Ways To Calculate Solar System Size For Your Home
If youre thinking about going solar, one of the first steps youll have to take is figuring out the right solar system size for your home.
Its hard to overstate the impact that the solar system size has on the process of going solar. The size of the solar system will determine:
- The total cost of your solar panel installation
- The amount of roof space required
- The proportion of your power bill youll be able to offset
- The total financial savings over the life of the panels
In other words, you need to first calculate solar system size in order to find out if going solar is worth it for you.
So, what exactly does ‘solar system size’ mean*? What factors affect what system size youll need? And how can you easily calculate the right solar system size for your home? We answer all those questions in this blog.
*If you thought that solar system size refers to the physical size of solar panels, sorry, thats not it!
How Many Batteries Are Needed To Power A House
How many batteries would you need to power the average home?
If your home consumes 30kWh every 24 hours and you want to have 24 hours autonomy, then you can easily work out how many batteries you would need.
There are two choices for home energy storage batteries lead-acid deep-cycle or lithium iron phosphate. I prefer LiFeP04 but as lead-acid are still the mnost common, Ill use them in an example.
Deep-cycle batteries can be discharge up to 80% of their capacity, but 50% is recommended in order to maximize battery life.
This means that we need to double the amount of energy required from the batteries, simply beacuse half of it isnt normally available. 80% Depth of Discharge is OK from time to time.
The calculation looks like this:
Energy for 24 hours = 30kWh
30kWh in battery amp-hours = 2500Ah
Total battery capacity needed for 24 hours = 2500Ah x 2 = 5000Ah
25 batteries rated at 200Ah will be required to power this home for 24 hours.
Sizing Solar Panels Batteries And Inverter For A Solar System
A true off-grid solar power system includes solar panels, a bank of batteries for energy storage and one or more inverters. This kind of system has no connection to the utility grid.
It is possible to have home battery storage, even when normally using the utility companys grid connection. The batteries automatically come on line if or when the normal electricity supply fails.
The usual procedure for sizing any kind of system is in this order:
Solar panel size is found by dividing daily load kWh by the locations irradiance to give solar kW rating. Inverter size is equal to solar panel rating. Battery size is found by multiplying the daily load by the number of days autonomy required, and dividing by system volts to give amp-hours.
How To Calculate The Number Of Solar Panels You Need
Our calculator below is the fastest, easiest, and most accurate way to find out how many solar panels your home needs – and you dont have to do any math.
Our solar panel cost and savings calculator is the fastest, easiest, and most accurate way to find out how many solar panels your home needs – and you dont have to do any math. Plus, well give you the average cost of a solar installation for your specific home and how much itll save you on your electric bills.
However, if you want to put pen to paper and work out the calculations for yourself, follow these four easy steps to find how many solar panels you need.
How Many Solar Panels Do You Need For Specific System Sizes
In our long example at the beginning of this piece, we determined that an 8 kW system would probably cover the average energy use for an American household if you live in an area with a production ratio of 1.6, which might be a realistic number for homes in most parts of California. Lets extend that a little further, and look at a few more examples. In the table below, weve compiled some solar panel estimates for common system sizes seen on the EnergySage Marketplace. Again, the big caveat here is that were using 1.6 as the production ratio of choice. For California shoppers, this might actually be realistic, but for folks in the Northeast or areas with less sun, these estimates might be a bit high on the production end and low on the number of panels needed.
How many solar panels do I need for my house? System size comparison
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Determine Solar Panel Placement
Solar panel placement is one of the single most significant contributing factors for maximizing DIY solar productivity.
Choose areas with little to no shade and face south or southwest.
If you place panels on the roof, they will most likely face south.
South-facing panels have the most optimal productivity throughout the day, but some experts now argue that southwest-facing panels make more sense for off-grid applications.
This placement aligns the solar panels with the suns direction at the time when energy consumption is typically highest.
However, south-facing panels may work best for you if you:
- Have a different schedule
- Maintain a good battery bank
- Sell excess solar production to your energy company
The Inverter Size Calculated Is Smaller Than I Expected Why
Running AC appliances on a solar system demands a lot of energy from the batteries.
