clarity on how system size translates into production per year

[LeeZee]

The following is part of a proposal from a solar company for installing solar panels on my roof. It says that the system size is 3.4 kW (or 3400 watts). How can production be 4,717 kWh if the production is only 3400 watts? Am I not understanding something, or is this an error on the part of the solar company rep? If my usable hours of sunlight a day=4, and there are 365 days in the year, then I get 4964 watts per year. Can anyone please shed light on this for me?
Number of panels
10

Watts per panel
340

System size
3.40 kW

Production in year 1
4,717 kWh

Production ratio
1.39



Thank you for any clarification in advance.

Lee

[littleharbor]

Short answer, You are not understand something.
Go to PV Watts online and enter all your data as accurately as you can and get their estimation of your annual output.

[SunEagle]

You are not including any losses for the conversion of DC to AC as well as any other losses that might occur that PVwatts takes into consideration.

[J.P.M.]

Be careful what you ask for. Since you seem to be asking: It seems to me that you need a lot of light to be shed. You can do most of that that on your own much faster and more thoroughly than here, at least with your present state of knowledge. There's a bit more to it than a few posts can cover. Not complicated, just lots of connected details.

One possible way to begin is with a read of a free net download: "Solar Power Your Home for Dummies". Most of your questions can be easily self answered with a read.Then, come back here and ask questions to fill in the gaps. You'll find a lot of help and information here, but you'll get the most out of it by learning to crawl on your own before you walk, and for that, some self initiative is necessary.

Download the book, or spend ~ $20 on an updated hardcopy. After a couple of hours of self education, you'll probably know more than most folks you'll talk to about the subject, including most of the solar peddlers who will otherwise use your solar ignorance to separate you from more of your money than necessary.

From your post and as an example of one necessary thing you will learn is the difference between a Watt (a unit of power) and a Watt-hr. (a unit of energy).

Welcome to the neighborhood and the forum of few(er) illusions.

[bcroe]

It would be more correct to say the PRODUCTION RATIO IS 1387 KWH PER YEAR, PER KW (of panels). Or 4717/3.4
Bruce Roe

[inetdog]

The following is part of a proposal from a solar company for installing solar panels on my roof. It says that the system size is 3.4 kW (or 3400 watts). How can production be 4,717 kWh if the production is only 3400 watts? Am I not understanding something, or is this an error on the part of the solar company rep? If my usable hours of sunlight a day=4, and there are 365 days in the year, then I get 4964 watts per year.

Keep a clear distinction between watts and watt hours.

3400W times 4 effective hours (probably an average, since higher in summer and lower in winter) give 13,600 watt hours per day. Or 13.6kWh.
13.6kWh/day times 365 days/year gives 4964kWh/year.
If you add in a correction factor for the panels not ever producing full rated power (mostly because of temperature), 4,717kWh/year is probably on the high side.

[LeeZee]

Keep a clear distinction between watts and watt hours.

3400W times 4 effective hours (probably an average, since higher in summer and lower in winter) give 13,600 watt hours per day. Or 13.6kWh.
13.6kWh/day times 365 days/year gives 4964kWh/year.
If you add in a correction factor for the panels not ever producing full rated power (mostly because of temperature), 4,717kWh/year is probably on the high side.

[QUOTE=inetdog;n336630]

Thank you for the clarity--I did forget to incorporate the .8 derate factor when converting. And did calculation too hastily, so didn't consider distinction.

However, this proposal for a system is the best I've received so far, even if it appears (after calculating the output of the system using PVWatts calculator) that it'll fall short of the 50% portion of the amount of electricity I want to offset.

According to PVWatts calculator, this system will only produce 3,834 kWh per year given my situation including: shading (somewhere between 18%-22% loss due to shading from being at the bottom of a 1625-ft hill to the West and due to trees in afternoon especially during the Winter); system production loss that the calculator factors in by default; direction side of roof we want to use faces; and all the other factors.

Based on 50% of my electricity consumption of 4317.86 kWh per year, and this company's proposal of installing ten 340-Watt panels, it seems like we need to add 1-2 panels.

system production = 3,834 kWh per year
panels = solar world
inverters with power optimizers = SolarEdge
net system price = $7,069
price per watt = $2.97
panel warranty = 25 years
Inverter warranty = 25 years
labor warranty = 10 years


We plan on staying in the house anywhere between five and eight years, so in factoring in deterioration over time, its seems like there's no real urgency to get premium panels especially if any incremental benefit from premium panels are minimal/negligible or at least are outweighed by the benefit of the $2.97 per watt cost.

