Author: Ian Shurtleff

Crown Battery Review: CR-430 Pros & Cons, Pricing and Specs

Crown Battery Review: CR-430 Pros & Cons, Pricing and Specs

Review: Crown CR-430 Flooded Lead-Acid Battery

The Crown CR-430 is our go-to battery pick for cost-effective solar energy storage. If you’re willing to perform routine maintenance on your battery bank, these flooded lead-acid batteries provide a low-cost entry point to solar storage.

Crown is our best-selling battery brand, accounting for more than 45% of all battery sales here at Wholesale Solar. In this Crown battery review, we’re going to look at what makes their flooded lead-acid line such an appealing option—especially for off-grid homes where the battery bank will see heavy daily usage.

Specifically, we’ll take a look at specs, pricing, and pros & cons of the Crown CR-430. This 6V / 430 amp-hour battery is the ideal voltage to pair with a wide range of ‘typical’ solar installations, like an off-grid family residence.

If you need a different size battery, take a look at Crown’s line of batteries in our shop. Most of the info in this article broadly applies to the entire line of Crown flooded lead-acid batteries. Your best choice will be the battery that is properly sized for your system.

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Crown CR-430: Price & Specs

  • Model: CR-430
  • Price: $325 (as of 6/10/19)
  • Dimensions: 12.38 × 7.19 × 15.29 inches
  • Weight: 122 lbs.
  • Nominal voltage: 6V
  • Cycling capacity @ 20 hour rate: 430 amp-hours
  • Projected cycle life at 50% depth of discharge: ~1200 cycles

Pros of the Crown CR-430 Battery

Lowest Up-Front Cost

For a lot of people, budget is the most important factor in the decision-making process. The main appeal of the CR-430 is its low price point. It’s the most cost-effective way to get into battery-based solar.

For $325 (at the time of publication), the CR-430 offers an estimated cycle life of 1200 cycles at 50% depth of discharge. A comparable sealed battery would be the Fullriver DC400-6, with a price tag of $583 and an estimated cycle life of 1250 cycles.

The upgrade to sealed batteries removes the need for regular maintenance (which we’ll cover later in this article), so they’re much more convenient to own. But in terms of cost-per-cycle, you’ll get way more mileage out of the Crown CR-430. See the chart below for a side-by-side comparison.

Tried and True Technology

Flooded lead-acid batteries have been around since 1859. It’s the oldest type of rechargeable battery on the market.

With 160 years of history, refinement and advancement of the technology, flooded batteries are very much a known quantity. The chemistry is stable and safe, and there’s no mystery to how long they should last or how to take care of them.

Other types of batteries have less history behind them. Lithium-ion rechargeable batteries were introduced in the 1970s and the industry is still testing specific chemistries and refining their product offerings.

There’s not as much of a track record with these technologies and we don’t necessarily know whether they will live up to their promises. The very well could, but we don’t have as much data about stability and failure rates on these batteries.

Flooded lead-acid batteries are a mainstay of the deep cycle battery market. If you go with the Crown CR-430, you won’t run into any surprises or kinks with untested technology.

Company Reputation

Crown Battery is one of the most established players in the flooded battery industry. They’ve been making batteries since 1926 and continue to be a prominent name in the market.

We’ve been working with them for quite a while and they have a good track record for consistency and responsiveness. They’re quick to respond to support calls, and they work with us on trainings and webinars to make sure the product is well-supported.

It’s reassuring to know they’re accessible in case any issues arise and proactive with their education efforts to reduce failure rates.

Lastly, Crown was founded in Fremont, Ohio, where their corporate and manufacturing facilities are located. It’s always nice to support American manufacturing and job creation efforts when the opportunity is there, and Crown is a company worthy of that support.

Cons of the Crown CR-430 Battery

Required Maintenance

The tradeoffs for flooded lead-acid batteries are pretty simple: they cost less, but you have to commit to routine maintenance to keep them working.

Every month or so, the batteries need to be refilled with distilled water which evaporates during the charging process. They also require periodic equalization charges, which is essentially a controlled overcharge to help the batteries stay healthy.

It only takes a couple of minutes, but you still have to commit to the maintenance on a regular schedule or else the batteries will be damaged prematurely. It’s a simple task, but there are drastic consequences if you skip it.

If you’d rather not be burdened by this responsibility, we’d recommend a sealed lead-acid or lithium battery, neither of which require you to commit to upkeep. In our review of the Fullriver DC400-6, we called this a “convenience upgrade.” You pay a bit more so you don’t have to worry about checking in on your battery bank.

