Author: Jeremy Champt

Battery Maintenance Tips: How To Care For Your Deep-Cycle Batteries

Battery Maintenance Tips: How To Care For Your Deep-Cycle Batteries

How Do I Maintain Deep-Cycle Batteries?

  • Program your voltage set points so that the battery bank charges at the proper voltage.
  • Refill flooded lead-acid batteries with distilled water every 2-4 weeks as needed.
  • Regularly check battery state of charge. Apply an equalization charge to flooded batteries every 90 days. (Do not equalize sealed lead-acid or lithium batteries.)
  • Clean terminal connections and cables to prevent corrosion.

Solar batteries are the most costly component of any off-grid solar system. It’s important to program them properly and stick to a regular battery maintenance schedule to keep them running efficiently for years. Neglecting the proper setup and maintenance routine can shorten the lifespan of your batteries and void the product warranty.

Some battery types, like Lithium-ion, require little to no maintenance after the initial setup. Other battery types (especially flooded lead-acid) need regular upkeep to stay in good condition.

No matter what type of batteries you own, this article will help you program your battery bank and give some battery maintenance tips to keep your system running smoothly.

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Initial Programming

The first time you bring your system online, you’ll need to program your battery chargers to the proper charging settings for your battery bank. These settings dictate parameters like charging voltage and current.

This is where you program voltage set points, the charging voltages applied to the battery during each stage of the charging cycle. Batteries typically charge in 3 phases—bulk, absorb, and float, which can be summarized as follows:

  • Bulk: High current to replenish charge and bring voltage up as quickly as possible (below 80%)
  • Absorb: Charge rate slows as batteries approach full state of charge (~80-100%)
  • Float: Batteries receive a trickle charge at 100% to stay fully charged

Each stage requires the charger to be set at a specific voltage, which is based on the requirements of your battery.

Programming the voltage set points accurately is critical to ensuring the long-term health of your batteries. Setting the wrong charge parameters will make your batteries charge improperly, shortening their lifespan.

There are other values to set during the initial programming phase as well:

  • Absorb time: The amount of time the charger spends in the absorb phase.
  • AC input amps: Maximum input current from grid or generator, to ensure the combined current from the battery charger and loads doesn’t exceed the rating of the generator. Depends on generator size or grid input breaker. See manual for details.
  • Max charge rate or charge current limit: Maximum charging current, either expressed as a percentage of the charger output or total maximum charging amps. This setting is used to limit charger output, to make sure your batteries are not overcharged with too much current.
  • Temperature compensation: Adjusts the battery charger for operation in various temperature ranges. Most chargers include a battery temperature sensor.

These settings are different for every battery and charger. Check the spec sheets or installation manuals for your batteries and chargers to find the specific values for each of the above settings.

Programming your equipment according to the settings recommended in the manual is the first step toward ensuring the long-term health of your battery bank.

Flooded Lead-Acid Battery Maintenance Tips

Flooded lead-acid batteries require regular maintenance to function properly. We recommend checks every 2-4 weeks to keep the battery bank tuned up.

Note: always follow proper safety procedures when working around batteries. Wear eye protection and gloves, remove any jewelry, and secure loose clothing and long hair.

Add distilled water every 2-4 weeks

Flooded lead-acid batteries lose water during the charge cycle. They must be refilled regularly with distilled water to function properly and stay healthy.

Note that you should only use distilled water. Non-distilled water (like tap water) will introduce small particles and contaminants, which weakens the battery chemistry.

Check water levels every 15-30 days and refill as necessary. Your watering schedule depends on your local climate, charge settings and specific application. It may be useful to keep a log to track how often your batteries need to be refilled.

  1. Check water level when batteries are fully charged.
  2. Open the vent well to check the water level.
  3. Add water to just below the maximum water level line. DO NOT overfill past this line. The battery installation manual should indicate where to find the maximum water level line.

Check battery state of charge (SoC):

Use a refractometer to keep an eye on how charged your batteries are. The refractometer measures the specific gravity of your batteries. This video explains how to use a refractometer:

Consult the charts published by your battery manufacturer to find your battery state of charge based on their specific gravity reading. An example chart is shown below.

If your batteries are not holding charge even after a full charge cycle and equalization, they are likely defective, damaged, or have reached the end of their lifespan and are starting to lose some capacity.