How do people who have solar world panels or know about them feel about these panels in terms of productivity, efficiency, etc. relative to others?

There are only six reviews that I found from this company out there including from the bidding platform I'm using. All reviews are extremely positive, but the N is low. Should I still be concerned?


Thanks in advance.

Happy Thanksgiving.

Lee

[ButchDeal]

Did you take into account that it was an optimized system when modeling in pv watts ?

http://www.solaredge.com/us/node/2303

[LeeZee]

Hi Butch,
No I didn't. Thank you for this!

[azdave]

We plan on staying in the house anywhere between five and eight years

That fact alone would tell me to not install solar. Even if you purchase your system you might not reach payback before you have to sell. Don't even think about leasing if you know you're moving while the lease is still in force.

[LeeZee]

That fact alone would tell me to not install solar. Even if you purchase your system you might not reach payback before you have to sell. Don't even think about leasing if you know you're moving while the lease is still in force.

Right, no, this would be a purchase.

But, shouldn't we factor in the value of the house increasing by between $15k and $20k?

[J.P.M.]

Right, no, this would be a purchase.

But, shouldn't we factor in the value of the house increasing by between $15k and $20k?

Who told you the addition of a PV system is guaranteed to increase the value of a property ? It may increase the value of a property, or in may make no difference, or it may decrease the value of a property. In any case, given the mix of desirable features of a property, with no 2 properties being absolutely identical, it's probably impossible to quantify. Follow the money on who to believe on that one. Adding resale value will probably make an inflated PV price easier to swallow for folks such as yourself who seem to want to believe a bill of goods that may or may not be true, but don't have enough solar savvy to separate the reality from the rose colored glasses B.S. Forget resale value and go for the most cost effective system based on your usage alone. Any adder for resale will wind up as a pleasant bonus at the end rather than a disappointment if it adds little or nothing. Either way, you'll never be able to quantify it beyond a SWAG. Continue your education.

[LeeZee]

Adding resale value will probably make an inflated PV price easier to swallow for folks such as yourself who seem to want to believe a bill of goods that may or may not be true, but don't have enough solar savvy to separate the reality from the rose colored glasses B.S.

That provided no useful information.

[J.P.M.]

That provided no useful information.

As usual, take what you want of my mental spoor and solar experience such as it may be. Scrap the rest. Otherwise, good luck.

[littleharbor]

From the systems I have removed to satisfy escrow provisions I have the feeling that solar generally adds zero to negative value to residential properties.

[ButchDeal]

Were they leased? With the number of installers putting in systems one companies removals would seem to be a small sample size .

[LeeZee]

From the systems I have removed to satisfy escrow provisions I have the feeling that solar generally adds zero to negative value to residential properties.

Thank you for the information--How many homes' systems have your removed and in what area? Based on the attached unbiased article on the extent to which pv systems add resale value to a residential house, it does seem like a number of variables need to be considered first to determine incremental value, if any:

1. Specific sale date--In the study, the homes were sold between 2011 and 2013.
2. location of sales.
3. demographics, utility rates and market conditions where home is sold.
4. The overall decline in PV system prices.

The closest area investigated in the study to where I live is San Diego, CA. I live in Woodland Hills, CA. The sample size for this San Diego area was 13 paired sales (they looked at similar home pairs with everything the same in value but whether there was a solar system or not. 13 is a small N and therefore any conclusions drawn from a study of this limited sample size suffers from problems associated with limited statistical power (please see bottom of page 14 for the San Diego related portion of the study).

While they say that the incremental increase in value was close to the net cost of the solar systems, they also anticipate later in the Conclusions section on page 30 that as govnt. incentives decrease or disappear, the incremental resale values will be closer to the gross cost of the systems.

Also, it makes sense that a purchased system will have a higher likelihood of adding resale value than a leased one.

[ButchDeal]

Well a leased system by nature adds zero to negative value. It isn't part of the home and does not conve with the home so arrangements must be made in addition to the home sale for it to be removed, taken over, or bought out, thus zero value.