Can’t Install Inside

Another reality of flooded lead-acid batteries is that they emit gases during operation. As a result, there are some restrictions on where you can install them. They need to be built according to local codes, in a well-ventilated enclosure, away from flammable materials and other hazards.

Due to the off-gassing, you likely want to build your battery bank in a shed or garage, or put it outdoors in a ventilated battery enclosure. In contrast, sealed lead-acid and lithium batteries do not off-gas, which means they can be safely installed inside your home.

This can also make flooded batteries more costly to install. Though the batteries themselves are cheaper, there can be extra costs associated with building a new enclosure for the battery bank, which should be taken into account when evaluating the true cost of ownership.

Ideal Application for the Crown CR-430

It’s pretty easy to understand why the Crown CR-430 has been one of our best-selling batteries for years. It doesn’t cost a lot up front, and the cycle life stacks up against much more expensive batteries so long as you commit to a few minutes of maintenance on a monthly basis.

Since flooded batteries require regular care, the ideal use case is off-grid properties that are occupied full-time. Flooded batteries self-discharge quickly and need to be recharged after every cycle, so it makes the most sense to build them in an application where they will be cycled on a daily basis.

Due to these restrictions, we don’t recommend using flooded batteries for vacation homes, industrial worksites, or other applications where people won’t be around to use the batteries on a daily basis or commit to their upkeep. Sealed batteries are better in those situations because you don’t need regular check-ins to keep them working.

Need more help with battery bank sizing, or just want some advice on finding the right battery for your project? Connect with us for a free consultation or grab a copy of our free solar battery guide linked below.

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Astronergy Solar Panel Review: Pros & Cons, Price & Specs (2019 Update)

Astronergy Solar Panel Review: Pros & Cons, Price & Specs (2019 Update)

Review: Astronergy 280W Solar Panels

Astronergy’s solar panels are among the most cost-effective on the market. In this review, we’ll cover pros & cons, pricing and specs of Astronergy’s 280W panel, as well as pick out some alternatives for those who prefer higher-efficiency, locally made options.

Astronergy’s 280W solar panels offer the best value on the market right now. If maximizing your budget is your primary goal, Astronergy’s pricing is among the most competitive of all Tier 1 solar panel manufacturers.

In this article, we’ll review the Astronergy 280W solar panel and go over its ideal use case. We’ll also cover some alternatives in case you prefer locally-made products, or need panels that are a little more efficient.

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Astronergy 280W Panel – Price & Specs

Let’s start with a quick breakdown of some key specs for Astronergy’s 280-watt offering:

  • Price: $150 (as of 4/15/19)
  • Wattage: 280W
  • Cost Per Watt: 54 cents/watt
  • Efficiency: 17.2%
  • Warranty: 25 years, backed by third party

Astronergy Solar Panels: The Pros


The main appeal of Astronergy panels is their low cost-per-watt. If you have plenty of space to build your system, Astronergy’s 280W panels are the most cost-effective option on the market. At 54 cents per watt, you won’t find a better value from any other Tier 1 manufacturer.

(“Tier 1” refers to a list published by Bloomberg that ranks solar panel manufacturers by financial stability, longevity and production volume. Companies on this list are mainstays of the solar industry.)

Astronergy 280W panels use polycrystalline cells, which are not the most efficient option available. For example, our Mission Solar 315W panel packs an extra 35 watts of production into the same frame size, which comes down to more efficient cell technology.

But higher efficiency often equates to higher cost-per-watt. While Astronergy’s panels are less efficient, they represent the best value around. Your array will take up more space, but the tradeoff is higher overall output per dollar spent.

Reinsured Warranty

Tier 1 solar panels are warrantied for 25 years. A lot can change in that time, and unfortunately, we’ve seen our fair share of solar panel manufacturers come and go due to the competitive nature of the manufacturing market.

When a manufacturer folds, customers can get stuck holding a useless warranty, because there’s no way to file a claim once the company goes bankrupt.

Astronergy offers protection against that scenario with a third-party backed warranty. Should Astronergy ever go out of business, the warranty is backed by a third-party reinsurance company called Munich RE.

Astronergy is also a part of the Chint Group, one of the largest electronics manufacturers in China. They were ranked the 4th largest company in China by Forbes in 2013. Their size and staying power offers an extra layer of protection for the warranty.

That kind of third-party backing is a nice bit of assurance that your system will be covered for the long haul.

Astronergy Solar Panels: The Cons

Overseas Manufacturing

Astronergy is headquartered in China, with manufacturing plants in a variety of countries overseas. This is a drawback for our customers who prefer to invest in American-made products.

