Vehicle-to-Home V2H Solar Design: NEC 705 & 702

A bidirectional EV charger can turn a parked vehicle into a home backup source, but the electrical design around it decides whether the system is safe, permitted and worth the money. The engineering questions for an installer are specific: which single-line diagram, which transfer switch logic, which sub-panel split, and which code path the authority having jurisdiction (AHJ) will apply. This guide walks through each decision for vehicle to home V2H solar design, and it works one illustrative example with every assumption stated.

Last updated: November 2026

In this engineering guide:

• AC-coupled vs DC-coupled single-line diagrams with conductor and overcurrent protection sizing
• Bidirectional charger selection criteria and what to read on a datasheet
• Transfer switch logic, sub-panel design, and the NEC 702 / 705 split
• EV battery cycle life under daily V2H cycling, worked as arithmetic
• CHAdeMO, CCS, NACS and ISO 15118-20 protocol status
• An illustrative 8 kWp + EV + stationary battery design for whole-home peak shaving
• Why behind-the-meter V2H avoids the export-rate problem under California NEM 3.0

This guide complements the sibling overview at V2H solar integration, which covers vehicles, costs and the consumer-facing comparison. This article is the design counterpart: what the solar design platform workflow has to produce for the permit set, the bill of materials and the inspector.

What V2H Means and How It Differs From V2G

V2H (vehicle to home) means the EV battery supplies household loads behind the meter, usually during peak-rate hours or a grid outage. V2G (vehicle to grid) means the vehicle also exports energy to the utility. The difference drives the whole design: V2H runs islanded from the utility, while V2G is an interconnected source that needs utility review.

The operating mode matters because it changes the code path. A V2H system that disconnects from the utility before it energizes local loads is generally handled like a standby source (NEC Article 702). A source that runs in parallel with the grid and can export is an interconnected production source (NEC Article 705, plus the utility’s interconnection rules). One example from the UK shows how this plays out: Octopus Energy describes its Powerloop trial as V2G, releasing energy from a Nissan LEAF battery back to the grid during the 4 to 7 pm peak. That is a different approval path from a V2H system that never exports.

V2H System Architecture: DC Bus vs AC Coupled

V2H system architecture splits into two families that shape every downstream decision. DC-coupled V2H connects the bidirectional charger to the same DC bus as the solar array and the stationary battery, with one hybrid inverter handling the DC-to-AC conversion. AC-coupled V2H keeps the solar inverter, the stationary battery inverter and the bidirectional charger on separate AC ports of the home panel, each doing its own conversion. See DC Bus Voltage Optimization for detailed guidance.

The architecture choice drives efficiency, cost, retrofit feasibility, and which trades touch the install. A retrofit on an existing string inverter usually favors AC coupling because nothing on the PV side has to be replaced. A new build can justify a DC-coupled stack because the hardware is bought once.

DC-Coupled Architecture Single Line

DC-coupled V2H uses one cabinet for solar input, battery interface, EV port and AC output to the home. The DC bus voltage and the supported vehicle connectors differ by product, so read the hybrid unit’s datasheet before drawing the diagram.

Solar input enters through an MPPT (maximum power point tracker, the circuit that holds the PV array at its peak-power voltage) channel. The stationary battery sits on the same DC bus through a DC-DC converter. The EV port connects through a second DC-DC converter that handles the vehicle connector and protocol. A single grid-forming inverter handles output to the home panel.

The single line looks like this in order:

1. PV array, DC isolator, MPPT input on the hybrid unit
2. Stationary battery, DC-DC converter, DC bus
3. EV port, DC-DC converter for the vehicle protocol, DC bus
4. DC bus, grid-forming inverter, AC output
5. AC output, automatic transfer switch, home panel and sub-panel

The grid-forming inverter holds the AC frequency reference during island mode. That single reference point is the architectural advantage of DC coupling. The home, the solar, the stationary battery and the EV all follow one source, so there are no handshakes between separate inverters that each want to lead.

