Okay, this is a challenging but interesting problem. Let's break down the considerations and explore potential solutions

Key Constraints & Considerations:
Existing Single-Phase Service

This is the biggest hurdle. Upgrading to 3-phase is prohibitively expensive, so you're stuck with it.

Large Array Size

130-150kW is substantial and requires careful design.

Long Distance

1500 feet is a very long run. Voltage drop will be your nemesis.

Voltage Levels

You're correctly considering 1500V and 600V inverter options.

Cost Sensitivity

The homeowner is already wary of large expenses (as evidenced by the 3-phase quote).

Reliability & Reputation

Avoiding questionable equipment manufacturers is crucial.

Code Compliance

(Obviously) All work must adhere to NEC and local codes.

Analyzing Your Proposed Solutions


Large 1500V Inverter with Phase Converter



Pros

Simple DC wiring from the array. Fewer inverters to manage.

Cons

The biggest problem is finding a reliable and reputable single-phase output phase converter for that size is incredibly difficult. As you have said, most are questionable companies, and I would have similar concerns. Even if you find one, the efficiency and reliability of these devices can be a concern. The initial cost might be lower, but the long-term operational costs and risk could be higher. Also, consider the audible noise of a large phase converter.2.

Multiple Smaller Single-Phase 600V Inverters



Pros

Uses readily available technology. Avoids phase conversion.

Cons

Significant voltage drop challenges due to the lower DC voltage. More individual inverters to install, maintain, and potentially fail. Higher AC combiners for the inverters. More conduit runs.

Alternative Solutions & Hybrid Approaches


DC-DC Converters with String Inverters at the House



Concept

Use DC-DC converters near the array to boost the voltage (e.g., from 600V to 1500V). This would reduce the current flowing over the long distance and thus, minimize voltage drop. Then, at the house, use multiple, single-phase string inverters compatible with the boosted DC voltage.

Pros

Reduces voltage drop significantly. Allows the use of standard string inverters with known reliability. DC-DC converters are becoming more common in PV applications.

Cons

Adds another layer of equipment (the DC-DC converters). Requires careful consideration of efficiency losses within the converters. Still necessitates multiple inverters.

Example

You might use DC-DC converters to boost from 600V to 1000V or 1500V, then run the high-voltage DC to the house, and use multiple 240V single-phase string inverters (e.g., SMA Sunny Boy, Fronius Primo). You would still have to combine the AC outputs of these string inverters.2.

Oversize AC Conductors and Multiple String Inverters



Concept

Stick with the multiple 600V inverter approach, but drastically oversize the conductors for the DC runs from the array to the inverters. Also, carefully optimize the string configuration to maximize voltage at the inverter input.

Pros

Simplest conceptually. Uses established technology.

Cons

Extremely expensive conductors. Difficult to manage the sheer size of the conductors. May still struggle to meet voltage drop requirements.

Mitigation

Consider using parallel conductors. This can reduce the size and improve flexibility, but it also increases labor and material costs.3.

"Split" the Array and Service



Concept

Physically divide the array into two smaller sections. Install two separate, smaller single-phase services from the utility. Each service would feed a portion of the array via its own set of inverters.

Pros

Avoids the extreme distance problem for the entire array. Keeps each sub-array size more manageable. Might be cheaper than a complete 3-phase upgrade.

Cons

Requires significant coordination with the utility. May involve additional fees for the second service. Requires more physical space at the house for the two services.

Feasibility

Highly dependent on the utility's policies and pricing.4.

AC Coupling with Battery Storage



Concept

Use a three-phase inverter to feed a battery bank that then inverts DC to AC power for the house.

Pros

Could be more cost effective to upgrade battery and inverter versus the $500K three-phase upgrade. Can also add backup capability to the house.

Cons

Batteries need to be replaced every 7-10 years. Adds an extra level of complexity to the system.

Recommended Approach (General Guidance)


Detailed Load Calculation

Start with a comprehensive load calculation for the house to determine the actual energy needs. This will help you accurately size the PV system and determine if a slightly smaller system could still meet the homeowner's requirements.2.

Voltage Drop Calculations (Critical)

Use accurate voltage drop calculators (there are many free online) and model different scenarios with different conductor sizes and string configurations. Factor in temperature derating of the conductors.3.

Utility Consultation (Mandatory)

Talk to the utility about the possibility of a second service and their requirements for parallel generation. Get firm pricing for any interconnection upgrades.4.

DC-DC Converter Investigation

Thoroughly research DC-DC converters specifically designed for PV applications. Get datasheets, efficiency curves, and references from other installers who have used them. Companies like SMA and others are starting to offer these.5.

Hybrid Approach Exploration

Don't be afraid to combine elements from different solutions. For example, you might use DC-DC converters to boost the voltage somewhat, then run a very large conductor for the long distance to minimize voltage drop.

Key Questions for the Homeowner



Budget

Get a clear understanding of the homeowner's total budget. This will help you prioritize cost-effective solutions.

Future Expansion

Is there any possibility of future expansion of the PV system?

Aesthetics

Are there any aesthetic concerns about running multiple conduits from the array?

Reliability Preferences

Does the homeowner prioritize uptime and redundancy, or is cost the primary driver?

Battery Storage

Is the homeowner interested in energy storage or a backup system?

Additional Tips



Software Modeling

Use PV system design software (e.g., Aurora Solar, Helioscope, PVsyst) to model different scenarios and accurately predict energy production and voltage drop.

Experienced Contractor

Work with a solar installer who has experience with large-scale ground-mount arrays and long DC runs. Their expertise is invaluable.

Grounding and Bonding

Pay meticulous attention to grounding and bonding throughout the system. This is especially critical with long DC runs to minimize the risk of ground faults.

Overcurrent Protection

Properly size and install overcurrent protection devices (fuses or circuit breakers) at the array, at the inverters, and at any DC combiners.

Documentation: Create detailed wiring diagrams, specifications, and as-built drawings.This is a complex project that requires careful planning and execution. By thoroughly evaluating your options and considering all the factors, you can develop a solution that meets the homeowner's needs and provides a reliable and cost-effective solar energy system. Good luck! Flag for review