Locally-made panels cost a bit more than imported products due to higher wages and stricter manufacturing standards. But for many people, the extra costs are a fair tradeoff to stimulate the local economy and support job creation in the US.

If you’d prefer to buy American-made goods, we’d point you toward the Mission Solar line, which are assembled in San Antonio, TX. At 71 cents per watt, you’ll pay a 25-30% premium to support American-made products.

The upside of the Mission Solar panels is that they come with higher wattage than Astronergy panels, making them a bit more efficient (which leads to our next point).

Low Efficiency

Most solar panels for residential use come in two standardized sizes: 60-cell and 72-cell. But these panels come in varying wattages, depending on the manufacturing process and the efficiency of the cell technology in use.

For example, Astronergy 280W panels are the same size as Mission Solar’s 315W panels. Both are 60 cells, but the Missions employ more efficient cell technology.

Higher efficiency panels take up less space on your property, because you need to buy fewer panels to hit your energy production target. Astronergy’s 280W panels are on the low end of this efficiency scale, so make sure you have plenty of room to build.

There are also super high-efficiency panels from the likes of LG, but they tend to have a prohibitively high cost-per-watt compared to other options using more established technology. The table below shows the trade-off between panel efficiency and cost-per-watt.

Ideal Application For Astronergy Solar Panels

Astronergy solar panels are best suited for residential applications without any space limitations.

If you have plenty of room to build your system, there’s no real downside to choosing less efficient panels. Your array may take up 10-20% more space, but you will enjoy more production at a lower overall cost.

We would not recommend the Astronergy 280W panels for commercial installs. Commercial systems rarely offset 100% of a property’s energy needs, so the goal is often to squeeze as much production as possible out of the available space.

These builds are more concerned with maximizing wattage per square foot than sticking to the least expensive option. They also tend to use 72-cell modules because there are fewer components to install and maintain.

Residential roof mount systems have similar restrictions. Compare the production of this 24-panel Astronergy system to this 20-panel Mission Solar system. The output is almost identical, but the Mission Solar array will take up roughly 71 square feet less space, which can often determine whether or not the array will fit on your roof.

In short: Astronergy makes the most cost-effective panels, but you need a bit more room to make them fit on your property.

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Solar Panel Warranty Guide: How Long Will My System Last?

Solar Panel Warranty Guide: How Long Will My System Last?

Solar panel warranties can be a bit of a headache to understand. They’re split into two categories (performance and workmanship), each with different warranty lengths and areas of coverage.

If your system stops producing the way that it should, it’s not always clear whether you’re covered. Since solar is a big purchase, it’s important to understand how solar warranties work to protect your investment.

For your peace of mind, here’s everything you need to know about how warranties work in the solar industry.

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How Solar Panel Warranties Work

What is a “workmanship warranty?”

The workmanship warranty on your solar panels covers any physical defects that stem from manufacturing errors. Some examples might be:

  • Imperfections in the frame or glass
  • Loose junction boxes
  • Faulty connectors
  • Bad cells or damaged cell connections
  • Defective backsheet

If the panel malfunctions due to a manufacturing defect, that is covered under the workmanship warranty.

What is a “performance warranty?”

The performance warranty guarantees your panels will produce near their rated output over the life of ownership.

Panel production naturally degrades over time, but it happens at a very slow rate—less than 0.5-1% production loss per year. While production loss will occur for any panel, the performance warranty ensures it happens at a reasonable rate.

For example, these Mission Solar panels output 360 watts. The warranty accounts for a 3% drop in production in the first year, then 0.7% every year after that. After 25 years, your panels should still produce 288.72 watts (80.2% of their original 360W rating).

A few premium panel manufacturers like LG offer better warranties (87% after 25 years) because their panels degrade at a slower rate.

The performance warranty ensures your system’s output is reliable and consistent. If a panel’s output suddenly falls off a cliff, it would be covered for replacement under the performance warranty.

Linear vs. Step Warranties

Most companies offer a linear performance warranty. Mission Solar’s guarantee of 0.7% production loss every year is an example of a linear warranty: it progresses at a constant rate year-over-year.

Some manufacturers offer “step warranties” on their panels. Under this warranty structure, the performance guarantee stays at a flat rate and steps down at certain milestones.

For example, certain Astronergy panels are covered at greater than 90% efficiency upon purchase, which steps down to 80% at year 10 and stays there until year 25.

Step warranties offer less coverage for under-performing panels. For example, if your panel is producing at 85% output in year 11 of ownership, you would be entitled to a replacement under a linear warranty, but not under a step warranty.

In general, companies have moved away from step warranties, but you may still find them offered on older modules, so it’s something to look out for.