AC-Coupled Architecture Single Line

AC-coupled V2H keeps the existing string inverter on its own breaker and adds the bidirectional charger as a parallel AC source on the load center. Bidirectional chargers that connect on the AC side of the home are installed this way.

The single line is more familiar to most installers:

1. PV array, DC isolator, existing string inverter, AC breaker in main panel
2. Stationary battery (if present), battery inverter, AC breaker in main panel
3. Bidirectional charger, AC breaker in main panel or directly to the transfer switch
4. Main panel, automatic transfer switch, critical-load sub-panel
5. Utility service, main panel, transfer switch line side

The AC-coupled design needs a careful look at the NEC Article 705 busbar rule, also called the 120% rule. The sum of the supply breakers, solar plus battery plus bidirectional charger, cannot exceed 120% of the panel busbar rating when sources are connected on the load side of the main breaker. On a 200 A panel with a 200 A main breaker that leaves 40 A of headroom (200 x 1.2 - 200 = 40 A). A 7.6 kW string inverter at 240 V needs roughly a 32 A breaker, which leaves about 8 A for the bidirectional charger. A charger of this class needs far more.

The usual fixes are a supply-side (line-side) connection or a main panel upgrade. A supply-side connection is made ahead of the main breaker, so the busbar rule does not apply to it, but it needs equipment rated for the available fault current and a compliant service disconnect. A main panel upgrade replaces the bus and main breaker with higher-rated equipment. Both add cost and permit steps, so price them at quote time.

Comparison Table

The DC-coupled premium pays back mainly when the homeowner is building solar plus V2H from scratch. For a home with a relatively new string inverter, AC coupling is usually the practical path.

Bidirectional Charger Selection: What to Check

Bidirectional charger selection comes down to five checks: vehicle compatibility, connector and protocol, power rating, listing and local approval, and software or firmware lock-outs for V2G mode. Compatibility is the one that trips projects up most often, because a charger and a car can both be bidirectional and still not work together.

Wallbox Quasar 2: Published Specifications

Wallbox describes the Quasar 2 as a CCS bidirectional charger. Its UK product page lists charging speed up to 12.8 kW (DC), a CCS2 connector with a 5 m cable, IP55/IK10 protection for indoor and outdoor installation, and a compact enclosure of 747 x 368 x 135 mm.

The same page also carries an important caveat for designers. Wallbox says the Quasar 2 can charge all CCS2 vehicles, but bidirectional functions are only permitted with certain vehicle manufacturers, with more expected later. Treat the vehicle compatibility list as the first gate in every project.

Specifications for North American variants, listings such as UL 9741, and pricing are not reproduced here. Take them from the manufacturer’s current datasheet for the region you are installing in.

Vehicle-Specific and Fleet Chargers

Some vehicle makers sell their own home integration kit, and some charger makers focus on fleets and commercial sites. Their specifications, supported vehicles and warranty terms are published on each company’s own site and change often, so this guide does not copy them. Use the manufacturer’s documentation for three things: which exact vehicle and model year is supported, which transfer switch or home interface the maker requires, and what the maker says about warranty coverage for bidirectional use.

Selection Decision Tree

The selection logic compresses into a short tree:

• Is the vehicle on the charger maker’s bidirectional compatibility list? If not, stop. The charger cannot do V2H with that car.
• Does the vehicle maker require its own home integration kit? If so, the charger and transfer switch choice is already made for you.
• Is the connector CHAdeMO, CCS or NACS? Match the charger to it, and note that NACS-only bidirectional charging is not yet a production path (see the protocol section).
• Is the site commercial or a fleet? Choose a charger with tariff and demand-response software.
• Is the home on a dynamic tariff? Check that the charger’s cloud service supports your supplier’s price signals.

Transfer Switch Logic and Island Mode Design

The transfer switch is the most important component for V2H safety and code compliance. It physically separates the home from the utility before the bidirectional charger starts supplying the load center. Without that separation, the charger could push power upstream into the service drop, which endangers anyone working on the lines.