Some inverters use a battery monitor to measure state of charge. These battery monitors typically rely on a shunt for measuring the total current coming in and out of the battery bank.

Battery monitors are a useful tool for daily monitoring, but they require proper setup. If they aren’t installed or programmed correctly they can provide false readings.

Even if you have a battery monitor, we still recommend checking the specific gravity with a refractometer on a regular basis. It helps verify the battery monitor is accurate and ensures your batteries reach a full charge.

Use a refractometer to check the specific gravity of your flooded lead-acid batteries.

Equalization Charges

Batteries should be equalized occasionally to make sure each cell is equally charged. Apply a controlled overcharge once every 30-90 days, or whenever individual batteries are imbalanced (reading a different voltage or specific gravity).

  1. Check water level before initiating an equalize charge.
  2. Turn off any loads.
  3. Set your charger at the Equalize voltage specified in your battery manual.
  4. Start the Equalize charge. Gassing and bubbling is normal during this process.
  5. Stop charging and take specific gravity readings every hour. The EQ process is complete when the specific gravity stops rising.

Other Routine Flooded Lead-Acid Battery Maintenance

  • Tighten the battery cable connections as needed. Wear gloves/eye protection and use insulated tools.
  • Clean terminal connections & cables to prevent corrosion. Mix baking soda and distilled water into a paste and apply with a wire brush. Rinse cleaning residue and dry with a cloth or paper towel.
  • Keep the top of the batteries clean from dust and debris to avoid creating a current pathway or electrical leakage across the top of the battery.

Sealed Lead-Acid Battery Maintenance

Sealed lead-acid batteries do not need to be filled with water or equalized. They require very little maintenance other than the occasional check-up on the battery’s state of charge.

Check Battery State of Charge (SoC):

Use a multimeter to keep an eye on how charged your sealed lead-acid batteries are based on the voltage. A multimeter is equipped with positive and negative probes which allows the meter to get a DC voltage reading from the battery.

Your battery manual should contain a chart that estimates the battery’s state of charge based on these voltage readings (like the one in the previous section).

To get the most accurate reading, your batteries should be tested in a resting state. Let your batteries rest for at least 2 hours (no charging/discharging) before taking the voltage reading. Attempting to use the multimeter when batteries are being charged or discharged is going to result in a higher or lower voltage, depending on the load.

If your batteries fail to approach 100% SoC even after a full charge cycle, they are likely defective, damaged, or have reached the end of their lifespan.

Equalization Charges

DO NOT equalize sealed batteries! This applies to flooded lead-acid batteries only.

Other Maintenance

  • Tighten the battery cable connections as needed. Wear gloves/eye protection and use insulated tools.
  • Keep the top of the batteries clean to prevent them from getting dusty and grimy.

Lithium-Ion Battery Maintenance

Fortunately, lithium batteries require little to no maintenance (one of the main appeals when comparing lithium vs. lead-acid batteries). Once they are set up properly, they don’t need any checks aside from the occasional state-of-charge reading to ensure they are holding a charge.

Lithium battery manufacturers sell a tool to gauge the battery’s state of charge (SoC). The tool typically communicates with the built-in Battery Management System (BMS) to get an accurate SoC reading. Simply hook the monitoring tool up to the battery and read the SoC value from the display screen.

Discover Battery makes their own monitoring tool called a Battery Discharge Indicator, while Simpliphi recommends Victron battery monitors for their batteries.

Other Maintenance

  • Tighten the battery cable connections as needed. Wear gloves/eye protection and use insulated tools.
  • Keep the top of the batteries clean to prevent them from getting dusty and grimy.

A Note About System Design

That’s it for our maintenance tips, but it’s worth pointing out that maintenance is only effective if your system is well-designed and your battery bank has been properly sized.

In our experience, many cases of battery bank failure can be attributed to poor system design. People buy the wrong size battery bank or solar array, not taking into account key factors like temperature, local sun hours, and discharge depth. If you simply don’t have enough panels to fully charge your batteries, they’re destined to fail at some point.

The solar array, battery bank and inverter all need to be the proper sizes for the batteries to stay healthy. You also need enough amperage left over to charge the battery bank after accounting for loads that need to be powered (15 charging amps per 100ah is recommended for lead acid batteries). Take a look at our off-grid system sizing guide for more info.