How Long Do Solar Panel Warranties Last?

Most solar panels come with a 25-year performance warranty. This is the industry standard from Tier 1 manufacturers at the moment.

Workmanship warranties cover a shorter timeframe: Mission Solar and Astronergy offer 10-year workmanship warranties, but that number varies by manufacturer.

When the warranty expires, that doesn’t mean your panels stop working! They’ll still be producing power, albeit at a reduced rate. A 360W Mission Solar panel should still produce 288W after the 25-year warranty is up.

They can still be used to power your appliances, but they’re no longer covered if the production starts to taper off. A study by NREL (National Renewable Energy Laboratory) shows that 4 out of 5 panels outperform their warranty, so it’s likely your system still has some life in it after the 25-year mark.

What Are Third Party Warranties?

25 years is a long time. What happens if you need to put in a warranty claim, but the company that made your panels has gone out of business?

For that, certain manufacturers like SolarWorld offer third-party warranties and other forms of warranty protection. In case of bankruptcy, the warranty transfers to a 3rd party insurer who continues to honor replacements and refunds under the original warranty.

Tier 1 manufacturing companies are quite stable, but a lot can happen in 25 years. This provides an extra layer of protection so you don’t get hung out to dry.

Solar Inverter Warranties

So far, we’ve only covered the warranties on solar panels. But there are other parts of your system covered under their own product warranties.

Panels have the longest warranty of the bunch at 25 years. Inverters and batteries generally have shorter warranties.

Here are the warranties for the inverters we supply:

If you opt for a string inverter like the Sunny Boy or HD-Wave, you should factor at least one inverter replacement into the lifetime cost of ownership.

Most inverter manufacturers offer extended warranty programs to cover these replacements. These cost a little bit extra up front, but it’s cheaper than replacing the inverter out of pocket down the road.

Solar Battery Warranties

Battery warranties are a bit trickier. Flooded lead-acid batteries cost less up front, but have regular maintenance requirements to keep them in working order. These batteries have the shortest warranties, and if you fail to perform regular upkeep, the warranty will be voided.

Sealed lead-acid batteries and lithium batteries cost more, but the maintenance requirements are removed and they have longer warranties to match the higher price tag.

Sample battery warranties:

  • Crown flooded lead-acid batteries: 3 years
  • Fullriver sealed AGM batteries: 7 years
  • Discover lithium batteries: 10 years

Read our in-depth cost comparison of lead-acid vs. lithium batteries.

Another thing to note is that the true lifespan of your batteries can vary greatly depending on the application.

Battery life is measured in charge cycles. The act of discharging your batteries (to power your appliances) and recharging them from your solar panels counts as one cycle. For example, this Fullriver AGM battery has a cycle life of around 1250 cycles at 50% depth of discharge.

In off-grid applications, your battery bank is your primary source of energy. You’ll be cycling it on a regular basis to provide uninterrupted power to your property. With heavy use, you’ll reach the expected cycle life at a much quicker pace.

However, if you’re using batteries as energy storage for a grid-tie property, they’ll see less frequent use—only at certain times of day to offset high time-of-use rates, or as backup power during a grid outage.

Though you might use the same exact battery, it will have a longer lifespan in this application because it is not constantly cycling.

Factors That Can Void Your Warranty

One last word of caution: warranties only cover your equipment when your system is properly designed and cared for.

All warranties carry clauses that essentially boil down to this: “if you use the equipment improperly, we’re not responsible for the damages.”

For example, string inverters have a voltage range in which they can operate safely. Your system must be sized so that panels supply the right amount of voltage to your inverter, a process known as string sizing.

If your panels send too much voltage into the inverter, it can fry your equipment. That damage would not be covered under warranty because the manufacturer would consider you to be at fault.

Learn how we calculate string size here (warning: lots of math ahead).

Similarly, battery banks must be sized properly so that they charge or discharge at a healthy rate. Completely draining lead-acid batteries when you cycle them will reduce their lifespan, another mistake that would not be covered under warranty.

This is where we come in. Our complete solar systems are packaged with these restrictions in mind, so you can be sure you’re getting a system that’s properly sized. If you’d like to put together a custom system, you can also consult with an experienced solar designer to ensure your system is up to code.

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Should You Buy a Solar Tracker? (No, Probably Not)

Should You Buy a Solar Tracker? (No, Probably Not)

Solar trackers are a special kind of solar mount that automatically follow the position of the sun in the sky.

The purpose of trackers is to maximize the output from your solar panels. Trackers automatically adjust your panels so they always face directly at the sun and get the most possible exposure year-round.

It sounds like a great idea. Who doesn’t want to get the most efficiency out of their panels?

