Hot Climate Solar Installation: Derating and Heat

Picture a 500 kWp commercial rooftop in a hot region. On a June afternoon the cell temperature reaches 78°C, and modules rated at 550 W lose around 18% of their STC power at -0.35%/°C. If the installer sized strings for cold-weather Voc and never checked Vmp at 78°C, strings can fall below the inverter’s minimum MPPT voltage during the hottest hours. This is a hypothetical example, but it shows why hot climate solar installation challenges are design problems and not just comfort problems.

Last updated: November 2026

Heat is a primary design constraint for projects in places like Phoenix, Dubai, Ahmedabad and Las Vegas. Cell temperatures well above 70°C are possible on dark rooftops in these regions. A panel rated at 550 W at 25°C STC and -0.35%/°C delivers about 450 W at 75°C. The temperature coefficient, the small number on the datasheet, decides whether your yield projection is accurate.

This guide covers temperature coefficients, NOCT versus STC power, NEC derating, inverter thermal limits, string sizing, crew heat safety and module selection for hot sites. The calculations are worked examples with stated inputs. Use datasheet values and local code for real projects.

In this guide:

• Temperature coefficient basics: what the datasheet number means for real output
• NOCT versus STC: why your 550 W panel rarely produces 550 W on a rooftop
• Power loss calculations for hot sites
• NEC derating: conductor ampacity, voltage calculations and current-based sizing
• Inverter thermal derating
• Module technology comparison by temperature coefficient
• String sizing in heat: the minimum MPPT voltage trap
• Cable and material selection for high-temperature operation
• Crew safety: heat protocols, hydration and shift scheduling
• Ground-mount versus rooftop: airflow and temperature
• Bifacial panels in hot climates
• A worked hypothetical design review
• Cost analysis: premium temperature coefficient panels versus standard panels
• Myth-busting: what installers get wrong about hot climate design

Temperature Coefficient Basics: The Number That Determines Real Output

Every solar panel datasheet lists a temperature coefficient for power (Pmax). This number tells you how much power the panel loses for every degree Celsius above 25°C. A coefficient of -0.35%/°C means the panel loses 0.35% of its rated power for each degree over 25°C.

At 45°C cell temperature, just 20 degrees above STC, a panel at -0.35%/°C loses 7% of rated power. At 75°C, it loses 17.5%. This is not theoretical. It happens daily on rooftops in hot climates.

The temperature coefficient depends on the cell technology and the specific module. Older P-type PERC modules commonly publish coefficients in the -0.35% to -0.42%/°C range. N-type TOPCon and HJT modules commonly publish lower magnitudes, and HJT often the lowest. The exact value is on the datasheet. As an illustration, the gap between -0.25%/°C and -0.42%/°C is 0.17 percentage points per degree. Over a 50°C rise above STC, that is 8.5% of rated power at the hottest hours.

Modules also publish temperature coefficients for voltage (Voc) and current (Isc). The voltage coefficient is negative, so voltage falls in heat. The current coefficient is small and positive. Power, the product of voltage and current, drops because the voltage loss dominates.

Manufacturers measure temperature coefficients under controlled laboratory conditions. Field results can differ because of non-uniform cell heating, spectral effects and measurement uncertainty. For design, use the datasheet value. For performance modeling, add a margin and compare with measured data once the plant is running.

NOCT Versus STC: Why Your 550W Panel Never Produces 550W

Standard Test Conditions (STC) define the laboratory benchmark for solar panels. Cell temperature is 25°C, irradiance is 1000 W/m² and air mass is 1.5. These conditions rarely occur in the field.

Nominal Operating Cell Temperature (NOCT) simulates more realistic conditions: ambient air at 20°C, irradiance of 800 W/m² and wind of 1 m/s. Under those conditions a typical module reaches around 45°C cell temperature. For a 550 W STC module at -0.35%/°C, the power is roughly 410 W (550 x 0.8 for irradiance x 0.93 for the 20°C rise), or about 75% of its STC rating.

NMOT (Nominal Module Operating Temperature) is the newer test condition defined in IEC 61215. Many datasheets still show a NOCT label, so check which one a manufacturer reports.

On a hot rooftop, real conditions go well beyond NOCT. Ambient air in a desert summer can reach 40°C or more, and the cell temperature adds a rise above that depending on the mounting. The table shows the temperature-only effect on power for a module at -0.35%/°C at full sun. Irradiance effects come on top.

