What do you think of my quote for 6KW in SoCal?

[silversaver]

I just recently added 2 more panels to my solar, and it is very expensive. I installed solar to enjoy my life style, not to conserve energy.

Solar is a long term planning. In next 10yrs, I think every family have at least 1 EV or plug-in vehicle.

[J.P.M.]

I was looking for concurrence that opting for 2 extra panels vs micro-inverters on a near zero shade roof was the right choice. It's probably rhetorical. Honestly, I probably should not do EITHER. I should probably use 24 panels and hope to get 9.8kWh/yr out of them (my current yearly needs). BUT, my baseline was micro-inverters and when the opportunity to maybe remove them and save $2,550 I reacted by asking about 2 additional panels. My thought was it was probably the cheapest time to put them up (I could easily be wrong on that assumption), because it's just "2 more panels". The contractor essential seems to have scaled the price....26 panels is (26/24) x original quote. Which really tells me there is really NOT any savings, per say. It's probably cheaper than paying them in 2 years from now to go plop 2 more panels up there, though. The other reason I'm considering it (besides thinking now was a way to get a "deal" on them), was to give me some breathing room. We really don't run our AC much, because it's expensive. Our house is pretty regimented on electricity usage (remember Seinfeld's "Soup Nazi"?)...2 additional panels MIGHT buy me some additional comfort. Plus, the wife might catch on to the fact that what little power we do buy from our PUC is cheaper than it used to be (our TIER 4 is $0.34), so our usage might well go up.

But, I'm realizing what most people already know, which is the tail end of your Solar power is the worst ROI. I just ran a few calcs and the 2 additional panels delivering approximately 833 kWh/yr, displacing TIER 1 at $0.14/kWh currently takes 11 years to recoup the $1,225 post-tax cost (no power cost inflation accounted for). So I'm just not sure if I save my $1,225 and stay in the "Energy Nazi" mode or go for it and live fat!

Now your getting to the logic about diminishing returns as f(array size), and a lot of the reason why replacing your entire electric load with solar may not be the most cost effective option. And, BTW, FWIW, and IMO only, something most people are absolutely clueless about both in concept, consequence and execution.

Keeping your same (very sane) logic that panels 25 and 26 will save you ~$117/yr., there's a pretty good chance that panels 23 and 24 will not save much more than that. That begs the question: if the last of 26 panels is not in your opinion cost effective, and, by extension, the last 2 panels of 24 are probably not that much more cost effective, then why do 24 in the first place ? Or, to it's logical end, from a cost effective standpoint only, why replace any tier 1 and 2 electricity at all? Or the converse, why not size the array to replace all but the tier 1 and 2 stuff ?

Assuming overall system cost effectiveness generally meets or is close to your criteria, one "smart money" way (of many) to look at the "most cost effective size" situation from a somewhat theoretical cost effective point of view only, is to do a solar array size such that the last Watt (panel actually) of solar capacity added just equals the Net Present Value (NPV) of the savings that last Watt of capacity will produce (Stick with me for a second here). A simple example using (very simply and somewhat incorrectly, but good enough for this example) your 11 years: Assuming each installed Watt will produce 1.6 kWhrs/yr., (11) X ($.14/kWhr.) X (1.6 kWhrs/yr.) ~~ = $2.46/Watt.-->> $ 2.46/.7= $3.52/Watt selling price to the vendor. What this means is, as a rough SWAG, if and until you can find someone to sell you the LAST Watt (panel actually) for an incremental pre tax credit cost of $3.52/Watt, it may not be cost effective to replace the tier one electricity when priced at $.14/kWhr. The net present value (NPV) is something similar to what most people call "payback", but different in a number of ways and takes into account the cost of funds, future fuel inflation and as many parameters as the user wants and/or situation warrants. I've used a NPV of 10 in the past for my situation. Everyone's can and probably ought to be different, depending on their choices.

Notice that doing the same thing out at tier 4 at $.34/kWhr., the incremental per Watt break even price goes up to ((11) X ($.34) X (1.6))/.7 = $8.55/Watt. There's a lot of decent equipment available from good vendors available for a lot less than that.