But when people call us up asking if they should buy a solar tracker with their system, we almost always tell them the same thing: no, it’s not worth it.

Why? Because the value proposition starts to crumble when you do some basic math on system parts.

Trackers made sense 10 years ago when panels cost way more than they do now. This NREL report puts panels at $3.57 per watt in 2008, which works out to just over $800 for a 225W panel.

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At that cost, it made more sense to pay extra for a tracker to maximize the value of each panel. But the cost of solar has consistently fallen 6-8% per year, and now the opposite is true. If you need more energy, it’s cheaper to buy more panels instead.

Let’s compare both options.

You can buy hardware for a standard fixed ground mount for about $80 per panel. A ground mount for a six-panel system will cost about $480 in materials.

Or, you could buy a tracker for $600-$1000 per panel…

If you put six 305W panels on a tracker, the rated output on your system is 1830W. You might pay $3600 to build it on an inexpensive tracker.

Trackers squeeze another 20-30% production out of your system, so you end up paying $3120 (the tracker cost minus ground mount cost) for an extra few hundred watts of production.

If you really need that extra output, what makes more sense: buying an extra panel for 250 bucks, or buying a tracker for 3 grand?

If space isn’t a concern, it is almost always cheaper to buy a couple more panels than overpay for a high-tech mount. In addition, trackers have moving parts, which translates to more frequent maintenance – making them less reliable than fixed arrays.

And that’s why we rarely sell trackers…the idea is great and the technology is interesting, but it doesn’t come close to making sense from a cost perspective.

Related: The most common racking types are fixed roof and ground mounts. Read our comparison of roof mounts vs. ground mounts to see which makes sense for your system.

The Exceptions: When Solar Trackers Make Sense

Trackers don’t save you any money. But they do save space.

The only time we ever recommend trackers is when you are working with space restrictions and you absolutely must maximize your production from a compact array.

This scenario usually comes into play in commercial and remote industrial projects.

On one hand, you have projects like this setup powering telecom equipment on the top of a mountain. There’s no room to build a larger mount, and they would have had difficulty digging footings in the rock.

Since they needed extra output but didn’t have room for more panels, a tracker made sense for them in this scenario. It enables them to power an industrial outpost within the constraints of their project.

Another scenario where trackers make sense is large-scale commercial installations.

At scale, the math changes. 20-30% of a 3 kW system isn’t a ton of power, but 20-30% of a 100MW commercial installation is quite a lot of additional power.

There are other considerations which make trackers more appealing in commercial and utility systems as well.

One: the cost of land. Trackers allow for more dense PV installations, which means you can fit more energy output into a smaller array. That reduces the amount of real estate needed for the system.

Two: the cost of installation. Large-scale systems cost a lot to install. Trackers are more scalable to install in commercial systems because they require less labor to connect fewer modules and inverters. Those costs add up, and the savings on labor eventually offset the extra money invested in trackers.

Wrapping Up

So do you need a solar tracker?

Commercial trackers sometimes make sense when you’ve run out of room to add panels to your system. But that’s about the only time we advocate for them.

If you’re building a residential system, you don’t need one. If you have space, just buy more panels and save yourself some money.

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60-Cell vs. 72-Cell Solar Panels: Which One’s Best?

60-Cell vs. 72-Cell Solar Panels: Which One’s Best?

What’s the difference between 60-cell and 72-cell solar panels?

The summary: 72-cells are about a foot taller, and they cost a bit less to mount in large-scale applications. However, both 60-cell and 72-cell panels use the same cell technology, and they work out to the same price from a cost-per-watt perspective. Either option can be used in residential installs—the ideal choice depends on your array layout and space constraints where you will mount your system.

The difference between 60-cell and 72-cell solar panels is simple: 72-cell panels are 12” taller and contain 12 more solar cells.

If that seems too obvious, I promise you: that’s pretty much all there is to it.

But there’s a reason we’re devoting article space to such a simple topic.

I was designing a system for a residential customer last week when she asked me, “I can’t use 72-cell panels at my house, right?”

For some reason, she had the impression that 72-cell panels are only for commercial use. Which couldn’t be further from the truth.

After some back-and-forth, I realized she had read a few articles online to help her decide which size panel to use. Turns out one of them had claimed 72-cell panels were only for commercial use, and require special hardware and extra labor to install.

None of which is remotely true.

So I wrote this article to help set the record straight.

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Dispelling myths about 72-cell panels

The big myth floating around the Internet is that 72-cell panels are not made for residential use.

That’s simply not true. In fact, roughly half of all residential systems we design at Wholesale Solar have 72-cell panels in them.

