Installing a solar pool heating system is a smart, eco-friendly way to extend your swimming season. At the heart of this system is a pump that circulates water from your pool through the solar collectors on your roof and back again. Choosing the right size submersible pump is crucial for your system to work efficiently, saving you energy and money while keeping your pool at the perfect temperature.

This guide will walk you through everything you need to know about selecting the correct submersible solar pump for your pool heating setup. We'll cover the essential factors to consider, from flow rate and head pressure to the specifics of your solar collectors. By the end, you'll have the confidence to choose a pump that maximizes your solar investment and keeps your pool comfortably warm.

Why the Right Pump Size Matters

Selecting an incorrectly sized submersible pump can lead to several problems. A pump that is too small won't have the power to push water through the entire solar collector system effectively. This results in poor circulation and inefficient heating, meaning your pool won't reach the desired temperature, even on sunny days. You'll be left with a system that doesn't deliver on its promise.

On the other hand, a pump that is too powerful will consume more energy than necessary, driving up your electricity bills. An oversized pump can also cause excessive pressure and flow, which can strain or even damage your solar collectors, pipes, and other pool equipment over time. This leads to costly repairs and a shorter lifespan for your entire system. The goal is to find a submersible solar pump that provides the perfect balance of power and efficiency.

Key Factors for Sizing Your Submersible Solar Pump

To determine the right size pump, you need to understand two key concepts: flow rate and total dynamic head.

1. Calculating Flow Rate

Flow rate, measured in gallons per minute (GPM), is the volume of water the pump can move in a given time. For a solar pool heating system, the required flow rate is determined by the size of your solar collectors.

Solar collector manufacturers typically provide a recommended flow rate for their products, usually between 4 and 10 GPM per collector panel.

How to calculate the required flow rate:

1. Count your solar collectors: Determine the total number of solar panels in your array.

2. Find the manufacturer's recommendation: Check the product specifications for the recommended GPM per panel. Let's assume it's 5 GPM for this example.

3. Multiply: Multiply the number of collectors by the recommended GPM.

Example: If you have 8 solar collectors and the manufacturer recommends a flow rate of 5 GPM per collector:
8 collectors × 5 GPM/collector = 40 GPM

In this case, you would need a pump that can deliver a flow rate of at least 40 GPM. This ensures that water moves through the collectors at an optimal speed to absorb heat efficiently.

2. Calculating Total Dynamic Head (TDH)

Total Dynamic Head (TDH), or simply "head," is a measure of the total resistance the pump must overcome to circulate water through the system. It's measured in feet and accounts for both vertical lift (static head) and friction loss in the pipes and equipment.

Static Head: This is the vertical distance the water needs to be lifted. For a solar pool heating system, it’s the height difference between the surface of the pool water and the highest point of the solar collectors on your roof.

Example: If your pool's water level is at ground level and your solar collectors are 20 feet high on the roof, your static head is 20 feet.

Friction Loss: As water flows through pipes, fittings (like elbows and valves), and the solar collectors themselves, it encounters friction, which slows it down. The pump needs to generate enough pressure to overcome this friction.

You can estimate friction loss using online calculators or by following this general rule of thumb for standard PVC pipes:

• Add 1 foot of head for every 10 feet of straight pipe.

• Add 1 foot of head for each 90-degree elbow fitting.

• Add 20-30 feet of head for the solar collectors themselves (check manufacturer specs for a more precise number).

How to calculate TDH:

1. Measure the Static Head: The vertical height from the pool water surface to the top of the solar panels.

2. Estimate Pipe Friction: Calculate the total length of the pipe run from the pump to the collectors and back. Add additional head for all the fittings.

3. Add Collector Friction: Include the friction loss from the solar collectors.

4. Sum it all up: Add Static Head + Pipe Friction + Collector Friction to get your Total Dynamic Head.

Example:

• Static Head: 20 feet

• Pipe Run: 100 feet total (10 feet of head)

• Fittings: 8 elbows (8 feet of head)

• Solar Collectors: 25 feet of head

TDH = 20 + 10 + 8 + 25 = 63 feet

So, you would need a submersible solar pump capable of delivering 40 GPM at 63 feet of TDH.

Using a Pump Performance Curve

Once you have your required flow rate (GPM) and Total Dynamic Head (TDH), you can use a pump's performance curve to find the right model. A performance curve is a graph provided by the pump manufacturer that shows the relationship between flow rate and head.

To use the chart:

1. Find your required TDH on the vertical (Y) axis.

2. Find your required flow rate on the horizontal (X) axis.

3. Find where these two points intersect on the curve.

You should select a pump where your calculated operating point (e.g., 40 GPM at 63 feet TDH) falls in the middle of its performance curve. This ensures the pump operates at its Best Efficiency Point (BEP), maximizing performance while minimizing energy consumption. Avoid choosing a pump where your requirements are at the extreme ends of the curve, as this indicates it will be overworked or underutilized.

The Advantage of a Submersible Solar Pump

For solar pool heating, a submersible solar pump offers distinct advantages. These pumps are designed to work directly with solar panels, converting solar energy into pumping power without needing a connection to the grid. This makes your heating system completely independent and cost-free to run during sunny days.

Because a submersible solar pump's performance varies with the intensity of the sun, it naturally aligns with when your solar pool heater is most effective. More sun means more power for the pump and more heat for the collectors. This synergy makes them an ideal choice for an efficient, off-grid pool heating solution.

Ready to Heat Your Pool?

Choosing the right size submersible pump is a critical step in setting up an efficient solar pool heating system. By carefully calculating your required flow rate and total dynamic head, you can select a pump that delivers optimal performance, saves energy, and extends the life of your equipment. A well-sized submersible solar pump ensures your pool stays warm and inviting, all powered by the free energy of the sun.

Don't let the technical details intimidate you. Taking the time to get these calculations right will pay off with a perfectly heated pool for years to come.