Refinance to Add Solar and Batteries? The Numbers to Check First

Refinancing your mortgage mainly to add solar and batteries can be a smart move only if the numbers stack up after all costs. That means your interest savings plus power‑bill reductions need to outweigh refinance fees, potential LMI and the risk of a bigger loan over time. For many borrowers, the right move is a targeted refinance with a separate short‑term solar split – not a full reset of the whole mortgage.

This guide gives you a decision process you can work through in a week so you know whether to refinance now, adjust your current loan, or use different finance for your solar upgrade.

Run the refinance, solar and cashflow numbers side by side before you commit.

1. When does refinancing for solar and batteries make sense?

Core test: do the savings beat the costs?

Refinancing for solar stacks up when all three of these are true:

1. You can improve your overall rate or structure, not just add debt.
2. You have enough equity to avoid or minimise new LMI.
3. The breakeven on refinance costs is reasonable (usually under 3–5 years).

A practical way to judge this is a breakeven calculation: divide your total refinance costs (application, discharge, registration, any new LMI) by your expected annual interest savings at the new rate, plus a conservative estimate of bill savings from solar.[4]

If the breakeven period is longer than you’re likely to keep the property or the loan, refinancing mainly for solar is usually not worth it.

When it’s usually a good idea

Refinancing to fund solar and a battery often makes sense when:

• Your current rate is clearly uncompetitive (e.g. ~0.75–1.00%+ higher than realistic new‑customer offers for similar borrowers).
• Your LVR after the solar top‑up will still be ≤80%, so there’s no new LMI.
• You can set up a separate loan split for solar with a 5–10 year term, rather than blending it into a 25–30 year mortgage.[1][2]
• You want to clean up messy loan structure at the same time (e.g. multiple splits, old fixed rates, unused offset).

For investors, refinancing can also be the point where you align solar spending with your broader strategy, as discussed in /insights/when-investors-should-refinance-or-sit-tight.

When you should think twice

Refinancing mainly for solar is often not smart if:

• Your post‑refinance LVR would be above 80%, triggering fresh LMI that may dwarf your bill savings.
• Your income is unstable or tight and you’re already close to mortgage stress (Roy Morgan estimates 28.2% of borrowers were ‘At Risk’ in early 2026).
• Your suburb is soft or values are slipping, pushing LVR higher and hurting flexibility – see /insights/refinancing-tight-lvr-soft-falling-suburb-values.
• You’re on a niche or non‑conforming loan with big break fees and no clean exit yet.

In those cases, it can be safer to sharpen your current deal, or consider a smaller separate loan for solar while you repair your refinance position.

2. Comparing ways to fund solar in a refinance

You generally have three broad options if you’re using your home to fund solar and a battery:

• Full refinance + equity release
• Top‑up with your existing lender
• Separate green/personal or business loan

Snapshot comparison

*Illustrative only – actual rates depend on lender, LVR, credit and product. Do not rely on these numbers for decisions.

A key principle from our broader solar guides: keep solar and battery costs in a separate home loan split with a shorter term (around 5–10 years) so you don’t pay 30 years of interest on a 15–20 year asset.[1][2][5]

For a deeper look at whether to use mortgage, personal or business finance, see /insights/questions-to-ask-broker-before-borrowing-for-solar.

3. Worked example: refinance + $25k solar and battery

Let’s say:

• Current loan: $600,000, 25 years remaining, 6.40% p.a. (P&I)
• Proposed new rate: 5.60% p.a. (P&I)
• Solar + battery cost: $25,000
• Refinance costs (application, discharge, registration): $1,800
• No LMI (LVR stays under 80%).

Step 1: interest savings on existing loan

Approximate monthly repayment now (ignoring small rounding):

• At 6.40% over 25 years: about $4,040 per month.
• At 5.60% over 25 years: about $3,870 per month.

Indicative saving ≈ $170 per month, or $2,040 per year in cashflow.

Step 2: structuring the solar split

Instead of adding $25,000 to the 25‑year loan, you create a separate 7‑year split:

• $25,000 at 5.60% over 7 years: repayment ≈ $360 per month.

If you had blended that $25,000 into the main 25‑year mortgage at 5.60%:

• Extra repayment ≈ $155 per month, but over a much longer term.

Total interest on the solar amount alone could be roughly $21k+ over 25 years vs around $6k–7k over 7 years – a dramatic difference from the shorter split.[1][5]

Step 3: bill savings and breakeven

Assume the solar + battery cuts your power bill by $1,600 per year after rebates (cross‑check with /insights/solar-system-costs-quotes-budgeting-before-you-borrow).

Combined annual benefit:

• Interest savings on refinance: ≈ $2,040
• Power‑bill savings: ≈ $1,600
• Total: $3,640 per year.

Breakeven on $1,800 costs:

• $1,800 ÷ $3,640 ≈ 0.5 years.

In this example, refinancing mainly to add solar is very compelling. But if:

• Your rate improvement was smaller, or
• You had to pay $8,000 of new LMI, or
• Your solar savings were more modest,

the breakeven could blow out beyond 5–7 years, which is marginal – especially if you might move or restructure again.