Walk a solar site survey with a seasoned electrician and you’ll notice the focus settles on two places before anyone points a phone at the roof: the electrical panel and the utility service. That’s not because panels are exciting. It’s because they govern what is possible, what it costs, and how smoothly your project will get permitted. A roof can be perfect, but a tired 100 amp panel or an overburdened service mast can stall the whole effort. Understanding what the surveyor is studying at your meter, main disconnect, and breaker layout helps you prepare for decisions that shape both budget and timeline.
This is the part of a solar project most homeowners never thought about until they start hearing acronyms like MSP, MSPU, and DER interconnection. I’ve performed and reviewed hundreds of solar site surveys, from mid‑century ranches with fuse boxes to new construction with pristine 200 amp gear. The patterns repeat. When a solar site survey company sends someone out, they’re documenting roof geometry, yes, but just as critically they’re documenting the electrical backbone and answering a simple question: can your home accept new generation safely, and if not, what’s the smartest path to upgrade?
What the surveyor is looking for at your panel
A good solar site surveyor does not rush panel photos. They read labels, trace conductors with their eyes, and check clearances. The first pass is an inventory. Is this a service panel or a subpanel? Where is the main disconnect? What’s the busbar rating and the main breaker size? Are there any open breaker spaces? What’s the condition of terminations and insulation? Does the enclosure have enough working clearance and proper labeling? The answers steer design choices like where to land the PV breaker, and whether the project can use a line‑side tap or needs a main service panel upgrade.
Busbar rating matters because of the 120 percent rule in NEC 705.12, which governs how much backfeed current a panel can accept. Imagine a common case: a 200 amp panel with a 200 amp main breaker and a busbar rated 200 amps. The 120 percent rule permits up to 40 amps of solar breaker at the opposite end of the bus from the main, because 200 amps x 120 percent equals 240 amps, and 240 minus the 200 amp main leaves 40 amps for PV. That supports roughly an 8 kW AC inverter on a 40 amp breaker. If your home has a 125 amp bus, the math tightens. With a 100 amp main breaker on a 125 amp bus, the allowed PV is 50 amps, which is comfortable. With a 125 amp main on a 125 amp bus, the allowable PV backfeed drops to 25 amps. The surveyor is doing these mental checks in real time.
They also note if the panel is a combination meter-main or a separate meter with a feeder to an interior panel. In older homes, I often see exterior meter-mains that are full, feeding an interior subpanel that has room. Unfortunately, placing the solar breaker in the subpanel may not satisfy the code backfeed rules unless the bus ratings and breaker positions align, and utilities often require the solar disconnect to be at the service equipment. This is where the site surveyor’s photos and measurements become decisive: can we reconfigure breakers, downsize the main, or install a small generation panel to avoid a full main service upgrade?
The telltale signs you may need a main service panel upgrade
Many homeowners start the solar journey believing a panel upgrade is automatic. It isn’t, and you shouldn’t be upsold without cause. That said, there are recurring factors that push projects toward new equipment. Panels older than roughly 30 to 40 years are frequent candidates. It isn’t just age, it’s the make and model. Certain legacy brands have well documented failure modes, a lack of listed breakers, or mounting concerns that make inspectors uneasy. An original 100 amp service on a house now carrying an EV charger, heat pump, and induction range often lacks headroom. If the 120 percent rule caps your PV breaker too low for the array you want, the design team will price either a main breaker downsizing or a full panel swap.
Physical constraints count. If the panel sits in a closet with inadequate working space, or the gas meter is too close per clearance requirements, an upgrade might include relocation. The surveyor will measure the working depth and side clearances because inspectors enforce that rigorously. Conductor fill and lug ratings can be a quiet roadblock. I’ve seen “just add a breaker” become a nonstarter because the panel’s bus stabs were already derated by heat discoloration or the neutral bar was overloaded with double‑lugged conductors.
A recurring question comes up at walkthroughs: can’t you just tap the line side? A line‑side tap, sometimes called a supply‑side connection, bypasses the 120 percent busbar limitation by connecting the solar output conductors to the service conductors ahead of the main breaker, typically inside the meter-main enclosure. It’s a legitimate method when done with listed hardware and room to work, but not every utility or jurisdiction allows it, and not every meter-main has space to tap safely. The surveyor documents the service entrance conductors’ size, the meter can’s make, and available knockouts. If space is tight or the utility forbids taps, a new panel becomes the path of least resistance.
