Seeking Advice - Mix Upgrade Panels for More Power?

[tom3096]

I have a rooftop installation from 2007. Specs are at the bottom. I would like to get more power from the system but cannot increase the footprint. I was considering replacing panels in one or both strings. In addition, I would get a new inverter. This will allow me to keep the rack and avoid the added costs of a complete tear down and installation of new system. I was considering replacing individual panels or an entire string with panels in the 400w range.

Any suggestions or pointers to previous posts that address this? What works, what to avoid, etc? Thanks


CURRENT SYSTEM:
- 4kw
- 2 strings: 12 panels each
- Fronius IG 4000 inverter

CURRENT PANELS:
- Kyocera 200GT
- Max power: 200w
- Max voltage: 26.3v
- Open circuit voltage: 32.9v
- Max power current: 7.61a
- Short circuit current: 8.21a
- Height: 56 inches/142cm
- Width: 39 inches/99cm

[Mike90250]

What ? Why ?
panel efficiency has only gone up a little bit, just a % or 2 since 2007. The labor and expense of all that new gear is going to take a LONG time to break even.

You have 15 years on your roof, would it make sense to re-roof the area where the panels are, if you are going through all the hassle ?

[SunEagle]

I agree with Mike. Why spend the money to get more power from your system. The payback will be long.

Besides your limiting factor is not the panels but the 4k inverter. So you can increase your panel wattage but you will need to also increase the inverter size, wiring and circuit breaker. Also mixing different wattage panels can cause more issues then going with all the same wattage and specs.

[tom3096]

Thanks for the advice. I have 4kw system. Solar company says I need 8kw to meet my usage. Plus I'm getting an EV this year. I currently pay about $1500 plus per year true-up bill. My thought was to replace my 24 200 watt panels with 24 370 watt panels + get a 8kw inverter for around $3k. Was thinking I'd be in it for under $15k in parts.

[J.P.M.]

I'd doubt you can get away for $3 K for an 8 STC kW system, even if you do it all yourself.

By the time you're done replacing the panels, wiring and inverter(s) as well as probably replacing the racking, you'll have a new system with respect to performance but it'll cost more because of the (likely) added cost to remove the existing racking and panels. You'll also probably at least need check for requirements for a building permit(s) and a new NEM agreement with the POCO. Maybe not, but better to enquire than be surprised. BTW, don't try to skunk those things. You will get caught. New arrays and lower bills are hard to hide. Just sayin.

I'd bet the old racking and attachments to the roof won't work with a new array. That'll be another PITA and headache to make sure the old roof penetrations get and (equally importantly) stay sealed. Since most of those would be under a new array and so most likely be mostly "uninspectable", I'd think long and hard about how to seal them up if that's what it comes to.

New panels will probably have an STC efficiency somewhere in the 18-20 % range vs. What you have now is at 14.2 % STC efficiency (per the GT200 data sheet) less time induced performance deterioration (@ 1%/yr. per the data sheet) that'll probably knock performance that back to around 12% +/- some at this time.

BTW, you have 4.8 STC kW of panels. I have no idea of the 2007 cost differential between a 4 kW and, say a 4.5 kW inverter, and I sure don't know your particulars, but if you're something close to "average", I'd have gone a bit larger on the inverter. Probably not 5 KW, but more than 4.0 kW.

So, all ballpark SWAG's here, if a new array were to have the same approx. footprint as the existing array, the new one would produce maybe (19/12)+1 ~ = 158 % of the existing array's annual production, provided the new inverter(s) don't clip much.

As a first cut, to do that will require ~ 6 kW of inverter(s), maybe a bit less.

Q: On that 8 STC kW estimate: Usually, unless they last resided in someone's fundament, estimates of array sizing require (among other things) an estimate of annual electricity usage. Did the vendor have your annual usage number in kWh/yr. ? If not, where did the 8 STC kW estimate come from.

What's your zip ?

Do you plan on placing any new array you acquire in the same location as the existing array ? In any case, what would any new array's azimuth and array tilt be ?

If it was me, and my goal was a lower electric bill rather than simply more electricity generation, I'd be looking at (tolerable) lifestyle changes first and then cost effective conservation measures and devices second. You don't pay the POCO for what they don't send you.

Welcome to the neighborhood.

[Mike90250]

I'll bet those new 370 w panels are larger than the 200's you have, which needs more roof area ?

[tom3096]

Thanks for all the good advice. I'm in central California - hot summers, cool winters, wildfires, and skyrocketing PG&E charges. But I've decided my best option for now is to just let the current system ride and enjoy the payoff. Maybe someday I'll figure out how to augment the current system withe the extra 4kw I need.

[J.P.M.]

Thanks for all the good advice. I'm in central California - hot summers, cool winters, wildfires, and skyrocketing PG&E charges. But I've decided my best option for now is to just let the current system ride and enjoy the payoff. Maybe someday I'll figure out how to augment the current system withe the extra 4kw I need.

If you're looking for reducing or at least mitigating the impact of electricity costs, conservation, after some tolerable and well considered lifestyle adjustments seem to be possible ways to save $$.

Good Luck.