Three transfer switch families serve V2H designs:

1. Service-rated automatic transfer switches (ATS). These sit between the meter and the main panel. Whole-home backup uses this class.
2. Sub-panel transfer switches. These sit between the main panel and a critical-load sub-panel. Partial backup uses this class.
3. Smart panel transfer interfaces. These replace the load center and embed transfer logic plus circuit-level monitoring in one cabinet.

The logic sequence during a grid outage is the same across all three:

1. Utility voltage drops, or frequency leaves the allowed range.
2. The transfer switch waits a short, set delay to confirm the outage is real and not a momentary sag.
3. The transfer switch opens the utility-side contactor. The home is now electrically islanded.
4. The bidirectional charger receives a dry contact or communication signal that the island is established.
5. The charger starts grid-forming output, and the EV battery begins discharging through the charger.
6. Loads on the backed-up bus draw from the EV through the sub-panel.

The return-to-grid sequence reverses the steps with a synchronization check before the utility side reconnects.

Sizing the Transfer Switch

The transfer switch must be rated for the current it carries and for the fault current available at its location. For whole-home backup, the switch ampacity matches the service. For a critical-load sub-panel, it matches the sub-panel feeder.

The interrupt rating matters as much as the ampacity. The available fault current at a residential service depends on transformer size and conductor distance, and the utility can tell you the figure. A switch with an interrupt rating below the available fault current can fail dangerously when it clears a fault, and an underrated switch is a common inspection failure.

The Island Mode Frequency Reference Problem

When the home goes off-grid in V2H mode, one device has to set the frequency. In a normal grid-tied system the utility sets 60 Hz (or 50 Hz in Europe) and the string inverter follows it. When the grid disappears, an anti-islanding-compliant inverter stops energizing within a short time, which is the safety feature that protects line workers.

In V2H island mode, the bidirectional charger or a battery inverter has to become the grid-forming inverter source. The string inverter then follows that reference as if it were the utility. Its anti-islanding protection has to accept the new reference and not trip on a perceived island.

That handshake depends on firmware on both sides. Some microinverter systems form their own AC reference during an outage, which can conflict with a charger that is also trying to form the grid. Whether two products can coexist is a question for both vendors’ compatibility documents, not a safe assumption.

NEC Article 705 vs 702: The Compliance Split for V2H

NEC compliance for V2H sits at the boundary between Article 702 (optional standby systems) and Article 705 (interconnected electric power production sources). The article that applies determines the permit path, the labeling requirements, the disconnect rules and the utility involvement.

NEC 705 covers grid-tied solar inverters, V2G systems and any source that operates in parallel with the utility. NEC 702 covers generators, backup batteries and sources that disconnect from the utility before energizing local loads. A V2H source that only runs when islanded behaves like a standby source, so 702 is the usual starting point. Article 625 (electric vehicle power transfer systems) also applies to the charger itself, and newer code editions add bidirectional-specific rules, so confirm the adopted edition with the AHJ.

The boundary blurs when the home exports solar while the EV discharges. If the solar inverter is exporting to the grid at the same time the EV discharges into the home, the system is interconnected and 705 applies on the solar side whatever the V2H operating mode. The two articles coexist on one installation, and the permit set has to label which source falls under which article.

Typical Article 702 Items for V2H

A standby source design typically needs:

• An automatic or manual transfer switch that separates the utility from the standby source
• Permanent signage at the service disconnect identifying the standby source
• Adequate capacity for the connected loads, meaning the charger and EV battery must serve the backed-up load center
• Equipment listed for the use, including the bidirectional charger
• Conductors and overcurrent protection sized under the NEC wiring chapters
• Grounding and bonding at the source

Exact section numbers differ between NEC editions, so cite the edition your AHJ has adopted on the permit drawings.

