New 2025 Data Reveals How to Boost Your Solar Payback

A new study shows solar can deliver strong returns for New Zealand households. Below is a practical guide that breaks down the research, with direct quotes from Energy Efficiency and Conservation Authority (EECA) senior analyst Gareth Gretton plus a few tech notes for anyone sizing up a system this year.

1. Orientation & shade - the first (and biggest) check

"So if you have a north facing roof, it's not flat, it's not shaded. You've got electric appliances in your home, you're able to use some of the electricity during the day and you've got a good price for your solar, it's going to be a good investment."

Don’t have much north facing roof? It’s not a dealbreaker. If space is limited, installing some panels on east and west facing sections can still deliver excellent performance and can even help spread your solar generation more evenly across the day, especially in the morning and late afternoon.

Why north facing is best: Panels that face north get the most direct sunlight during the middle of the day, when the sun is strongest. This means they generate more power over the year compared to east or west facing panels, sometimes up to 10-20% more, according to EECA.

If your roof has some shade from trees, chimneys or nearby buildings, panel choice becomes even more important. That’s where AIKO INFINITE panels can help, their advanced design allows them to produce up to 30% more power in shaded conditions compared to standard panels.

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2. Roof angle - good to get right, but not a dealbreaker

EECA found that a 30° roof angle is ideal for solar, but it’s not critical. According to EECA’s Gareth Gretton, you’ll only gain or lose a few percentage points if your roof is steeper or flatter.

“Unless your roof is flat or nearly flat, just put them parallel with the roof plane,” said Gretton.

If your roof is flat and you’re thinking about installing angled mounting frames, it’s worth knowing this can add extra cost.

In most cases, keeping panels flush with your roof is the most practical and cost-effective option and still delivers great performance.

3. System size - why adding more or higher power solar panels makes sense

One of the smartest ways to get more from your solar system is to slightly oversize your panels compared to your inverter. This means adding around 6 kW of panel capacity with a 5 kW inverter for example.

"What we found is the way to optimise the package is to put in something like 6 kW panel capacity and a 5 kW inverter… you're actually maximizing the value of the inverter and the whole system by making the inverter run at full capacity more of the time."

EECA’s modelling shows this setup can boost your annual power output by around 10%, without needing a more expensive inverter - a clever option if you’re short on roof space but still want strong performance.

4. Sunshine vs. power prices - why returns vary

It’s easy to assume that sunshine is the main driver of solar performance, but electricity prices play just as big a role. According to Gareth Gretton from EECA, even cities with fewer sun hours can still see strong returns if power prices are high enough.

“There’s a pretty wide range of return but it’s pretty much never below 6 percent… At the very extreme end, and I should stress these numbers are unusual, but nevertheless they're real, there were returns of up to 14 percent”

Annual returns can reach up to 14%, depending on your home’s roof orientation, local power prices and how much of your solar energy you use. Selecting a suitable energy plan can also help maximise returns by aligning tariffs and buy-back rates with when your home generates and uses power. Even in less sunny areas, solar can still deliver great value, especially for households with high electricity usage.

5. Exporting to the grid - more room, more reward

One of the common limits for solar homeowners has been how much power they’re allowed to send back to the grid. But recent changes to voltage regulations are making it easier for networks to accept more solar exports.

“This basically gives the networks more headroom to receive this electricity from inverters.” - he said

What this means: in many areas, the old 5 kW export limit is being raised to 10 kW, allowing homeowners to install larger systems without wasting surplus energy during peak sun hours.

If you’re sizing a system to charge an EV, run a heat pump, or offset more of your power bill, higher export caps, combined with the right system size, can reduce wasted midday generation, ensuring more of your power is used or exported. The result: your system works harder and can pay off faster.

6. Price & warranty - two things you can control

While you can’t control sunshine or power prices, you can choose a system that offers better value and long term protection. As Gareth Gretton from EECA points out:

“If you’re able to get a really competitive installation price, you’re guaranteed to have higher returns… Look at warranties on performance, ie output and how long it is guaranteed to not break for - you want long warranties on both.”

At Harrisons, we supply AIKO INFINITE panels with a 25 year product warranty and a 30 year performance guarantee - giving you peace of mind that your investment will deliver for the long haul.

We also back our systems with a Best Price Promise to help you secure a great installation price, and we've proudly been voted New Zealand’s #1 Most Trusted Solar Installer by Reader’s Digest for three years running (2022–2025).

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Key Takeaways for Homeowners

1. North facing roofs work best and keeping shade to a minimum makes a big difference.
   
   
2. Add more panels or get more powerful ones: for example, pairing 6 kW of panels with a 5 kW inverter helps boost output.
   
   
3. Power prices matter: homes with higher electricity costs often see faster payback.
   
   
4. Export limits are improving so you can send more power back to the grid.
   
   
5. Look beyond the price tag, good warranties and better panel tech can save more long term.
   
   
   

Curious what these findings mean for your roof?

Harrisons can run a free, data-driven assessment to model orientation, shading, panel choice and export rules for your exact address, giving you the numbers before you commit.

Solar has tipped in favour of Kiwi households; the right design simply locks in the payoff.

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