It’s true that commercial applications lean toward 72-cell panels. They require less racking rail, fewer electrical connections, and fewer clamps to secure in place. That means 72-cell panels are cheaper to install on a large scale.

But there’s no reason residential customers can’t get the same benefits from a 72-cell solar panel.

Are 72-cell panels harder to install?

I’ve also read claims that 72-cell panels are harder to install. This concern is somewhat overblown.

Yes, 72-cell solar panels are a bit bigger and heavier. But it typically takes two people to move and set a solar panel in place, regardless of size. Since there’s usually 2-3 people on an installation crew, finding a way to move the panels isn’t much of an issue. Any crew worth their salt will be able to handle the larger panel size.

Though the work may be a bit more physically taxing, the install tends to take less time overall. Since the system contains less panels, you’ll spend less time making electrical connections and fastening clamps.

You don’t need to buy stronger racking to support larger panels, either. Solar panel racking is universal.  The size of the panel you choose will not limit your mounting options.

While it is possible to buy a thicker rail, we only recommend that option to provide a stronger foundation in areas threatened by hurricanes, heavy snow and other extreme weather conditions.

You don’t need to spend more on “heavy duty racking” just to support heavier 72-cell panels (which is a very common misconception). The standard options will work just fine.

In fact, in most cases 72-cell panels will actually save you money on racking. Modules are mounted with rails running across the width of the panel. Because 72-cell panels have the same width as 60-cell panels (about 40” wide), they require the same amount of racking material to mount more solar power.

When to choose 60 cell vs. 72 cell panels

If the only difference between 60- and 72-cell solar panels is their size, how do you choose one over the other?

The ultimate decider is panel value, measured in cost-per-watt.

Divide the price of the panel by the rated panel output (typically 250W-375W per panel). This will give you a baseline to compare panel value, regardless of size.

Our advice is to go for the best cost-per-watt option that fits the space where you will install your system.

Here’s an example. If your mounting space is 35’ wide and 10’ tall, you can only fit a row of 10 panels. You can install more power by using 72-cell panels because you have enough space to accommodate the taller panel size.

Standard Solar Panel Sizes:

60-cell panels: 39″ x 65″

72-cell panels: 39″ x 77″

On the other hand, if your mounting space is 35’ wide and only 6’ tall, you’d have to use 60-cell panels.

Exceptions to the rule

There’s one scenario where 72-cell solar panels are less common. This exception comes when you build a system around micro-inverters.

Micro-inverters work on a 1-to-1 system, where each inverter is hooked up to an individual panel. The benefit of this type of system is that it is modular: if one part stops working, it doesn’t affect the rest of your array. This makes it easy to repair and expand your system.

Micro-inverters have a cap on how much AC wattage they can handle. For example, Enphase micro-inverters can only process 290-315 watts from the panels (depending on the model). If a 72-cell solar panel produces 350 watts, that’s more than the micro-inverter can process.

Your panels would still work, but you’re simply wasting electricity – and by extension, wasting money. You’d essentially pay a higher price for your panels without getting the benefit of additional output.

The key takeaway is that micro-inverters have limited capacity, and the panel needs to be sized to match. There are some 300 watt 72-cell panels that would be appropriate to pair with a micro-inverter. But this is a rare case, and most of the time it just doesn’t make sense to go this route.

Mixing and matching 60-cell and 72-cell solar panels

It’s possible to mix and match 60-cell and 72-cell panels if necessary.

For example, let’s say you have a triangle-shaped roof with less space near the top. You might install a row of 72-cell panels in the middle of the roof. Then you can add smaller 60-cell panels on the sides / top to hit your target system size.

It’s possible to mix panel sizes like this to fit the usable space on your roof. But keep in mind that different components run on different voltages, and you’ll need to pair each panel with a compatible inverter.

If you build a system like this, it’s worthwhile to spend some time with an experienced design consultant to make sure you aren’t wasting power or damaging your equipment.

Need help planning your system? Connect with a solar designer to get started.

Our advice: go with what fits

In short: buy the panels that fit your space. Don’t worry about individual panel size or cell count. Overall system cost is what really matters.

All other things being equal, go with the panels that give you the best cost-per-watt, regardless of size. The ultimate goal is to cover your energy usage as efficiently as possible.

And remember: don’t believe everything you read on the internet . . . except us, of course.

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How Many Solar Panels Do I Need?

How Many Solar Panels Do I Need?

How Many Solar Panels Do You Need To Power Your Home?