Typical Article 705 Items for the Solar Side

The solar side of a V2H installation still needs:

• A listed grid-tie inverter with anti-islanding (UL 1741 SA or SB)
• A busbar calculation under the 120% rule where sources connect on the load side
• Rapid shutdown under Article 690 for PV on or near a building
• A production or interconnection meter if the utility requires one
• A source disconnect where the code and the utility require it

The two sets stack. A V2H plus solar plus stationary battery installation usually carries one permit application with two electrical schedules, one for the 705 solar and battery side and one for the 702 standby side. An AHJ that has not seen the split before may ask for a single Article 705 permit. Bring the charger’s listing documents and a clear single-line diagram that shows where the transfer switch separates the sources.

EN 50549 and UK Rules: The European Equivalent

The European parallel is EN 50549-1 for generating plants connected to low-voltage distribution networks. In Great Britain, Engineering Recommendations G98 and G99 set the connection process: G98 covers small generating units up to 16 A per phase, and G99 covers larger installations. Ask the distribution network operator (DNO) how it classifies a bidirectional charger and any stationary battery, since a V2G-capable charger is treated differently from a V2H-only one.

Sub-Panel Design and Critical Load Selection

The sub-panel split decides what stays on during an outage and what can run during peak-rate V2H discharge without overloading the charger. A charger rated near 12 kW cannot run a whole-home HVAC compressor, an electric dryer and an induction range at the same time. The sub-panel design enforces the load priority.

Three sub-panel strategies serve V2H. The whole-home vs partial backup tradeoff applies directly.

1. Whole-home V2H. A service-rated transfer switch sits in front of the main panel and every circuit is backed up. It needs load-shedding logic in the charger or a smart panel.
2. Critical-load sub-panel. A sub-panel fed through a smaller transfer switch carries only the essential circuits. The rest of the home goes dark during an outage.
3. Smart panel with circuit-level control. A smart panel replaces the main panel, every circuit becomes individually controllable, and loads shed automatically based on EV state of charge.

Critical Load Selection

For partial backup, the critical-load panel list is a conversation with the homeowner that usually lands on 8 to 12 circuits. The table gives planning values only. Read the nameplates on the actual equipment before you size anything.

Add the continuous loads, then add the largest motor starting surge on top, and compare the total with the charger’s continuous and peak output. A sub-panel feeder has far more capacity than a single bidirectional charger can supply, so the charger rating, not the panel, is the limiting number.

HVAC compressors are the deciding line. A residential air conditioner compressor draws a locked-rotor inrush several times its running current, and that surge can exceed what a single bidirectional charger can deliver. Soft-start kits reduce the inrush and can keep a compressor on the backed-up bus. Without one, leave HVAC on the non-backed-up side. Check the compressor and soft-start manufacturers’ data for the actual figures.

Sub-Panel Cabinet Selection

The transfer switch and the sub-panel can share one enclosure or sit in two adjacent enclosures. Combined cabinets save wall space and conduit runs. Separate cabinets simplify warranty replacement when the transfer switch fails.

A smart panel is the most flexible long-term answer, but it replaces the whole load center, which adds electrician time and cost. For most partial-backup retrofits, a separate transfer switch plus a small sub-panel is the simpler answer. Get quotes from your suppliers, because prices vary by region and change often.

EV Battery Cycle Life Under V2H Load

Battery cycle life under V2H load is the homeowner’s first question and the installer’s key sizing input. The battery cycle life depends on chemistry, depth of discharge per cycle, temperature, and how the vehicle’s battery management system (BMS, the firmware that protects the cells) is calibrated.

The first step is to convert V2H use into equivalent full cycles. A daily discharge of 30% of pack capacity is 0.3 equivalent full cycles per day, which is about 110 equivalent full cycles a year (0.3 x 365 = 109.5). Then compare that with the cycle life the battery maker publishes for the cell chemistry at a similar depth of discharge.

LFP (LiFePO4) and Cycle Life

LFP batteries are widely regarded as better suited to frequent cycling than NMC because they tolerate deep and repeated discharge well. How many cycles a particular pack reaches to 80% state of health is stated by the cell or pack maker, and the numbers differ by product and test condition. Use the datasheet for the pack in the vehicle, and do not substitute a number from a different product.

