How Many Solar Panels Are Needed to Run a House?

Harnessing the abundant energy of the sun is becoming an ever more popular means of powering everything from outdoor lighting to automobiles, and there are many good reasons to do so, but the number one usage of solar power is providing electricity to our buildings, both residential and industrial.

There are millions of square feet more every year, converting sunlight to electricity and we haven’t even scratched the surface; the energy from the sun is enough to power every electrical commodity, gizmo, tool, and home on the planet many times over.

Looking solely in the residential sector, there are lots of things you should know before you begin, and many questions that would-be consumers of solar energy are looking answers to, and “how many solar panels are needed to run a house?” is probably the most frequently asked; but we need to address a few key areas which raise further questions.

Yes, this can be confusing and stressful, but we’re here to minimize the jibber-jabber so you can capitalize on your own little pocket of the solar market.

Some of the other questions you need answers to, before getting to the big one, are:

How much electricity do you currently use?

Where you are located? Which state/city etc.?

How much electricity can you expect a solar panel to provide?

And, how much available space do you have, and need in which to install solar panels?

The combination of the answers to these questions will hopefully provide a clearer picture of whether you want to completely put an end to electricity bills, or drastically reduce the bulk of energy that you pay for.

Sizing your system to estimate the amount of power you need to run your home efficiently will help you plan and set a budget accordingly; there should be fewer surprises along the way with ample research and preparation.

So, grab your pen and paper, calculator, or other weapons of math destruction, and roll up your sleeves – it’s about to get technical.

How much are your utilities?

Whether you live in the sunny state of Florida or the biblically dreary Oregon (where some areas see as little as 50 days of sunshine!), you are going to want a solar installation that meets your needs, and that means knowing what you use on an annual basis – though it wouldn’t hurt to know what your monthly usage is either; allowing for seasonal variances may help you estimate more accurately, especially if your home is heated using electricity as opposed to gas.

Depending on where you live; how old your house and domestic appliances are; how well insulated; and how many people live there, plays a massive part in determining the figures you see on your monthly electricity bill.

Older houses tend to have older and less efficient windows, and wall and roof insulation compared to newer builds.

You will find better energy ratings on white goods and other domestic appliances manufactured in the last five years than you will in the five previous; generally, the products of today are built with lower ranges of electrical consumption than those of yesteryear.

A home with three kids and two parents will use more electricity than the home of a single person of comparable size.

Your utility company will give you your monthly usage on each bill, and some may even show you what you have used in the last year; the important figure you need now is not in dollars but in kWh (Kilowatt Hours), which equates to one Kilowatt Hour or a thousand Watts sustained during one hour.

In 2017, the average household in the United States used almost 10,400 kWh; yet, depending on which city or hinterland you live in, you could see averages swing between 3,000 kWh less, to over 10,000 kWh more than the average.

As an example; if, say, your television uses 200 Watts per hour and you watch it for 5 hours, that’s 1000 Watts, divided by 1000 to give 1 kWh – so for the average home of 10,400 kWh, that’s almost like having six TV’s on, all day, every day, for a year.

Modern appliances come with an energy rating, stating how many Watts per hour they will use, helping us to monitor which uses the most electricity and our consumption behaviors, allowing us to introduce energy-saving habits, to further reduce our impact on the environment.

At this point now, you should know approximately how much electricity you use throughout the course of a year and are projected to use in following years (new babies, or home entertain systems notwithstanding), you have a grasp on what you are going to need from a solar panel installation.

What level of exposure do you get?

You know what you did last summer…

Were there ominous looking clouds and the cawing of crows, or skies full of bumblebees, barbeque smells, and sunshine?

How much sunlight you receive annually will largely depend on where you live, and how much of that sunlight will be utilized by conversion to electrical energy.

The climate varies year in – year out; season to season; state to state; valley to valley – visit for average percentages and average hours of sunshine where you live.

Multiply the hours of sunshine by the percentage of sun, to get a rough estimate of your daily level of direct sunshine.

Other factors involved in quantifying how much exposure to sunlight you get on a yearly basis are, the shape of the landscape around you; the degree of your roof; and orientation of your home in relation to trees, the neighbors, and most importantly, the sun.

Expert engineers working for whichever installation company you choose will be more able to advise on your installation, accounting for all these variables to ensure you get the system that benefits you most.
You may even need to consider installing a “grid-tied” or hybrid solar system to be able to enjoy a reduction in your electrical costs and reduce your carbon footprint if 100% off-grid is not a viable option.

