How long does solar last?

Solar panels last 30 years or more. The industry standard panel warranty is this:

  • 10 year workmanship warranty
  • 25 year power warranty

Some modules, such as Trina, have a linear power warranty. Most however, have a two-tier step warranty that guarantees this:

  • 90% power at year 10
  • 80% power at year 25

Solar panels degrade gradually over time with exposure to sunlight, wind and weather. Panels are typically warranted 25 – 30 years and have a design lifespan of over 30 years. Energy production is expected to degrade by about one-half of one percent per year.

Inverters are warranted for 10 – 15 years and have an expected lifespan of 15 – 20 years. Future inverters will likely have longer lives. You may need to replace an inverter once in the system’s lifetime and we figure that cost into our financial predictions.

All other system components have service lives over 30 years.

What if the solar panels produce more electricity than we need?

Grid-tied solar electric systems automatically feed power into your house. Any excess electricity produced by the solar system and not used by your home is put onto the electric grid and spins your electric meter backward. Your utility credits you on your bill at the retail rate for the kWh produced.

How solar panels work

Solar panels operate in this manner: When sunlight is on them, solar panels produce DC electric current. The DC electric current is passed through an inverter and converted to AC current synchronized with the local utility lines. The utility company provides power as normal. The solar panel system serves as an additional power source, fully integrated with the home or building’s existing power sources and the utility grid.

Damage to solar panels

Most of the potential issues facing modules are covered by manufacturer’s warranties. Apart from those issues, we have replaced panels for the following reasons, not covered by warranties:

  • Tree branch fell on array
  • UPS truck backed into array
  • Bullets fell from sky and pierced panels

This is what insurance is for.

However, the bulk of potential solar panel damage can be mitigated by choosing an experienced solar installer and using top-quality equipment.

We know of other installers who have replaced modules for these reasons:

  • Baseball cracked modules mounted in the outfield of a ballpark
  • System caught fire due to combination of poor design and poor installation
  • Wind blew apart a poorly designed or poorly installed solar array

Hail damage to solar panels

Solar modules are certified to withstand hail – not Texas-sized hail balls, but your typical hailstones. One quality solar panel manufacturer put it this way: “The panels are tested by shooting balls of ice at terminal velocity at the module in 11 specific spots. The ice balls can be of different sizes and the firing velocities change based on size. Typically solar panels are tested using 25mm balls fired at 23 m/sec. However, the spec also defines larger and smaller ball sizes from 12.5mm fired at 16 m/sec to 75mm fired at 39.5 m/sec. I have yet to see a panel with tempered glass fail using any size ball/velocity. I have seen a few cases of the roof being damaged beyond repair by hail and the unbroken solar panels need to be removed so the roof can be replaced. 

In short, we test our solar panels extensively for hail survivability. They pass quite well. However – all panels must pass this testing or they could not be certified to put on the roofs of houses, so this may not be a unique selling point.”

In other words, it is a common question, but usually a non-issue. Hail that will break car windshields is hail that will break solar panels. How often do we see such hail? Hardly ever.

AC/DC derate

“A competitor says his system has an AC-DC derate of 95%. Why is yours so low?”

On his blog, Dave Beumi notes: “Derates are the various locations and instances in a PV system where power is lost from DC system nameplate to AC power. This includes inverter loss, resistive factors, environmental conditions and issues relating to maintenance… The PV industry and its financing partners rely on simulation modeling software, which provides a fairly accurate multiple year forecast of energy production and economics, including [solar] financial payback. These models are thorough, sophisticated software packages which take into account the many variables which affect a PV system’s performance including weather, environmental conditions, technology and product performance, government subsidies, and cost of money among others… While the model takes into account the derate factors and a detailed weather history for a given location, its important to note that annual fluctuations in weather conditions is an important variable which can be significantly different year to year. Overall, simulation models are quite accurate and are a fairly good gauge for finance companies to make an informed investment decision.”

PVWatts makes it calculations using whatever derate number the user inputs. Our experience has born out that 81% is a reasonable but conservative derate. There are technical reasons why we could use a higher or lower factor, but that would take several pages of explanation and probably put you to sleep.

Suffice it to say, that 95% total derate is a physical impossibility. Any solar installer telling you that is not being truthful.

Solar energy production estimates

“Another company gave me a much greater energy production estimate than yours.”

We hear this occasionally. When asking the question, “How much electricity will a solar energy system produce” people sometimes get different answers from different companies.

Our production estimates are conservative — we try not to over-state the amount of energy you can expect to get from a specific-sized solar energy system. An internal company mantra of ours is, “Under-promise and over-deliver.”

That said, we use standard industry tools to make our energy production estimates. For most of our energy production estimates we use PVWatts, which is a publicly-available tool for solar energy estimating put out by the National Renewable Energy Labs (NREL) for anyone to use.

Like any calculator, NREL’s takes a bit of skill and knowledge to use. We have, on occasion, walked a prospective customer through the process to help them understand proper data input as well as how to interpret the results.

There are other solar companies that offer sky-high estimates and unrealistic promises. We do not.


Low cost solar panels

We have sourced, tested, and used low-cost Asian solar panels — from reputable manufacturers. We don’t just investigate the panels themselves, we background-check the company that makes them. Solar panels carry 25-year warranties, and we want to make sure their manufacturers are financially sound and reputable, and will be around to support those warranties. This kind of careful research is an important part of the value we deliver to our customers.

How much solar system cost is in the panels?

We have a computerized pricing system that generates the total price for your solar project, based on the size of the system and your project specifics.

In general, the cost breakdown for a solar electric system is about 55-60% for the equipment itself (including panels, inverter, wire, conduit, switchgear, etc.); about 10-15% for overall project management, design, paperwork, permits and fees; and about 25-35% for the installation costs.

We can deliver excellent pricing on our projects thanks to two advantages: First, we pool our buying power with a national group of solar installers in a member-owned purchasing co-op to get advantageous pricing on the very best equipment (we will not compromise on quality where our reputation is at stake). Second, we are crazy about efficiency, and have been working for 14 years on how to deliver the very best-performing and longest-lasting solar installations with the least waste possible, thereby turning our customers into raving fans. It is a formula that works.

Solar energy production estimates: ours and theirs

Solar is a new, emerging industry. To date, there are no industry standards for how to predict the energy output of a completed solar system in the real world. Each solar sales person can use his own assumptions in making this prediction. Some are intentionally optimistic, some are naïve and don’t have enough experience to make realistic predictions. As a company, our approach is to be intentionally conservative in making performance predictions. We live by our reputation and we want you to be very satisfied with your solar system. We’d rather lose the sale than make an overly-optimistic prediction and have you end up disappointed in a couple of years. Our company mantra is, under-promise and over-deliver. We feel it’s the best way to be as a company. And it is one of the reasons why we are a B Corp.

We build great solar electric systems. We under-promise and over-deliver. And we sleep very well at night.