
Ill finish by saying while I regularly hear from homeowners who wish they put on more solar panels when they had the chance , I have never heard anyone complain theyve installed too much solar power.
Choose The Right Solar Panels
If you have a small or odd-shaped roof, solar panel size is an important consideration when deciding on the size of a solar system. Take these factors into account:
- With a large usable roof area, you can buy more larger panels to get to your target energy output.
- If your usable roof area is limited or partially shaded, using fewer smaller high efficiency panels will ultimately be the most cost-effective, long-term solution. You can add more panels later on to accommodate increased energy needs.
Also Check: How Much To Install Solar Panels On A House
What About Snow Cover & Shading
We rarely have the ideal location for solar panels steep slopes, perfectly south facing, no shading, no snow in winter etc. The previous section showed how to calculate solar energy yield for locations across the world, and for all different orientations and tilt-angles. What it did not explain yet is how to deal with snow cover in winter, and shading. Unless you have a death-wish and plan to climb on the roof in winter to sweep the snow off the panels, snow cover is something we need to take into account for almost all locations in Canada!
First, let us take a step back and think for a moment about those annual energy yield numbers we have been calculating. In actual life every year will see a different amount of sunshine, and those numbers are an approximation, an average. They are not accurate to three decimal places, what they are is a pretty good idea of what to expect from solar PV for your particular location and case. The way we deal with snow cover should be seen in that light. We are just trying to improve our estimate, and get a better approximation:
For panels that are mounted at a tilt-angle of 40 degrees or more we expect snow to slide off pretty well in winter, and no correction is needed.
For panels that are mounted at a tilt-angle of 30 degrees or less we expect them to be covered in snow for part of the winter. So how do we account for that?
Corrected energy yield with snow cover = PV-Watts estimated yield Half the December yield January yield
Should You Buy A Solar Battery
If you want your solar PV system to pretty much cover all of your energy needs, youll also require a solar battery.
If you dont use solar-generated electricity immediately after it is created, then it will go back into the grid. Homeowners with solar panels need to be in their house during the daytime in order to use their solar energy, or else it will go to waste.
However, with a solar battery, you can store up all the solar energy that doesnt get used. Then, once youre back home in the evenings and the sun has gone down, you can still power all your appliances with solar energy. Whats more, electricity from the grid is even more expensive in the evenings when demand is higher, so youre dodging the priciest time for grid power.
You can find out more in our complete guide to solar batteries, which includes information about typical costs, pros and cons, and the best models on the market. Naturally, its the biggest batteries that are most capable of taking you entirely off-grid, such as the Tesla Powerwall 2.0 or the Sonnen Batterie eco .
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The Energy Requirements For Your Home
The first thing you need to do is take a look at how much energy your home uses. You can do this by taking past electricity bills and looking for an average usage. You will want this to be a daily average, so if your bill does not show this then divide it accordingly. So, if it is monthly, divide it by 30, and if it is annual, divide it by 365. Your answer will also be in kilowatt hours . This is how much power you are using at any given time, multiplied by the total time the power is used for. So, if you run a 60w light bulb all day, you will be using around 1,440 watts, or 1.4kWh.
How To Properly Size A Battery System
By John Connell, VP of Crown Batterys SLI Products Group
Oversize your solar panels, inverters and batteries and youll waste money. Undersize your system and youll compromise battery life or run out of power particularly on cloudy days. But if you find the Goldilocks zone of ample battery capacity, your solar-plus-storage project will work seamlessly.
By sizing your system using the ROI method Reduce electrical demand Observe power draw and calculate amp-hour requirements and Incorporate a safety buffer you can ensure the best combination of solar and storage will be used to fulfill your energy needs.
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Getting Started With Solar System Sizing
Before you begin to size a solar system, youll want to figure out the main constraints on the project and use those restrictions as the starting point for the design. You can approach the project from one of three angles:
- Budget constraints: Build a system within your target budget.
- Space constraints: Build a system that is as space-efficient as possible.
- Energy offset: Build a system that offsets a certain percentage of your energy usage.
Take into consideration other sizing factors and common stumbling blocks that may impact how to size a solar system:
The Cost Of Solar Panels Per Square Foot
It can be difficult to determine how much solar panels will cost you per square foot. This is because there are several factors such as size, type, and quality, that will affect the total cost of the panels. However, it is possible for a tough calculation to be given for the cost per square foot. The prices below include the following:
This will cover an estimated 225 square feet. Looking at a mid-range system once again, the average cost for this would be around £5,000 in total. This works out to £22,12 per square foot.
- 4kw System
This would cover an estimated 301 square feet. Taking another kid-range system, it would cost around £7,000 to install. As a result of this, the cost per square foot would be £23.26.
Also Check: Do Solar Batteries Qualify For Tax Credit
Considerations For Standalone Pv System
Calculation of Energy Demand
The size of the standalone PV system depends on the load demand. The load and its operating time vary for different appliances, therefore special care must be taken during energy demand calculations. The energy consumption of the load can be determined by multiplying the power rating of the load by its number of hours of operation. Thus, the unit can be written as watt × hour or simply Wh.
Energy demand Watt-hour = Power rating in Watt × Duration of operation in hours.
Thus, the daily total energy demand in Wh is calculated by adding the individual load demand of each appliance per day.
Total energy demand Watt-hour = .
