Solar Investment Feasibility: How Is the Right Capacity Determined?

Solar feasibility does not start by calculating how many panels fit on the roof. The first question is usually simpler: at which hours does the facility consume electricity, how much of this consumption overlaps with solar generation, and within which limits can the existing connection infrastructure carry the investment?

This distinction matters. Two factories with the same roof area may need different solar capacities. One facility may run with continuous daytime load on weekdays, while another may have seasonal production or sharply lower weekend consumption. Sizing installed capacity only by usable area can increase surplus generation; keeping capacity too conservative can limit the cost-reduction effect of the investment.

A healthy feasibility study therefore reads technical, commercial and regulatory data in the same table. Roof structural suitability, transformer capacity, connection opinion, consumption curve, financing cost, O&M expense, insurance, generation-loss assumptions and settlement effect should be modeled together.

Initial Data Set

At the beginning of feasibility work, asking only for the electricity invoice is not enough. The invoice shows total cost; the real details that affect the investment decision are often in hourly consumption and site conditions.

The initial data set should include:

• Last 12-24 months of electricity invoices
• Hourly consumption records or remote meter data
• Current contract demand, installed capacity and connection information
• Roof structural status or land zoning conditions
• Transformer, panel, MV cell and cable route information
• Shift and production calendar of the business
• Existing solar, generator, cogeneration or compensation records, if any
• Supply contract, tariff group and eligible consumer status

Capacity Decision

When determining installed capacity, the maximum installable area should not be the only reference. How much generation overlaps with consumption determines the economic quality of the investment. Especially under hourly settlement, assuming that noon surplus will automatically close night consumption is not healthy.

In projects with high self-consumption ratio, electricity cost decreases directly. In projects with high surplus generation, settlement and market conditions become more critical.

In practice, preparing three capacity scenarios is more accurate.

Conservative capacity

It is designed close to the facility’s daytime base load. Surplus generation risk is low, and payback may be more predictable. However, part of the roof or land potential may remain unused.

Balanced capacity

Annual consumption, hourly matching and connection limits are read together. This is the first scenario that should be evaluated for most corporate facilities. Both self-consumption and reasonable surplus generation are considered.

Maximum capacity

It approaches the upper limit allowed by usable area and connection possibility. Investment amount increases; surplus generation, paid production limit, settlement and market revenue assumptions become more sensitive.

Site Suitability: Roof, Land and Electrical Infrastructure

In rooftop solar projects, structural suitability, roof covering type, fire safety, walkways, maintenance access, shading and drainage should be checked early. Layouts prepared only with satellite images may require revisions during implementation.

In land-based projects, zoning status, agricultural classification, slope, soil, road access, expropriation risk, distance to connection point and cable route can significantly affect investment cost. A land parcel that looks cheap can become an expensive project because of connection and infrastructure cost.

In electrical infrastructure, transformer capacity, main panel suitability, protection settings, metering cell, connection type and distribution company process should be evaluated separately. Since a solar project does not consist only of panels and inverters, these items should be shown clearly in the financial model.

Financial Model

Payback period in solar investments depends on investment cost, financing cost, maintenance expenses, generation forecast and electricity price assumptions. Therefore, feasibility should be prepared with sensitivity analyses, not a single scenario.

The model should include at least the following breakdowns:

• EPC investment cost and payment plan
• Financing interest, maturity and currency risk
• Annual generation forecast and performance degradation
• O&M, cleaning, security, insurance and remote monitoring expenses
• Consumption growth or shift-change scenarios
• Electricity price, supply contract and tariff assumptions
• Surplus generation and settlement effect

Calculating payback only with "today’s electricity price" can be misleading. When consumption profile, shift order or capacity utilization changes in industrial facilities, the economic effect of solar also changes.

Pre-Project Checklist

Before the investment decision, the following questions should be clarified:

• Does the facility’s hourly consumption profile overlap with solar generation?
• Is the planned capacity compatible with the connection and call letter process?
• Is the roof or land technically ready for implementation?
• Are fire, maintenance access and occupational safety requirements included in the project?
• Are generation loss, inverter failure and maintenance durations included in the model?
• Does the supply contract match the net withdrawal profile after solar?
• Is the investment decision for one location or for the whole portfolio?

Conclusion

Correct feasibility accelerates the investment decision and reduces surprise costs during implementation. Calculations made without modeling capacity, site and consumption together remain incomplete.

The healthiest approach for a solar investment is to turn the question "how much can we install" into "which capacity best matches the business’s consumption, connection and financial targets."