My solar savings are lower than the installer projected — why and what to do

Solar installers typically quote projected savings based on your historical Synergy bill, the size of the system, and assumptions about how you use electricity. When actual savings fall short of the estimate, it's frustrating — but the cause is usually identifiable and often fixable.

Here are the five most common reasons Perth households see lower solar savings than projected, and what to do about each.

Reason 1: consumption shifted to times when solar isn't generating

What happened: The installer calculated your savings assuming your household consumption pattern matches a typical Perth profile — with a significant portion of use during daytime hours (when solar generates). If your actual consumption is predominantly at night or in the early morning, you'll self-consume less solar and import more from the grid, reducing savings.

Signs:

• Your monitoring app shows high solar generation, but your Synergy import hasn't dropped much
• Your evening import charges remain similar to pre-solar levels

What to do: Run the reconciliation: if your generation figure from the monitoring app is what the installer projected, but your import hasn't fallen, consumption timing is the issue — not the system. Shift discretionary loads (dishwasher, washing machine, EV charging, pool pump, hot water) to 9am–3pm solar hours.

Reason 2: actual generation is lower than projected

What happened: The system is generating less electricity than the installer estimated. This can happen due to:

• Shading that wasn't fully accounted for in the design (tree growth, neighbouring structures)
• Soiling (dust, bird fouling) not accounted for
• System facing/tilt that differs from quote assumptions
• Panel or inverter underperformance (fault, early degradation)

Signs:

• Your monitoring app generation total is significantly below the installer's projected annual figure
• PR (performance ratio) calculated from actual data is below 0.72

What to do: Calculate your actual performance ratio (actual kWh ÷ (system kW × 1,825)). Compare to the installer's projected annual generation. If the shortfall is > 10%, contact the installer with your monitoring data and request a site inspection.

Reason 3: Synergy billing errors or DEBS not activated correctly

What happened: Your DEBS export credits aren't appearing on bills, or the import/export rates are incorrect. This is more common than most people assume — Synergy billing updates for new solar customers have occasional errors, particularly around:

• DEBS not activated after smart meter installation
• Import billed at the wrong rate
• Export credited at old REBS flat rate instead of DEBS time-of-use rates (or vice versa)
• Supply charge not correctly applied

Signs:

• DEBS credits don't appear at all on the bill despite having a smart meter
• Your import charges seem too high for a household with solar
• The export credit rate doesn't match expected DEBS rates (2c off-peak / 10c peak)

What to do: Compare your monitoring app export total to the Synergy bill export figure. If they're significantly different, contact Synergy. Request a bill review and, if DEBS is not correctly set up, ask Synergy to correct it retroactively (they can typically back-date credits for up to 12 months in clear cases of setup error).

Reason 4: the installer's estimate was too optimistic

What happened: Some installer projections use average-best assumptions: full Perth PSH (5.0), no shading deductions, performance ratio of 0.85+, and a self-consumption ratio that may not match your household's actual pattern. A projection built on best-case assumptions will consistently outpace actual savings.

Signs:

• Your system is generating what you'd expect given its size and direction
• Your self-consumption appears reasonable
• But the projected savings figure on the quote seems to have assumed higher self-consumption or higher consumption to begin with than your actual usage

What to do: This is disappointing but not a fault — it's a mismatch between projection and reality. Ask the installer for the assumptions behind their savings estimate (PSH used, assumed self-consumption rate, assumed annual generation). Compare to actuals. If the assumptions were unreasonable, note this for other Perth households who use the installer — and switch to using actual generation data for future year projections.

Reason 5: your consumption pattern changed after solar installation

What happened: Households sometimes change behaviour after installing solar — using more air conditioning because "it's free," buying an EV, or running appliances during evening hours without adjusting for solar generation. If total consumption increased after solar installation, some of the potential savings are offset by higher overall usage.

Signs:

• Your import charges are similar to pre-solar, but your monitoring shows good generation
• You've added new loads (EV, spa, new appliance) or increased AC usage since installation

What to do: Compare total consumption (import + solar self-consumed) before and after solar installation. If consumption has increased, the solar savings are still real — they're just being partially offset. Redirect discretionary consumption to solar generation hours (9am–3pm) to maximise self-consumption.

How to calculate your actual solar savings

Rather than relying on the installer's estimate, calculate your actual savings:

Step 1: Total solar generation from monitoring app (past 12 months)

Step 2: Estimated self-consumption = generation − DEBS export (from Synergy bill)

Step 3: Value of self-consumption = self-consumed kWh × A1 tariff (33.26c/kWh) [or Midday Saver rates if applicable]

Step 4: Value of DEBS export from Synergy bill (shown as credits)

Step 5: Total solar saving = self-consumption value + DEBS export value

Compare this to the installer's projected annual saving. The difference identifies the gap to investigate.

Upload your Synergy bill and enter your monitoring app generation total to BillWise to run this reconciliation automatically and identify which factor is driving your savings shortfall.