Here is the math every hot climate installer should do before finalizing a design. The formula is simple:

Power Loss % = Temperature Coefficient x (Cell Temperature - 25°C)

Cell temperature is not ambient temperature. It is ambient plus a rise that depends on mounting type, roof colour, wind and irradiance. The ranges below are planning assumptions, not measured data. Replace them with site-specific modeling.

Hypothetical example: hot desert city, July afternoon

• Ambient temperature: 43°C
• Flush-mounted on a dark roof
• Assumed temperature rise: +35°C
• Cell temperature: 78°C
• Temperature delta from STC: 53°C

In this example the lowest-coefficient module produces 44 W more per module than the highest at peak heat. On a 500 kWp system with 910 modules, that is about 40 kW during the hottest hours. The annual gain is smaller than that peak gap, because the hot hours are only part of the year.

Hypothetical example: hot coastal desert, August midday

• Ambient temperature: 45°C
• Rooftop with modest standoff
• Assumed temperature rise: +28°C
• Cell temperature: 73°C
• Temperature delta: 48°C

A -0.35%/°C panel loses 16.8% at 73°C, and a -0.26%/°C panel loses 12.5%. On a 1 MW system, that 4.3% difference equals about 43 kW during the hottest hours. For a complete design walkthrough, read designing a commercial solar system.

The module technology you choose changes how much heat costs you. PERC was the dominant technology for years, and N-type technologies such as TOPCon and HJT have been gaining share. Their temperature performance is one reason hot climate buyers look at them.

The ranges below are typical datasheet ranges for the technology class. Your module’s own datasheet is the only number to use in a design.

How much that coefficient advantage is worth over a year depends on how many hours the modules spend hot. A better coefficient does not only win at the hottest hour. It wins at every temperature above 25°C, so the benefit accumulates across the year. Modeling with local weather data shows the total, and the result is usually smaller than the peak-hour gap.

For hot climate installations, a practical decision approach is:

• Utility-scale desert projects: compare bifacial options on LCOE using measured or modeled yield
• Commercial rooftop in extreme heat: weigh the lowest-coefficient modules against price and tariff
• Residential with a budget constraint: a mid-range coefficient may be enough
• Older PERC modules: compare their coefficient against newer options before specifying them. See the bifacial solar panel design guide for more

NEC Derating for Hot Climate Solar Installations

The National Electrical Code addresses temperature through several sections. For hot climate solar, three areas matter most: temperature correction of conductor ampacity, voltage calculations for PV systems, and current-based conductor sizing. See the NFPA 70 (NEC) page for the code itself. Section numbers and tables change between editions, so confirm the edition your authority having jurisdiction enforces.

Conductor Ampacity Derating

The NEC requires ampacity correction for ambient temperature, and conductors in raceways exposed to sunlight on rooftops must be treated as if the ambient were higher, using the code’s adder table for raceways above the roof. The correction factors fall quickly as effective temperature rises above about 40°C. Do not use a rule of thumb: read the factor for your conductor insulation rating from the correction table in your NEC edition.

As an illustration only, if the table gives a correction factor of 0.65 at the effective temperature you calculate, a conductor’s allowable ampacity at that temperature is 65% of its base ampacity. That is why hot climate designs often need conductors one or two sizes larger than initial calculations suggest.

Voltage Calculations: The Hot-Weather Check

The NEC requires calculating maximum system voltage using the lowest expected ambient temperature. That is the cold-weather over-voltage concern. Hot climate designers must also verify minimum string voltage.

At high cell temperatures, Voc and Vmp both drop. A string that produces 400 V at 25°C may produce only about 340 V at 75°C. If the inverter’s minimum MPPT voltage is 350 V, the string drops out of the MPPT window during peak heat, and the inverter either shuts down or operates at reduced efficiency.

Verification formula:

Vmp(min) = Vmp(STC) x [1 + TempCoef_Vmp x (Tcell_max - 25)]

Where Tcell_max = Ambient_max + Temperature_rise

For a hypothetical panel with Vmp = 41.2 V and a Vmp coefficient of -0.30%/°C:

• At 78°C cell temperature: Vmp = 41.2 x [1 - 0.0030 x (78 - 25)] = 41.2 x 0.841 = 34.7 V per panel
• For a 10-panel string: 347 V string Vmp
• If the inverter MPPT minimum is 350 V: the string drops below the MPPT range

The fix: use 11-panel strings (381 V at 78°C) or select an inverter with a lower MPPT minimum. Always recheck the cold-weather Voc limit with the longer string.

