How To Calculate Kw For Solar Panels

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.

Find Your Total Electricity Use

The number of solar panels you install on your home is dictated by the amount of electricity you use its the most basic piece of data when calculating system size. Most homeowners install enough solar panels to cover 100% of their electricity use. If you use 10,404 kWh of electricity each year , you want to install a solar installation that produces around 10,404 kWh of electricity each year.

So, the first step to figure out exactly how many solar panels you need is to find your total annual electricity use. Utilities make this incredibly easy. Just open up your online account and look at your last 12 months of usage. Above, youll see the authors own usage over the last 12 months.

My house unfortunately isnt a candidate for solar , Ive of course wondered how many solar panels I would need for my own home. So to satisfy my own curiosity and to provide an example we can all follow along with, lets figure it out.

You can see that my household uses very little electricity, typically around 200 to 300 kWh/month. You also see that monthly usage varies quite a bit, as the summer heats up and we turn on the air conditioning. That monthly fluctuation is why adding up an entire 12 months of energy use is so important!

Heres my own energy use, compared to the national average:

Last 12 months of Energy Use

Now Lets Get Straight To Calculations

The latest ACs come with a nameplate having details mentioned, e.g., power consumption, rating, size, etc. That power consumption thing comes in handy when calculating how much power your AC will use approximately annually or in your desired days. OR If you want to figure out your AC power consumption manually, use a Kill A Wattmeter. You have to plug your AC wire into the meter and connect the meter to a socket. It is recommended to study the readings for at least seven days. To calculate how many watts would be used by your AC in a day, multiply the number of hours you want to use by power consumption. To calculate the number of watts for a whole year, multiply the result by 365 days, or if you want to run for summer, four months, then multiply it by 120 days. Not to mention, less power AC starts consuming after constantly cooling for two to three hours, so calculations would be rough, not exact. For the sake of calculations, we assume your AC adds 3000kW to your bill annually, your solar panel system would have to be producing equal or more to offset additional load.

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Required No Of Solar Panels

Now the required No of Solar Panels we need for the above system as below.

Scenario 1: DC Load is Not Connected = Only Battery Charging

We know the famous power formula

P = VI

Putting the values of batteries and charging current.

P = 12V x 20 A

P = 240 Watts

these are the required wattage of solar panel

240W/60W = 4 Nos of Solar panels

Therefore, we will connect 4 Solar Panels in parallel.

The above calculations and system was only for battery charging to AC electrical appliances, which will get power through inverter and DC loads via Charge controller

Scenario 2: DC Load is Connected as well as Battery Charging

Now suppose there is a 10A directly connected load to the panels through inverter . During the sunshine, the solar panel provide 10A to the directly connected load + 20A to the battery charging i.e. solar panels charge the battery as well as provide 10A to the the load as well.

In this case, the total required current

In this case above, total required current in Amperes,

20A + 10 A = 30A

Now, I = 30 A, then required Power

P = V x I = 12V x 30A = 360 Watts

I.e. we need 360 W system for the above explained system

Now, the number of solar panels we need

360/60W = 6 Nos of Solar Panels

Therefore, we will Connect 6 Nos of Solar panels in parallel

• Parallel Connection of Batteries with Solar Panel

Is 1 Kw Enough To Run A House

Considering the average household in the United States uses roughly 29kWh per day, and 1kW of solar will give you 4-5kW of power with 5 hours of sunlight, this will not be enough for most homes.

That being said, it can certainly help lower your dependence on mains power and save you money on electricity bills.

It also helps to look at your energy requirements and usage, and see where you can save on power. For example, using a solar geyser to heat water, a gas fridge, and a stove, and heating your home with a fireplace or gas heater will save a ton of power overall.

In my home, a have a 1kW solar system that provides me with more power than I need, since I save on energy usage by using gas appliances and a solar geyser. This is more than enough to run lights, computers, a TV, and other small appliances.

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Picking The Right Battery

So, which solar battery is right for you? There are a few different battery types commonly used for off-grid storage systems:

Flooded Lead Acid

• No maintenance, no venting
• Highest efficiency, faster charging, more usable capacity

The two main battery chemistries for off-grid are Lead Acid and Lithium. These two chemistries have unique characteristics. Lithium batteries are more efficient, which means less power is wasted in the charge/discharge process. They also have a greater discharge depth allowing you to fully utilize all of your battery capacity.

Lead acid batteries are sensitive and need to be fully recharged every day, where Lithium batteries can stay at a partial charge without any adverse effect. Lead acid batteries also have a more limited amount of usable capacity and are typically discharged only 50%.

Because of the better efficiency and deeper discharge depth, Lithium battery banks tend to be only 50-60% of the size of a comparable lead acid bank! The Lithium batteries we use are purpose-built for off-grid solar, and utilize a special Lithium chemistry called Lithium Ferro Phosphate .

This type of Lithium battery is engineered to provide a long service life while also being safe, with a stable chemistry and sophisticated electronic protection features.

This is not intended to be a comprehensive guide on off-grid design.

How Many Solar Panels Are Needed To Power An Average House

This is a seemingly simple question, but it is not. Since your locations can heavily influence the solar output, you need to take the weather conditions, direct sun hours, and something else into consideration when thinking of this question.

Also, different houses have unique solar panel systems for distinctive purposes. So you may need different numbers of solar panels. But to figure out the typical panel numbers, you can check out in an article the average number of solar panels required to power the average home in each state.

