Solar Calculator | Panel battery cost, savings, size, payback ROI
Use the simple Solar Calculator to get an instant price estimate for solar and batteries.
It is important to note, that you neither want to pay too much nor too little for a solar system. It might sound strange that you would not want to pay too little but think about it as if you were going out to dinner. If you pay a small price, you might get a reasonably tasty meal, but it probably won’t leave you feeling particularly spritely afterwards. It is the same with solar in that if you buy a cheap system, you are far more likely to have a headache later on. In order to install cheap systems, the company will need to cut corners somewhere. Either on the components that are being installed or on installation costs.
With solar, as with eating out, there is a pricing sweet spot. Our Solar Calculator is not perfect (see the disclaimer before using it), but you can use it to get a rough idea of what you should pay. This is another reason why we recommend getting multiple quotes when buying solar, so you have a reference point.
Solar Payback ROI Calculator
Is solar a good investment?
Use our Solar Calculator to get instant solar savings and payback estimates. Whether solar makes financial sense largely depends on where you live. Your location will dictate how much solar you can produce and the relative cost of solar energy vs buying energy from the grid (factors that dictate your return on investment). There are very detailed answers, and many variables for these different factors, so for this guide, we will give an overview of the average payback period for solar in some key regions. You can always use our Solar Calculator for more detailed analysis in your area.
Australia has some of the best payback periods worldwide, due to having lots of sun, good government support, and relatively expensive conventional electricity. The average payback period for a 5kW solar system in Australia, if you use 50% of the solar you produce, it is around 4 years (in 2018). According to the consumer advocacy group Choice, that varies from as little as 2 to 3 years in Adelaide, up to 5 or 6 years in Melbourne, Hobart, and Darwin.
In the US, the average payback on a residential solar system is typically 6 to 8 years, according to the solar quote comparison website, EnergySage. Interestingly, according to the Indian Solar market, the payback period for residential systems in India is also approximately 6 to 8 years.
Battery Storage Payback ROI Calculator
Are batteries a good investment?
Use our Solar Calculator to get instant battery storage cost and payback estimates.
Similar to the desire for us to provide a safe and comfortable home for our family, many humans also seem to have an innate, evolutionary desire to be able to have full control of our energy needs. However, this desire is usually at odds with both the financial and environmental reasons for going solar. In order to be fully energy independent, you need to be completely off-grid, which means you’ll need an awful lot of solar, batteries and a backup generator to keep you going in the depths of winter. However, if you live or are moving to an area without the grid, you have little choice but to be energy independent.
Going solar (without batteries) will not give you much energy independence, it will allow you to consume some power that you produce, but if the grid goes down your solar system is designed to go down with it (lest exporting energy to the grid and electrocuting anyone working on getting it back up again).
See our Battery Storage article for all you need to know about buying solar with batteries.
Solar system size calculator
How many panels should I get?
Use our Solar Calculator to get instant feedback on the right size solar system for you.
There are a surprising number of factors you can consider when deciding on what size solar system to get. It is worth looking at all of these factors if you are on a budget and have the time, but the very short answer to this question is that the majority of households are getting as much solar as they can fit on their roof (or are allowed by their electricity distributor).
For Australian properties with single phase electricity (that’s most of us) you can usually install up to 6.5kW of panels, with a 5kW inverter, and often you’ll be able to get as much as a 10kW inverter.
US households are not often restricted in system size by the power company, and the usual system size is between 10-20kW. The average is a bit bigger than in Australia because of fewer restrictions, higher electricity consumption, and larger houses.
That is the short answer, but if you want to know the full details, the long answer is below. In the last section, I will also explain why it’s often a good idea to oversize your inverter (get a larger array of panels [6.5kW] than the inverter size [5kW]).
How much solar can you install?
Every electrical distributor (the company that manages the poles and wires) in Australia has different rules about the approval process for installing a solar system. However, the majority will allow up to 5kW for single-phase (which are the vast majority of residential homes) and 30kW for three-phase (generally commercial properties). The system size is usually limited by inverter output not the nominal panel output, so you can install a larger panel array, but you may be limited to a 5kW inverter. In some areas, you are allowed up to 10kW on a single-phase connection if you add battery storage. Unfortunately, in some rural areas, you might be limited to as little as 2 or 3kW. A good solar company will know all these rules in your area and be able to submit an application to find out how much solar you can export and offer options to increase your self-sufficiency.
