Central vs String Inverter: When to Choose Which

Feature	Central Inverter	String Inverter
Typical capacity	500 kW to multiple MW per unit	~10 kW to 250 kW per unit
Best suited for	Utility-scale and large commercial farms	Residential and small-to-medium commercial installations
Panel-level control	No	Yes (especially with optimizers or micro-inverters)
Efficiency	High overall efficiency at scale	Slightly higher module-level MPPT efficiency
Reliability impact	High (whole system offline if fails)	Localized failure only affects part of the system
Maintenance density	Low (few units centralised)	Higher (distributed units across the array)

A string inverter—commonly used in residential and commercial solar photovoltaic (PV) systems—is an electrical device that:

• Converts DC power generated by groups of solar panels (called “strings”) into AC power for household or grid use.
• Typically mounted near your electrical service panel and connected to dozens to hundreds of solar panels in series.

---

⚙️ How It Works

• Multiple panels are wired in series to form a “string,” boosting voltage (e.g. 600–800 V DC) at lower current.
• The string feeds into a single inverter that uses Maximum Power Point Tracking (MPPT) to adjust current and convert incoming DC to grid-level AC

---

✅ Advantages of String Inverters

Benefit	Description
Lower system cost	One inverter handles many panels, reducing purchase & installation expenses.
Efficient cabling	High-voltage, low-current lines reduce conductor size and DC losses.
Easier maintenance	Accessing one centralized inverter is simpler than rooftop electronics.
Scalable and modular	Multiple inverters allow redundancy: if one fails, other strings still produce.

---

⚠️ Considerations & Drawbacks

• Shading or underperformance on one panel affects the entire string—performance defaults to the weakest panel.
• Lack of panel-level monitoring unless paired with add-on optimizers.
• Shorter lifespan, typically 8–12 years (vs. up to 25-year warranties on microinverters).
• Single point of failure: if the inverter fails, the whole string goes offline.

---

🔄 Microinverters & Optimizers: Why Compare?

• Microinverters are installed on each panel and convert electricity at the module level, avoiding string dependency. They enable per-panel monitoring and mitigate shading impact.
• Power optimizers can be added to a string inverter system to condition panel output individually, improving efficiency without converting to AC at each panel.

---

🏠 Ideal Use Cases

You value panel-level diagnostics and maximum yield.

String inverter systems are ideal when:

Panels receive uniform, unshaded exposure.

You want a lower upfront cost for medium-to-large installations.

You prefer easier servicing via a centralized unit.

Consider optimizers or microinverters when:

Your roof is shaded or sections face different orientations.

Creating a solid installation agreement is crucial for both you as the installer and your clients. It ensures clarity regarding responsibilities, timelines, costs, warranties, and other important aspects of the project. Here’s a basic outline of what you might include in a solar on-grid system installation agreement:

1. Parties Involved: Clearly state the names and contact information of both parties involved in the agreement, including the installer (your company) and the client.
2. Scope of Work: Detail the specific services to be provided by the installer. This should include everything from initial site assessment to final system commissioning.
3. Timeline: Specify the expected start date and completion date of the project. Include any milestones or deadlines for key phases of the installation process.
4. Payment Terms: Outline the total project cost and the payment schedule. Specify any upfront deposits required and when final payment is due. Include details on accepted payment methods.
5. Equipment and Materials: List the specific solar panels, inverters, mounting hardware, and other equipment to be used in the installation. Specify whether the equipment is new, refurbished, or leased.
6. Permits and Approvals: Clarify which party is responsible for obtaining necessary permits and approvals from local authorities, utility companies, and homeowners’ associations.
7. Warranties: Detail the warranties provided for the solar panels, inverters, and other equipment, as well as any workmanship warranties offered by the installer.
8. Insurance: Specify the insurance coverage held by the installer, including general liability insurance and worker’s compensation insurance. Clarify any insurance requirements for the client.
9. Maintenance and Support: Outline any maintenance services provided by the installer, as well as procedures for addressing warranty claims or service requests.
10. Cancellation and Termination: Include provisions for canceling the agreement or terminating the project early, including any associated fees or penalties.
11. Dispute Resolution: Specify procedures for resolving disputes that may arise during the installation process, such as mediation or arbitration.
12. Governing Law: Indicate the jurisdiction whose laws will govern the agreement in case of legal disputes.
13. Signatures: Provide space for both parties to sign and date the agreement, indicating their acceptance of its terms and conditions.

It’s important to have a qualified legal professional review your installation agreement to ensure it complies with applicable laws and adequately protects your interests as an installer.