How Big Of A Solar System Do I Need

Factors That Affect Solar Panel Output Efficiency

All things being equal, the design of the solar panel determines how efficient it is. This, in turn, specifies how well each square foot can convert sunlight into energy.

For example, gridlines on most panels reduce the active surface area. Therefore, they are not as efficient as those without them. In addition, grid panels are susceptible to peeling, further reducing efficiency.

Quality plays a role, too. For example, if the construction is subpar and introduces corrosion and cracking, it can also impact the ability of the panel to absorb sunlight.

But as a rule of thumb, expect residential solar panels to give you between 150 370 watts. This translates to an average solar panels wattage per square foot of 15 watts.

Physical Size Of Solar Panels

A 5kW solar system may produce enough energy to power your home, but you may not have enough roof space for a system of that size. Solar panels for households typically come in the standard dimensions of 1.70m x 1.00m, thats around 1.7m2 for every panel installed. However, the wattage output of the panels will likely vary between 250W and 360W for a more efficient module.

As a guide, youll need 4 x 250W panels, or 3 x 330W for every 1kW of your solar system. If youre considering a 5kW system, thats between 15 and 20 solar panels that will require anywhere between 25.5 34m2 of roof space.

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.

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Looking For Solar Panels

Your minimum aim is to cover as much of your household consumption as reasonably possible for a typical day. If your power consumption is 30kWh on some days, but on most days it’s 20kWh, it might not be worth adding extra panels just to cover those few 30kWh days. You could go with a 5kW solar PV system and just accept paying for more power than usual from the grid on those occasional high-consumption days.

But solar panels are relatively cheap now, and there’s an economy of scale in installing a larger system, so it’s worth talking this through with your installer to consider how big a system you could get. Typical solar PV systems installed in 2021 are at least 6.6kW in size and we think that’s a good size for most homes to aim for right now.

That said, bigger systems of 810kW are becoming more common, especially for systems that include a storage battery.

You might think it’s better to oversize your system because any excess will be exported to the grid, and you’ll be paid for it via the feed-in tariff. But the feed-in tariff for new solar PV systems is generally very low typically from four to eight cents per kWh, though you can get better deals from some energy retailers and it’s unlikely on its own to justify the cost of a larger system.

Read more: Are solar feed-in tariffs worth it?

Power usage shifting

Online calculators

So How Does This Compare To The Output Of A Solar Power System

The output of a solar system depends on which way your roof is orientated, and now we are getting into the specifics of maximising the benefit of a solar power installation. The Solaray Team will often advise people to go for a split array. Yes, having the panels facing north is best, however, this creates a rough bell-curve of output where you get a peak generation period during the middle of the day. Are you going to be able to use most of the solar power most of the time if you have an output curve like in the image below?

This is a 5kW system in March, turning on as the sun comes up and turning off again at around 7 pm. As an aside, one of the most important points from this image is the maximum output. A 5kW system almost never gets close to 5kW of output at any one time due to the angle and the orientation of the panels. This system has produced 959W in 15m, so around 3.8kWh in the middle of the day. This could be improved with sun tracking, however, the cost of installing and maintaining an array that follows the sun does not pay for the increase you will get in output. It is much cheaper to just get a few extra panels.

Look at google maps to see what roof sections you can install solar panels on. Anything north of west or east is usable.

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Or Will You What Can Affect Solar Panel Output Efficiency

The Standard Test Condition rating is based on ideal conditions converting the suns energy into power. But the solar system itself is not 100 percent efficient in converting the energy into power.

• A solar system requires an inverter to convert the Direct Current power the photovoltaic cells receive from the sun to Alternating Current power used in our homes. Power is lost as it goes through the inverter, which can be a single inverter per system, or a single inverter per solar panel. It is estimated that about three percent of electricity is lost passing through the inverter.
• Different materials used to manufacture the cells can resist the flow of electricity as can resistance passing through the cables.
• Inevitably, solar panels will pick up grime and dirt from the atmosphere, blocking full sunshine.
• Temperature can effectively create power losses as well. While it seems that a hot, sunny local would be ideal, the fact is that the STC is based on a temperature of 25 degrees Celsius . The flow of electrons across the photovoltaic cells is not as efficient at higher temperatures. All in all, solar companies estimate a de-rating factor of around 20 percent.

