Solar panel choice

Henry · June 2010

Ready to install residential solar power in NJ. Two companies have made proposals very close in price. My choice, Sunpower 230 or Sharp 240. Which one do I pick?

solar_dave · June 2010

Re: Solar panel choice

Really you need to tell us more about the total install, inverter, size, cost per watt.

BB. · June 2010

Re: Solar panel choice

Either brand should be fine (Sunpower--the German panel company?).

This is for a grid tied system I presume? Sunpower requires positive grounded solar panels and a GT inverter that supports positive ground (not usually a problem).

If off-grid, not many controllers/equipment/systems are wired for positive grounded systems (telephone systems are positive grounded).

-Bill

Henry · June 2010

Re: Solar panel choice

Sharp 240
Inverter- Sunnyboy 8000us
8.64k
10,236kwhs
5.75

Sunpower 230
Inverter ?
8.28 kw
10,331 kwhs
price per watt $6.60

solar_dave · June 2010

Re: Solar panel choice

Henry wrote: »

Sharp 240
Inverter- Sunnyboy 8000us
8.64k
10,236kwhs
5.75

Sunpower 230
Inverter ?
8.28 kw
10,331 kwhs
price per watt $6.60

Looks like bang for the buck it is your first choice, $0.85 a watt difference in price?
Is there any reason to choose one installer over the other?

BB. · June 2010

Re: Solar panel choice

Is that pricing before or after tax breaks/rebates? If that is before the tax breaks--really nice.

SMA Sunnyboy inverters are very good.

If you are into logging your power usage--look at the options between the different inverters/companies... Some logging hardware is quite expensive.

Or look at other loggers clipped onto your home wiring that can support net metering (like T.E.D. and others).

Are all of the panels on the same roof plane facing mostly south? Have full sun free of shadows? No trees/nearby property building where new shade can happen?

-Bill

Henry · June 2010

Re: Solar panel choice

The pricing, $49,600. for the Sharp and $54,600. for the Sunpower is before the 30% Fed credit and our SREC program in NJ.

Henry · June 2010

Re: Solar panel choice

This will be a ground mount. Prelim shading check showed 94%. They said we could tweek that by moving the array a little. I have 3 acres, but I do not want the array to be too obtrusive.

mike95490 · June 2010

Re: Solar panel choice

Henry wrote: »

Prelim shading check showed 94%. They said we could tweek that by moving the array a little.

Move the array. Shaded cells kill the power in that string. Or insist on 2 smaller inverters, and have the shaded portion feed it's own inverter, so you don't loose power on the whole system.

Also - look into management/monitoring, so you can see before a nasty electric bill arrives, if you have a problem in a string or inverter.

Henry · June 2010

Re: Solar panel choice

Can an array be wired in such a way so that a small amount of shading does not kill the entire system during the shading, or are two inverters required?

BB. · June 2010

Re: Solar panel choice

Think of 4 strings of batteries in parallel... Shading reduces the capacity/amperage/voltage of one string--that one drops out and the other 3 strings carry the load.

There have been many bytes spent on this discussion... Each system is different and each installation has its own issues--And shadows move during the day. To create a general and accurate solution to the problem is probably not possible across the Internet.

If you have two high voltage strings (10-20 panels). One or a few panels that are partially shaded at times in one string and the other string that is not at all--Optimally, then each should go to its own GT inverter.

If you have one 10-20+ panel series string---then there is no wiring changes to be made and you have the optimum setup for "shading". You will be able to shade as many panels until the Vmp-shaded voltage falls below the GT inverter's minimum input voltage (typically with an operating range of 200-500+ volts).

In practice, the Vmp/Imp curves are fairly flat. If you have two 20x panel strings in parallel (40 panels total) and one panel or even two panels are shaded in one string--Then, most likely the system will lose only 1-2/40 of its power (not much).

If more than two or three panels on one string are shaded in a two string system--then you may lose 1/2 the system power (those three panels lower string voltage so much, that the other string supplies most of the voltage/current).

Enphase (and others) have pushed the one inverter per panel option as a solution to shading problems (and addressing other issues too).

I am not sure there is a really good solution other than to minimize shade. Solar PV electric systems just do not do well with partial/full shading.