NMC and Other Higher-Energy Chemistries

NMC (nickel manganese cobalt) packs deliver higher energy density and longer range per kilogram of cells. The trade-off is that many NMC products are specified for fewer cycles than LFP products. The same method applies: convert your V2H use to equivalent full cycles per year, then divide the maker’s cycle rating by that number.

The table below shows how the arithmetic works for a daily 30% depth-of-discharge cycle. The cycle ratings in the first column are example inputs, not published figures for any product.

Cycle count is only one limit. Calendar aging, temperature and the vehicle’s own driving use also reduce battery life, so treat the result as the best case for V2H wear and not as a prediction.

Warranty Coverage

Vehicle warranties differ on bidirectional use. Some makers cover V2H when it is done with their approved equipment, some have not published bidirectional warranty language, and some do not support it at all. Do not assume coverage from a press release. Ask the vehicle maker for written confirmation that names the exact model year, the charger and the use case, and keep it in the project file. For a broader look at how stationary chemistry choices compare, see LFP vs NMC battery for solar storage.

CHAdeMO vs CCS V2X Readiness: Protocol Status

The communication protocol between the EV and the charger determines what works in production today and what depends on future firmware. For designers, the practical question is always the same: which connector and protocol does this specific vehicle support for bidirectional use?

CHAdeMO

CHAdeMO has supported bidirectional (vehicle-to-load and V2H) operation for years, and it is the connector on vehicles such as the Nissan LEAF, which Octopus used in its Powerloop trial. Few new vehicle models launch with a CHAdeMO inlet today, so a CHAdeMO-only charger is a risk if the homeowner will change vehicles within a few years.

CCS and ISO 15118-20

CCS (Combined Charging System) gains bidirectional capability through the ISO 15118-20 communication standard, published in 2022. The standard defines the digital handshake for bidirectional charging, plug-and-charge authentication and grid-service participation. Wallbox describes the Quasar 2 as a CCS bidirectional charger and states that bidirectional use is enabled only with certain vehicle makers, which is the situation across the industry: the charger can be ready while the vehicle is not.

NACS

NACS (the Tesla connector, now standardized as SAE J3400) supports DC fast charging and is being adopted widely in North America. Bidirectional operation over NACS depends on vehicle and charger firmware that each maker has to release. Until a specific vehicle and charger pair is documented as supporting it, do not design around NACS V2H. Adapters for charging exist, but bidirectional use through an adapter should not be assumed to be certified.

AC Bidirectional Paths

Some vehicles supply AC power to a home through an onboard inverter, while others supply DC power to an external bidirectional charger. The two paths use different hardware, listings and transfer equipment. Identify which path the vehicle maker supports before choosing the charger and the transfer switch.

Solar software that models V2H needs to handle that mix, because a home can have two different vehicles on two different protocols. A household with an older CHAdeMO car and a newer CCS car needs either two chargers or a dual-protocol unit that the maker confirms for both vehicles.

NEM 3.0 in California: Why V2H Pencils Where Export Does Not

California’s Net Billing Tariff, widely called NEM 3.0, was adopted by the CPUC in decision D.22-12-056 on December 15, 2022. According to the CPUC Net Billing Tariff page, it applies to customers who submit an interconnection application on or after April 15, 2023.

Under net billing, energy exported to the grid is credited at an hourly export rate that is lower than the retail import rate. Exact export values come from the utility tariff and change over time, so look them up in the current tariff sheet and do not rely on a number in an article. The principle is stable: a kWh used at home avoids the full retail rate, while a kWh exported earns less.

V2H operates behind the meter. The charger discharges into home loads and nothing exports, so every V2H kWh displaces an imported kWh at the retail rate for that hour. That is why V2H and stationary self-consumption look better under net billing than export-focused designs.

Illustrative Savings Arithmetic

The example below uses assumed prices, not tariff data. Replace each assumption with the customer’s actual rates.

