Maximizing Value for Solar Systems as they Age
- dylan099
- 7 days ago
- 7 min read
For many of our customers that have systems that have been installed for over 12 years, we see some common questions and concerns.
Why do I still have a high energy bill even with solar?
Is my solar system operating efficiently?
Can I add more solar to my existing system?
How will this affect my PG&E agreements?
Can I use my solar to back-up my home during utility outages?
What is best: a generator or battery storage?
I need to reroof, how is my solar impacted?
Can First Response Solar offer services to work with my roofer?
My solar inverter is 15 years old, is it still good?
Micro-inverters and hybrid inverters with storage.
We will answer these questions in the following article and solutions we are offering to our customers. Before we start, let's pack our bag with a few terms and a little history to make our journey a little easier.
First the good news: most solar systems that have been installed for over 7 years have paid for themselves in savings from utility costs. Utilities offered Net Energy Metering (NEM) programs, paying customers at retail or near retail rates for all solar energy exported to the grid (Blog Posting About NEM Agreements).
Back in these earlier days, energy storage systems (ESS) were used primarily for home back-up (providing power when the utility was down) and were hard to justify, since power could be sent to the utility “grid” at near retail rates. NEM systems were grandfathered for 20 years, and while customers could add ESS to these systems, expanding the solar system would cause a customer to lose their grandfathering and go to the current program available from PG&E.
The current program offered by PG&E is Net Billing Tariff (NBT) offering over a 75% reduction in compensation of energy exported to the grid when compared to NEM. Because of NBT, most systems are now designed with an ESS system (Blog on back-up or savings batteries) to minimize exporting power to the grid at the low rates offered.
Now that our bags are packed let’s dig into the original 5 questions posed by our customers.
Why do I still have a high energy bill even with solar and is my older solar system operating efficiently.
When we dig into this issue with our customer it usually relates to the following issues.
Increase electrical usage since installing solar: Adding an electric vehicle (EV) eliminates gasoline or diesel, and electrifying our homes (adding heat pumps, induction stoves and electric water heating) saves natural gas and propane, but both add to our electrical usage. Other increases in usage include adding swimming pools, hot tubs, granny units, out buildings, more people living on the property and for country properties on wells, increased irrigation.
Over 150% rate increases in the past 15 years: Many early solar systems were designed as “tier shaving” solar systems. If you go back to 2010, PG&E offered a customer a baseline usage amount (E1-residential) at a low rate and 4 additional tiers (based on a baseline usage). For example, a customer could pay $0.12 per kWh for the first 300 kWh, Tier 3 (130-200% of baseline) would more than double to $0.29 per kWh and tier 5 (over 300% of baseline) would pay over 3 times more than tier 1, $0.40 per kWh. Because of these tiers, many installers installed smaller systems to eliminate upper tiers, not customer usage. As a note, today’s blended rates from PG&E are over $0.47 causing an almost 3 times cost usage for baseline usage.
For systems over 20 years old: If your system is over 20 years old, it has lost the 20-year NEM grandfathering and is now currently being billed under Net Billing Tariff, see above. This means that while the solar system may be operating fine, the customer is now receiving over 75% less for all power exported to PG&E. If your system is over 20 years old, give FRS a call to evaluate adding Energy Storage Solar ESS to your system, and if adding new solar makes sense (losing NEM grandfathering no longer applies).
Solar systems do lose efficiency over time: Solar modules are very reliable and while they do lose some efficiency it is usually modest. Jeff Mathias from Mathias Consulting says that the biggest issue he finds when he evaluates older systems is modules have not been cleaned. Tied for second is vegetation that is shading the modules and inverters (convert DC power to AC power our homes use) no longer working or degraded. It is important to maintain systems and have a viable maintenance provider like First Response Solar.
Can I add more solar to my existing system.
The easy answer is yes, but you may lose your NEM if you add more than 10% of the system or 1 kW of solar (whichever is greater). In some cases, it does make sense to add solar when utility bills/true up bills are high, usage has significantly increased, or customer goals have changed. In almost all cases, adding additional solar will be paired with storage to maximize the financial benefit of the expanded system.