A system should be designed for the worst-case scenario i.e. for the day when the energy demand is highest. A system designed for the highest demand will ensure that the system is reliable. If the system meets the peak load demand it will meet the lowest demand. But designing the system for the highest demand will increase the overall cost of the system. On the other hand, the system will be fully utilized only during the peak load demand. So, we have to choose between cost and reliability of the system.
Inverter & Converter Ratings
Converter and Charge Controller Sizing
Size of solar charge controller in amperes = Short-circuit current of PV × 1.25 .
Suppose the PV module specification are as follow.
- PM = 160 WPeak
- VOC = 21.4 A
- ISC = 10 A
How To Use Pv
The previous section assumed that you can mount solar panels at an ideal location: Perfectly south facing, with a great tilt-angle, and without any shading. What if your roof, or other location, is not quite that good? In most cases we can still accurately figure out what it will take to produce the kWhs needed. All we need is a little help from the US tax payers!
The US government, and NREL in particular, has created a very handy online tool that can calculate solar PV yield for any place on earth, taking orientation, angle, and even the local weather patterns such as cloud cover into account. It is called PV-Watts and clicking this link should open it up in a separate window. First we enter the location of the solar panels, or Ottawa to stick with our previous example. PV-Watts now finds the nearest location that it has weather data for, and displays that. Go to the next screen, and for our example we need to change a few parameters. The DC system size is how much solar PV you have, in kW. We want to know what each kW of panels will produce so change this to 1. The module type of Standard should be fine for most, we can also leave Array type to the default of Fixed . The system losses of 14.08% are fine too. For the Tilt we will change this to 45 degrees, the latitude of Ottawa, just like our earlier example, and the Azimuth is fine at 180 degrees .
Correction factor = PV-Watts reported yield per kW of panels / Actual yield per kW of panels
Recommended Reading: How To Size A Residential Solar System
Comparing The Pv Size Estimation To A Simulated Result
Since this is a rough estimate, how does it compare against an actual, comprehensive design for a home with the same characteristics?
Using the same conditions as above, a PV system design software found that the required system size to be 4 kW, which is almost identical to the answer from the estimation conducted above.
Although the answers are very close, its important to note that this may not always be the case. For instance, when there is shading on the panels, a significant reduction in power output can occur. Although a shading term is included when calculating a derate factor, it can fail to accurately capture the effect that shading has on a PV systems power output. Therefore, expect the results to be less close when modeling a location with shading.
Solar Pv: Smart Export Guarantee
Interesting times … The Smart Export Guarantee came into affect in January 2020. The Smart Export Guarantee is an obligation set by the government for licensed electricity suppliers to offer a tariff and to pay small-scale low carbon Generators and Micro-generators for any electricity that they export to the National Grid.
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The Climate Of The Area And Peak Sunlight Hours Calculation
The sunlight hours available to your location will directly impact the watts generated from the solar set up.
The more hours of sunlight available the less number of panels required to generate a given output.
Inversely, with lesser sunlight hours, more solar panels will be required. By dividing this average hourly wattage requirement by the number of sunlight hours daily at the location, you calculate the watts your panels need to produce every hour. Using this figure you can select the panels required. The sunlight hours and sun angles vary by season. This will also be a factor for calculating the number of available sunlight hours and thus the panels required.
Lets look at a simple calculation to understand this concept better.
Lets say the summer season sunlight at the location is available for 6 hours and for mid winter it is 4 hours. Then in mid winter a 10w panel will provide 10w * 4h = 40watt-hours of DC power into your battery. In summer the amount would be 10w*6= 60watt-hours. There would be a little energy lost due to resistance through the regulators, cables, and batteries chosen. In calculating the solar power system you would built some assumption of loss into the final calculation.
System Size Based On Daylight Electricity Use
The average Australian household consumes 18kWh of electricity each day. If we use a house in Adelaide as an example, you would need a 5kW solar system to generate this amount of power. However, if the household only consumes 40% of its electricity during daylight hours, there is no point in installing such a large system. In this instance, a system that generates on average 7.2kW of electricity per day would be sufficient. Therefore, a 3kW system is likely to deliver the most affordable solution.
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How To Size An Off Grid Solar Pv System For The Home
What is currently happening in our world
With the planet continuing to warm up and the increased pressure on humanity to ditch fossil fuels and embrace other forms of energy that dont harm the planet, renewable energy has seen a steady rise in its popularity and usage.
Amongst the renewable energy sources of wind, solar and geothermal, Solar is increasingly becoming dominant. The main component of any solar energy installation are Solar PV panels. Although still relatively inefficient, the rise of Solar PV panels has been astronomical.
Solar PV installation in the rooftop of houses are increasingly becoming popular as we race to reduce our carbon footprint and keep the planet safer.
Basic Things to know Before you Start Your Solar PV Sizing Project in the Home
To successfully implement an off grid solar PV installation in the roof top of your house, there are some basic things you need to be aware of before you embark on this journey:
1.What is your load requirement?
2.Do you want to power all your loads when off grid ? Or
3.Do you want to power some loads and leave some on grid?
4.What is your budget for this project?
5.Can your budget finance a project where all your loads requirements can be taken off grid and powered by the Solar PV installation?
6.What is the average level of sunlight insolation in your location where the project is being planned?
Basic components of a Solar PV Installation in the Home
1.Solar PV panels