How much energy does a solar panel produce?

Energy follows one simple rule; so, say the physics guys – energy cannot be created, and it cannot be destroyed; it can only be exchanged from one form of energy to another.

The Photovoltaic (PV) cell is made of layers of semiconducting materials such as silicon or organic polymers and they stimulate electrical flow by using the transfer of energy from photons (particles of light) to electrons (negatively charged particles); meaning that we can only get out of it in terms of electrical charge proportionate to the amount of light energy going in – in theory.

However, the reality is that many PV cells will have an efficiency lower than 20% – the best being around 23% and the record in 2014 of 46% (laboratory result only) – so only that amount of the energy from the photons hitting the semiconducting materials in the cells will be converted into electricity; some will reflect off the surface, and some will be converted into heat energy.

Bear in mind that the hotter the cell gets, the less efficient it becomes; they need plenty of ventilation to prevent loss

The uses of solar power has come a long way since the Dark Ages and again since the Bell Solar Cell of 1954 and efficiency has increased and is set to improve as technological advances in the field of solar energy science pave the way to a greener future – hopefully to the theorized “grid parity”, where producing electricity with solar panels will become as cheap as it is to buy from the grid.

Supposedly by 2020… we’ll see.

For now, however, the standard for residential solar panels of sixty photovoltaic cells, the general range of output is between 260 and 300 Watts per hour in ideal weather conditions.

These tend to be the most widely utilized types of panels as they are smaller and lighter, therefore easier to install than the hefty panels of seventy-two solar cells, which will produce 360 – 400 Watts of electricity.

Each panel model – just like your white goods – will give you a rating in Watts and this should be your expected output per hour of direct sunlight.

You might have a day of twelve hours of sunlight, but only a certain number of those hours will be useful in calculating your daily electrical gain.

The standard 285 Watts panel – in northern latitudes – will produce 1140 Watts per average clear day of four hours useful sunlight.

That’s 1.14 kWh of electricity per panel, per day or 416.1 kWh per year; now scale that up to cover the amount of electricity your home consumes in a month or a year, and we’re one step closer to getting an estimate of how many solar panels you need.

Compare solar panels for efficiency ratings to get the best array that suits your need and then compare prices.

How much space do I need?

The more room you have, the more panels you can potentially install; whether on your roof or another area of your property.

The average American home has roughly 3,000 square feet of roof, of which only half will be of any use (and only if it is South to South-West facing) to someone planning to install a solar system; but for smaller or older homes, a ground-based installation may be perfect for you.

Most standard panel dimensions are around 65 by 39 inches, giving a total of 17.6 square feet.

Divide your available, useful roof space by 17.6 to get a rough estimate of panels you might be able to install – it all depends again on the dimensions of your roof; skylights, porch peaks, and chimneys will interfere with what area you have at your disposal.

But let’s take a 1,500 square foot roof with no obstacles; divided by 17.6 is 85 solar panels – you won’t want or need that many.

Considering that the average panel may produce 1.14 kWh per day, to meet the energy requirements of the average home (10,400 kWh per year/866.66kWh per month), you will need 25 solar panels to produce enough electricity to power your home.

If your need is higher, you install more panels – if it’s lower, install less, or install panels with a greater or smaller expected output.

Your system size will then be your daily output requirement divided by the number of hours direct sunlight per day, times the number of days in a month (just go with thirty).

866.66 / (4*30) = 7.2 KW system

It is important to remember that we’re talking in averages; climate will dictate how much sunlight you will receive per day.

Take Louisville, Kentucky, where there are an average of 2514 total hours of sunlight per year – out of which less than half are going to be useful (3.83 hours a day); to cover a 2,000 square foot home (1,500 square foot roof), using approximately 12,000 kWh per year, with 285W panels installed, would need an 8.7 KW system of 30 panels, covering over 534 square feet.

There is a multitude of solar panel calculators out there, and most will take your basic information to search their databases to give you an estimated quote of what size of system you might need and how many panels that system requires to function.

But, where’s the fun in that? Right?

Final Thoughts

We’ve covered what we know are the most pivotal factors in determining how many solar panels are needed to run a house (annual energy consumption; annual exposure to direct sunlight; solar panel output; and space required) and to arm you with the tools to work out the knick-knackery.

There are a lot of things to think about before diving in at the deep end and splashing out your hard-earned dough; hopefully, this has given you food for thought and if there is any wisdom that we hope we have imparted, it is to research, calculate and budget appropriately.

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