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Please Note: The figures above are just an estimate. To figure out your exact costs and savings, we recommend to talk to trusted local installers we work with. You can get several quotes from friendly installers, and decide which route is the best for you.
Our calculator provides you with quick estimate for your Solar Power system savings and costs options. We base our estimates on your location, roof shadow, your current electric bill and available deals in your location.
We all know that solar power helps save you money. Plenty of money—often tens of thousands of dollars.
But those numbers can be hard to pin down, too. From sunshine-hours to kilowatt-hours, there are so many things to consider.
What you need is a calculator to help you tally the costs. As well as to rack up the benefits.
Which is exactly what we’ve laid out for you here: Solar Nation’s very own Solar Power Calculator!
Not so much ‘solar numbers for dummies’. More like a solar power calculator for the savvy. After all, there’s nothing dumb about turning your roof into a lean, green, money-printing machine.
Let’s run through some of the questions that matter on calculating solar’s benefits—and its costs.
What are the factors to consider when calculating my solar power costs?
So, let’s take a step back, and take a peek at what makes a typical solar-powered roof tick. Then at how much each of them is likely to cost you.
Your Solar System
The most visible part of your PV system are the solar panels placed onto your roof, or racked-up in your yard (you don’t have to put solar panels just on your roof). A great big banner that says “this home is being powered by sunlight.”
But there’s a lot more needed to turn all that sunshine into electricity that your air-con can use to keep you cool in summer. There’s racking, inverters, wiring, and switches.
And the costs don’t stop at all the clever bits of hi-tech that need to be wired up, either.
You’ll need to factor in money to pay for planning, design and installing the system. And you’ll want a little set aside to keep the panels in humming in top condition over their 30-plus years of operation.
|Fixed costs for a 5 kW system (for solar installer)|
But let’s start with costs of the shiny blue-black panels on your roof:
Once these were the most expensive part of a residential solar system. But years of advances in making those silicon wafers has slashed costs hugely. They’ve actually crashed by 60% in the last 3 years.
Today you’ll be looking paying between $750 to $850 for every kilowatt of capacity your system has.
Of course your panels aren’t just tacked onto your roof. They’re mounted on a supporting grid of metalwork, known as the racking.
This secures the panels, so they stay up there for the duration of their 30-year plus lifespan. Come rain or shine (hopefully more shine!).
Once the sun starts shining on your panels, they’ll immediately start kicking out electricity. The problem is, it’s the wrong sort.
Solar panels produce a direct current (DC), but everything on your ring main is running alternating current (AC).
That’s where inverters come in. They turn all that lovely DC electricity into useful AC. As such, the inverter is the most important part of your system, after the panels themselves.
So, how much for an inverter?
Again, we usually look at costs per kW capacity of your system. That’s so we can compare differently sized systems more easily. These days, your installer will be shelling out around $250 per kW rating of your system for the inverter.
It’s not just silicon sitting up there on your roof. There’s plenty of copper too. It’s needed for the wiring that joins solar modules together, connects the inverters, and wires the whole lot into your mains.
So far we’ve been thinking about hardware, which adds up to $7,500 to $8,000 of outlay. But an equal-sized chunk of the cost is in the labor. The work it takes to get you solar system from online quote to powering your home.
Putting it all together
One last thing to note here—all these numbers are the cost to the solar developer. They’ll obviously have a markup on these items, so you, the homeowner, will pay a little extra.Ho much depends on the location and the firm.
That will push the cost over the $15,000 mark in total (and somewhat more in the more expensive U.S. states) for our 5kW system.
How much electricity will I get from my solar power system?
Well, basically it all comes down to three things:
- How much sunshine you in your little corner of the U.S.A.
- How much space you have on your home’s roof, and how it’s laid out.
- And how much silicon wafer you decide to spread across that roof.
This is probably the most important factor. The amount of electricity you get from a solar system depends on the amount of sunshine it receives. The sunshine hours. And you’ll get a lot more sunshine in Florida than in Arizona.
But how exactly do you measure sunshine?
Well, the way solar calculators do this is to look at something called solar irradiance. That’s the amount of sunlight energy falling onto a square meter every hour (or every day). They then turn this into the total amount of energy that can be collected by your solar photo voltaic (PV) panels.
But the sunshine varies by the minute, by the day, and by the season—as well as by how close you are to the equator.
The simplest way to take all this into account, and find out your solar irradiance number, is to look at one of the excellent maps produced by NREL.
These show how much energy, in theory, you can expect to receive every day from a square-meter covered by PV panels. This averages out all the seasonal and daily changes for one whole year.
So, simply you look at the map, pick out your location, and check the color-scale on the map. That gives you a theoretical best for energy production per day.
Here are some examples we picked off of the map ourselves:
KWh energy per sq-meter (PV) per day
|San Diego, CA||6.5|
|Los Angeles, CA||5.0|
Bring on the sunshine!