Be aware that system sizes are calculated inversely in the United Kingdom and the United States.

Thus, a typical 1 kWh system in the UK is estimated to produce 850 kWh unit per year, a 2 kWh would create around 1,700 kWh units per year and a 5 kWh system is estimated to create 4,500 kWh .

Average Annual Yield From Solar Panels

As you can see in the table above, the larger your solar PV system, the greater its annual energy output . A 1kWp system will produce about 850 kilowatt hours of electricity, while a 4kWp system will churn out a whopping 3,800kWh.

But what actually is a kilowatt hour? Quite simply, its the quantity of energy that a 1,000-watt appliance would use if it was switched on for one hour. For example, if you turned on a 50-watt light bulb, it would take 20 hours for it to use 1kWh of electricity. In contrast, a 2,000-watt oven would use 1kWh of electricity in just 30 minutes.

Youll notice in your energy bills that your monthly electricity usage is measured in kWh, so it makes sense to quantify a solar panels electricity output in the same way.

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How Many Solar Panels Do You Need To Power Your House

Example Sizing solar panel PV systems

How many solar panels and their power rating would be needed for a fixed solar system to cover the energy consumption of an average U.S. home?

Lets say the house is in Burns, Oregon USA, with an average electricity consumption per day of 33 kWh.

Checking the site Global Solar Atlas, we see that the irradiation in this location is 5.83kWh/m2/day.

Use historical irradiance data to find suns energy in your location

• Geographic Location: Burns, Oregon, USA
• Average daily energy consumption: 33kWh/day
• Irradiation for Burns, Oregon is 5.83kWh/m2 per day

PV System Losses

I previously said that system losses can be 23%, but they can also be higher. Ill use 30% as the overall system loss, to make sure I dont underestimate the number of solar panels to cover the homes energy needs.

With 30% losses in mind, the energy needs are:

33kWh/day x 1.44 = 47.5 kWh/day load.

Now to take into account the efficiency of inverter, which is about 96%.

The power to be supplied to the inverter = 47.5/0.96 = 49.5kWh/day.

The average daily irradiation is 5.83kWh/m2

49.5kWh/day of power can be produced by:

49.5/5.83kWh/m2= 8.5kW or 9kW of solar panels working at 100% capacity rating.

To find the number of solar panels needed, divide the wattage needed by wattage of each solar panel :

Number of panels needed = 9kW/300 watts per panel = 30 solar panels.

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Your rate of self-consumption will depend the amount of energy that you use on a daily basis, the pattern of your consumption throughout the day, and the size of the system that you install.You can increase your solar self-consumption ratio by running more of your devices during daylight hours possibly manually, on timers or using a home energy management system.

The table below contains very rough solar self-consumption ratio estimates for a range of popular solar system sizes and energy consumption levels. If the cell is red, the system is probably too large . If the cell is green, the system size is likely have a favourable payback period .

Remember: The table above is a highly generalised, indicative guide it does not take into account your location or the tilt & orientation of your roof not to consider system prices or financial details like payback period. If youd like to take a more detailed look, use our Solar PV System Payback Estimator or our Simple Solar System Sizing Estimator.

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The Climate Of Your Area

Well, as you might imagine, a home in a temperate climate uses less energy than somewhere colder or hotter.

In hot climates, fans do not suffice, and people turn to A/C to have a comfortable temperature around.

So, having the A/C on for most of the day will consume more energy than with a fan, right? So, having A/C at home means that you will need to install more solar power.

A small home in a mild climate area uses around 200 kWh per month. But if you go south where the A/C power demand occupies a large share of the energy consumption, that figure could go up to 1700 Kwh.

Same story goes to heating.

How Many Days Storage Back Up Do You Require

The most expensive part of any solar power system is the batteries. Because you can only use a maximum of 50% of your battery per cycle to ensure you dont damage them and they last longer, you generally need a minimum of 2 x energy requirement in storage space.