• Assumed daily energy delivered to the home by V2H: 8 kWh
• Annual energy delivered: 8 x 365 = 2,920 kWh
• Assumed peak-hour import price avoided: $0.45 per kWh
• Assumed cost of the energy used to recharge (solar surplus or off-peak): $0.15 per kWh
• Assumed round-trip efficiency of the V2H path: 85%, so each delivered kWh needs about 1.18 kWh of recharge energy
• Recharge cost per delivered kWh: 1.18 x $0.15 = about $0.18
• Net saving per delivered kWh: $0.45 - $0.18 = about $0.27
• Annual saving: 2,920 x $0.27 = about $790

Compare that with the installed cost quoted for the charger, transfer switch, sub-panel and permits to get a simple payback. The result is most sensitive to the peak-to-recharge price spread and to the round-trip efficiency. Put your own tariff into the generation and financial tool workflow before you present a payback to a customer.

DNO Approval and Utility Coordination

The utility’s role in a V2H installation depends on the country, the state and the service territory. In the US, the AHJ handles permitting and the utility handles interconnection. In Great Britain, the DNO coordinates the G98 notification or G99 application.

US Utility Coordination for V2H

Utilities differ in how they treat a V2H-only installation. Some treat a non-exporting standby source as outside their interconnection process, while others want a notification or an application. The AHJ issues the permit, and the utility may ask for documents on the charger and the transfer switch.

The utility’s interest rises if the charger is V2G-capable and its firmware can switch between V2H and V2G modes. Ask each utility in writing whether export must be disabled, how it wants that shown at inspection, and whether a notification is required. Keep the reply in the permit file.

UK DNO Coordination

UK DNOs operate under Engineering Recommendations G98 (small generating units up to 16 A per phase) and G99 (larger units). Ask the DNO how it classifies the charger and any stationary battery before you order equipment. A V2G trial such as Powerloop follows the supplier’s own arrangements, which are not a template for an ordinary V2H-only home.

EU Country Variation

EU member states implement EN 50549 with local variation. Germany uses VDE-AR-N 4105 for grid connection, Italy uses CEI 0-21 and Spain uses RD 1699/2011. Each adds local labeling, disconnect and certification requirements on top of EN 50549. Engage the local distribution system operator (DSO) before specifying equipment, and get any firmware configuration needed for the local grid code confirmed in writing by the charger maker. For related market context, see solar subsidies in Germany.

Illustrative Example: 8 kWp PV + EV + Stationary Battery

The example below brings the sections together. It is an illustrative design with assumed inputs, not a real project and not measured results. Every number is either an assumption stated here or arithmetic on those assumptions.

Site and Load Profile (Assumptions)

• Home: single-family, 200 A service, gas water heating, electric range, central AC
• Average daily load: 30 kWh, which is 10,950 kWh a year
• Existing PV: 6 kWp, with 2 kWp added for a total of 8 kWp
• Assumed specific yield: 1,400 kWh per kWp per year (replace with a site-specific simulation)
• EV: 12,000 miles a year at an assumed 3.4 miles per kWh, which is about 3,530 kWh a year for driving
• Goal: whole-home peak shaving plus outage backup, with V2H discharge of 8 kWh a day

Design Decisions

The first decision is solar array size. At the assumed yield, 8 kWp produces about 11,200 kWh a year, against a household load of 10,950 kWh and a driving load of 3,530 kWh.

The second is architecture. The existing string inverter keeps running the original array, and the new 2 kWp uses its own inverter path. AC-coupled V2H wins here for retrofit reasons.

The third is the bidirectional charger. Choose it from the vehicle maker’s compatibility list first, then check connector, power rating and listing.

The fourth is the stationary battery. A stationary battery gives a grid-forming reference during outages when the EV is away, and it can cover the first hours of the evening peak before the EV starts discharging. Whether the project needs one is a design decision, not a requirement.

The fifth is the transfer switch. A service-rated switch handles whole-home backup, with its interrupt rating checked against the utility’s available fault current figure.

