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Adding Solar Panels To An Existing System

Updated: Apr 24

add solar panels to existing system

Even if the solar system was designed to produce all the home’s power, it’s possible for energy needs to change over time. Maybe the residents now drive electric vehicles and use more electricity because they have a home EV charging station. Some homeowners are switching over to electric space heating with heat pumps, increasing their electricity consumption. But is adding solar panels to an existing system an option?

It isn’t rare for solar energy system owners to want to expand their arrays. If the solar power system isn’t producing 100% of the home’s power and there is room on the roof for more panels, expanding the system makes a lot of sense. In other cases, simple modifications like trimming a tree that is shading the roof or adding power optimizers might be another way to boost solar electricity production.

Can You Add Solar Panels To An Existing System?

Yes, expanding most solar energy systems is possible, but it isn’t always cost-effective for various reasons. In some cases, adding solar panels might be more complicated and expensive than it may seem, but it is typically feasible.

Adding solar panels to a house roof might involve modifying or adjusting part of the original system setup. For example, if the system has a string inverter and it doesn’t have additional capacity, you will need to supplement or upgrade the inverter. If the system is a ground mount, you might need to add another racking system. If the homeowner wants to add a battery bank and solar panels, installing a larger inverter might also be necessary.

Assessing How Many Solar Panels to Add to a House

Just like solar installers size systems depending on household electricity consumption, the same is necessary for expanding an existing solar PV system. First, start by evaluating the energy bills for the house since the contractor installed the solar panel system.

Next, determine if your clients have plans to increase their electricity usage. Common reasons that home electricity use may increase include:

  • Getting an electric vehicle and installing a home EV charging station

  • Swapping out a gas water heater, dryer, or range for an electric model

  • Installing heat pumps and replacing or displacing the existing natural gas or propane heating system

Of course, it is critical to consider the local climate when estimating the system's renewable energy production.

Sometimes, the homeowners can take simple steps to decrease energy consumption. For example, adding water-saving shower heads reduces the consumption of hot water. If they have an electric water heater, it can reduce their electricity bills. Likewise, swapping out inefficient appliances or electric heaters can promote energy savings.

Considerations Before Adding Solar Panels To An Existing System

Although it is usually feasible to expand a solar array, it is critical to think it through before getting started. These are some of the top considerations during the planning phase.

Available Roof Space for Solar Panels

It is certainly easiest to add solar panels if there is additional capacity on the roof; however, there are ways to work around this. If there is no available space due to the existing panels, placing extra panels on a garage roof, carport, shed, or ground mount might be possible. However, the number of panels may be limited by available space.

Solar Inverter Upgrades

Determine the string inverter capacity and if it can handle additional solar panel output. If not, it will be necessary to replace the old inverter.

If the solar system has microinverters, it's a bit easier to expand. Systems with microinverters have a small inverter mounted on the underside of each solar panel. Instead of replacing the string inverter, you would just need to install more microinverters on the new solar panels.

Solar Permit Requirements

The PV permitting requirements will vary depending on whether you will replace the solar inverter, if you need to install a pole mount, and local solar permitting requirements. However, expanding the solar array may require a new solar permit from the jurisdiction to show the system complies with applicable electrical and building codes. 

It is also possible that the Authority Having Jurisdiction (AHJ) will require that the existing system be modified to meet current solar code requirements if you add solar panels. Changes in the National Electric Code (NEC) now require module-level rapid shutdown, which might not have been required when the solar system was first installed.

GreenLancer specializes in engineering and solar permitting services. Join the GreenLancer platform for free to begin shopping for permit-ready solar plan sets, engineering reviews and more.

Net Metering

Typically, you must notify the utility company that you have expanded the PV system to update the interconnection agreement. However, beware that changes in net metering programs can impact how utility companies compensate your customers for the surplus electricity they supply to the power grid. 

For example, some states, including California, Arizona, Hawaii, and Nevada, decreased the amount they compensate customers for solar electricity. However, older solar systems are grandfathered into older versions of the net material program with more favorable terms. Expanding the array may cause your customer to have the new, less favorable net metering programs if this is the case. 

adding solar panels to existing system

Solar Battery Storage

Because the price of home energy storage systems has fallen dramatically in the last decade, many homeowners want to add battery storage to their solar PV systems. If you are also adding solar panels, now might be a convenient time to add a battery bank. It might be necessary to install a new inverter, depending on the type of battery you use. For example, the Tesla Powerwall 2 has its own built-in inverter and is an AC-coupled solar battery.

Aesthetic Considerations

Consider what the expanded system will look like and try to match the panels' appearance as much as possible. In some cases, you can install the same or a very similar model of PV modules, even if the solar panel wattage is slightly different.