Note: that's the incremental cost/Watt of the LAST Watt (panel) purchased, NOT the average cost/Watt. for the entire system. Finding that incremental cost is often the rub. As a practical matter, asking for vendor pricing for varying sizes is probably a PITA for them, and they'll probably smell a rat in your request. Also, because of use patterns, the last panel added will almost always displace some tier 2 or 3 stuff. PVWatts can help some in this regard, but some working knowledge of rate structures helps a lot. Just remember PVWatts uses average pricing, not tier pricing so the PVWatts costs and savings will be incrementally incorrect.

As you say, it's more complicated than that. Believe me when I say I absolutely agree in many ways - family situations, other priorities and an uncertain rate structure future are but a few of the considerations, most of which trump the cost effectiveness card, depending on your priorities/choices. Amen and glory in the freedom of choice. But starting with common sense and educated guesses about the future as you have done puts the solar yes/no/if so what size/price decisions on somewhat firmer footing. I'd respectfully suggest that sizing upward and justifying the size by checking the incremental cost on the way up against your own criteria rather than a knee jerk, emotional "replace all the POCO stuff" (non)method is a better, saner way of decision making than simply throwing $$'s at an energy bill. Anyway, a reasoned analysis in no way negates or implies restrictions on your choices. Probably the worst thing that can happen is it just may shed some light and information on the possible consequences of those choices.

[silversaver]

Here is an example of current usage with 1 EV on a 7.1kW system:

[Ward L]

Design for easy cleaning

OP is still in design stage and there's no need discuss about cleaning the panels. There are few posts about clean the panels. All you have to do is read. I don't think it is necessary to "clean" the panels before "buying" the panels. You can clean your panels every month or every other month, really depends on how easy to access to the roof.

I think you are prpbably the solo Graph Solar owner I seen on this forum. How is the Graphe working out for ya?

I think it would be worthwhile to know how often you need to clean your panels before you install them. I didn't realize the need to clean my panels at all. If I had realized the need to clean, I might have made panels easier to access. As it is now, I have a brittle tile roof and the panels are up about 30' off the ground. I live in an area with little rain, dust and dew. If I leave my vehicle outside, after about 2 weeks it is filthy dirty. I can only assume my panels are pretty dirty after a couple of months.

Assuming you mean Grape Solar.... I am pleased with my Grape Solar panels. They seem to have a pretty consistent output panel to panel and crank out the kW every day. But what do I know....

[J.P.M.]

I think it would be worthwhile to know how often you need to clean your panels before you install them. I didn't realize the need to clean my panels at all. If I had realized the need to clean, I might have made panels easier to access. As it is now, I have a brittle tile roof and the panels are up about 30' off the ground. I live in an area with little rain, dust and dew. If I leave my vehicle outside, after about 2 weeks it is filthy dirty. I can only assume my panels are pretty dirty after a couple of months.

Assuming you mean Grape Solar.... I am pleased with my Grape Solar panels. They seem to have a pretty consistent output panel to panel and crank out the kW every day. But what do I know....

You can clean your array as often as you think necessary, provided it's accessible. No cleaning will inhibit performance. How much of a performance penalty, how much it costs vs. the cost of cleaning, or how often to clean are somewhat open questions at this time. The mechanisms and rate of fouling is, and probably will continue to be, a subject of much discussion. I'd suggest the rate at which panels foul, as well as the nature of the dirt is very local, sometimes down to your array fouling differently than the person next door.

FWIW, I'm checking "instantaneous" array performance at the minute of minimum solar incidence angle every 10 days since last cleaning my array on 06/21/2014 as best as I can taking/recording irradiance measured with a pyranometer next to the array and all 16 panel temps w/an infrared thermometer from the underside of the array by hand (yes, I can get at/under them all - that was a design requirement.) into account, until it rains around here and probably after that as well. Last set of readings was yesterday. Results for those latest efforts will be a day or two. I'll report what I found after it rains, probably sometime in the fall. Maybe some intermediate results.