Current-Based Conductor Sizing

The NEC sizes PV source and output circuit conductors from the module short-circuit current (Isc) multiplied by 125% twice (a 156% combined factor) before correction factors. This is the base requirement before temperature derating.

Hypothetical calculation for a hot rooftop:

• Module Isc: 14.5 A
• Base sizing current: 14.5 x 1.25 x 1.25 = 22.7 A
• Assume the effective temperature calculation gives a correction factor of 0.65 (read the actual value from your NEC edition)
• Required conductor ampacity at base rating: 22.7 / 0.65 = 34.9 A
• Check the conductor size against the ampacity table for the insulation rating, then apply any conduit fill adjustment

If conduit fill derating also applies, the required size can step up again. Run the calculation for each circuit rather than copying a size from another project.

Inverters are not immune to heat. Many string inverters reduce output when ambient temperature exceeds a stated limit, and the datasheet shows the derating curve. Above the threshold, output drops until the inverter reaches its maximum operating temperature and shuts down. Derating thresholds and rates differ by manufacturer and by model, so quote them only from each manufacturer’s own datasheet.

What to check on a datasheet:

An inverter in direct sunlight on a dark wall can run much hotter inside than the ambient air, so derating can begin earlier than the ambient forecast suggests. Moving an inverter to shade can restore output at no cost beyond labour, so check mounting position early in the design.

Inverter installation rules for hot climates:

• Do not mount in direct sunlight
• Follow the manufacturer’s minimum clearances on all sides
• Use shaded walls or structures
• Consider enclosures or cooling options where the manufacturer allows them
• Include thermal derating in your loading ratio analysis. Shadow analysis software identifies shading issues before installation

Most designers focus on maximum Voc for cold-weather string sizing, which prevents over-voltage damage to inverters. In hot climates, the opposite problem is equally important: minimum Vmp during peak heat.

The trap works like this. A designer sizes a string based on cold-weather Voc limits, and the string looks fine. At a high cell temperature, Vmp drops below the inverter’s MPPT minimum, and the string produces no power during the hottest, sunniest hours.

Verification process for hot climate string sizing:

1. Calculate maximum Voc at the lowest expected ambient temperature (cold-weather check)
2. Calculate minimum Vmp at the highest expected cell temperature (hot-weather check)
3. Verify both values fall within inverter specifications
4. If Vmp(min) is below the MPPT minimum, increase string length or select a different inverter. If Voc(max) is too high, reduce it

Hypothetical example: hot-climate commercial rooftop

• Panel: 550 W, Voc = 49.8 V, Vmp = 41.2 V
• Voc coefficient = -0.28%/°C, Vmp coefficient = -0.30%/°C
• Lowest ambient: 5°C, highest ambient: 47°C
• Temperature rise: +30°C (rack-mounted)
• Maximum cell temperature: 77°C
• Assumed inverter: 600 V maximum input, 350 V MPPT minimum

Cold check (cell temperature 5°C):

• Voc = 49.8 x [1 + 0.0028 x (25 - 5)] = 49.8 x 1.056 = 52.6 V per panel
• 12-panel string: 631 V, above the 600 V limit
• 11-panel string: 579 V, within the 600 V limit

Hot check (cell temperature 77°C):

• Vmp = 41.2 x [1 - 0.0030 x (77 - 25)] = 41.2 x 0.844 = 34.8 V per panel
• 11-panel string: 383 V, above the 350 V MPPT minimum

In this example 11 panels per string passes both checks, and 12 fails the cold check. If the inverter’s MPPT minimum were 400 V, the 11-panel string would fail the hot check and you would need a different inverter. Check both extremes every time.

For software options, see 7 best HelioScope alternatives.

Cable and Material Selection for High-Temperature Operation

Solar cables in hot climates face temperatures well above standard ratings. Conduit on dark rooftops in direct sunlight gets very hot, and module junction boxes also run hot. Standard materials degrade faster under thermal stress, so check each material’s rated temperature against the temperatures your design calculations produce.