The other limiting factor is obviously your roof space. See Is my house right for solar for more specifics on this. In short, bear in mind that you can only install the amount of solar that can physically fit on your roof.
How much will you get paid for the solar that you export?
See the solar rebates article for details on what you will get paid for exporting your solar. The key point when considering this in relation to sizing your system is that if you get paid a lot for exporting your solar (close to, or more than what you pay for your electricity from the grid) then you will be happy to get a big system and export a lot of your power so you can get paid that high price for it. However, if you do not get paid much (or anything) for exporting, you will likely be better off sizing your system closer to your daytime electricity consumption, in order to maximise your own consumption (and therefore offsetting what you would normally buy), and minimising selling your power for a low price.
Most of the US uses net metering, so you will get paid the same for what you export as the cost for what you consume, so if you are in the US you don’t need to worry about this section.
In Australia, if you search around, you should be able to find a retailer that will pay you 50% of what you pay for your electricity, although many will offer closer to 30%. With a feed-in tariff of 50% of what you pay (for example 15c per kWh, if you pay 30c per kWh for consumption), that is still a pretty decent amount you are getting paid for your solar, and by getting the ‘standard’ 5kW inverter with 6.5kW of panels you will likely still get a very good payback period.
What is your current daytime consumption?
If for whatever reason you are getting a very low, or non-existent feed-in tariff, then you will want to size your system closer to your daytime consumption. Although, don’t worry about being too precise with this calculation, as your consumption will likely change over time anyway.
Have a look at your electricity bill, and work out your daily average usage. Let’s say you use 20kWh per day on average. Then work out roughly how much of that power you use during the day (this will vary considerably during summer and winter, so just use an average). Let’s say 50%. That is 10kWh that you use during daylight hours. In most parts of Australia, you will generate at least 4kWh of electricity for every 1kW of solar that you install. Therefore in this scenario, you would only need a 2.5kW solar system to cover your own usage. Some apps and add-on energy meters such as Solar Analytics can give you detailed information about your electricity consumption.
Other useful solar power calculators:
Here is a quick guide on how to use the calculator.
Disclaimer: The provided calculator is for informational and educational purposes only. By using this calculator you acknowledge that we can’t be held responsible for any damages as a result of using this calculator
How many KiloWatts-Hours (kWh) do you use per month?
You are asked to quote your monthly consumption according to your monthly electricity bill.
What percentage of this power will be used by renewable solar energy?
If your home is connected to a utility grid, it is rather uncommon to offset all of your consumption to a solar electric system. A fair percentage is usually 30 to 40, you are free however to choose a lower or a higher percentage value.
Average Sun Hours per day?
You can find below information on how to find Average Sun Hours per day also known as Perfect Sun Hours/PSH/ for location in the USA, Europe, Australia, and New Zealand, and rest of the world:
3.1 You can take this value for the USA by clicking on the following link:
expand the ‘Solar Resources’ folder on the left and tick the ‘Avg. Annual Tilt at Lat’ checkbox. After that, you will see a map of the United States with Average Sun Hours plotted on. Then by clicking on the little black arrow right to the checkbox, you can expand the legend and see the value of Average Sun Hours for your location after zooming in the map as much as you need to find the place where you live.
Eventually, you get the minimum and the recommended size (in Watts) of the solar system you need. ‘System size’ means the total power of the solar panels that need to be installed on your roof to meet the electricity consumption target you want to offset to the solar system.
3.2 You can find the Average Sun Hours per day value for Europe by clicking on the following link:
Please don’t forget to divide the value of the yearly sum of global irradiation in KWh/m2 by 365 to obtain the value for average Sun Hours per day.
3.3 For Australia and New Zealand:
3.4 If you live outside the USA and Europe you can find the Average Sun Hours per day value for your country by using the World map of direct normal irradiance, which means that these values are applicable for the solar panel held perpendicular to the sun rays. In other words, the tilt of your solar panels is equal to the latitude of your place.