Can I use my solar to back-up my home during utility outages and what is better, a generator or Energy Storage Systems (ESS).
Back-up power is one of the primary reasons NEM clients add ESS to their solar systems. ESS provides quiet power to a home when the utility is down and uses the sun to recharge the batteries. ESS can also be less expensive when factoring in long term maintenance cost of generators (oil changes etc). Adding batteries (ESS) will also sets a customer up for the future when NEM is no longer available. (Blog on Cost of Generator vs ESS)
I need to reroof my home, how is my solar impacted.
One rule of thumb we often use is if your solar modules are over 15 years old or under 200 watts, it may be a good time to replace them. Why?
New solar modules are over 400 watts compared to modules usually under 200 watts 12-15 years ago. Since modules are twice as efficient, we need only half as many to generate the same wattage. This means we can put more wattage where solar production is the best, double solar production in a similar solar footprint while reducing the cost of labor and racking costs.
Almost all new systems come with online solar monitoring, the ability to see how a system is producing from a customer’s phone or computer. Less than 20% of the systems installed 15 years ago had monitoring, making it difficult to evaluate if they were running properly as they aged.
Panels from 15+ year ago are generally smaller than today’s high-efficiency models. To support them properly on a new roof, attachments must be placed closer together than they would for a modern system. While that works initially, most panels have a productive life of 20-25 years. By the time your NEM agreement expires (in roughly 5 years or less for many older systems), your current panels may begin to underperform or fail.
If you later decide to upgrade to larger, newer panels, the closely spaced attachments from the recent roof job may not align with the new array layout. Correcting this could require costly modifications, or even replacing portions of the new roof, to accommodate the different mounting requirements.
Before moving forward with a roof replacement, consider the trade-offs: reinstall the old panels temporarily, or invest in a full system upgrade now with modern, higher-output panels that integrate better with batteries and future needs. A professional assessment can help clarify which path offers the best long-term value.
Finally, many customers who are planning a roof replacement have systems that are now 15–20 years old and are approaching (or have already reached) the end of their 20-year NEM grandfathering period. Over that time, household energy usage often changes significantly, and PG&E rate structures have evolved as well. In this situation, it can make good sense to reevaluate the entire solar setup: repositioning panels to optimize production on the new roof, replacing older lower-wattage modules with modern high-efficiency ones, or even installing a completely new system. While adding or replacing solar at this point would mean transitioning from the old NEM agreement to the current Net Billing Tariff (NBT), the long-term benefits frequently outweigh the initial increased cost, especially when paired with energy storage. Now is often an ideal time to add an ESS (battery system) to maximize self-consumption and savings under NBT, or at minimum to begin planning for the post-NEM future when your grandfathered status expires.
Solar inverter reliability after 15 years creates options with storage, better shade mitigation and monitoring.
Your inverter converts DC power from the panels into usable AC power for your home. Inverters while highly reliable, are the number one component to fail in solar systems. Depending on the type (string inverter or microinverters), inverters typically come with a 10-25 years warranty. If your system is 15+ years old and still has its original inverter, inverter failure is just a matter of time. Watch for warning signs like reduced production or error codes.
When the inverter does fail, it may make more sense to install a more forward-thinking solution like a hybrid inverter that incorporates the inverter and storage into one unit. These inverters come with a new warranty, prepare the customer for net billing tariff, reduce utility dependency and provide monitoring for long term support.
Final Thoughts: Plan Ahead for Your Solar Future
Older solar systems have been a great investment for countless Sonoma County homeowners, but thoughtful planning now can help you maintain, and even enhance, those benefits for years to come. Whether it’s preparing for the end of NEM grandfathering, coordinating with a roof replacement, or proactively addressing inverter concerns, the right decisions today can save significant time, money, and hassle tomorrow.
At First Response Solar, we’re dedicated to helping Sonoma County residents navigate these transitions smoothly. If this blog speaks to your situation, we’d be happy to help navigate your situation and discuss your best long term options. Visit us at https://www.firstresponsesolar.com/ or reach out directly. We’re here to support your clean energy goals.
Stay powered and prepared, Sonoma County!
Dylan Mathias
Owner, First Response Solar
707.888.1243
License #: 1039876
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