The utility’s role and why the meter matters
Your interconnection is a partnership with the utility whether you love them or not. That is why the survey includes photos of the meter socket, the service mast or lateral, the grounding electrode system, and the point of attachment. Utilities want to see that the service equipment is safe before they approve a bidirectional meter. Many will not energize a net meter if the panel is a brand on their “do not energize” list or if the meter socket is damaged. If the service drop is undersized or the mast is cracked, they can force a service upgrade.
Overhead versus underground service changes the calculus. For an overhead service, upgrading from 100 to 200 amps can be as straightforward as replacing the meter-main, upsizing the service entrance conductors and mast, coordinating a short power cut with the utility, and transferring branch circuits. For underground service, especially in older neighborhoods, upsizing the conductors between the transformer and your meter pedestal involves trenching and utility scheduling, which can extend timelines by weeks and introduce cost uncertainty. A solar site surveyor near me once flagged an underground lateral with aluminum conductors so degraded they crumbled during handling. The project pivoted to a more modest system with a downsized main breaker and a generation panel rather than chasing a months-long trench permit.
How the 120 percent rule shapes system size
Walk through a typical example. A two‑story 1990s home with a 200 amp panel, bus rated 200 amps, main breaker 200 amps, and several open spaces. Under the 120 percent rule, a 40 amp solar breaker is allowed when placed at the opposite end from the main. That supports roughly 9.6 kW DC of modules paired with a 7.6 to 8 kW inverter, depending on design. If the homeowner wants a 12 kW system, the installer can either split to a pair of inverters and breakers totaling no more than 40 amps of backfeed, or propose a main breaker downsizing to 175 amps, which increases PV allowance to 65 amps on a 200 amp bus. Downsizing often triggers a load calculation to ensure the home’s demand still fits the reduced main. Your survey notes include appliance nameplate ratings, HVAC size, and any electric heating to support that calculation.
In smaller panels, say 100 or 125 amp service, options narrow. You can install a 30 amp PV breaker in some configurations, but larger arrays overwhelm the math. That’s when design teams consider a supply-side connection, a dedicated generation panel, or a main service upgrade. The surveyor’s job is to document enough detail that the designer can choose the least intrusive option that meets code, satisfies the utility, and fits your goals.
Panel brands, listings, and the inspector’s eye
Inspectors remember problem children. Certain historic panel lines have reputational baggage for weak breaker retention or heat issues. Even when code does not outright ban them, the lack of listed replacement breakers or labeling can stall a permit. A competent surveyor photographs the interior label where bus ratings, maximum breaker sizes, and series ratings are printed. They also look for aftermarket breakers that are not listed for that panel. I’ve had projects where the entire path hinged on whether a specific series of breaker was listed as “CL” for use in that load center. If it wasn’t, the cleanest path forward was a replacement panel, not a patchwork.
Another subtlety is service disconnect location. Some regions require the main disconnect to be on the exterior within a certain distance of the meter. If your service disconnect is buried in a basement behind a washer, adding solar can trigger a requirement to relocate or add an exterior disconnect. The surveyor documents that to prevent surprises during inspection. When homeowners ask why their neighbor avoided that cost, it usually comes down to jurisdictional differences and the specific layout of the service equipment.
When a main breaker downgrade beats a full upgrade
It can feel counterintuitive to reduce your main breaker rating when you’re adding electric loads like an EV charger. But in many homes with gas heat and typical appliance mixes, demand rarely exceeds 120 to 160 amps except during short surges. An NEC load calculation or, better, data from a smart panel monitor can demonstrate that a 175 amp or even 150 amp main is adequate. By downsizing the main on a 200 amp bus, you open headroom for more PV breaker capacity under the 120 percent rule. The cost difference between a $150 main breaker swap and a $3,000 to $6,000 service upgrade is not trivial.
I’ve worked with homeowners who feared the lights would dim after a downgrade. In practice, the breaker rating isn’t a throttle on normal service. It sets the trip threshold for extended overloads. If the calculation is honest and the largest loads don’t coincide, the experience is unchanged. The site survey’s appliance inventory and conductor sizing make that downgrade defensible to the inspector and utility.
Storage changes the conversation
Add batteries to the plan and the panel story evolves. Hybrid inverters and energy storage systems often come with their own subpanel, sometimes called a backup loads panel. If your priority is resilience rather than whole‑home backup, you can leave the main panel alone and move selected circuits into the backup panel. That approach avoids a main service upgrade, because the backup panel connects near the service equipment and handles the new power paths with listed equipment. The surveyor looks for wall space to mount the batteries, clearances from meters and windows, and a path for new conduit runs. They also identify whether the service neutral and grounding electrode system are bonded correctly, which becomes critical for systems that create a neutral reference in backup mode.