Your energy usage in kilowatt-hours (kWh) dictates the size of your system. Panels have a broad range of wattages (275W-360W is common as of early 2019), and other factors like local sun exposure, mount orientation and the presence of a battery bank also play a part. Read this article and use our solar cost calculator for help finding an accurate estimate.

One of the most common questions our design technicians get is: “How many solar panels do I need?”

The answer is pretty complex, and frankly, most people approach it from the wrong angle when they start to look into solar.

We’re often asked to quote a system to power a 3-bedroom home or a support a family of 4. In these situations, it’s impossible to provide an accurate estimate until we know more about the household’s energy needs.

In reality, the best place to start is to evaluate your current energy use based on past electric bills. Past usage data is the best baseline to figure out how many panels you will need.

Lifestyle, climate and panel efficiency all play a role in figuring out the size of your solar system. Here’s the process we use to make an accurate estimate.

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How many panels for grid-tied systems?

In order to figure out just how many panels you need, you’ll want to gather up 6 months to a year’s worth of electric bills. If you live in an area with snowy winters or blistering hot summers, look at a larger sample of bills to understand when your usage spikes. Take peak periods into account as you estimate how many panels you’ll need to cover your energy usage.

Some companies provide a 12-month summary of how much electricity you use on every bill. Depending on your utilities provider, you may just need one bill to find an estimate for the year.

Got your paperwork in order? Great – you want to look for how many kilowatt hours (kWh) of electricity you use per year.

Wait, what’s a kilowatt hour?

A kilowatt hour (kWh) is a measurement of energy. If an appliance rated for 1 kilowatt (1000W) runs for an hour, then one kWh of energy has been used.

The energy company measures total energy usage in kilowatt hours. Your total usage in kilowatt hours determines how much you are billed each month.

Example 1: A fridge rated at 250 watts runs for 4 hours per day. 250W x 4 = 1000W, or 1 kW. This fridge uses 1 kWh of energy over the course of a day.

Example 2: An oven is rated at 2000 watts (2 kW). Cooking in this oven for half an hour would consume 1 kWh of power (2kw x 0.5 hours = 1kWh).

Find how many kWh of energy you use per year. That will give you a good jumping off point for estimating your energy needs – but you’re not there yet.

Divide that number by 365 to get your daily energy usage in kWh.

Once you have your daily energy usage, use this formula to estimate your total system size:

Daily Usage (kWh) ÷ Sun-Hours ÷ 0.9 inefficiency factor = Minimum Solar Array Output

Sun-hours refers to how much sun you get each day where you live. You can find that info on our US sun-hours map. More on this a bit later.

The inefficiency factor simply accounts for circumstances that would make your system run below its optimal output, like shade, extreme temperatures, voltage drop and equipment inefficiencies.

Take your daily usage and divide it by these two numbers to get an estimate of the overall output of your system.

For example:

According to the U.S. Energy Information Administration, the average American household used 10,766 kWh of electricity annually in 2016. That’s about 29.5 kWh per day.

Let’s say you live in Arizona, which gets 5.5 sun-hours per day.

29.5 kWh per day ÷ 5.5 sun-hours ÷ 0.9 = 5.9595 kW capacity system.

That would give you an approximate system size of 5.96 kW, or 5959W (remember, 1 kilowatt = 1000 watts).

From there, the last step is to divide by the energy rating of each individual panel. Solar panels are graded by how much power they use. The panels you would use in a residential setting typically range from 275 to 350 watts per panel.

Let’s say we want to use Astronergy 335W panels. Take your system size and divide by the panel wattage to figure out how many solar panels you need in your system:

5959W ÷ 335W = 17.78 panels

Round up the final number, since you can’t buy partial panels. In this scenario, we would need 18 panels rated at 335 watts apiece to cover our energy needs.

We can’t stress this enough: this calculation is a very rough estimate. It should only be used to ballpark system size and make early pricing estimates.

But don’t take this estimate as gospel – there are too many factors that can change the size of your system in practice.

Additional considerations for off-grid systems

Calculating power consumption needs for an off-grid system is a tad more complicated. People who live off-grid need to focus on daily power usage rather than monthly or annual consumption.

You’re not staring down a power bill each month – you’re independent and responsible for covering your own day-to-day power needs. The system needs to be able to produce enough (and store enough) to keep things running smoothly.

Without power bills as a starting point, it’s best to start by listing out your major appliances and estimating how much you use them on a daily basis. Input this list into our Load Evaluation Calculator.

If you’re not sure how much power an appliance uses, follow the appliance electrical consumption table as a guide. You can also check for the EnergyGuide sticker, or use a meter to measure energy consumption if possible.

This form will give an estimated daily usage.