Cable Insulation Ratings

For hot climate rooftop installations, specify cable insulation with additional thermal headroom for conduit runs in direct sunlight on dark roofs, and price the extra cost against the derating it avoids.

Sealant and Adhesive Performance

Standard silicone sealants can degrade at high temperatures. On rooftops where module frames and junction boxes run hot, sealant failure is a real risk. Use sealants rated for the temperatures your design calculation produces, and follow the module and junction box manufacturers’ guidance.

Thermal Expansion of Rails and Attachments

Aluminum rail systems expand roughly 0.023 mm per meter per °C. A 6-meter rail section experiencing a 50°C temperature swing expands by about 7 mm. In hot climates with large daily swings, thermal expansion stresses mounting hardware.

Mitigation:

• Use slotted rail connections that allow longitudinal movement
• Do not over-torque rail splices, allow slight play
• Specify stainless steel fasteners with matching thermal expansion coefficients
• Inspect rail connections annually for loosening

Conduit and Junction Box Materials

PVC conduit can soften and deform under sustained heat. On dark rooftops in direct sun, use metal conduit (EMT or RMC) where the code and the design allow, or follow the conduit maker’s temperature limits. Junction boxes should have an adequate ingress-protection rating, and thermal cycling can degrade gaskets, so inspect them on a schedule.

Solar installation crews work on rooftops and open ground in direct sun. They lift heavy panels, drill holes and run conduit. Physical exertion combined with radiant heat creates a severe heat illness risk.

Regulatory Framework

Federal OSHA enforces heat hazards through the General Duty Clause (Section 5(a)(1) of the OSH Act), which requires employers to provide a workplace free from recognized hazards likely to cause death or serious physical harm. OSHA uses WBGT (wet bulb globe temperature) to determine whether a heat hazard is present, and states including California, Washington, Minnesota, Oregon and Colorado have their own heat laws, according to the OSHA heat exposure page. That page also lists an OSHA national emphasis program on outdoor and indoor heat-related hazards, issued in April 2026.

OSHA recommends water, rest and shade as prevention and treatment, shorter shifts or morning scheduling, and a gradual build-up of exposure for workers new to hot conditions. Rule-making and state rules change, so check the current federal and state requirements for each jurisdiction in which you work, and keep penalty amounts out of your planning until you have read OSHA’s current schedule.

Practical Heat Safety Protocol for Solar Crews

Scheduling:

• Start roof work early in summer months
• Complete the hottest roof tasks before the afternoon peak
• Move to ground work or indoor tasks during peak heat
• Schedule heavy lifting and drilling for the coolest hours
• Monitor WBGT, not just air temperature

Hydration:

• Provide water within easy reach of every worker
• Alternate water with electrolyte drinks where appropriate
• Encourage drinking before thirst, because thirst is a late indicator
• Limit caffeine and energy drinks, which can increase dehydration

Rest and Shade:

• Provide pop-up canopies or shade sails at ground level
• Rotate workers between roof and ground tasks
• Schedule rest breaks that increase with the heat level
• Use a buddy system so each worker monitors a partner for heat illness symptoms

PPE Adjustments:

• Light-colored, breathable long-sleeve shirts when possible
• Wide-brim hard hats with neck flaps
• Cooling towels or vests for extreme conditions
• UV-rated safety glasses

Heat Illness Recognition

Every crew should have a trained first aid responder. Every site should have an emergency action plan with the nearest hospital address and phone number posted.

Ground-Mount Versus Rooftop: Airflow and Temperature Data

The mounting choice has a direct impact on operating temperature. Ground-mounted panels benefit from unrestricted airflow beneath the array. Rooftop panels can trap heat between the module and the roof surface.

The size of the annual energy difference depends on climate, wind and module coefficient, so model it for each site. For utility-scale projects, ground-mount is often the natural choice when land is available.

For commercial rooftops, a practical approach is to maximise standoff height where structure and wind loading allow. More standoff means more airflow and cooler cells. The energy gain from better cooling can justify some additional racking cost, but compare it using your own yield model.

