Expanding Your Off-Grid Solar System? Here’s What You Need to Know

Expanding Your Off-Grid Solar System? Here’s What You Need to Know

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JEREMY CHAMPT, Senior Sales Tech at Wholesale Solar​

There’s nothing quite like the sense of independence that comes from living off-grid.

But with that sense of freedom comes the responsibility of providing for your own energy needs – and it can be frustrating if your solar system struggles to supply power for the things you do on a daily basis.

You might find that your energy needs have evolved over time. Or maybe the system wasn’t sized to accommodate surges of heavy usage, and you need a little extra juice to cover peak output periods.

Thankfully, most off-grid systems can be expanded with additional panels, inverters, and a bigger battery bank.

When does it make sense to expand?

Before we tell you how to expand your off-grid system, you should work out why you need to add on to your system in the first place.

There are a few situations where modular expansion makes sense:

  • Budget constraints. It’s fine to start with a small system, then expand in the future as your budget allows.
  • Increased energy consumption. Your energy usage can change if more people move on to the property, or you buy more stuff that needs to be powered.
  • Insufficient solar production. If your system wasn’t sized to account for high-usage periods, it might need a few tweaks.

Budget Constraints

An off-grid solar system is a big purchase. Not everyone has the cash on hand to buy a system that will cover 100% of their energy needs.

Fortunately, you can build your system in small installments rather than make one large purchase outright. It’s a great way to approach your off-grid installation  but it requires a bit of planning in advance.

Our designers always recommend building a system with future expansion in mind. Regardless of whether you choose a roof-mount or ground-mount racking system, make sure your setup leaves space to tack on extra panels.

You should also be aware that inverters and batteries have their own capacity limits. If you add more panels, you’ll likely pair them with new inverters and batteries to keep pace with the extra output.

Not sure what size system you need? Calculate an estimate here.

On the flip side, it’s also worth considering how much more expensive this piecemeal installation method can be the long run. You should be aware of the drawbacks of building a system step-by-step:

  1. Panel Consistency

If you go years between additions to the system, it could be challenging to find panels that are the same make and model as your existing system. Solar tech advances rapidly, and companies update their product lines to keep in line with the latest innovations.

Thankfully, this is not too big of an issue. Most panels have a standard voltage and size, so a new panel will likely be compatible with an old system. There will be cosmetic differences, but a mix-and-match system should function just fine.

In general, it’s fine to mix and match panels as long as they are within 1 volt. Electrical specs and sizes are standardized (60-cell and 72-cell panels are common). For example, if you have 60-cell panels, you’ll be able to expand with more 60-cell panels, regardless of make or model.

  1. Extra Installation Costs

When you purchase your system in installments, you end up paying a lot more in shipping and installation.

And if you’re working with a contractor, you’ll have to pay the same service fees twice. The labor always costs less if you can get the whole project done in one go.

But these surcharges are minor compared to the overall cost of the system. And it may be worth it to be able to break the purchase into installment payments.

And depending on your setup, you may be able to skip the contractor and handle any additions yourself.

The process for adding on new panels isn’t too complicated. It involves minor adjustments to the mounting hardware, like adding different clamps. Depending on the brand and frame size of your panels, you might be able to bolt it on to your existing hardware without any changes at all.

Do keep in mind that if you upgrade your system to produce more solar energy, you may also need to add another charge controller and make adjustments to your wiring so you don’t overload the existing circuitry. Electrical expansion can be complex and requires a healthy bit of knowledge and research or the aid of a certified electrician.

Our support rep Ricky learned first-hand that making wiring changes to his system was more challenging than it initially appeared. Read his story:

Going Off-Grid? Please Don’t Make the Same Battery Mistake I Did

Increased Energy Consumption

Sometimes your energy needs simply change over time, and you need to expand your system to keep up.

Did you install a well pump? Add a second refrigerator? Or maybe your household has grown recently  either new roommates or a new addition to the family  and you just need a bit more to cover the expanded usage.

In that case, you can add on to your existing solar system by purchasing more solar panels, inverters, or a battery bank expansion. It’s a great idea to talk to a DIY solar tech to understand which parts you’ll need to keep the system stable. If your current equipment isn’t on the market, they can recommend parts that are compatible with your current system.

