Hydraulic Performance Testing of PVT Collectors: How Pressure Drop and Flow Characteristics Affect System Desi

Introduction

For photovoltaic thermal (PVT) collectors, thermal output is not determined only by optical efficiency or heat loss coefficients.

A PVT collector is also a hydraulic component.

The heat transfer fluid must circulate through internal channels, absorb thermal energy from the collector, and transfer this energy to the connected system.

Therefore, engineers must understand:

• how much pressure loss occurs inside the collector,
• how flow rate affects heat extraction,
• how collectors influence pump selection,
• how multiple collectors should be connected into arrays.

Hydraulic performance testing provides the engineering data required to design reliable PVT systems, especially when PVT collectors are connected with:

• brine heat pumps,
• ground source heat pump systems,
• solar-assisted heat pumps,
• residential heating systems,
• commercial renewable heating projects.

The Intertek test report for Solis PVT collectors includes hydraulic performance evaluation through pressure drop measurements according to ISO 9806:2017 thermal collector testing procedures.

Quick Summary

Evidence Callout

Independent Laboratory Evidence

Evidence Source

Independent laboratory test report:

Intertek Test Report No. 240312065GZU-001

Tested product:

Solis PVT collector models:

• PVT430
• PVT450
• PVT550
• PVT580
• PVT600
• PVT670

The laboratory evaluated the collectors according to:

• EN 12975:2022
• ISO 9806:2017

The report states that submitted samples complied with applicable requirements of EN 12975:2022 and ISO 9806:2017.

Hydraulic Performance Evidence

The report includes:

• pressure drop measurements,
• pressure drop coefficients,
• flow-pressure relationship curves.

The hydraulic test was performed using water with measured pressure drop characteristics.

For the tested PVT670 collector, the report provides:

1. What Is Hydraulic Performance Testing?

Definition

Hydraulic performance testing evaluates the relationship between:

• fluid flow rate,
• pressure difference,
• internal hydraulic resistance.

For a PVT collector, the basic relationship is:

$$\Delta P=f(Q)$$

where:

• ΔP = pressure drop between collector inlet and outlet
• Q = fluid flow rate

A higher flow rate normally increases pressure losses because fluid friction increases inside the absorber channels.

2. Why Hydraulic Performance Matters for PVT Systems

A PVT collector has two energy functions:

1. Generate electricity through PV cells.
2. Extract thermal energy through fluid circulation.

The thermal side depends on effective heat transfer.

If flow is too low:

• heat extraction decreases,
• collector temperature increases,
• thermal efficiency may decrease.

If flow is too high:

• pumping electricity increases,
• system efficiency may decline.

Therefore, the engineering goal is not maximum flow.

The goal is:

Achieve sufficient heat transfer with optimized pumping energy.

3. Pressure Drop: The Key Hydraulic Parameter

What is Pressure Drop?

Pressure drop is the pressure difference between collector inlet and outlet.

ΔP=Pin−Pout\Delta P=P_{in}-P_{out}ΔP=Pin​−Pout​

It represents the resistance that the circulation pump must overcome.

Engineering Meaning

Lower pressure drop:

Advantages:

• smaller pump requirement,
• lower electricity consumption,
• easier system balancing.

Higher pressure drop:

Potential impacts:

• larger circulation pump,
• higher operating cost,
• more complex hydraulic balancing.

4. How Pressure Drop Is Measured

According to the Intertek report, hydraulic performance testing included:

• controlled fluid circulation,
• measured flow rates,
• measured pressure differences.

The report provides a pressure drop curve showing the relationship between:

• flow rate [L/h]
• pressure drop [Pa]

5. Understanding Flow Rate

What Is Flow Rate?

Flow rate describes how much heat transfer fluid moves through the collector.

Common engineering units:

• L/h
• kg/s
• kg/(s·m²)

The correct flow rate affects:

• thermal output,
• collector temperature,
• heat pump operating conditions.

6. Relationship Between Flow Rate and Thermal Performance

Hydraulic performance and thermal performance are connected.

A simplified relationship:

Higher Flow Rate
        ↓
Higher Heat Removal
        ↓
Lower Collector Temperature
        ↓
Lower Thermal Loss

However:

Higher Flow Rate
        ↓
Higher Pressure Drop
        ↓
Higher Pump Power

Therefore, engineers must optimize the balance.

Engineering Comparison Table

Low Flow vs High Flow Operation

7. Using Hydraulic Test Data for Heat Pump Design

For PVT heat pump systems, hydraulic data helps engineers determine:

Pump Selection

The circulation pump must provide:

• required flow rate,
• sufficient pressure head.

Collector Array Design

When multiple collectors are connected:

Engineers evaluate:

• series connection pressure increase,
• parallel flow distribution,
• hydraulic balancing.

Brine Heat Pump Systems

For brine loops:

Hydraulic performance affects:

• seasonal efficiency,
• pump electricity consumption,
• system reliability.

8. Hydraulic Performance of Solis PVT Collector

The Intertek tested collector family includes multiple PVT models.

The tested samples include:

• PVT430
• PVT670

The report identifies PVT collectors with absorber channels and hydraulic connections designed for liquid heat transfer applications.

The pressure drop evaluation provides engineers with verified hydraulic behavior rather than relying only on manufacturer calculations.

9. Engineering Interpretation

Measured Data

From Intertek:

• pressure drop coefficients,
• measured pressure drop curve,
• flow test data.

Standard Requirement

ISO 9806 defines standardized collector testing methods, including thermal collector performance evaluation.

The standard provides the testing framework.

Engineering Judgement

Engineers must combine:

• pressure drop data,
• required thermal output,
• heat pump flow requirements,
• system piping layout.

A collector with excellent thermal performance may still perform poorly if hydraulic design is inappropriate.

Application Connection

Hydraulic performance testing is especially important for:

Brine Heat Pump Systems

PVT collectors often operate as outdoor heat exchangers.

Hydraulic data helps optimize:

• brine circulation,
• pump sizing,
• collector field layout.

Ground Source Heat Pump Replacement

Compared with buried ground loops:

PVT collectors provide:

• above-ground heat exchange,
• easier installation,
• measurable hydraulic characteristics.

Residential Heating Systems

For residential systems:

correct hydraulic design improves:

• seasonal efficiency,
• operating stability,
• maintenance reliability.