But remember that’s just the potential energy. There are a whole lot of steps between sunshine hitting your panel and it running your dishwasher.
Sadly, they all tend to take that number down, rather than up.
The next thing you need to take into account is your home. Or most likely your roof.
You’ll need to know your roof’s shape, size, and pitch, if you’re to properly calculate the electricity you can produce from it.
Partly that’s because your roof places limits on exactly what size and arrangement of solar modules you can put up there. Partly it’s because the orientation and pitch of those panels limits how much of the sun’s energy you can actually capture.
Let’s break it down
This is an obvious one. The more roof you have, the more panels you can fit on it. But you’ll need to take into account usable space too.
Fire regulations and building codes place a limit on how much of that space you can use. And roof-top features like chimneys and vents can limit the space available.
Roof Orientation & Slope
This one might not be quite so obvious. But the thing to remember is that those sunshine energy numbers we just worked out assumed a perfect pitch.
That is, the numbers only apply if your panels are perfectly sloped to make the most of the sun. Usually that equates to panels that are on a south-facing root that’s angled a little less than your latitude.
Learning to love the latitude
Well, for those a little shaky on Geography 101, latitude is just a measure of how far you are from the equator—expressed in degrees, as an angle.
So if you’re at the equator, your latitude is 0 degrees. And the north pole is 90 degrees north. Most of the U.S lies between 30° N and 50° N.
The best roofs for solar power are those that are south-facing, with a slope that’s a little less than that. Say 25° in San Diego or 40° in Seattle. That way they’ll soak up 70% or more of the incoming sunlight.
If your roof isn’t south-facing, or isn’t at the best angle, you’ll need to make an adjustment to the solar energy numbers. These calculations aren’t simple. You could use a solar calculator, like our simple one we’ve provided here.
Your Solar System
Now we get into the nitty-gritty. The devil in the detail (yep, we’ve only touched on the easy bits of the calculation so far!).
We know how much sunshine energy we should get in practice on our roof. But lots of things get in the way of the theory.
Things like the efficiency of panels you’re using. Like how they’re connected. Like the energy loss when you go from DC to AC (remember those inverters?). Or even whether you want to get really clever, by tracking the sun.
Let’s run through a few of these aspects of your solar system. Then you can calculate how much electricity you’ll actually get when you turn on your solar panels.
First a bit of bad news. Not a lot of the yearly sunlight energy your panels receive gets converted into electricity. In fact, the efficiency of the conversion ranges between 15% and 20% for most panels.
That’s better than it was. But certainly less than you’d want.
Note: It’s also worth remembering, though, that the efficiency of solar panels has increased a lot recently. The world record is rapidly heading to 25% and higher.
So now we have a reduced—but still decent—sized flow of electric current coming from your panels. The next thing we need to do is convert that from DC to AC using our inverter.
But guess what happens in the process?
Yep, you guessed it. The conversion from DC to AC shaves a little off the amount you get. For most inverters this is around a 6% to 10% loss.
But is there any way to boost those numbers?
Yes. You can make a really positive difference to your solar system’s efficiency. You just need to follow the sun.
So far, we’ve been working through what happens with your solar panels when they’re installed pointing in the best overall direction—but locked in place. Such an arrangement is called a fixed tilt system. It’s the simplest, cheapest way to do solar.
But there are other ways of doing things. You can manually adjust your panels to follow the sun, as it lowers in winter and raises in summer. Or you can buy a system that does this automatically, on one axis.
You can even get a system that moves panels on two axes. Then they can follow the sun daily, just like a sunflower. That way you get the best of the sunlight, day-by-day, month-by-month. But of course those sorts of systems can cost.
So, the question is—will the extra energy be worth the extra spend?
Let’s work out some numbers on how much you might expect to save from your bill, for a simple system, first.
Can I calculate my electricity savings as well?
Sure you can. We’ve got a rough idea of how much electricity we can produce from your system. And every kilowatt-hour of electricity produced by the sun means one less kWh on your bill.
So we’ll need to figure out what you’re paying on your bill. And then finally you’ll get some big smiley “dollars saved” numbers out of our Solar Power Calculator.
How does your electricity bill look?
In order to work out your savings, then, you’ll need to delve into your utility bill. To keep things simple, total the kWh numbers for your electricity bills over your most recent year.
Then you’ll need the rate you’re being charged to use that electricity.
[blue]Example: Let’s assume that we’re using the average amount of electricity for a U.S. household. In 2015 that was 10,900 kWh. Now, the average utility rates in California were $0.17 per kWh in 2015.So the annual electricity bill for that year would be $1,850.
But we know that our production from our 5kW system could be as much as 8,400 kWh. So your bill is now only $425. You’ve saved over $1,400 in one year!!
Will my choice of panels effect the calculation?
Yes, it can make a big difference. First, no two module manufacturers are the same, each having different efficiencies at converting sunlight to electricity.
The technologies differ too.