Please don’t forget to divide the value of the yearly sum of direct normal irradiance in KWh/m2/y by 365 to obtain the value for average Sun Hours per day for your location
On-Grid Solar Calculator Assumptions: Recommended System Size assumes 85% solar system efficiency or in other words 15% total system losses.
How to calculate the number of solar panels needed for your solar system?
The number of solar panels needed= Recommended System Size in Wats/Chosen Panel in Watts. Round up the calculated value
For example, you have calculated that you need a Recommended System Size of 5000Watts.
You have chosen your system voltage to be 12V and your solar panel to be 240Watt for the 12V solar system.
Then the number of solar panels that you need is:
The number of solar panels needed=5000/240=20.8 solar panels. After rounding it up we receive that you need to buy 21 solar panels.
Please, use the update button below the calculator body to update the calculated results if those results are not updating automatically.
Using the off-grid system solar panel calculator
What is the total Watts (W) you electronics will consume?
You need to sum the wattages of all the electrical devices you use on a daily basis and therefore you want your off-grid solar system to support. Each device has its wattage on its back label. So, please enter the sum of Watts your electronics consume daily.
For how long are you planning to run these devices?
You should decide for how long you have all these devices plugged in every day so that the solar system will be able to power them. Here you need to enter the average daily hours of operation rather than the maximum ones.
Charge Controller efficiency (PWM: 80%, MPPT: 92%)
The charge controller is a device that manages the battery of a solar system. PWM charge controllers are less expensive than MPPT charge controllers but they are also less efficient.
Average Sun Hours per day?
As it has been explained above for the off-grid solar system
Off-grid system calculator assumptions
Lacho Pop, Master of Science in Engineering
Lacho Pop, MSE, holds a Master’s Degree in Electronics and Automatics. He has more than 15 years of experience in the design and implementation of various sophisticated electronic, solar power, and telecommunication systems. He authored and co-authored several practical solar books in the field of solar power and solar photovoltaics. All the books were well-received by the public. You can discover more about his bestselling solar books on Amazon on his profile page here: Lacho Pop, MSE Profile
Blog Table of Contents
- Mixing solar panels – Dos and Don’ts
- Types of Solar Panels – Pros and Cons of the Most Used PV Solar Panels
- How to Choose The Best Solar Panels for Your Solar Power System
- Do Solar Panels Save You Money?
- How Many Solar Panels Do I Need?
- Free Solar Panels: What’s The Catch
- What Are Solar Panels Made Of- How Do Solar Panels Work
- Where Are Solar Panels Used
- Which Solar Panels Are Best For Camping?
- Solar Panels For RV
- Solar Panels For A Caravan: What Is The Best Type
- The Best Solar Panel For a Motorhome
- Solar Panels Mounting Exposed
- Essential Guidelines on Mobile Solar Power for RVs, Caravans, Campers or Boats
- Solar Power Systems For Your Home Or Business
- Solar Power Systems Unveiled: The Definitive Gide
- 15 Blunders That Can Ruin Your Solar Power Project
- Solar Power System Components Demystified
- What Are The Problems With Solar Power
- Solar Energy
- Uses of Solar Energy
- What Is the Cost of Using Solar Energy
- Energy Efficiency and Going Solar
- Solar FAQs
- Can Solar Panels Power a House?
- How to Perform a Solar Site Survey: Costly Solar Mistakes Related to Solar Site Survey
- Preparing For Solar-Important Tips Before Going Solar
- The Ultimate Off-Grid and Mobile Solar Power Bundle: 2 Books in 1
- Off-Grid Solar and RV Solar Power For Everyone
- The Ultimate Solar Power Design Guide: Less Theory Practice
- The Truth About Solar Panels Book
- The New Simple And Practical Solar Component Guide: Your Personal Solar Advisor
- 40 Costly Common Solar Power Mistakes Exposed
- Solar Power Demystified Free Book
- Free Ebook: Solar Panel Basics Exposed
- Free Ebook: Top 20 Solar Mistakes
- The Definitive Guide to MPPT and PWM Charge Controllers in Off-Grid Solar Power Systems
- PWM Charge Controller Calculator
- Solar Battery Monitors Demystified: Battery Monitor For RV And Off-Grid Solar Power Systems
- Solar Load Calculator For Off-Grid and RV Solar Power Systems
- Free Solar Panel Calculator For Off-GridOn Grid Solar Systems
- Free Solar Cable Size Calculator
- Free Solar Battery Calculator: Calculate Fast Easy The Solar Battery Bank Capacity And The Number Of Batteries In Series Or Parallel
- Free PWM Charge Controller Calculator
- Solar Panel Output Calculator- Estimate the Real Energy You Can Get From Your Solar Panels
- Solar Sizing Software
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What size solar system do I need for my home?