I have a suspicion that PERHAPS one common, but by no means universal attribute of performance penalty due to fouling may that it has a somewhat asymptotic nature. That is, an array is cleaned and after a week or 2, a lot/most of the performance degradation due to dirt/guano/etc has returned. After another week or 2 performance has dropped more, but not as much as the prior period. A couple more weeks, a little more, but at a still lower rate, etc., eventually leveling off at some point until rain or a cleaning restores some of the performance. If so, some folks may choose, or be forced due to accessibility issues, to accept a certain penalty for dirt up front either by reducing expectations or increasing the size of the array, or a combination of measures. (But not to imply or suggest the gross oversizing vendors railroad solar ignorant customers into.)

Somewhat anecdotally, I've noticed that after I clean my array, as I've done several times since 10/1014, after about 10 days - 2 weeks or so, the array looks as if it hasn't been cleaned in a long time, or at all - i.e. most of the dirt APPEARS to be back after a relatively short period of time. That's part of what put me on to this long term instantaneous performance measurement quest.

Question : has anyone else found anything like what I've seen that ? Ian ? Silver ? Anyone else ?

So far, most of the literature on the subject suggests/assumes a linear nature of performance penalty as f(time) assuming no rain. That may be true in some cases and hard to dispute in areas with frequent rain.

Lots to consider.

[bcroe]

Need to clean panels will vary with the location. I've never "cleaned" my panels,
but the air isn't blown dust, precipitation hits them quite regularly, the finger test
and the meters indicate they are at full performance. Bruce Roe

[russ]

Here I have seen it rain mud when there is a big sandstorm in Libya or Egypt and wind conditions are right.

[silversaver]

You can clean your array as often as you think necessary, provided it's accessible. No cleaning will inhibit performance. How much of a performance penalty, how much it costs vs. the cost of cleaning, or how often to clean are somewhat open questions at this time. The mechanisms and rate of fouling is, and probably will continue to be, a subject of much discussion. I'd suggest the rate at which panels foul, as well as the nature of the dirt is very local, sometimes down to your array fouling differently than the person next door.

FWIW, I'm checking "instantaneous" array performance at the minute of minimum solar incidence angle every 10 days since last cleaning my array on 06/21/2014 as best as I can taking/recording irradiance measured with a pyranometer next to the array and all 16 panel temps w/an infrared thermometer from the underside of the array by hand (yes, I can get at/under them all - that was a design requirement.) into account, until it rains around here and probably after that as well. Last set of readings was yesterday. Results for those latest efforts will be a day or two. I'll report what I found after it rains, probably sometime in the fall. Maybe some intermediate results.

I have a suspicion that PERHAPS one common, but by no means universal attribute of performance penalty due to fouling may that it has a somewhat asymptotic nature. That is, an array is cleaned and after a week or 2, a lot/most of the performance degradation due to dirt/guano/etc has returned. After another week or 2 performance has dropped more, but not as much as the prior period. A couple more weeks, a little more, but at a still lower rate, etc., eventually leveling off at some point until rain or a cleaning restores some of the performance. If so, some folks may choose, or be forced due to accessibility issues, to accept a certain penalty for dirt up front either by reducing expectations or increasing the size of the array, or a combination of measures. (But not to imply or suggest the gross oversizing vendors railroad solar ignorant customers into.)

Somewhat anecdotally, I've noticed that after I clean my array, as I've done several times since 10/1014, after about 10 days - 2 weeks or so, the array looks as if it hasn't been cleaned in a long time, or at all - i.e. most of the dirt APPEARS to be back after a relatively short period of time. That's part of what put me on to this long term instantaneous performance measurement quest.

Question : has anyone else found anything like what I've seen that ? Ian ? Silver ? Anyone else ?

So far, most of the literature on the subject suggests/assumes a linear nature of performance penalty as f(time) assuming no rain. That may be true in some cases and hard to dispute in areas with frequent rain.

Lots to consider.

Yes, the panels get dirty in 2 to 3 weeks. Thats why I suggest clean the panels once per month or every other months, to keep the panels from tough stain build up, not for performance gain. With the water and time spend on clean the panels, it might be cheaper to add 1 addition panel if looking for performance loss. Again, I have always suggest people to plan the solar little larger. It is cheaper and you wont be sorry. If you add the EV into solar calculation, your ROI will be lot less time. You get better saving from gasoline than from POCO. Why? There is no way you can keep your electricity bill in Tier 1 or 2 if you own an EV.

