Degradation and performance

[thebfamily]

I’m probably buying Panasonic panels (25 year performance warranty) with built-in Enphase microinverters.

Am I tasked with monitoring degradation and performance to ensure the panels stay within specifications? Or is that something the installer normally does?

[peakbagger]

Its highly unlikely that once the check clears that anyone really cares about your production or degradation. If you think there is an issue, it will be up to you to prove to whatever party is responsible for a warranty claim. The actual testing for degradation is pretty involved. There is a year to year seasonal variation that would overwhelm changes in degradation. In theory your Enphase microinverters are monitored and you will access to the monitoring. Its not unusual that at some point they will start to fail and you will be able to see the panels that have failed microinverters. After a few years you will be able to trend your yearly production and realize if you are short or long on production but realize yearly variations may be 10%. Be aware for many folks, their usage will increase as their power bills drop.

I expect someone will sell you a long term monitoring plan but I dont think you will get a lot of value out of it for a residential system. Start getting into a large commercial solar field and then there is more cost benefit ratio to long term monitoring. I have heard of at least one large payout to a owner of large field for under performing panels

[bob-n]

Peakbagger is exactly right.

Your system will probably come with a gateway device that bridges information between the microinverters and the internet. Enphase calls it an Envoy. With an Envoy, you can use a cell phone or web browser and see your production every day, every week, etc. In theory, they never lose data, so any Enphase customer can access their data from as many years back as they've had the system. The data is per panel as well as overall, so if one panel fails or degrades fast, it will be obvious. Make sure that your installer gives you the password and other information you'll need to access this data.

With that, you'll be able to see production vs year. It will probably show undetectable change with time - difference from year to year that is in the noise. Even if you do see something, as peakbagger said, using that information to claim that the system degraded will be too difficult, unless the change with time is really severe.

Many things could cause a system to produce less, such as tree growth in the area, weather variations leading to more smog or haze, and dirt buildup on the panels.

As an analogy, we buy fuel efficient cars. They claim 38 MPG highway. If mileage decreases from 38 MPG to 33 MPH over 5 years, would we notice? Could we prove it? Could it be tires, gasoline formulation, driving style, or something else unrelated to the engine? After five years, would we really care? Is there any way we could hold the manufacturer responsible?

[thebfamily]

Thanks for the feedback. That all makes good sense.

With my Panasonic panels, labor *is* covered. So, isn't there theoretically incentive for the installer to ensure I'm getting proper production (at least for an initial period)?

[bob-n]

Yup. They know what to expect and will make sure that you get it, at least to the accuracy level that they can see on the monitoring software.

But they're not going to bring expensive lab equipment out to your roof every year to take measurements unless something really looks bad.

[solarix]

Panel degradation is about the last thing you should worry about. But putting boxes of electronics with not so great track records under those panels is something to be concerned about. PV panels are wonderfully reliable - don't couple them with microinverters that are much less so. Somebody is going to have to work on those one-by-one as they fail sooner or later. Yes, they warranty them for 25 years - knowing they will have to give you replacements well before that. Its a marketing ploy. Enphase has already offered to replace for free all the 1st generation units they have out there.
Production guarantees are just a form of insurance that you pay extra for. The company provides a conservative estimate of what to expect and uses those funds to compensate the rare case that is underperforming. Just install a good quality system by a local installer with a good "solar reviews" reputation, include internet monitoring that you can watch yourself, and you will be better off.

[J.P.M.]

Panel degradation is about the last thing you should worry about. But putting boxes of electronics with not so great track records under those panels is something to be concerned about. PV panels are wonderfully reliable - don't couple them with microinverters that are much less so. Somebody is going to have to work on those one-by-one as they fail sooner or later. Yes, they warranty them for 25 years - knowing they will have to give you replacements well before that. Its a marketing ploy. Enphase has already offered to replace for free all the 1st generation units they have out there.
Production guarantees are just a form of insurance that you pay extra for. The company provides a conservative estimate of what to expect and uses those funds to compensate the rare case that is underperforming. Just install a good quality system by a local installer with a good "solar reviews" reputation, include internet monitoring that you can watch yourself, and you will be better off.

IMO only, this post ought to be a sticky.