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Calculating Your Electricity Consumption

What you want to look for is kilowatt hours . Add up the kWhs for all 12 months. Divide that number by 12 to get an average. Then, divide the monthly consumption by 12 to arrive at your daily kWh usage.

To get even more detailed and this is a great opportunity to accurately assess where you could be saving electricity add up the kWhs of anything that uses electricity. Your electric bill doesnt itemize the energy draw of heating, cooling, lights, kitchen appliances, washer/dryers, hair dryers, power tools, computers, and other devices so its great to know how much certain devices use so you can eliminate them or upgrade to more efficient units.

How do you arrive at kWh energy usage of your appliances and electronics? This is a labor-intensive assessment thats generally not needed for calculating your solar system size but its a great way to audit your homes actual energy needs.

For example:

• One 20W fluorescent garage light on for 2 hours per day = 40 W/hrs
• One 50W ceiling fan on for 24 hours per day = 1200 W/hrs or 1.2k Wh
• One 70W LCD TV on 6 hours per day = 420 W/hrs
• One 50W laptop on 8 hours per day = 400 W/hrs
• One 10W Wi-Fi router on 24 hours per day = 240 W/hrs
• One 200W refrigerator on 24 hours per day = 4800 W/hrs or 4.8 kWh

Solar Panel Sizing 101

Much like lightbulbs, solar panels come in different sizes. For the most part, individual solar panels range in size from 250-watt up to 400-watt. Once you know the total number of watts your solar system needs to be, determining how many panels you need is simple math. A 5kW system is going to require at least twenty 250-watt panels . MOXIE commonly uses 350-watt to 370-watt solar panels. This size panel is generally a good compromise between 1) available space for the panels and 2) cost per panel.

Pro tip: When performing solar system calculations you should also factor in seasonal weather patterns and equipment deratingover at least 25-years.

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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.

Rating Of Charge Controller

As we have calculated above that the charging current for 200Ah battery is 20-22 Amperes , therefore we can use a charge controller about 30-32 Amp.

Note: The above calculation is based on ideal case, so it is recommended to always choose a solar panel some bigger then we need, because, there are some losses occurs during battery charging via solar panel as well as the sunshine is not always in ideal mood.

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Determine The Daily Sunlight Average In Your State

As weve mentioned, the amount of sun hitting your roof can determine how many panels you could need. To ballpark this figure, find the average daily peak sunlight hours in your state. We used North Carolina, POWERHOME SOLARs headquarters, for our example.

North Carolina receives an average of 4.71 hours of daily peak sunlight.

Key Points About Solar Panel Output

• Standardized residential solar panels on the market are quoted to generate averagely between 250 and 400 watts an hour.
• Typical domestic solar panel systems are rated to produce power ranging from 1 KW to 4 KW.
• The actual output of a solar panel depends on many factors, such as its size, capacity, location, orientations, and weather conditions.
• You can compare different output quotes of a solar panel and see how solar panels with different capacities will influence your particular solar system. You can search on the EnergySage to find more specific information.

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Rooftop Area Needed To Install Solar System:

Once you know the number of solar panels you need to install then use the below formula to calculate the area needed to install it.

Area required for solar panels = Total number of solar panel x area of one panel.

For example for a 7.5 kW system has 23 solar panels each of 320 watts which means area needed to install 7.5 kW of solar panels is,

Area for 7.5 kW of solar panels = 23 x 21.50 = 495 sq.ft

This is just the area required to mount all the solar panels back to back and side by side to each other.

In real life we have to leave space between rows and columns of solar panels so that we can easily clean the solar panels every now and then, and also have safe access to perform maintenance if and when needed.

You can use the table below to get a rough idea on how much rooftop area is needed to install solar panels.

In the area column the values on the left indicates the minimum area you will need to install those many solar panels and the values on the right indicates ideal area you will need to install those many solar panels keeping in mind the cleaning and maintenance space.

The area should be shadow free area, meaning this area should receive direct sunlight for at least 5 hours in a day ideally between 10:00 am to 04:00 pm.

How Many Kwh Does A House Use Per Day

On average, the daily kWh consumption for an average home in the United States is just under 29 kWh hours. This accounts for using energy-heavy appliances like geysers and heating, both of which can be substantially reduced.

This energy usage is also dependent on the size of your home, the building materials of your home, and the number of residents. Also, people living in colder climates will naturally use a significantly higher amount of power to warm their homes.

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What Are Solar Panels Made Of

Solar panels are made up of polysilicon, metal, and glass. A solar panel’s solar cells, the photovoltaic component of the solar PV panel that creates electricity, is made up of silicon as well.

Most of the solar panel is made up of PV cells which are then covered by glass and a back sheet for protection. These layers are held together by a metal frame that can be fitted to solar racking on a roof.

Each solar panel also has a junction box on the back of it. This box is what holds and protects the important wiring that carries electricity to the inverter.

Dig deeper: Read more about how solar panels are made.

How Many Solar Panels Do You Need: Panel Size And Output Factors

How many solar panels does the average house need? How many solar panels do I need for a 3-bedroom house? How many solar panels do I need for a 2000 sq. ft. home? These are all common questions for an aspiring solar homeowner. Determining how many solar panels youll need for your home requires first knowing what your goals are.

Do you want to minimize your carbon footprint? Maximize the return on your investment? Save as much money as possible?

Most people want to save money while minimizing their environmental impact.

To calculate how many solar panels you need, you need to know:

One simple way of answering the How many solar panels do I need question is to consult a professional solar installer, who can give you a free home solar evaluation.

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