-Bill

mike95490 · June 2010

Re: Solar panel choice

Grid tie is tricky, you want high enough voltage to stay in MPPT mode on a hot day, when the panel output is low, but not so high that on a cold morning, you overvoltage and fry the inverter. Sometimes the "good" window is small enough, that a shaded panel can drop you out of MPPT and you loose a lot of efficiency. With MPPT, if one string is shaded, it can confuse the heck out of the controller and you loose power. Shade is bad, and must be avoided, or else isolate it to it's own controller so it does not affect ALL the system.

hmansour · July 2010

Re: Solar panel choice

We installed a 10KW under Ontario Fit Program, we used DuPont Apollo 100 W A2 North American Model with Tigo Maximizer and Sustainable energy Inverters. This turned to cost us with all connections and installation by MindCanada contractor $55000 CDN Dollars. This is the best solution in the market (Canada) today

AntronX · July 2010

Re: Solar panel choice

hmansour wrote: »

We installed a 10KW under Ontario Fit Program, we used DuPont Apollo 100 W A2 North American Model with Tigo Maximizer and Sustainable energy Inverters. This turned to cost us with all connections and installation by MindCanada contractor $55000 CDN Dollars. This is the best solution in the market (Canada) today

So, your system cost you $5.24/Watt (in US $). Seems too high considering those panels cost around $1/Watt, and grid-tie inverters are around $0.66/Watt. Why did they charge you $3.58/W for labor and bunch of wires? I've read on this forum somewhere, that the going rate for superior polysilicon panels grid-tie installation is around $5.5 - $6 per watt.

hmansour · July 2010

Re: Solar panel choice

AntronX wrote: »

So, your system cost you $5.24/Watt (in US $). Seems too high considering those panels cost around $1/Watt, and grid-tie inverters are around $0.66/Watt. Why did they charge you $3.58/W for labor and bunch of wires? I've read on this forum somewhere, that the going rate for superior polysilicon panels grid-tie installation is around $5.5 - $6 per watt.

DuPont Apollo Panels are sold 10KW or less for $1.80 per Watt, 10 KW inverter are $1.00 per Watt, good non penetrating mounts about $150-$2 per Watt. Installers and electricians would cost over $1, In Canada $5.50 Cdn per Watt for 10KW is pretty cheap as I have two other quotes for Mono and Poly and they were above $6.50 per Watt. Do not forget the Ontario Domestic Content requirement. In the US the Going price for turnkey is $3.50 - $4.25 no problem with that. In Ontario this is not true. By the way Poly-silicon compared to Thin Film is not superior as we tested two poly panels next to the DuPont thin Film DuPont were better 20% on the average and they produced more power even facing south. That's why went with thin film.

BB. · July 2010

Re: Solar panel choice

Thin film tends to be around 1/2 as efficient per sq.ft/sq.meter... If you have the space for thin film and the extra mounting does not cost too much--can be a nice cost effective solution over poly/mono crystalline panels.

I do have one other question... In times past (few years ago), amorphous panels tended to lose upwards of 20% of their output in their first 6 months or so of sunlight exposure. So the vendors had to derate their panel's out of the box power output to make up for the initial drop (crystalline panels may drop about 3% output in their first few months).

After that, I have read that they lose efficiency about the same rate as P/M crystalline panels, or that they loose it faster.

What has your testing/research shown so far?

-Bill

johnl · July 2010

Re: Solar panel choice

In NW Ontario, the going rate for a 10kW grid-Tie microFIT system using poly-silicon panels is about $6.00 to $9.00 per watt. Panels do not have to be domestically sourced for projects completed before Dec 31 under the Ontario microFIT rules. The domestic content requirements for this year can be fulfilled with Ontario-made racking and inverters that have prices very comparable to US prices.

There is a rather healthy profit margin being made by installers in Ontario on microFIT systems at current prices. That's not necessarily a bad thing for the industry, but something that joe homeowner should know before signing any contract.

hmansour · July 2010

Re: Solar panel choice

BB. wrote: »

Thin film tends to be around 1/2 as efficient per sq.ft/sq.meter... If you have the space for thin film and the extra mounting does not cost too much--can be a nice cost effective solution over poly/mono crystalline panels.

I do have one other question... In times past (few years ago), amorphous panels tended to lose upwards of 20% of their output in their first 6 months or so of sunlight exposure. So the vendors had to derate their panel's out of the box power output to make up for the initial drop (crystalline panels may drop about 3% output in their first few months).

After that, I have read that they lose efficiency about the same rate as P/M crystalline panels, or that they loose it faster.

