Production Guarantee?

[easye]

All this banter. It's going to produce what it's going to produce. If you want to be sure, run PVwatts and figure it out. If you want 18.5k then get the number of panels you need. Whether that is a waste of money will be up to the state you live in and the lawmakers that get get bought off by the local POCO and how fast they get bought off. States be falling left and right.

[Ian S]

How big was the range? did they specify kWh or percentages?

My problem is - is my second choice over sizing or is my 1st choice under sizing?

Basically same hardware, same layout.
My PVWatts calculations for (36) panels, 14% default loss, is 17,200 kWh
A Third competitor calculates that (36) panels will produce 17,000 kWh

1st choice system is $42,048 for 36 panels
2nd choice system is $45,500 for 39 panels
Both claim 18,500 kWh annually

I've attached my SunPower system production guarantee. The first year IIRC production was 12,400 kWh which was pretty much in the middle of the range.

When you are considering future usage, you need to also account for improved efficiencies in future appliances, HVAC, lighting, etc.of the home. Maybe you've done all that already, but if not, you'll probably be doing them down the road and using less electricity than currently. I just installed a new HVAC system and it appears that the AC efficiency much better than the old. The other distinct possibility is rate changes that penalize over-producers. Here in Arizona, APS gives you a paltry $0.029/kWh for excess electricity at your annual true-up. While your utility may currently have a more generous implementation of net metering, there is no guarantee that they will maintain that and indeed, utilities can and do make excellent arguments that such paltry payouts for excess are fair as your over production should be treated as if you were a supplier of electricity and paid accordingly. Demand metering and high minimum billing amounts are other ways utilities are putting the squeeze on their solar customers.

Most around here are rightly skeptical of the cost effectiveness of over production in the long run. But in the end, it's your money. ScreenHunter_13 Jun. 13 18.23.jpg

[Ian S]

How big was the range? did they specify kWh or percentages?

My problem is - is my second choice over sizing or is my 1st choice under sizing?

Basically same hardware, same layout.
My PVWatts calculations for (36) panels, 14% default loss, is 17,200 kWh
A Third competitor calculates that (36) panels will produce 17,000 kWh

1st choice system is $42,048 for 36 panels
2nd choice system is $45,500 for 39 panels
Both claim 18,500 kWh annually

I've attached my SunPower system production guarantee. The first year IIRC production was 12,400 kWh which was pretty much in the middle of the range.

When you are considering future usage, you need to also account for improved efficiencies in future appliances, HVAC, lighting, etc.of the home. Maybe you've done all that already, but if not, you'll probably be doing them down the road and using less electricity than currently. I just installed a new HVAC system and it appears that the AC efficiency much better than the old. The other distinct possibility is rate changes that penalize over-producers. Here in Arizona, APS gives you a paltry $0.029/kWh for excess electricity at your annual true-up. While your utility may currently have a more generous implementation of net metering, there is no guarantee that they will maintain that and indeed, utilities can and do make excellent arguments that such paltry payouts for excess are fair as your over production should be treated as if you were a supplier of electricity and paid accordingly. Demand metering and high minimum billing amounts are other ways utilities are putting the squeeze on their solar customers.

Most around here are rightly skeptical of the cost effectiveness of over production in the long run. But in the end, it's your money.
ScreenHunter_13 Jun. 13 18.23.jpg

[J.P.M.]

That is kind of what it boils down to....

In looking at some of the other 'production guarantees' that are out there (SunPower for example) - you can't really say that a system is going to produce a specific number of kWh per year. It does make more sense to say that the output will vary based on weather conditions, etc and may range 16,650 kWh up to 18,500 kWh (10%)

I guess my problem is my First Choice in Installers is using the 18,500 kWh target as the top of their range, while my Second Choice Company is apparently using the 18,500 target as the bottom of their range (since they will reimburse me for not producing 18,500)

Since our family and electrical usage will be growing (just added a second granddaughter) and the panels will certainly degrade over time - why is producing over 18,500 kWh a waste of money? I am of the mindset to do it right the first time and if I had to call someone in to add panels down the road, it would cost me more money than just having to do it now

Producing excess is not such a big problem. The up front cost to provide that excess is where the rub is.

Look, none of this is hard and fast. Weather will vary, arrays will perform differently in different climates and orientations. None of it is rocket science. A few to 5 -10 % /yr. variation is to be expected.

You still appear to be uncertain about a decision. Have you read "Solar Power Your Home for Dummies " yet ? If not, do so. It's a free net download. It may fill in some gaps and help clarify your thinking.

[Git]

Hi Ian

Thanks for the attachment. That basically reinforces my opinion that one company is using the higher number of the range for their design and the other company is using the lower number of the range. Obviously both are valid - but it would certainly effect the number of panels used and ultimately the total system cost

thanks