For whole‑home backup, the picture tightens. The transfer equipment must handle the full service rating. An older 100 amp service often can’t support both the desired solar size and whole‑home backup without an upgrade. In those cases, the survey’s measurements of wall space, conduit routes, and utility clearances determine feasibility more than pure electrical capacity.
Structural and trenching surprises that drive cost
Electrical work lives in the physical world. The best design on paper can falter because the conduit path crosses a deck or an interior finish that the homeowner doesn’t want touched. Site surveyors trace routes with a flashlight and tape measure. They check whether the attic has clear space for running PV homeruns to the service equipment. They assess whether stucco, brick, or siding will be penetrated, and where a roof jack can exit without creating a drainage problem. For main service upgrades, they look at the service mast’s attachment to the roof or wall, the drip loop, and the height of the service drop above grade and driveways. Utilities care about those details and will require corrections during a service upgrade. Those corrections add hours and materials that show up in quotes.
Underground service upgrades multiply these concerns. If the lateral crosses concrete or a landscaped area you want to preserve, the project may require directional boring, which costs more and demands coordination. The survey document should note utility easements, transformer location, and distances. Installer estimators rely on those notes to avoid underbidding.
How to prepare for your solar site survey
You can help the process along with simple prep. Clear access to all panels, the meter, and equipment areas inside and out. If you have appliance documentation, leave it handy. If you’ve added any loads recently, like a hot tub or a mini split, mention them. I’ve been on surveys where a hidden tankless electric water heater under a sink changed the load calculation, pushing a design away from a main breaker downgrade. Transparency at this stage saves change orders later.
If you’re at the stage of searching for a solar site surveyor near me, ask prospective companies a couple of direct questions. Do they perform in‑house load calculations and panel bus assessments, or do they outsource? Can they offer alternatives like main breaker downsizing, line‑side taps where allowed, or generation panels, before they jump to a full main service upgrade? The right solar site survey company will show you options, annotated with code references, not one path padded with assumptions.
Reading the survey report like a pro
A thorough report includes labeled photos, panel and meter makes, busbar rating, main breaker size, conductor sizes where visible, grounding electrode details, roof planes with azimuth and pitch, shading notes, exactusenergy.com solar electrical engineering and pathways for conduits. Focus on the electrical page. Look for:
- Busbar rating versus main breaker size, the proposed PV breaker size and location, and whether the design relies on the 120 percent rule, a main breaker downgrade, a supply‑side connection, or a new generation panel. Utility requirements called out explicitly, including meter socket condition, service mast notes, and any clearance issues that must be corrected before a net meter is installed.
If the report glosses over these items, ask for an addendum. Missing details here often show up later as change orders.
The cost ranges and what drives them
Main service panel upgrades vary widely by region, but ballpark numbers help. A straightforward swap from an aging 100 amp panel to a modern 200 amp combination meter-main on an exterior wall, with minimal conduit and no stucco repair, often lands in the $2,500 to $4,500 range in markets where permitting is predictable. Add trenching for an underground lateral or relocation to meet clearance rules and $6,000 to $10,000 is common. If the utility requires a transformer upgrade or scheduling is tight, timeline expands more than cost, but labor hours rise as well.
By contrast, a main breaker downgrade to create PV headroom usually costs a few hundred dollars plus the engineering time to prepare the load calc. A supply-side connection, where permitted, sits in the middle because you’re adding penetrations, lugs, and sometimes a tap box, but you are not transferring every branch circuit the way you would in a full MSP replacement. When quotes arrive, compare not just sticker price, but what problems the option solves and what risks it avoids.
Permitting and timelines, without wishful thinking
Solar permits fold in electrical permits. When a main service upgrade is part of the scope, the permit set expands and the sequencing changes. The utility must schedule a disconnect and reconnect, and inspections often happen twice: once for the service upgrade, then for the solar. In busy jurisdictions, the service upgrade can take an extra two to four weeks, longer if underground work is required. It pays to ask your installer how they phase the work. A smart team will complete roof and interior solar rough‑in while waiting for the utility window, then swap the panel and complete final connections in one coordinated push. The site survey notes about utility clearance and mast height will help avoid failed inspections that force another appointment.