If not, find solar panels with a similar appearance. If the original solar panels are polycrystalline and have a blue color, adding monocrystalline panels with a black appearance might look odd. If the original panels have a silver frame, avoid installing all-black panels with a black frame, or else they will stand out.

Future Electricity Bills

In many areas, customers will not get compensated by the power company for surplus power they feed to the grid above and beyond household consumption. For example, most utility companies will not compensate customers at the retail rate for power beyond the number of kilowatt-hours the household consumes in a year. This means that the solar system can offset use through bill credits, but these credits often expire after one year.

That means oversizing the solar PV system will not usually result in greater energy bill savings. Therefore, it is critical to not oversize the system, or else the supplemental power output won’t provide additional benefits to your customers.

Age Of The Existing Solar System

If a solar system is older than a certain age, typically around 10-15 years, it may make more financial sense to start over rather than expand it. Older systems may have outdated components that are less efficient at generating solar electricity and may require costly upgrades to accommodate additional solar panels. Also, older inverters or other equipment may not be able to handle the increased load from additional panels, leading to decreased performance and potential reliability issues.

Quality Of Original PV System

Many solar companies are reluctant to add new panels to an old system, especially if they aren’t the original installer. They may be concerned about voiding solar equipment warranties, code violations, wiring errors, or low-quality installations. If your solar company didn’t install the original solar panels, it’s important to consider what issues you may encounter.

Solar Incentives When Adding Solar Panels

Unfortunately, most homeowners will not be eligible for solar incentives when expanding their systems. For example, they probably cannot claim another federal tax credit. It is critical to be upfront with customers about this, so they understand the incentives before deciding to expand their solar system.

However, there are exceptions to this rule, and it is helpful to research local incentives when applicable to determine if your customers will qualify because there may be some options available. For example, the Self-Generation Incentive Program (SGIP) in California currently provides rebates when adding solar battery storage to existing or new systems.

When Is Adding More Solar Panels a Bad Idea?

Installing more solar panels to an existing system may be a bad idea if your customer's array already meets their energy needs, there is insufficient roof space available, or local regulations or incentives hinder further expansion. Also, if the cost of adding solar panels to an existing system outweighs potential energy bill savings, it might not be financially beneficial. Evaluate your customer's energy goals, space constraints, solar regulations, incentives, and financial considerations before deciding to expand their solar power capacity.

How Much Does It Cost To Add Solar Panels To An Existing System?

The cost of adding solar panels to an existing system can vary depending on several factors, including the size of the additional installation, the type and quality of the panels, any necessary upgrades to the existing system, labor costs, and local regulations. On average, homeowners can expect to pay anywhere from a few thousand to tens of thousands of dollars for this type of expansion if they are adding just solar panels and not battery storage.

Alternatives To Adding Solar Panels To An Existing System

If a homeowner expresses interest in expanding their solar system, it's critical to know why. This can help determine if adding solar PV panels is the best action.

Add Power Optimizers to the Solar Panels

Alternatively, if the PV system has a string inverter and no power optimizers, you can bump up the solar energy production by adding them. This is especially true on shaded roofs or where the panels have different orientations.

Reduce Solar Panel Shading

If there is shade on the roof, can this be reduced? Sometimes, trimming a few branches off a tree can significantly increase energy production. In other cases, the solar panels are shaded by other buildings or dormers, and this can't be avoided.

Replace Existing Solar Panels

If there isn't sufficient space to add more solar panels and they have an older system, you could replace the existing solar panels. The efficiency of solar panels has increased significantly in the last decade. For example, if your client has 250-watt solar panels, you could replace them with 450-watt modules.

Add a Solar Battery

Although it won't increase the total solar power production of the system, adding battery backup will allow homeowners to have electricity during power outages and during peak sun hours. Even if you can’t expand a solar system, you could likely add battery storage instead. If your customer lives in an area with time-of-use electricity rates, a solar battery can increase their utility bill savings significantly.

Consider All Factors Before Adding Solar Panels To An Existing Solar System

If you have homeowners who want to be net-zero and they aren’t currently, expanding a current system by adding PV panels might be a great option. Adding solar panels is feasible for many households, although it might involve mounting PV modules in another location, such as a garage roof. Also, it might be necessary to replace the existing inverter or to install microinverters on each solar panel to comply with National Electrical Code updates.

Expanding an existing solar system can be expensive, and many homeowners cannot take advantage of solar incentives. Ensure your customers understand if they do not qualify, so they can make an informed decision.

Need solar plan sets or engineering services? The GreenLancer team is here to help with solar permitting services and PE stamps. Complete the form below to learn more.


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