Your Solar Panels Aren’t Producing Enough

If your panels aren’t putting out as much energy as you originally thought they would, the issue might not be related to the size of your system.

Other factors can contribute to lower energy output: temperature, shade, and the direction your panels are facing. Poor setup may cause an otherwise well-sized system to underproduce. In certain cases, reconfiguring your system can bring it up to its expected output.

Mounting Direction & Angle

If you live in the Northern Hemisphere, your panels should face true south. Facing panels directly into the sun during peak hours will maximize the energy you generate.

However, you can’t exactly change the orientation of the roof on a house you already live in. Many people have to settle for placement that’s “south-ish” or a split between east and west.

In this case, adding more panels is more cost-effective than trying to find the perfect orientation with your existing system. It doesn’t hurt to fine-tune your mounting orientation if you have an adjustable mount.

For a fixed tilt angle, your array should ideally be tilted at an angle approximately equal to your latitude, for optimal year-round production. If you use an adjustable pole mount, you can tilt to a steeper angle in the winter to optimize production throughout the year.

Realistically, it’s a lot of work to adjust mounts, and most people would rather leave it alone to avoid the hassle. But it is an option if space is limited and you need to squeeze that extra bit of efficiency out of your system.

Temperature & Location

Solar panels are rated at standard test conditions (STC). The tests are run in a controlled environment, with temperatures regulated to 77°F and an ideal amount of light shining down on the panels.

In reality, your living environment rarely matches these optimal conditions.

In fact, most panels produce about 10% less power than their rating due to heat, clouds, and other factors. A 300W panel might only put out around 270W on an average day. The maximum output is rarely achieved, except during clear sunny days with ideal conditions.

There is another rating system called PTC, which tries to account for real-world conditions. PTC ratings tend to give a more accurate picture of how panels will perform in the real world.

Before you size a system, take your local climate into account. Extreme climates translate into a larger knock on the rated efficiency of your system. Keep this in mind when sizing up an expansion for your solar array.

Shade

Solar panel production will be impacted by shade, and a few small shadows can have a big impact on your solar panel output. Solar panels need to be installed in full sunlight for optimal performance.

Some modern panels have features including bypass diodes and half cut cells that can help with shading. But if you are experiencing lower output, check to make sure the array is not being shaded throughout the day. Over time, it’s possible for trees to grow up and cast shade on your solar array, reducing its performance.

Also make sure your panels are clean from pollen, dust, leaves and other debris. Over time this can build up and start reducing performance if not cleaned off by rain and snow. Clean your solar panels with water and if needed, a small amount of mild detergent.

Aging Equipment

Over time, solar equipment will age and and drop in efficiency. Solar panels usually last for 30+ years, but the output decreases slightly every year. Most solar panels are guaranteed to produce 80% of their rated power after 25 years.

It could take years to notice the impact, but over time your panels and batteries will decline in efficiency. After 5-10 years, you may find that your production has dipped below your energy needs.

You should design your system to account for this efficiency drop. But if you didn’t take this into account from the start, it isn’t too hard to add parts to compensate for expected efficiency losses over the life of the system.

Adding To Your Off-Grid Solar Array

If you’re ready to move forward with an expansion, some of the easiest parts to add on to your solar system are the panels themselves. Most of the off-grid solar systems we sell have panels wired in strings of three. That means if you’re adding panels, you will do so in multiples of three (3, 6, 9, 12, etc.) – not one at a time.

Depending on your system, you may be able to add a few more panels to the existing charge controller(s). You could also install multiple charge controllers, but be aware: your battery bank can only handle a given amount of charge current. Eventually, if you add a lot of solar panels, you will have to upgrade your battery bank so that it can handle the additional influx of power.

Adding Panels To A Ground Mount

Because off-grid living is usually synonymous with wide-open spaces, many off-grid customers install a ground-mount system. Since you don’t have to climb on your roof to make adjustments, it’s very easy to bolt on new panels whenever you need.

This could work to your advantage if you plan to build your system over time. If you have the space, go with a ground-mount racking solution. You’ll have easy access to the system any time you need to make an addition or perform maintenance.