What has your testing/research shown so far?

-Bill

Bill,
You Know efficiency is not the whole game. The real game is howmuch you spend and howmuch you produce to sell at 80 cents in Ontario.
I agree if you have the space, your best choice may be Thin Film, If you have a limited space you choice may be mono.
Out of the systems we installed at the begining most 100 Watt panel came out of the box rated at 99.6 volts but when tested we got way above 100 Volts some gave 105 Volts after three month we did not see any change to the power for similar days. It would be difficult to judge until we have a year passed and check output and compare but as it looks Thin Film and Mono have similar power efficiency and they are warranted to 80% after 20 years so I am not scared as this is done by DuPont and we know who is DuPont.

BB. · July 2010

Re: Solar panel choice

Oh--it looks like you are measuring Voc (voltage open circuit). Not really a very useful way of verifying output capacity. Voc, once you have a minimum amount of light, is not proportional to sunlight or to energy output.

If I understand the cells correctly--The decay over time is really in the Imp/Isc (max power; short short circuit) output current, not the Voc/Vmp... (don't quote me, I am not a solid state physicist).

In the end Pmp=Vmp*Imp and that is what really needs to be monitored for panel performance. Isc can be a quick way of checking for issues. But it is still possible to have other failures that don't show up with a Isc test.

-Bill

hmansour · July 2010

Re: Solar panel choice

BB. wrote: »

Oh--it looks like you are measuring Voc (voltage open circuit). Not really a very useful way of verifying output capacity. Voc, once you have a minimum amount of light, is not proportional to sunlight or to energy output.

If I understand the cells correctly--The decay over time is really in the Imp/Isc (max power; short short circuit) output current, not the Voc/Vmp... (don't quote me, I am not a solid state physicist).

In the end Pmp=Vmp*Imp and that is what really needs to be monitored for panel performance. Isc can be a quick way of checking for issues. But it is still possible to have other failures that don't show up with a Isc test.

-Bill

I agree with You, VOC is good to speed test the panel, but Pmp is the Game here that's why we tested with 40 Watt DC lamp on the panel output and we got 88 Volts facing South and 76 Volts facing North.
We did the same test with Sharp panel they did not even compare. Very low output with the 40 Watts on a 180W panel while facing north.

BB. · July 2010

Re: Solar panel choice

Again, what kind / rating of 40 watt bulb... Not a very scientific test. You do know that some panels are "bi-facial"--they can generate power with light shining through the back of the panels too.

The Dupont panels may be somewhat bifacial too (appears to be a white backing material instead of opaque silver type found on many other panels).

Do the same test with opaque backing material behind both types of panels and see what the values are then.

Nothing wrong with bifacial panels--and the mfg. like to say that bifacials mounted on a white roof are the cats meow.

-Bill

hmansour · July 2010

Re: Solar panel choice

BB. wrote: »

Again, what kind / rating of 40 watt bulb... Not a very scientific test. You do know that some panels are "bi-facial"--they can generate power with light shining through the back of the panels too.

The Dupont panels may be somewhat bifacial too (appears to be a white backing material instead of opaque silver type found on many other panels).

Do the same test with opaque backing material behind both types of panels and see what the values are then.

Nothing wrong with bifacial panels--and the mfg. like to say that bifacials mounted on a white roof are the cats meow.

-Bill

BB
The back panel is made from black sheets encapsulation. On the Other hand it is a known fact that Thin film would not require direct sunlight to function optimally, as matter of fact in shade situations they would produce far more power than Poly or mono under same conditions. If facing the sun it would exceed its rated power guaranteed. I am waiting for your e-mail to send you the DuPont study,
my e-mail is husni.mansour@trilliumenergy.net

stephendv · July 2010

Re: Solar panel choice

hmansour wrote: »

If facing the sun it would exceed its rated power guaranteed.

How old was the panel? All a-si panels produce about 20% more than rated power for the first 3 months and then stabilise to their rated Watts.

BB. · July 2010

Re: Solar panel choice

I am not going to get too worked up about 20% better performance when they ship with higher than rated performance... Now, that may be a good thing (always nice to get more than you pay for) or not (if these panels, like other amorphous panels--lose 20% of their output in the first 6 months--then it becomes equal with other panels).

Don't get me wrong--if you can get XX% more power--that can be the difference between profit and loss for many companies that have to work with tight profit margins.