As a general rule a home solar power system needs 6 solar panels each rated 300 watts with average irradiance of 4kWh/m2/day for every 5kWh of daily energy consumption. The average US home consumes about 30kWh per day and will need 36 solar panels rated at 300 watts.
Video – How many solar panels do you need for your home?
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How to calculate home energy consumption
You could add up the wattage of all your appliances and estimate how many hours they are used each day, but this is very cumbersome and not accurate.
For example, some appliances, such as refrigerators, are difficult to estimate. This is because they have compressor motors on board and have variable instantaneous power values.
Discover your solar saving potential
By far the easiest way is to take it from last year’s utility bill, which normally shows the full year’s energy consumption in kilowatt-hours (kWh).
Simply divide this figure by 12 to get the monthly consumption, or 365 for the average daily consumption.
The average amount in the US is about 30kW per day, but your own will depend on where you live.
How do I calculate solar panels for my home?
Once you have found your daily energy consumption, it can be used to size your solar panels.
It needs to be said that solar panel power ratings are not an accurate reflection of the actual power generation in real-life conditions.
In fact, there are many losses associated with a working home solar system. As much as 23% is normally lost and must be deducted from the solar array power rating – see infographic below:
The calculator I provide later on in the post takes these losses into account, but for this example I’ll go through the process manually step-by-step.
Download this web-page as PDF
How many solar panels do I need for 5000 watts?
You light think it’s obvious, but the answer isn’t as simple as it sounds. If we propose to use 300 watt solar panels then in theory you would divide the power required by 300, giving 16.6, or 17 panels if rounded up.
Unfortunately, the real world isn’t like that!
Solar panels are rated at 300 watts, but this is the very best you can expect in the laboratory, or Standard Test Conditions (STC), which specifies an irradiance level of 1000 watts per square meter, among other things.
- 5000 watts x 1.44 = 7000 watts
- Number of solar panels needed = 23 panels each rated at 300 watts
What size solar system do I need to run a fridge?
The average size refrigerator consumes about 350kWh each year, but older ones definitely consume more, so add 5% for each year of use. Modern fridges are very efficient and don’t cycle so much. This is important, as compressor motor surge current pays a big part in driving up the energy consumed.
How many solar panels does a fridge need?
A 100 watt solar panel generates 400 watts per day at an average irradiance of 4 peak-sun-hours. This is equivalent to 146kWh for the year.
Always round-up to the highest whole number, so 3 solar panels would be needed. I would use 4 solar panels, as they are relatively cheap nowadays – it takes care of poor power generation on cloudy days!
You’ll need an inverter, which should be as close to 300 watts as you can make it (400 watts if you go for 4 panels.) This is because inverters are most efficient when fully loaded. You need to be as efficient as possible overall, because sometimes the inerter will be very lightly loaded when the fridge compressor isn’t running.
You will also need a 100Ah deep-cycle battery, preferable Lithium Phosphate, to run the fridge through the night when the solar panels don’t provide power.
Do solar panels work on a flat roof?
Solar panels do work on a flat roof but don’t generate as much power as when mounted at the optimum angle for the location. However, the loss in power is not as great as you might imagine.
Flat roof solar panel calculator
The table below shows the monthly irradiance difference throughout the year in Phoenix, Az. Solar panels at a fixed angle of 57 degrees will generate just 10% more power than a flat installation. The amount of power difference between flat/angled panels will be different according to the location’s irradiance.
Irradiance for Phoenix Arizona by month (kWh/m2/day – Peak-Sun-Hours)