Stuck on system design? Get in touch for a free consultation with one of our solar designers. We provide design advice that is tailored to your application, and our in-house tech team closely reviews proposed plans to avoid the common pitfalls outlined above.

More Battery Maintenance Resources

If you follow this guide, you’re well on your way to ensuring a long lifespan and peak performance from your battery bank. For more battery advice, grab our free Solar Battery Guide linked below.

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What are the Best Solar Batteries? (Updated For 2019)

What are the Best Solar Batteries? (Updated For 2019)

What are the best solar batteries on the market in 2019?

Without a battery bank, you won’t be able to store energy generated by your system. If you’re tied to the grid, no battery means no backup power when the utility grid suffers an outage. If you live off-grid, your system simply won’t work at all.

Batteries are crucial to keep your system running. So what are the best solar batteries on the market?

Since you’re busy, we’ll put our recommendations up front. Keep reading for a breakdown on where each battery shines:

Best Overall Battery for Off-Grid Homes

Best Value Battery for
Off-Grid Homes

Best Battery for
Off-Grid Vacation Homes

Best Battery Backup for Grid-Tied Systems

Best Battery for Storing and Reselling Energy

Best Battery for RV, Marine, Small Off-Grid

What Are The Different Types Of Batteries?

To understand why we chose the above batteries, let’s review what the different types of batteries are. When selecting a battery for your solar system, you have three options: flooded lead-acid, sealed lead-acid, and lithium batteries.

Flooded Lead Acid Batteries

Lead-acid batteries have been used for the last 150 years. These batteries are affordable and about 99% recyclable. They are easy to get rid of at the end of their lifespan.

There are two types of lead-acid batteries: flooded and sealed.

Flooded lead-acid (FLA) batteries are designed to handle daily charge cycling. They do emit gas as a byproduct, so they must be ventilated properly.

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They also require regular maintenance. The plates of every cell in the battery must be submerged in water to function properly (which is why they are called “flooded” batteries). You’ll need to add water every 1 to 3 months to keep the plates submerged. It’s smart to check on them once a month.

FLA batteries are ideal for people who prefer to be hands-on with their system. They’re the most affordable option, but require occasional upkeep to work properly.

Sealed Lead-Acid Batteries

If you won’t be around to perform regular check-ups on your battery, sealed lead-acid batteries are a better option. These batteries are spill-proof and non-hazardous. There are two types of sealed lead-acid batteries with fairly similar characteristics: AGM (absorbent glass mat) and gel.

Sealed batteries are a self-contained system. They don’t need to be refilled with water, like flooded batteries. For that reason, they work well at properties that aren’t occupied full-time, like an off-grid vacation cabin you visit once or twice a year. Sealed batteries won’t self-discharge as fast if they sit idle for extended periods of time while you’re away.

Lithium Batteries

Finally, lithium batteries are a newer technology that hit the market in the 1970s. They are common in laptops and cellphones, but have become more popular in the renewable energy space lately.

Lithium batteries are more expensive, but there are several benefits to justify the higher price tag:

  • Longer lifespan
  • No maintenance
  • More efficient power usage
  • More usable storage capacity (deeper discharges)
  • No off-gassing / ventilation

Best Solar Batteries of 2019: Our Recommendations

So what’s the best battery for your system?

Picking the right battery depends on a combination of factors like application, budget, and expectations for upkeep (like regular maintenance and replacement interval). Your living situation will determine the smartest battery choice for your project.

Here’s our breakdown of the best batteries for a wide variety of situations:

Best Battery for Off-Grid Homes (Overall)

If you live in an off-grid home full time, you need a battery that can keep up with your power demands on a daily basis.

Our recommendation for the best overall battery for off-grid homes is the Discover 48V Lithium battery. It has a long lifespan and affords flexibility if you want to expand your system down the road.

Lithium batteries are a premium storage option. They have a longer lifespan and charge faster than other battery types. And because they can handle deeper discharges, you need less overall capacity than you would with a comparable lead acid battery bank.

They also make it easier to expand your system over time. Let’s say you add a new well pump to your property down the line. With lead-acid batteries, it can be difficult or even impossible to expand your battery bank, depending on the age and how they are wired.