Rooftop temperature mitigation strategies:

• Use light-colored or reflective roof membranes where the roof is being replaced anyway
• Maximise standoff where wind loading allows
• Leave gaps for airflow between rows
• Consider white gravel ballast for flat roofs, which increases albedo and cools the roof surface
• Specify modules with lower temperature coefficients

Bifacial Panels in Hot Climates: Cooling Gain and Albedo Effects

Bifacial panels capture light from both the front and rear surfaces. In hot climates, they offer two advantages: rear-side airflow cools the module, and high-albedo ground surfaces boost rear-side gain.

Temperature Reduction

Bifacial panels mounted with generous ground clearance can run cooler than monofacial panels, because the rear surface is exposed to airflow. In desert conditions, that cooling adds a small yield benefit on top of the bifacial gain itself. Measure it with a model rather than assuming a figure.

Albedo Gain by Surface Type

Albedo Gain by Surface Type

Bifacial gain depends on how much light the ground reflects (albedo). Brighter surfaces give more rear-side gain.

In desert environments with sand or white gravel, bifacial modules can capture meaningful rear-side energy. The combination of a better temperature coefficient, rear-side cooling and high albedo makes bifacial N-type modules attractive for desert utility-scale projects. Run the site model to see whether it beats the alternatives on LCOE.

Dust Considerations

Desert environments bring dust and sand, and soiling losses depend on tilt, cleaning schedule and local conditions. Some designs use vertical east-west orientation, which can accumulate less dust and gives a morning-and-evening generation shape that may match demand better than a single midday peak. Model soiling for the site rather than assuming a percentage.

A Worked Hypothetical Design Review

A design review should catch heat problems before the modules ship. This hypothetical 500 kWp rooftop (910 modules at 550 W) puts the temperature, voltage and cost checks in one place. All inputs are assumptions for illustration.

Step 1: Peak-heat output. At a 78°C cell temperature, the module output from the table above scales to the array: a -0.40%/°C module gives about 433 W x 910 = 394 kW, a -0.30%/°C module about 463 W x 910 = 421 kW and a -0.25%/°C module about 477 W x 910 = 434 kW at those hottest hours.

Step 2: String voltage. Run the cold and hot checks from the string sizing section with the actual module and inverter datasheet values.

Step 3: Conductors. Calculate base sizing current at 125% x 125% of Isc, then apply the temperature correction and conduit fill adjustments from your NEC edition.

Step 4: Inverter placement. Place inverters in shade with the manufacturer’s clearances, and check the derating curve against the design ambient.

Step 5: Economics. Compare the extra module cost against the extra yield, using your own tariff.

Real project data, such as measured performance ratio and peak cell temperature from your own monitored plants, is the best way to calibrate these checks. If you have it, use it in place of any assumption in this guide.

The technology choice in hot climates is a financial decision as well as a technical one. Modules with a better temperature coefficient usually cost more upfront and generate more energy in heat.

Premium payback formula:

Payback (years) = Extra module cost / (Extra annual energy x Tariff)

Hypothetical example with assumed inputs:

Change any input and the answer moves. At a lower tariff or a smaller yield gain, payback stretches. At a higher tariff, it shortens. Use the generation and financial tool to model the specific project with local parameters, and get the extra yield from a site simulation rather than a rule of thumb.

Myth-Busting: What Most Installers Get Wrong About Hot Climate Design

Myth 1: “Higher wattage panels always produce more energy in hot climates.”

Reality: A 600 W PERC panel and a 550 W HJT panel on the same hot rooftop can produce nearly identical output. At a 75°C cell temperature (50°C above STC), a 600 W module at -0.40%/°C produces about 480 W, and a 550 W module at -0.25%/°C produces about 481 W. The lower-wattage panel catches up because it loses less in heat.

Myth 2: “Inverter clipping is the main summer production loss.”

Reality: Inverter clipping and temperature derating are both real losses, but they are different problems. Temperature losses in hot climates can be large and affect every sunny hour, while clipping is controlled by your DC/AC ratio. Optimising only for clipping can leave the bigger loss untouched. Model both with local weather data. See the glossary entry on inverter loading ratio.

Myth 3: “All solar panels perform similarly in heat, the differences are marketing.”

Reality: The 0.15 percentage point gap between -0.25%/°C and -0.40%/°C translates to a 7.5% power difference at a 75°C cell temperature. The difference is on the datasheet and it is physical, so compare coefficients before you specify modules.

Myth 4: “Rooftop temperature adders are the same everywhere.”