There are monocrystalline silicon panels, polycrystalline panels, and amorphous silicon. All have different costs, different efficiencies—and different savings for you.
Then there are single axis tracking systems and two-axis tracking systems, to boost your savings. But will cost you more.
And the technology and costs just keep on evolving. Exciting, but quite a lot to get your head around.
Is that everything covered for our Solar Power Calculation?
You might think so, but no.
In fact, we’ve actually been keeping things pretty simple, above. There are plenty more complexities that matter. Let’s touch on a few.
We’ve assumed that your panels aren’t being shaded by trees or other buildings. This can have a big impact, especially with solar modules that use ‘string’ inverters.
A design using micro-inverters can help reduce the reduced efficiency from shading. But to get the proper numbers, you’ll need to map how that shade affects your roof throughout the day.
All the solar power calculations so far assume the panels are perfectly clean. Which they are most of the time, especially after its rained.
But accumulations of dust and dirt can knock off 1% off the panels output.
Snow can be a two-edged sword. Obviously, a layer of snow can block a lot of sunlight getting through.
But snow often melts off of black solar panels quite quickly in the morning. Then, all the reflected light of the snowy landscape can actually boost the amount of light the panels absorb.
A 1% allowance of loss for snowy locations is common applied, though.
Degradation over time
Like most things exposed to the elements, the components of a solar panel system are prone to a slow weathering. This reduces the performance gradually, over the years.
Allow for around 0.5% degradation in performance per year.
There are extra costs associated with solar panels we well. There are maintenance checks and upgrades needed for wiring and inverters. And an insurance policy against damage is essential.
But whether you pay for these depends on whether you decide to pay for solar outright, or lease them with zero money down (or get them as part of a PPA, or power purchase agreement).
Incentives & rebates & tax exemptions & performance payments
Solar power isn’t just a money-saver. It’s a plant-saver too. And the more forward-looking of state governments want to harness solar’s green power to clean up their electricity generation.
But every state has a different set of regulations governing how much help they offer. There are all kinds of measures available, from incentives and rebates to tax exemptions and feed-in tariffs.
See the DSIRE database to see what your state has to offer. Or check out one of our helpful overviews of solar in your local state.
Hourly electricity load & time-of use
There’s one last wrinkle to all of this number-crunching which may affect things for you. Many utilities don’t bill at a constant rate throughout the day. They’ll charge more for peak-load, which varies according to the season and the time of day.
So, where can you turn?
Who else can help with calculations?
You might think so, but no.
One option for trying to work out the costs and benefits without blowing a gasket is to use an online solar power calculator. There are hundreds of these online. Some are simple, some are complex. PV WATTS is perhaps the best known, free-to-use and issued by the respected NREL.
Because it’s backed by the NREL, it’s numbers can be trusted. It does, however, still make some simplifying assumptions.
Why there are different results when using different calculators?
This is partly because there are so many factors to take into account. Some models may not use all of these. Or they gloss over some of the complexities.
It’s also because the economics and technologies of solar power are constantly changing. Not all calculators are kept up-to-date with these details.
Solar panel installers
There is one group of people who do keep themselves ahead of the curve, when it comes to Solar Power Calculations—solar installers. After all, it is their business.
If they get their numbers wrong, they lose money.
How do solar panel installers do their calculations?
The biggest difference with other methods is that a solar system installer won’t make assumptions. They’ll want to know everything they can find out about you, your house, and your needs.
They’ll visit your home to take detailed measurements. They’ll use the most relevant local weather data for your location. They’ll be able to make best use of the many incentives, rebates, and tax breaks out there in your location.
In short, because they’re professional, they’ll take a professional approach. Giving you he solar numbers that are applicable to you only.
How can I get the most accurate calculations?
For the most accurate calculations, there is really no substitute for a local solar company.
They can combine an intimate knowledge of local conditions with an in-depth assessment of your house.
And given that you’re talking about an investment that will save you money for decades, you want those calculations done right.
A trusted installer can visit your home for free, and provide you with a firm quote, with no strings attached.
Is it better to have a solar company visit my home for accuracy?
Yes, it is. As long as you make use of trusted installers.
We recommend that you have several installers come to your home. That way you can check the accuracy of the measurement they make, and decide which solar firm best suits the way you would like to go green with the sun.
Ok, I now have an estimate of installation, now what?
[yel]If you’re ready to go from number-crunching to bill-saving, check out our simple form. Once you’ve entered a few details, we can tell you who’s ready to get these money-saving, planet-greening panels onto your roof, now![yel]
Calculating the numbers around solar power isn’t rocket science. It just seems like it.
Whatever way you slice and slice those numbers—on a spreadsheet, using our Solar Power Calculator, or on the back of an envelope—eventually you’ll need to get the experts in. They can turn the theoretical into the practical. To go from planning to reality.
And it really is time to get those solar panels on your roof—and to start saving money. With costs so low, and the incentives under threat in many U.S states, you’ll need to move fast.