Battery-ready versus future-proof in a fast code cycle
Code cycles move, and what was acceptable three years ago may be obsolete on your next project. If you plan to add storage later, ask your surveyor and designer to leave capacity for it. That might mean choosing a panel with a couple of extra breaker spaces, installing a larger raceway from the array to the service equipment, or setting aside wall space near the panel that meets fire and working clearances for batteries. I’ve seen homeowners paint themselves into a corner by installing cabinetry where batteries would go, forcing a battery system to end up outside in less favorable conditions.
A generation panel, sometimes a small load center dedicated to PV and future storage, can be an elegant compromise. Your solar backfeed lands there, you stay within busbar limits, and when batteries arrive, the interconnection is already organized. The site surveyor can suggest that path if they see room and understand your longer‑term plans.
When the smartest answer is to do nothing yet
Occasionally, the survey reveals that the house needs more work than makes sense for a modest array. If the service is undersized, the panel is a model with limited listings, the mast is noncompliant, and the utility requires trenching, the upgrade cost can overshadow solar savings for several years. In those cases, I counsel clients to wait until another trigger appears, like adding an EV or switching to a heat pump, so the upgrade cost supports multiple goals. A reputable solar site surveyor will put that in writing, even if it means they pause the sale. You want a partner who frames the decision in your favor, not theirs.
A brief homeowner checklist for the panel question
- Ask your installer to explain the busbar rating, main breaker size, and proposed PV breaker location in your design set, and why that choice fits your panel. Confirm whether the plan uses the 120 percent rule, a main breaker downgrade, a line‑side tap, a generation panel, or a full main service panel upgrade, and why alternatives were rejected.
Keep this short list on hand when you review the survey report. A two‑minute conversation here prevents a two‑week delay later.
The quiet value of a meticulous survey
There are parts of a solar install you will admire every day, like the clean array lines on the roof. Then there are parts you will rarely see again, like the neatly torqued lugs inside a new main service panel. The latter keeps you safe and keeps your system interconnected for decades. A careful solar site survey sets the tone. It translates your home’s electrical history into a clear roadmap. It names the constraints, quantifies your options, and de‑risks the permit and utility review. Whether you find a solar site surveyor through a national brand or a local shop, judge them by their thoroughness on the panel, the meter, and the service. If they treat that part as an afterthought, move on.
Over years of projects, the best outcomes cluster around the same habits. The surveyor reads every label, notes every clearance, and anticipates inspector questions. The designer chooses the simplest compliant interconnection and resists unnecessary upsizing. The installer builds what was drawn, not a field improvisation. And the homeowner understands why their panel and main service upgrade, or their lack of one, makes sense for the home they live in today and the one they plan for tomorrow.
Business Name: Exactus Energy
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Phone number: +1 833-392-2887
What permits are needed to install solar panels?
Installing solar panels usually requires a building permit to confirm structural safety, an electrical permit to ensure code compliance, and utility approval for grid connection. In many cases, zoning reviews or fire code checks may also be required, especially for ground-mounted systems. Additional permits may apply if battery storage is included. The exact permits vary by city, state, or province, so checking with local authorities is essential.
Why do solar permits take so long?
Solar permits can take weeks or months because each authority having jurisdiction reviews plans for safety, code compliance, and utility coordination. Delays often come from backlogs at building departments, missing documents, or varying local requirements. Inconsistent processes between municipalities also slow things down. Having a complete and well-prepared application usually speeds up approvals.
What is a US solar permit?
A US solar permit is official authorization from a local building or electrical authority allowing the installation of a solar energy system. It confirms that the project meets national and local safety codes, zoning laws, and fire standards. The permit process typically includes plan reviews, inspections, and utility approval. Without this permit, the system cannot be legally connected or energized.
Is it hard to get out of a solar panel contract?
Exiting a solar panel contract can be challenging because agreements often lock customers into long-term financing, leases, or power purchase arrangements. Cancellation may involve penalties, repayment of incentives, or transferring the contract to a homebuyer. Some companies offer limited cancellation windows, but once installation begins, options are usually restricted. It’s important to review terms carefully before signing.
Are you allowed to install your own solar panels?
In many places, homeowners are legally allowed to install their own solar panels, but the work must meet electrical and building codes. Permits and inspections are still required, and some utilities mandate that a licensed installer handle grid connections. DIY installations can be risky if you’re not experienced in electrical work. Hiring a licensed professional ensures compliance and safety.
How much is a solar permit in California?
In California, state law caps residential solar permit fees at $500 for rooftop systems and $1,000 if battery storage is included. Commercial projects may have higher limits based on system size. Some cities charge less, and online permitting systems can reduce costs further. Always confirm fees with your local building department, since exact amounts vary by jurisdiction.
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