[J.P.M.]

Yes, the panels get dirty in 2 to 3 weeks. Thats why I suggest clean the panels once per month or every other months, to keep the panels from tough stain build up, not for performance gain. With the water and time spend on clean the panels, it might be cheaper to add 1 addition panel if looking for performance loss. Again, I have always suggest people to plan the solar little larger. It is cheaper and you wont be sorry. If you add the EV into solar calculation, your ROI will be lot less time. You get better saving from gasoline than from POCO. Why? There is no way you can keep your electricity bill in Tier 1 or 2 if you own an EV.

Thank you. I'm not sure, however, that I agree with the idea of not being able to stay out of tier 3. I planned my system on a 10,000 - 10,500 kWhr./yr. usage which will include about 3,800-4,000 kWhrs./yr. to an EV. What's left to buy from the POCO will be ~1,400 - 1,500 kWhrs./yr., all of it at tier one. The EV is still a few yrs. or so down the road.

[silversaver]

Thank you. I'm not sure, however, that I agree with the idea of not being able to stay out of tier 3. I planned my system on a 10,000 - 10,500 kWhr./yr. usage which will include about 3,800-4,000 kWhrs./yr. to an EV. What's left to buy from the POCO will be ~1,400 - 1,500 kWhrs./yr., all of it at tier one. The EV is still a few yrs. or so down the road.

I just spent 2 days in San Diego. The weather is definitely cooler than where I'm from (inland OC). Which EV are you looking for or still undecided?

[J.P.M.]

I just spent 2 days in San Diego. The weather is definitely cooler than where I'm from (inland OC). Which EV are you looking for or still undecided?

It may be awhile, if ever on an EV. I don't think one exists that would fill my requirements at this time, nor is one on the horizon. I bloviated recently about buying an EV with the following requirements:

1.) 2 each 300 mile range batteries good for 1,000 or more charge/discharge cycles.

2.) Changeover one battery to the other on the fly.

3.) Swappable batteries and home charging capabilities.

4.) Usual bells/whistles.

5.) $35K or less driveoff.

I think I'll be waiting a while.

As for the weather, at my house, in inland North County S.D., we're about 10+ deg. F. higher than the coastal areas in summer, ~86 deg. F. ave. high in Aug. last 6 yrs., about 62 deg. F. ave. high 12/15 - 01/15 last 6 yrs. at my house. Clearness index varies ~ .62 to .73, Dec. to July, so the sun shines most of the time. The air quality may be a bit better than the O.C., which I get to watch from my kitchen window.

[silversaver]

It may be awhile, if ever on an EV. I don't think one exists that would fill my requirements at this time, nor is one on the horizon. I bloviated recently about buying an EV with the following requirements:

1.) 2 each 300 mile range batteries good for 1,000 or more charge/discharge cycles.

2.) Changeover one battery to the other on the fly.

3.) Swappable batteries and home charging capabilities.

4.) Usual bells/whistles.

5.) $35K or less driveoff.

I think I'll be waiting a while.

LOL

I don't think it will ever happen within a year or 2......

[JCP]

LOL

I don't think it will ever happen within a year or 2......

We're a ways away from 1000 cycles...

[silversaver]

We're a ways away from 1000 cycles...

1000 cycles are easy and done. All of them can handle more than 1000 cycles.

1. 2 batteries that handle 300 miles each can be done now, but you will be missing lots space and $$$$

2. change battery on the fly is easy, but why not make a bigger capacity battery than 2?? It is the same.

3. all the batteries are swappable, but how much labor involve? All electric car are capable of home charging, It is matter of time. With the big battery like 150kW to handle 2 X 300 miles, how long does it take to charge? Your house only have like 200A service panel. It is an easy calculation for anyone.

4. standard stuffs

5. $35k or less? I'll pay you double of the amount now if you can deliver me one.

[JCP]

1000 cycles are easy and done. All of them can handle more than 1000 cycles.

Really. I thought that LiPo were stuck at 400-500 cycles.