Pay close attention to December and January when you estimate your energy needs. Those months tend to have the highest power usage and the lowest output by your system.

When you live off-grid, you will need a battery system that’s large enough to store enough power for the day and then use solar power to recharge them in a timely manner. It’s common to lean on a backup generator during the winter, when there won’t be enough sunlight to fully power your solar system.

Once you know how much power you use in kWh per day, a solar design technician can determine the minimum battery size needed with a formula that accounts for things like inefficiencies and temperature coefficients.

Here are the basic formulas we use to size off-grid systems:

Minimum Battery capacity (for lead acid batteries):

Daily usage (kWh) x 2 for a 50% discharge depth x 1.2 inefficiency factor = Minimum Battery Capacity

Minimum Solar Array Size

Daily usage (kWh) ÷ Sun-hours ÷ .9 inefficiency factor = Minimum Solar Array Output*

*Ensure solar array meets battery charge requirements, typically around 10 charging amps per 100ah battery capacity.

You may need a larger array or battery bank based on your location, ambient temperature, your usage patterns and other factors. Take a look at our Battery Bank Sizing Calculator to help figure out how many batteries you need to power your system.

Factoring in sun-hours based on your location

“Sun-hours” refers to how much solar energy hits a given area over a certain amount of time.

Your local climate determines how many peak sun-hours you get each day. This number can change drastically based on where you live. If you live in the United States, you can check out our Solar Insolation Map to get an estimate of how many sun-hours you receive in your area.

It’s important to keep in mind that the term “sun-hours” doesn’t just refer to the hours of daylight that your area receives. The peak hours occur when the sun is at its highest in the sky, which will change based on the season and how close you are to the equator. In the winter, the average sun-hours in your location could decrease by 25% to 50%.

So how do sun-hours affect the number of panels on your solar system? If you live in an area with less sun-hours, you’ll need more panels to capture what you need to cover 100% of your energy usage. However, if you live in an area that gets 5-6 sun-hours per day, you might be able to get by with a smaller system.

Quality vs. quantity: panel efficiency isn’t everything

Another aspect that affects the size of your system is the efficiency of the solar panels themselves. Most residential panels range from 275W to 360W. If you go with a 275 watt option, you’ll need several more panels to build your array.

When it comes to solar, efficiency isn’t always the most important factor to consider when you build your system. It really depends on what your specific goals are.

For example, if you look at your solar panels primarily as an investment and a quick ROI is your biggest goal, you might be better off with a lower output, lower cost panel.

“If a panel is 50% more efficient, but costs 100% more, you’re better off paying for [a larger system] of less efficient panels.”

-Brady Schimpf, technical marketing engineer at Ironridge

Brady Schimpf, technical marketing engineer at Ironridge, he had a few thoughts on this matter. He said one of the most common mistakes he sees people make is that they buy into ultra-efficient, high-quality, and technically advanced system, and it might not be worth it – especially if ROI is your biggest concern.

“While a lot of the proprietary systems like that have really good equipment, it is important to look at the cost per watt,” he explained. He urges consumers to consider this: “How much are you paying for the total wattage/production of the system?

“It doesn’t really matter how efficient a panel is if it costs a lot more. If a panel is 50% more efficient, but costs 100% more, you’re better off paying for [a larger system] of less efficient panels.”

But there are some circumstances where having a smaller yet more efficient solar system makes sense. For example, if your roof space is really limited, you might need a more efficient system to cover your energy needs within that given area.

Compare: Astronergy 280W panels vs. Mission Solar 360W panels

Considering other variables when designing a solar system

We can’t stress this enough: this breakdown only serves as a very rough estimate and a starting point for planning your system.

It’s great to get you closer to a ballpark figure on the cost of panels. It will help as a benchmark when you measure your roof to see if you can fit a system up there.

But when you get deeper into planning your system, unexpected hurdles always come up and the system size tends to change.

What if you decide to go with 275W panels instead of 350W panels because the cost-per-watt is lower? What if shade covers your system, or your roof doesn’t directly face the sun? What if harsh weather causes your equipment to perform below its rated efficiency? What if you start using more energy than you did in the past?

Yup . . . you’ll need more panels.

Although this breakdown can give you an estimate of how many solar panels you’ll need in your array, at the end of the day it’s just an estimate. There are several other variables that can determine the size of your solar system, but this process is still important as it gives you an idea of what to look for before you seek out quotes on solar systems.

If you’re interested in going solar, the best thing you can do is speak with a solar design technician that can help you find the ideal system for your unique situation. Bring your estimate as a starting point. We’ll go over any potential problems and tweak the design to suit your location and lifestyle.

Download our free solar panel buying guide!