Single Line Diagram

Utility service drop
    |
    +-- Meter
    |
    +-- Service-rated automatic transfer switch (interrupt rating >= available fault current)
        |
        +-- Main panel
            |
            +-- Breaker -> existing string inverter -> 6 kWp PV
            |
            +-- Breaker -> new inverter path -> 2 kWp PV
            |
            +-- Breaker -> stationary battery (grid-forming reference)
            |
            +-- Breaker -> bidirectional charger -> vehicle
            |
            +-- Remaining household circuits

V2H Dispatch Logic

The hourly dispatch logic that the controller needs to implement:

1. Solar surplus hours. When solar exceeds load, surplus charges the stationary battery first, then the EV up to a target state of charge.
2. Peak-rate hours. The stationary battery discharges first. When it reaches its reserve, the charger starts V2H discharge from the EV, stopping at a minimum EV state of charge the owner sets.
3. Off-peak hours. The charger tops up the EV from the grid if state of charge is below what tomorrow’s driving needs.
4. Outage. The transfer switch opens, a grid-forming source sets the reference, and the charger follows it to extend runtime.

Annual Energy Quantities

Total demand on the system is household load plus driving load plus V2H recharge energy, or 17,915 kWh. Solar generation of 11,200 kWh is about 63% of that on an annual basis, so the rest comes from the grid unless the array grows. That is the point of running the numbers: the annual balance shows how much of the V2H recharge energy can come from solar surplus, and the hourly model shows when.

Common Mistakes in V2H Solar Design

Five mistakes recur across V2H designs. Scan the list before any V2H quote goes to a homeowner.

1. Underrated transfer switch interrupt rating. A switch rated below the available fault current is a failed inspection at best. Always get the available fault current from the utility before specifying the switch.

2. Mixed grid-forming firmware without a coordinator. Two sources that both want to form the grid can conflict during island mode. Get written compatibility confirmation from both vendors, or use a single grid-forming source.

3. Forgetting HVAC starting current. A compressor on a critical-load sub-panel without a soft-start kit can trip the charger on locked-rotor inrush. Check the compressor data and plan for a soft-start kit on larger compressors.

4. Treating one connector as a long-term standard. Specifying a CHAdeMO-only charger for a household that will change to a CCS or NACS vehicle within a few years can strand the asset. Check which connectors the household’s next vehicle is likely to use.

5. NEC 705 busbar violation on AC-coupled retrofits. Adding a large breaker for the charger to a panel that already carries a solar breaker can exceed the 120% rule. The fix is a supply-side connection or a panel upgrade, and both must be budgeted at quote time, not discovered at permit review.

Solar Design Software for V2H Modeling

Modeling V2H accurately needs hourly dispatch simulation and not just an annual energy balance. The value of V2H depends on the hour of day, the time-of-use schedule, the seasonal load curve, and when the EV is home and available.

Solar design software used for V2H work should support:

• Hourly load profiles with separate EV charging schedules
• Time-of-use rate schedules, including the import-versus-export price gap under net billing
• EV availability windows, meaning when the car is home and dispatchable
• Battery degradation assumptions that adjust usable capacity over the project life
• Critical-load filtering for outage scenarios

SurgePV’s published product scope covers energy-yield modeling, financial modeling, shading analysis, bill-of-materials output and proposal generation. Its public product claims do not list V2H dispatch or EV scheduling as a feature, so ask about those specifically in a demo and check the result against your own spreadsheet. Results always depend on the source data, assumptions and equipment models you enter.

For complex V2H designs with several EVs, varied weekly schedules and dynamic tariffs, hourly modeling is the only way to confirm that the design pencils. An annual energy balance hides the seasonal mismatches that drive real V2H performance.

Where V2H Is Heading

Three developments shape V2H adoption, and none of them depends on a forecast number.

1. Vehicle support. Bidirectional use is enabled per vehicle maker, and Wallbox says on its own site that more makers are expected to enable it with the Quasar 2. Every new compatibility announcement widens the market for installers.
2. Tariff design. Where utilities widen the gap between import and export prices, behind-the-meter V2H and stationary self-consumption look better than export. California’s net billing tariff is the clearest current example.
3. Charger availability. More CCS-based bidirectional chargers are reaching market, which reduces reliance on CHAdeMO hardware.