Reality: Temperature rise varies dramatically by roof type, color, mounting height, and wind exposure. Suppose a flush-mounted panel on a dark roof runs 35°C above ambient and the same panel on a light roof with more standoff runs 20°C above ambient (assumed values). The 15°C difference changes a -0.35%/°C panel’s output by 5.25%. Site-specific thermal modeling is essential.

Myth 5: “Crews can work through the heat if they are tough enough.”

Reality: Heat illness is a physiological limit, not a toughness issue. As heat and humidity rise, the body loses the ability to cool itself through sweating. The most productive approach is to work during cooler hours and follow the heat plan, not to push through. Split shifts can match or beat a single long shift in hot weather.

What to Check on 2026 Datasheets

Module and inverter products change quickly, so rely on current datasheets over any general claim.

• Module temperature coefficient (Pmax, Voc, Vmp): compare these across the modules you are considering
• NOCT or NMOT: confirm which one the manufacturer reports
• Bifaciality factor and rear-side data: relevant for elevated and reflective sites
• Inverter derating curve and maximum operating temperature: check against your design ambient
• Soiling mitigation: coatings and cleaning plans claimed by suppliers should be backed by test data
• Control features: some inverters offer temperature-aware control; ask the manufacturer what the feature does and what data supports it

Conclusion: Three Action Items

Hot climate solar installation challenges are solvable with the right design approach. The technology, the codes, and the safety protocols all exist. The gap is in execution.

• Verify string sizing for both cold and hot extremes. Use temperature-adjusted Voc for maximum voltage and temperature-adjusted Vmp for minimum MPPT voltage. A string that works in winter may fail in summer.
• Compare temperature coefficients on the datasheet and model the year. The hot-hour gap between modules is easy to calculate, and the annual value depends on the site’s temperature profile and your tariff.
• Implement heat safety protocols. Split shifts, hydration and WBGT monitoring are operational requirements that protect your crew and keep productivity up.

To model temperature-adjusted yield for a specific hot-climate site, book a SurgePV demo and bring a real roof.

Tools and Further Reading

Continue exploring related SurgePV resources:

• Plan layouts and strings in the solar design platform
• Look up terms in the solar engineering glossary
• Run quick checks with the solar calculators

Frequently Asked Questions

How much power do solar panels lose in hot climates?

Power loss equals the temperature coefficient times the cell temperature above 25°C. At a 70°C cell temperature, a panel at -0.35%/°C loses 15.75% and a panel at -0.25%/°C loses 11.25%. Cell temperature is ambient plus a rise that depends on mounting, roof colour and wind.

What is the best solar panel technology for hot climates?

Modules with a lower temperature coefficient lose less power in heat, and N-type cell designs such as HJT and TOPCon typically publish lower coefficients than older PERC modules. Compare the Pmax temperature coefficient on each datasheet rather than relying on technology labels. Then weigh it against price and your tariff.

What temperature do solar panels reach on rooftops in summer?

Cell temperature is ambient temperature plus a rise that depends on mounting, roof surface and wind. Flush-mounted panels on dark roofs run hottest, and raised or ground-mounted arrays run cooler. Use site-specific modeling instead of a single rooftop figure.

How does NEC address hot climate solar installations?

The NEC requires temperature correction for conductor ampacity, with extra temperature adders for raceways exposed to sunlight, and requires current-based conductor sizing at 125% of Isc and a further 125% in the PV source circuit rules. Check the table and edition adopted locally. String voltage at peak heat against the inverter MPPT minimum is a separate design check.

At what temperature do solar inverters start derating?

It depends on the model, so read the output derating curve on the manufacturer’s datasheet. Many inverters reduce output above a stated ambient temperature, and direct sun on the enclosure makes it worse. Mount inverters in shade with the clearances the manufacturer requires.

What are OSHA heat safety requirements for solar installation crews?

Federal OSHA enforces heat hazards under the General Duty Clause and uses WBGT to judge heat hazards. Several states, including California, Oregon and Washington, have their own heat rules. OSHA recommends water, rest, shade and gradual acclimatization for new workers.

Should I choose ground-mount or rooftop for hot climates?

Ground-mount arrays usually run cooler because air flows under the modules, so they lose less power in heat when land is available. Rooftops with little standoff or dark surfaces run hotter. The trade-off is land cost and longer cable runs, so model both options.