Keeping the number of AC appliances to a minimum will help keep the size of the system down.
Weve calculated the inverter size to run only your largest AC appliance with no other AC appliances running at the same time.
If you already have a larger inverter, use that but keep your maximum load as low as possible or youll drain the batteries fast.
For more information and to understand the implications of a large inverter on your solar system, check out our inverter calculator.
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Which One Solar Panel We Select
Among lots of brands and material of solar panels like c-Si, String Ribon, Thin Film Solar Cells or , Amorphous silicon ,Cadmium Telluride Solar Cells, Copper Indium Gallium Selenide Solar Cells, BIPV: Building Integrated Photovoltaic Panels, Hybrid Solar Cells and PV Panels, We have discussed in a very details post different types of solar panels with advantages/advantages, cost, and applications This way, you will be able to find which is the best type of Solar Panel for Home Use?
Calculate Your Kwh Usage
To determine your homes energy usage more accurately, use our home appliances power consumption table to find out how many kWh your appliances would use per month.
If your utility provides a favorable net metering policy, the energy your system generates can be banked with the utility as a credit that can be used later. Not all utility companies give you credit check with your local provider.
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Using The Kill A Watt Meter
As an example, the average US household uses 900 kWh power per month. For 30 days per month we get 30 kWh per day, and for an average day you might get between 6 and 10 hours of effective sunlight. The answer you get is between 3 kW and 5 kW per hour. So this monthly average wattage is what your solar panel system should be equipped to generate.
The calculations done this way will not be accurate. There are other factors affecting the generation of solar energy. The daily production might fluctuate greatly on a daily basis.
You could calculate a solar energy system power consumption of an electronic appliance using a low cost plug in device, called Kill A Watt meter. Once you know how much power an appliance is consuming per day, it will help you to determine your power consumption. Use a solar power price calculator.
You can use this device to count watts in kilowatt/hours . This device is made up of a three-prong electrical plug-in, along with some buttons and a display monitor. Once you plug the monitor into the wall, you also plug any appliance into the monitor. The device tells you exactly how much is the electricity being used by the appliance, including situations when the appliance is just plugged in only without being turned on.
Here is a video to watch the working of kill a watt meter.
What Is The Difference Between Agm Fla And Lithium Batteries
There are many differences between these batteries. But the main difference is the depth of discharge or DOD.
A lithium battery can be safely discharged up to 90% without shortening its lifespan. AGM and FLA batteries should only be discharged up to 50%. The less you discharge per cycle, the longer the batteries will last.
Because of these discharge rates, you will need a larger AGM or FLA battery for your system than you would with Lithium. You can read more about batteries here.
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Fast Payback On Additional Kws
The cost of increasing the size of the system to 5kW is only $657 per kW. If we assume that you receive a feed-in tariff of 11.1c for every kWh you export back to the grid, it will only take 4 years to pay back the extra 2kW this is assuming that all of the additional solar power output is exported back to the grid. If you self-consume the power, it will pay back much faster. You can expect the panels to continue generating solar power for another 20 years.
Solar Panel Size Guide: How Many Solar Panels Do You Need
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The size of a solar panel is a huge determining factor for placement, production and optimization. In our solar panel size guide, we will highlight everything you should know about your solar panel sizing and possible power output.
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How Many Solar Panels Do You Need
If youre wondering how many solar panels you need to power your home, there are a few important elements to consider. With a few calculations, you can get an idea of how many panels are needed for your home, but if you use a qualified solar panel installer, they will make sure you have an appropriate solar panel system.
To determine how many panels you need, you should know how much energy you use every year. Energy usage is measured in kilowatt-hours and refers to how much energy it takes to run a 1,000-watt appliance for one hour. The amount of energy you use depends on how many appliances are running in your home and how often they are running.
According to the U.S. Energy Information Administration, the average household in America uses 10,649 kWh of electricity each year. To see how much power you use, look at your utility bills from the last 12 months.