Adding Panels To A Roof Mount

In order to expand the solar array on the roof, you’ll have to add on more racking and connect the panels to the existing combiner box and charge controller, as long as it can carry the increased load of power.

Expanding a roof-mounted system can be a bit trickier, since space is limited. A portion of your roof may not provide a viable build space, if it faces the wrong direction or is covered in shade.

What happens if you run out of space on your roof?

The first option is to replace some modules with higher efficiency versions to bring you up to speed. If that’s not enough, you can also pair your solar array with an alternate power source like wind or hydropower. Be aware that these options are limited depending on access to local resources  it won’t be an efficient option in areas with low wind speeds or strong water currents.

Mixing and Matching Panels

Take care when mixing and matching old and new parts from different brands. As described in this article in Home Power:

“Solar panels have changed dramatically over the years…not that long ago, 80W 12V nominal modules were common; today, 200W (or larger)…are more typical.”

It is okay to mix and match panels, but make sure the new panels have the same or as close to the same operating voltage, watts, and amps possible.

For example, you could add a 270W panel to your existing array of 250W modules; both of these are 60-cell panels that operate at the same voltage. As long as the panel voltage is within 1 volt, the system will be fine.

Permitting & Code Compliance

Additional permitting may be required when you expand your system. Depending on the size of your expansion, you may have to have the plans approved by the authority having jurisdiction (AHJ) – in most cases, the county or city planning department.

Build your system by the books to avoid headaches down the line. Download our Solar Permitting Cheat Sheet to ensure your system is up to code.

Even if you’re off-grid and miles away from civilization, it never hurts to have all of your permitting taken care of. If you or your neighbor ever sell or appraise your land, permits will be useful to prove the system is built within your property lines and up to code.

All panels and equipment should ideally be certified by UL to be permitted in the U.S. UL is an organization that ensures PV equipment passes rigid safety and quality standards.

More Inverter Power!

Most of the off-grid inverters we sell are “stackable,” which means you can nest multiple inverters together for increased power output. This is especially useful if your usage increases over time and you need more power on tap.

Adding another inverter isn’t always simple. The circuit breakers and wiring in your system likely aren’t designed to support another inverter. In some cases, the entire inverter system may need to be rewired. But if you anticipate expansion when you build your system, expandable power centers are designed for this purpose. You can add extra inverters and rewire them to a central hub — no extra wiring necessary.

A bigger inverter may require a larger battery bank to handle the increased output. The inverter manual should indicate minimum battery bank size, typically 200-400 amp hours minimum per inverter.

Expanding Your Battery Bank

The process for expanding your battery bank depends on the type of battery you have – either lead acid or lithium.

When you add a new lead acid battery into an old bank, the new battery takes on the capacity and other characteristics of the existing batteries. When you add more batteries, they drain down to the level of the old ones.

This might not be a big deal if the battery bank is only a year old. But it’s usually it’s not a good idea to expand a lead acid bank after it’s been used for a several years. Simply put, your new batteries won’t hold as much power as they could when you mix them with older batteries.

This is one area where we recommend planning for extra capacity to future-proof your system. With proper maintenance, you can extend the life of lead acid batteries to 7-10 years. You don’t want to tack on more batteries halfway through and instantly have the new batteries run at sub-optimal efficiency.

You can increase your battery capacity by wiring in more batteries in a parallel circuit. A parallel circuit combines the positive and negative battery connections, to increase the current (in amp hours) while maintaining the same voltage.

Diagram showing series wiring versus parellel wiring

However, there is a limit on the number of lead acid battery strings that can be wired in parallel. Three parallel strings of batteries is the recommended maximum. One or two is more ideal: they will charge and discharge more evenly, which makes them last longer.

Lithium battery banks are easier to expand because there are built-in electronics to manage the battery charge and balancing. Certain off-grid lithium batteries can be expanded over time, including Simpliphi and Discover AES batteries.

If you’re pre-arranging your system for future expansion, lithium batteries are the more modular and expandable option.

They are also more efficient, safer and tend to last longer – which comes with a price premium, of course.

If you’re not sure where to start with your system expansion, our design techs can help you sort it out. Get in touch with a system designer to help ensure your upgrade is compatible and covers your increased energy needs.

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