The installer skill gap is a larger limit than hardware. AHJs and utilities in areas without V2H precedent ask more questions than areas with installed examples. The first few V2H installs in a territory take longer than later ones, so document each approval and reuse it.

Conclusion: What to Do Next

V2H design is now a defined engineering task. The hardware exists for certain vehicles, the permit path follows known articles, and the economics depend on the tariff spread and the round-trip efficiency. The remaining work is vehicle compatibility, AHJ familiarity and careful transfer switch design.

Three concrete next steps for installers entering V2H design:

1. Run the illustrative example above in your own design tool with a local time-of-use tariff and a representative home load. Confirm that V2H beats the stationary battery payback in your market before you pitch it. If V2H does not pencil locally, do not lead with it.

2. Choose one bidirectional charger to standardize on for your first installs, starting from the vehicle compatibility list for the cars in your market. Build the bill of materials, the permit set and the commissioning checklist around that one unit.

3. Engage the AHJ and the utility before the first quote goes out. Confirm the NEC 702 path for the charger, the NEC 705 path for the solar, and the utility’s stance on V2G lock-out. Keep the answers in a precedent file. For the wider workflow, see solar EV charging integration.

Want to see a V2H project built from roof layout to proposal? Book a SurgePV demo and bring a real load profile.

Frequently Asked Questions

What is vehicle to home V2H solar design and how does it differ from V2G?

V2H solar design integrates a bidirectional EV charger into a solar-plus-storage system so the EV battery can power household loads during peak rates or outages. V2H runs islanded behind the meter and is usually handled as a standby source under NEC Article 702. V2G exports to the utility, which brings NEC Article 705 and the utility’s interconnection review into play.

Do I need a hybrid inverter for V2H or can I keep my existing string inverter?

You can often keep an existing string inverter by using an AC-coupled V2H design with a separate bidirectional charger. A hybrid inverter is needed mainly for DC-coupled V2H or when you want one cabinet to form the grid during outages. Whichever you choose, get written compatibility confirmation from the charger and inverter vendors.

What size transfer switch do I need for whole-home V2H backup?

A whole-home V2H system needs a service-rated transfer switch whose ampacity matches the service, for example 200 A on a 200 A service. Its interrupt rating must be at or above the available fault current, which the utility can provide. A critical-load sub-panel can use a smaller switch matched to the sub-panel feeder.

How does V2H cycling affect EV battery warranty and degradation?

V2H adds battery cycles, and warranty coverage for bidirectional use differs by vehicle maker. A daily discharge of 30% of pack capacity is about 110 equivalent full cycles a year. Compare that with the cycle rating on the pack datasheet and get written warranty confirmation for the exact vehicle and charger.

Does CHAdeMO still matter for V2H or has CCS taken over?

CHAdeMO still matters for existing vehicles such as the Nissan LEAF, but CCS with ISO 15118-20 is the direction for new bidirectional chargers. Wallbox describes its Quasar 2 as a CCS bidirectional charger and says bidirectional use is enabled only with certain vehicle makers. Always check that the exact vehicle and charger pair is supported.

Can V2H work under California NEM 3.0 without exporting to the grid?

Yes, V2H can work without exporting because it discharges into home loads behind the meter. The CPUC adopted the Net Billing Tariff in D.22-12-056, and it applies to interconnection applications on or after April 15, 2023. Under net billing, exports earn less than the retail rate, so self-consumed V2H energy is usually worth more than exported energy.

How do you size solar PV for a home with V2H capability?

Size the array for the household load, the EV driving load and the energy needed to recharge for V2H. As an illustration, 30 kWh a day, 3,530 kWh a year of EV driving and 8 kWh a day of V2H at 85% round trip add up to about 17,915 kWh a year. Run an hourly model to see when that demand is met by solar.