Once you know how much energy your household needs, you can begin looking at panels. Solar panel sizes and wattage vary significantly to make it easier to find a system that will work for you. The wattage of a panel, also called the power rating, tells you the electrical output of that panel under ideal conditions. Typically, a panel produces between 250 and 400 watts of power.
You can calculate the production ratio by dividing the energy output by the total wattage of the system. Your production ratio should fall somewhere between 1.3 and 1.6.
System size / production ratio / panel wattage = Number of panels
How Do I Know All The Electrical Devices Ill Use
Underestimate it and you may run out of power.
Overestimate and youll probably spend more money and make your setup more complex than necessary.
Work through your typical day, considering all the appliances youll use along the way.
Dont forget any gas or diesel appliances that need power to start them up.
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What Affects Solar Panel Output Efficiency
Heres where solar panel quality makes a difference. Not all solar panels are alike. Photovoltaic solar panels come in wattages ranging from about 150 watts to 370 watts per panel, depending on the panel size and efficiency , and on the cell technology.
For example, solar cells with no grid lines on the front absorb more sunlight than conventional cells and do not suffer from issues such as delamination . The construction of our cells makes them stronger and more resistant to cracking or corrosion. And a microinverter on each panel can optimize power conversion at the source, in contrast to one large inverter mounted on the side of the house.
Because of these wide variations in quality and efficiency, its difficult to generalize about which solar panels are right for you or how many youll need for your home. The main takeaway is that the more efficient the panels are, the more wattage they can produce, and the fewer you will need on your roof to get the same energy output. Conventional solar panels usually produce about 250 watts per panel, with varying levels of efficiency. In contrast, SunPower panels are known to be the most efficient solar panels on the market.*
To figure out how many solar panels you need, divide your homes hourly wattage requirement by the solar panels wattage to calculate the total number of panels you need.
So that average U.S. home in Dallas, Texas, would need about 25 conventional solar panels or 17 SunPower panels.
How To Calculate Solar Panel Output
Heres a simple formula for calculating your solar panels power output.
Solar panel watts x average hours of sunlight x 75% = daily watt-hours
As an example, lets say you have 250-watt solar panels and live in a place where you get 5 hours of sunlight per day. Whats that 75 percent for? Thats to account for all those variables we’ve been going over.
250 watts x 5 hours x .75 = 937.5 daily watt hours
To translate this into the more familiar kilowatt hours youre used to seeing on your electricity bill, simply divide by 1000.
937.5 / 1000 = 0.937
To round up and make it pretty, thats 0.94 kilowatt-hours per solar panel.
Of course, you dont have to do this math yourself. Vivint Solar experts will help you through these calculations to find the optimal solar panels for your home. We do this every day and we think its fun. Since we get a lot of questions about how to calculate solar panel output, we decided to share it with you.
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Calculate A Solar Energy System Requirement
You need to match the kilowatt hours of your solar PV system to the kilowatt hours that your appliances will use. To approximately estimate the energy requirement for a period of time, we need to multiply the hourly power consumption by the number of hours of intended use. An example for the same would be a 40W appliance in domestic use that will be used for 2 hours per day. The daily energy consumption for it would be 40*2 = 80 Wh.
Repeat that exercise for every appliance individually to calculate the daily energy requirement for your solar energy system. Add in any appliance that will use power while connected to the solar panel. The result will give you an indicative total energy requirement for the solar panel to produce for the day. You can work out the number of panels needed a few ways.
You calculate how many solar panels you may need by dividing the maximum hourly solar energy system output by the wattage output of one single panel. The number of solar panels of the size used in the calculation will theoretically meet that energy demand during a sunny day.
Another way is to multiply the households hourly energy requirement by the peak sunlight hours for the area. Then divide that answer by the wattage of the solar panel intended to be used.
Why Didnt You List All Of The Components I Need Wires Fuses Ect
Your wire size is going to vary greatly depending on how far you are running them. Read our wiring guide for more details on how to size your specific system. It is difficult to predict how much wiring each different van build will have and the lengths needed, and we dont want to have you ordering things that you dont need.