Your solar system used to pay for itself. Now it feels like it's costing you. Here's what's changed — and what you can do about it.
When you went solar back in 2013, 2015, or 2017, the promise was straightforward: put panels on your roof, reduce or eliminate your electric bill, and enjoy decades of clean energy savings. For the first few years, it probably worked. Your true-up bill was low or even zero. Your monthly utility statements showed credits. Solar felt like one of the best investments you'd ever made.
But somewhere along the way, the numbers stopped working. Your true-up bill started climbing. Your utility credits shrank. And now you're wondering if those panels on your roof are even doing anything anymore.
If your solar system was installed before 2018 — whether by Sunrun, Vivint Solar, SolarCity, or a local installer — there's a good chance several factors are working against you simultaneously. The good news is that most of them are fixable once you understand what's going on.
Solar technology and the energy landscape in California have both changed significantly since the early-to-mid 2010s. Here's how systems from that era compare to what's available now:
| Factor | Pre-2018 Systems | 2024+ Systems |
|---|---|---|
| Panel efficiency | 15–17% | 20–23% |
| Inverter type | Often string inverters | Microinverters or optimizers standard |
| Monitoring | Basic or not set up | Panel-level monitoring standard |
| NEM plan | NEM 1.0 (most favorable) | NEM 3.0 (net billing) |
| Battery storage | Rarely included | Increasingly common |
| Rate structure | Peak hours aligned with solar production | Peak hours shifted to evening |
The irony is that if you went solar early, you're likely on a more favorable NEM plan (NEM 1.0 or 2.0) than new customers get today. That's actually a significant financial advantage — but only if your system is performing well enough to take advantage of it. An underperforming system on a great rate plan still results in a high true-up bill.
Every solar panel degrades over time. The industry standard is roughly 0.5–0.8% per year. That might not sound dramatic, but over 8 to 12 years, it adds up. A system installed in 2014 producing 8,000 kWh in its first year might only produce 7,200–7,500 kWh today. That 500–800 kWh gap, at current SCE rates of $0.30–$0.45 per kWh, represents $150–$360 in lost annual savings.
And that's assuming normal degradation. Panels with manufacturing defects, microcracks, or hot spots can degrade much faster. Without panel-level monitoring, you might have one or two panels producing at half capacity and never know it.
If your system uses a central string inverter — which was the standard for residential systems before 2017 or so — it has a typical warranty of 10 to 12 years and a practical lifespan of 10 to 15 years. If your system is approaching or past the 10-year mark, your inverter is likely one of the most vulnerable components. Even before it fails outright, inverters can lose efficiency, clip production on high-output days, or develop intermittent faults that reduce your annual output by 5–15%.
This one catches a lot of pre-2018 solar homeowners off guard. When your system was installed, utility peak hours typically ran from about noon to 6 PM — right when solar panels produce the most. That meant the energy you exported to the grid was credited at the highest rate.
California utilities have since shifted peak hours to 4 PM–9 PM. Your panels are producing the bulk of their energy during what's now considered "off-peak" or "mid-peak" hours, earning lower credits. And you're pulling energy from the grid during the expensive evening peak. The same system producing the same amount of electricity is worth less under the new rate structure.
Think about your household's energy consumption in 2015 compared to today. Many homeowners have added energy-intensive changes without thinking about their solar system's capacity: electric vehicles that charge at home, home offices with computers and monitors running all day, larger or additional refrigerators, upgraded HVAC systems, pool or spa equipment, and the general accumulation of connected devices and electronics that draw power 24/7.
Your system was sized for the household you had when it was installed. If your electricity needs have grown by 20–30%, your system can't keep up — and the shortfall shows up on your true-up bill.
Solar systems are sometimes marketed as "maintenance-free," but that's not quite accurate. Panels get dirty — Southern California's dry, dusty climate means significant soiling between rain events. Bird droppings, pollen, and construction dust can reduce output by 5–10%. Beyond soiling, racking hardware can loosen, roof penetrations can develop leaks, and wiring connections can corrode. Most pre-2018 system owners have never had their system professionally inspected or maintained since the day it was installed.
Here's what makes this so frustrating: none of these individual factors might seem catastrophic on their own. But they compound. Take a system that's degraded 6%, has a slightly underperforming inverter (another 5% loss), accumulated soiling (another 5%), and the TOU rate shift reducing the value of credits by 15–20%. Suddenly, a system that was covering 100% of your bill is now only effectively covering 65–70%. That gap is your true-up bill.
Get a system health check. An independent inspection that measures actual panel output, inverter performance, and overall system health is the single most valuable thing you can do. It turns guesswork into data.
Clean your panels. If you haven't cleaned them in over a year, start here. Professional cleaning typically costs $150–$300 and can recover 5–10% of lost production immediately.
Evaluate an inverter upgrade. If your string inverter is past its warranty period, replacing it — potentially with microinverters that offer panel-level optimization and monitoring — can both restore lost production and give you visibility into how each panel is performing.
Review your rate plan. A quick call to your utility can determine if there's a better rate plan available for your solar setup. This is free and can make a noticeable difference.
Consider adding battery storage. A battery lets you store excess daytime solar production and use it during expensive evening peak hours instead of exporting it at low midday rates. For pre-2018 systems on NEM 1.0 or 2.0, adding a battery can significantly improve the economics.
SoCal Solar Check specializes in evaluating older solar systems installed by Sunrun, Vivint, SolarCity, and other major installers. Our free assessment tells you exactly how your system is performing, what's costing you money, and what your best options are going forward.
Get Your Free System AssessmentGoing solar before 2018 was a smart decision. You likely locked in a favorable NEM rate plan that new customers can't get anymore. Your panels still have 15–20 years of productive life ahead of them. But like any investment, solar requires some attention to keep performing. The homeowners who get the most out of their systems are the ones who understand what's happening on their roof and take action when something isn't right. Don't wait for another disappointing true-up bill to find out.