But, physics wise, I keep comming back to this:

--some numbers:

• sunlight on an average day ranges from 32 000 to 100 000 lux
• TV studios are lit at about 1 000 lux [i.e. 1000 lumens
per square metre]
• a bright office has about 400 lux of illumination
• At sunset and sunrise, ambient outdoor light is also about
400 lux (if the sky is clear).
• moonlight represents about 1 lux
• starlight measures a mere 0.00005 lux

A panel facing the sky (no direct sunlight, no major backscattering from clouds) is going to be on the order of 400 Lux. Full sun (rated power) is 100,000 Lux:

400 L / 100,000 L = 0.004

Or about 0.4% of the energy of full/rated sunlight flux vs back scatter/near sunset/sunrise conditions.

For a panel to output 80% of its power in these conditions simply violates physics.

That is why I believe that we have some fundamental miss-understanding about your testing. You are doing something that I don't understand.

If any solar panel was able to produce substantial power per your statement:

The back panel is made from black sheets encapsulation. On the Other hand it is a known fact that Thin film would not require direct sunlight to function optimally, as matter of fact in shade situations they would produce far more power than Poly or mono under same conditions.

Even if the thin film was 100% more efficient than crystalline panels under "indirect lighting" -- Then you are talking about 0.8% of rated out put vs 0.4% per (rough) measured lighting levels.

If you want to do A:B Testing... Get some small decent solar panel / photo diode / even kit solar cell and connect to a DMM set to Amps (or mAmps if smaller cell). The output of that cell is proportional to flux (probably linear to within 5% of true intensity--close enough to our work here). Then take your thin film and crystalline panels with some sort of defined load--and see how the two panels differ in output vs measured solar intensity (blocking real lighting--if applicable).

You can even build your own meter with these instructions or get a kit from these guys:

www.microcircuitlabs.com

-Bill

solarix · July 2010

Re: Solar panel choice

My question is: How are they going to install a 8kW inverter? Most homes are 200amp service, and the most you can backfeed into them is 20% or 40amps to meet NEC code. 125% of max current output from a 8kW inverter is 41.6 Amps. Code won't allow it unless you downsize the main breaker (usually have to go way down to 150A), replace the service entry with larger ($$$) or do a line side tap which is impossible on most residential services. Make sure you have this resolved with your installer ahead of time. Probably should back off to a 7kW system.
Prices here are running about $5.00/watt using Trina or Canadian modules.

solar_dave · July 2010

Re: Solar panel choice

solarix wrote: »

My question is: How are they going to install a 8kW inverter? Most homes are 200amp service, and the most you can backfeed into them is 20% or 40amps to meet NEC code. 125% of max current output from a 8kW inverter is 41.6 Amps. Code won't allow it unless you downsize the main breaker (usually have to go way down to 150A), replace the service entry with larger ($$$) or do a line side tap which is impossible on most residential services. Make sure you have this resolved with your installer ahead of time. Probably should back off to a 7kW system.
Prices here are running about $5.00/watt using Trina or Canadian modules.

This depends on how much stuff is in the 200 amp panel, If the loads are under 150amp and you add a 60 amp breaker this still meets code. The problem comes when your 200 amp panel is mostly consumed already with loads. This was my exact problem and I had to up my service to a dual 200 amp service, and a 400 amp transformer feed.

drees · July 2010

Re: Solar panel choice

solarix wrote: »

Prices here are running about $5.00/watt using Trina or Canadian modules.

I know a guy in Tuscon who just added 6 Schott 225 panels/Enphase micro-inverters to an existing system for just over $5/watt. Prices are very good in Arizona!

solar_dave wrote: »

This depends on how much stuff is in the 200 amp panel, If the loads are under 150amp and you add a 60 amp breaker this still meets code. The problem comes when your 200 amp panel is mostly consumed already with loads. This was my exact problem and I had to up my service to a dual 200 amp service, and a 400 amp transformer feed.

