Sol Viva

Designing a Solar System to Minimise Export

Nov 26, 2025By John Wallace
John Wallace

One of the biggest surprises for homeowners going solar in Portugal is that exporting electricity back to the grid is not as valuable as most people expect.

In fact, for most families, the smartest design is a solar system that feeds as little as possible back into the grid and instead maximises the amount of solar electricity used inside the home.

This article explains why that matters, how different types of power flow in your solar system, and how to design a plant that gives you the best return on investment.

The 5 Types of Power in a Solar Home

Before we talk about design, let’s get clear on the different types of power your solar system deals with every second of the day:

1. Solar Power (PV Output Power)

This is the electricity generated by your panels.  It is the cleanest, cheapest energy available to you.

You want to use as much of this as possible inside the home.

2. Load Power (Home Consumption)

This is how much electricity your home is using at any moment.
It includes:

  • Fridges, freezers
  • Lights
  • Pool pumps
  • Air conditioning
  • Washing machines
  • EV chargers
  • Anything plugged in

Your solar power must first try to supply your load power.

3. Battery Power

A battery can either:

  • Charge (absorbing spare solar)
  • Discharge (providing power when solar isn't enough)

Batteries help you:

  • Use more of your own solar
  • Avoid buying expensive peak-time energy
  • Reduce export
  • Achieve greater energy independence

4. Grid Power (Import)

This is electricity you buy from the utility.

The goal is to reduce how often you need grid power.

5. Feed-In Power (Export)

This is electricity your system sends back to the grid when:

  • Your solar panels produce more than your home needs, and
  • Your battery is already full

In Portugal, this is usually the least valuable form of energy.

Why Minimising Export Matters in Portugal

Here’s the simple economics:

  • You buy electricity for ~€0.20 to €0.28/kWh
  • You sell exported solar for ~€0.05 to €0.07/kWh

That means exported solar earns you only a quarter of what grid electricity costs.

Put another way:

  • Every kWh you export is money lost.
  • Every kWh you consume yourself is money saved.

This is why system design matters so much.

The Goal: Maximise Self-Consumption

Self-consumption means using your own solar directly in the home.

Good:

  • Solar → Home Load
  • Solar → Battery Charging
  • Solar → EV Charging
  • Solar → Pool Pump
  • Solar → Heat Pump

Bad (financially):

  • Solar → Grid (export)

A well-designed system aims to keep your self-consumption above 75–85%.

How to Design a Solar Plant That Minimises Export

There are four key principles.

1. Size the solar system correctly

Bigger is not always better.

If your panels produce more than your home can use during the day, the excess will be exported.

A good designer will analyse:

  • Your daily consumption
  • Your time-of-use patterns
  • Your peaks
  • Seasonal variations

And then choose a size that:

  • Covers daytime needs
  • Fills a battery
  • Doesn’t dramatically overshoot into export

2. Add a battery (even a small one helps)

A battery absorbs spare solar that would otherwise be exported.

A 5–10 kWh battery can:

  • Charge during high solar hours
  • Discharge when the sun drops
  • Reduce grid imports
  • Reduce exports
  • Allow more of your solar to stay in the home

Batteries are the most effective tool for minimising export.

3. Use smart energy shifting (HEMS)

A Home Energy Management System (HEMS) can automatically turn on loads when excess solar is available.

For example, it can:

  • Run the pool pump during sunny hours
  • Heat water with a heat pump or immersion relay
  • Charge the EV when solar is overproducing
  • Trigger the dishwasher or washing machine

This ensures “extra” solar has somewhere to go. 

4. Avoid oversizing

Many installers push bigger systems because they earn more from the sale.

  • But an oversized system leads to:
  • High export
  • Lower self-consumption
  • Worse ROI
  • A system that produces energy you can’t use

Sol Viva’s approach is always:

Right size, not oversized.

What Happens If You Export Too Much?

If your system is incorrectly sized, you’ll notice:

  • High solar output (red line)
  • Large export (black line)
  • Low home consumption (blue line)
  • Battery frequently full
  • Grid consumption still happening later in the day

This leads to:

  • Money lost
  • Longer ROI
  • Lower efficiency
magnifying glass with example words and green background.

Real Example (Simplified)

Two homes generate 30 kWh/day of solar power:

Home A – Good design

  • Uses 24 kWh internally
  • Exports 6 kWh
  • Saves money on 24 kWh
  • ROI ~6 years

Home B – Oversized design

  • Uses 14 kWh internally
  • Exports 16 kWh
  • Saves money on 14 kWh
  • ROI ~10+ years
  • Same production.

Totally different financial outcomes.

Final Thoughts

Solar is one of the best investments a family can make — but only when the system is designed to maximise self-consumption and minimise export.

To get the best results, your system should:

  • Match your usage
  • Include a battery (if budget allows)
  • Use smart load shifting
  • Avoid unnecessary oversizing

At Sol Viva, we design every system using detailed energy analysis to ensure homeowners get the fastest payback and the highest return.