That’s not the case with lithium batteries. More batteries can be added over time, because each battery operates independently with its own internal Battery Management System (BMS).

Lithium batteries can handle extended periods of time without being recharged. This situation would actually damage lead acid batteries because they need to be recharged every day, and will be damaged after several days without a full charge.

That’s why the Discover 48V Lithium battery is our pick for the best overall battery for daily off-grid use.

Best Battery for Off-Grid Homes (Best Value)

Looking for a more cost-effective option? The best value battery for off-grid systems is the Crown CR430 flooded lead-acid battery.

People who live the off-grid lifestyle tend to be more comfortable with hands-on DIY projects. If you don’t mind doing the occasional tune-up on your battery bank, the CR430 is an excellent option.

The 430 amp-hour capacity can’t be beat for the price, and Crown is a reliable American manufacturer (they show up on this list 4 times for a reason). CR430s are built in Fremont, Ohio at Crown’s advanced manufacturing plant.

Best Battery For Off-Grid Vacation Homes

What if you have an off-grid vacation home that you don’t visit on a regular basis? You want a battery that doesn’t require regular maintenance, since you’ll only be on site a few times a year.

In these cases, a sealed AGM battery is the best option. Our recommendation is the 415Ah FullRiver DC400-6. The lower capacity is fine because you don’t need year-round storage. We also skipped out on the premium lithium option, because it’s overkill for a system that will only be used a few times a year.

These batteries are relatively inexpensive, so you don’t have to make a huge investment into a property where you won’t be spending that much time.

The Best Batteries For Living Grid-Tied With Battery Backup

If you have a grid-tied system with battery backup for emergencies, you won’t need a battery with a tremendous amount of storage power. It will only see use when your power goes out, and hopefully that doesn’t happen more than once a year.

Similar to the previous section, you want a battery that doesn’t require maintenance – it should simply work in the rare cases you need it. For that reason, we recommend the same battery as above: the FullRiver DC400-6 with a sealed AGM.

Best Battery For Storing & Selling Energy

In certain areas, the utility company charges more during peak use times – around 4 to 9 pm, when people get home from school and work.

Energy storage allows you to store daytime energy and sell it back to the utility company for a profit.

The goal is to store energy generated during the day, and sell it back in the evening, when rates hit their peak.

For this type of use, we recommend the Discover AES 6.6kWh or the SimpliPhi 3.5 kWh batteries. Both are 48V lithium options. We recommend lithium here because the battery will be cycled more heavily than in a vacation home or battery backup application. The lithium option will have a much longer lifespan and can be just as cost-effective as lead-acid batteries in terms of cost-per-cycle over the life of the battery.

This setup helps protect you from future changes in your utility rates, and is a must if you live in an area with time of use rates (TOU), high demand charges, or no net metering.

The Best Batteries For RV, Marine, Remote Industrial & Small Off-Grid Use

This article has mostly covered residential use cases. But what if you need to power a smaller application, like an RV, boat or small outbuilding on your property?

Let’s say you have a wood shed on your property and want to power it independently. The shed has some lights and wall outlets, but there’s not much else to power. In a situation like this, you just need a compact battery with modest capacity.

For a light use cases like these, we recommend the Crown 6CRV220 sealed AGM battery. This battery was originally designed to power golf carts. As a result, it has a very low profile, but can still withstand deep cycling over a long lifespan.

We’d recommend this battery for tiny homes, boats, and RVs – any application where space is at a premium and you just need to power the essentials. You can also go with the Crown 12CRV110, which is the exact same size and overall capacity.

Battery Math:

The 6CRV220 and 12CRV110 have the exact same size and overall capacity.

6 Volts x 220 amp hours = 1320 watt hours

12 volts x 110 amp hours = 1320 watt hours

This is also our pick for remote industrial applications. It can power small-scale industrial equipment in remote areas not accessible by power lines. Common applications include lighting, pumps, traffic signs and monitoring equipment.

No matter what kind of off-grid system you’re looking for, your battery bank is a key component. Visit our deep cycle battery page to learn more, or check out our battery banks to find a pre-packaged solution.

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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

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.

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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:

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.

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.

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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.

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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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