Well - kind of. Depending on your load calculations you may not be able to downsize your main breaker and feed in more PV - but the total feed into your residential main load center can't be more than 120% of the panel's busbar rating. You could have no loads on the panel and you'd still have to downsize the main breaker if you want to feed in 60A of PV. An electrician will be able to tell you if this is the case or not. Shouldn't take much longer than 30 minutes to run the calcs. I can't imagine that you wouldn't be able to downsize unless you have a large house (3000 sq/ft+), all electric appliances and a lot of AC or heat-pumps.

solar_dave · July 2010

Re: Solar panel choice

drees wrote: »

Well - kind of. Depending on your load calculations you may not be able to downsize your main breaker and feed in more PV - but the total feed into your residential main load center can't be more than 120% of the panel's busbar rating. You could have no loads on the panel and you'd still have to downsize the main breaker if you want to feed in 60A of PV. An electrician will be able to tell you if this is the case or not. Shouldn't take much longer than 30 minutes to run the calcs. I can't imagine that you wouldn't be able to downsize unless you have a large house (3000 sq/ft+), all electric appliances and a lot of AC or heat-pumps.

This is true, my second 200 amp panel has a 175 amp main per code guys with a 60 amp solar back feed while it is the only thing installed there.

(200 amp X 1.2) - 175 = 65 amps

jcgee88 · July 2010

Re: Solar panel choice

Henry wrote: »

Ready to install residential solar power in NJ. Two companies have made proposals very close in price. My choice, Sunpower 230 or Sharp 240. Which one do I pick?

The generic answer is: what is more important,
maximum capacity or lowest cost?

I recently did a runoff between Sunpower and
Sharp. I started out wanting Sunpower, and I
ultimately selected Sharp.

Sunpower makes higher efficiency PV modules,
and this gets manifested in the product as a smaller
footprint. The nominal output of the panel is the
same (235ish watts), and the Sunpower collects a
premium for the smaller footprint.

Ultimately, another reason forced me off Sunpower
(they don't support Enphase), but even if they had
I would have gone with the Sharps. That's because
my roof could not take full advantage of the slightly
smaller form factor - I could add only one more panel
to my original 13. That 8% gain was not worth the
extra cost and the loss of the Enphase inverters for me.

Note that if my roof were laid out differently, say, with
one large and consistent target area, I definitely would
be open to Sunpower.

John

BB. · July 2010

Re: Solar panel choice

solar_dave wrote: »

This is true, my second 200 amp panel has a 175 amp main per code guys with a 60 amp solar back feed while it is the only thing installed there.

(200 amp X 1.2) - 175 = 65 amps

Dave, out of curiosity--is this a sub-panel or a main panel?

For example, say you had a 200 amp main panel and this 175 amp was a sub-panel... I would expect that the 60 amp breaker/circuit/gt inverter would be too large if the main panel was 200 amp rated with a 200 amp; breaker?

-Bill

solar_dave · July 2010

Re: Solar panel choice

BB. wrote: »

Dave, out of curiosity--is this a sub-panel or a main panel?

For example, say you had a 200 amp main panel and this 175 amp was a sub-panel... I would expect that the 60 amp breaker/circuit/gt inverter would be too large if the main panel was 200 amp rated with a 200 amp; breaker?

-Bill

It is actually a second 200 amp main from a 400 amp transformer/meter feed, the utility came out and pulled new larger gauge wire to the transformer. It looks like a sub but my main has 2 separate slots for 200 amp main breakers, one for the internal breaker buss and one for an external breaker buss. In the attached pics the old load center shows the builder original 200 amp service entrance, the Breaker panels shows the arrangement of the current setup with the second 200 amp load center hung off the side with a 2 inch conduit and the main breaker shows the 2 main breakers (now a 200 & 175 amp) and the house load breaker set up as ported off the old panel. You can see the PV disconnect and the required second meter which is owned by me for the PV output. At year end the Utility requires me to fill out a 3X5card and mail it to them with the overall PV output to hold my generation rates. I suspect they use those number to qualify how much local PV generation as business to meet their mandated by law green generation. The main meter is a digital meter that has 8 different data items for TOU rates, etc. in it and has the LCD arrows to show direction of the electron flow.

The bright green sticker is the very difficult code department approval, added after 3 trips by the inspector. (on the last trip the electrician was there and made all the needed changes)

:D:D It actually took the electrician 4 trips as the utility had a change for him too. (the electrician met the utility representative as well)

Probably to my benefit as they had the grounding a mess.

Edit: BTW this whole mess was a $4300 cost over run, this is why I warn larger PV grid tie folks to evaluate the current load center and consider this as a possibility. At least it was added to the overall cost by the contractor so it qualified as part of the 30% tax credit. Really I was going to have to upgrade it anyway as I am adding a 750 sq. ft building this summer to the property so better that I get Obama to pay his share!

Solar panel choice

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