PV watts and panel efficiency losses at higher temps

Re: PV watts and panel efficiency losses at higher temps

No, PV watts does not take temperature into account--just a rough 0.77 derating overall (for Grid Tied systems). You can plug in different numbers, if you wish.

PV Watts Derating Explanation

Realistically, when one starts looking at 1-2% differences in harvest efficiency--it is a lost cause... Overall, just weather can account for 10-20% changes year over year (depending on local weather patterns, etc.).

Efficiency is a good thing--high efficiency means controllers/inverters run cooler and can result in smaller units (because smaller heat sinks needed). Also, if you can avoid fans--that increases reliability (fans are usually the first to fail in these units).

-Bill

Re: PV watts and panel efficiency losses at higher temps

For my "original install"--PV Watts was pretty accurate.

With 6 year newer panels and GT inverter--my system may generate 10%+ better...

However--The PV Watts site is at SFO -- Which is 10 miles north of me, and in a location that does not get as much sun as my area. And, our area is subject to marine and valley fogs--Which can vary by 20% year over year pretty easily.

Add the fact that solar panels are usually guaranteed to 80% of rated capacity after 20-25 years--You would probably like a 10-20% "over-sized" to allow for component aging (and battery aging if Off-Grid/Battery Backup). As well as allowing for increases in loads as time goes by.

For solar panels themselves... Usually for the Crystalline Panels, they are all pretty similar in performance and your first stop is to look at $$$/Watt pricing... If you have limited area for panels (roof top, boat, etc.)--then you may look at the "more efficient" mono-crystalline or other types that offer more Watt*Hours from the same roof area.

On the flip side, the thin film panels are about ~1/2 as efficient and require 2x the square footage for the same Watt*Hour collection. That means more racking, electrical connections, and roof/yard space for the panels. In many cases, the cheap $1.00 per Watt pricing of the thin film panels ends up being almost a "wash" when compared with the $2-$3 per Watt pricing of crystalline panels when all of the costs and labor are added together.

Also, I am not quite sure that all "good quality" thin film panels will last as long as crystalline panels--Thin film are more susceptible to water/oxygen contamination/failure than crystalline panels.

But what do I know--My "good quality" mono-crystalline panels lasted a bit more than 5 years before I had to switch them all out due to junction box failures (I think). At least my vendor stood by their warranty (albeit, it took 3+ months to get new panels).

-Bill

Re: PV watts and panel efficiency losses at higher temps

From my point of view--The go/no go decision needs to take on the Power Company/State Regulatory/PUC current and future (as best you can guess) plans going forward.

For my system, when I put it in 5 years ago, I got a great plan. 1 year net metering, noon-6pm weekday peak rates about 3x my off peak rates (during summer--and lower overall rates in winter) which let me not use power noon-6pm weekdays and "bank" 3x the cost of power generated by solar PV GT for use at night/off peak/weekends (i.e., I got paid ~$0.27 per kWH and bought my power back at ~$0.09 per kWH at off peak).

It was a really great deal.

However, they changed the plans and now it is a complex plan that runs peak/partial peaks from 10am to 9pm at night (summer time of use rates). And people to install net metered solar, had to take that plan (could not even stick with flat rate power). What ended up happening was many people installed a "small system" to get their feet wet and see how it worked...

Since they where forced to a Time of Use plan that penalized daytime/evening power usage--and the small system did not offset that power usage--their overall energy bill went up because they used the most power during the day/evening. Was a very big problem.

Anyway--make sure you understand your power company's billing/rate plans and any possible changes in the future to ensure that your "investment" is going to have a fair chance of breaking even or (hopefully) saving some money.

As long as you have done all the conservation possible for your area (insulation, double pane windows, weather stripping, as efficient heat pump/dehumidifying system as possible, heat pump hot water, reducing power use through laptop computers, turning unused stuff off, things the make sense in your climate, etc.)... To reduce your power needs--then looking to solar PV grid tie as the next step.

-Bill