For example, if you need 5kwhrs per day, and you want to be able to store 1-day backup in case there may be no sunlight for 24 hrs, you would need:

5kwh x 2 = 10 kwh x 2 = 20 kwh

20 kw hours in battery terms for a 12v battery that is a 250amph would be:

= 6.666 batteries required

Now that you have the totals, you know what size solar power system you need:

Max peak power: i.e. 2000w

Your Daily usage: i.e. 12kwh

Battery storage: i.e. 1 day back up

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How Many Solar Panels Do I Need

The number of solar panels that you need depends on the system size that you select. However, you can have a different number of panels for the same size system. A 5kW solar system can be made up of 20 x 250W panels, or 15 x 333W panels, it all depends on the efficiency of the solar panels you select. The higher the efficiency, the less solar panels you will need.

Buy with confidence

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:

Infographic showing solar panel losses solar calculations must consider losses

The calculator I provide later on in the post takes these losses into account, but for this example Ill go through the process manually step-by-step.

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How Does Solar Energy Work

Our sun is a natural nuclear reactor. It releases tiny packets of energy called photons, which travel the 93 million miles from the sun to Earth in about 8.5 minutes. Every hour, enough photons impact our planet to generate enough solar energy to theoretically satisfy global energy needs for an entire year.

Currently photovoltaic power accounts for only five-tenths of one percent of the energy consumed in the United States. But solar technology is improving and the cost of going solar is dropping rapidly, so our ability to harness the sun’s abundance of energy is on the rise.

In 2017,the International Energy Agency showed that solar had become the world’s fastest-growing source of power marking the first time that solar energy’s growth had surpassed that of all other fuels. Since then solar has continued to grow and break records around the globe.

What Is Solar Energy

Simply put, solar is the most abundant source of energy on Earth. About 173,000 terawatts of solar energy strike the Earth at any given time – more than 10,000 times the world’s total energy needs.

By capturing the sun’s energy and turning it into electricity for your home or business, solar energy is a key solution in combating the current climate crisis and reducing our dependence on fossil fuels.

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How Does A Solar Panel System Work

Here’s an example of how a home solar energy installation works. First, sunlight hits a solar panel on the roof. The panels convert the energy to DC current, which flows to an inverter. The inverter converts the electricity from DC to AC, which you can then use to power your home. It’s beautifully simple and clean, and it’s getting more efficient and affordable all the time.

However, what happens if you’re not home to use the electricity your solar panels are generating every sunny day? And what happens at night when your solar system is not generating power in real-time? Don’t worry, you may still benefit through a system called “net metering.”*

A typical grid-tied PV system, during peak daylight hours, frequently produces more energy than one customer needs, so that excess energy is fed back into the grid for use elsewhere. The customer who is eligible for net metering may receive credits for the excess energy produced and can use those credits to draw from the grid at night or on cloudy days. A net meter records the energy sent compared to the energy received from the grid. Read our article on net metering and how it works.

If you’d like to see how much your home or business can save, schedule a time for us to create a personalized design and potential savings quote.

The Different Sizes Of Solar Pv System

See below for a breakdown of the four key solar PV system sizes, and all the specifications that come with them.

Please note that the annual energy output figures are just estimates, as the output of your solar PV system will vary widely depending on numerous environmental factors. Likewise, the costs are also estimates.

To learn more about how much youre likely to pay for a new solar array, take a look at our guide to solar panel costs.

The more solar panels you have, the more money you can save

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Determine Your Budget For Solar

How much solar you need is determined more by your budget than any other factor. 190 Watt Solar panels each have a cost associated with their purchase and installation. If you have a large budget , you can most likely skip this step. If you have a smaller budget, then this may be the overall limiting factor of your RV Solar system.

Sample RV solar kit cost as of January 2020

• 190 Watt Solar Panel Kit with 30 Amp PWM Charge Controller ranges from $600 to $700
• 190 Watt Solar Panel Kit with MPPT-40 Amp ranges from $950 to $1050
• Each additional 190 Watt solar panel expansion kit ranges from $440 to $540 dollars each

How much solar can I get on my RV for around $700?

Currently, the most efficient panels on the market are around 190 watts. These panels will give you the greatest bang for your buck while minimizing the number of panels needing to be mounted. A 190 watt solar kit with wires and charge controller from a quality brand will run you less than $700.00 if you use a PWM controller.

What is the best solar panel to use?

The best solar panel today is the 190-watt solar panel. It produces about 9.6 amps and very efficient. A high-quality 190-watt panel will produce about 9.2 amps on a 70-degree sunny day with an average altitude in the southern U.S.

Can I add more solar as funds become available?