Solar panels

booboo · April 2007

I am seriously considering a grid tie system on the home we are currently building. Our electric company will rebate us $4 per watt up to 2000 watts. Our plan is to put 2000 watts on now and another 2000 watts with the rebate money. The electric company will give us the rebate on the second 2000 watts as well.

My problem is our local solar contractors want $7 per watt for the solar panels and the rest of the hardware is priced really high as well. My plan it to buy the solar panels and inverter and let the installer hook it all up for me.

I have a back yard patio cover that has about 1000 sq foot of roof. What would be the best panels and mounting hardware to get for this patio?

BB. · April 2007

Re: Solar panels

Retail is about $10 per watt installed near SF California (+/- 1.5 years ago). Probably could have done better if I shopped more--There was a serious panel shortage at the time so I "paid" for a guaranteed source.

You might post your city and see if there is anyone that people here can recommend as a supplier/installer. Regarding doing your own "contracting" for buying panels/components and subing the Electrician--Check the exact rules for the rebates--many of them are only valid if specific warranties are backed by the installer (IIRC a 10 year one is required for California's rebates).

Grid Tied installations usually require a licensed Electrician, building permits, and Electric Company OK (varies by state/location). Also, different states have differing requirements for how your electric bill is adjusted for having solar (1 year net metering is probably the best for a consumer).

While I have Grid Tied solar for my home--I did this after I fully insulated, double pane windows, new heater, appliances, CFL lighting, etc. as conservation is usually cheaper than installing solar electric.

If you have AC, you might look into the ground sourced units (save lots of electricity).

And, solar hot water is quite a bit cheaper to install and requires smaller roof space (saving $60 per month for electricity vs $60 per month for gas--is still saving money). Drawback (from my point of view) for solar hot water is possibly more maintenance issues, extra hot water tank(s) for storage, and design issues/choices for areas if freezes are possible.

booboo · April 2007

Re: Solar panels

I am in Sierra Vista Arizona.

The $7 per watt was just for the panels not installation. I can buy the same panels for $4.5 per watt. I can save over $5,000 if I buy and install the solar panels myself. The local electric company will allow that they just want a contractor to hook it all up.

niel · April 2007

Re: Solar panels

there's nothing wrong with doing it yourself if you know what you are doing. check with local public servants on any install rules and you may need an electrician as a consultant too. they may also advise you of any possible structural reinforcements that will be needed as a result of the added strain pvs will place upon that patio cover. it sounds like it will need reinforced. having some familiarity with electricity also helps greatly. you may also read around this forum for some enlightenment. if you still wish to shop for an installer you may want to check with the forum sponcer, northern arizona wind and sun or get a free copy of home power magazine and look in the back for installers near you.

Mangas · April 2007

Re: Solar panels

I know an excellent solar electrician in Sierra Vista.

crewzer · April 2007

Re: Solar panels

I am seriously considering a grid tie system on the home we are currently building… Our plan is to put 2000 watts on now and another 2000 watts (later)… I have a back yard patio cover that has about 1000 sq foot of roof… I am in Sierra Vista Arizona.

What would be the best panels and mounting hardware to get for this patio?

There are plenty of perfectly good PV modules available. Part of selecting the “best” PV modules will include determining the correct electrical interface between the PV array and the inverter. A good solar energy designer/installer’s price should include this fairly sophisticated design work.

If you want to do this design work yourself, you may find Xantrex’ GT Series PV Array Sizing Tool to be helpful. Required temperature data for your location is available from www.weather.com. I don’t now if similar tools are available for other grid-tie inverters such as SMA and Fronius.

This link will give you an idea of what PV modules are available from this site sponsor’s store in Flagstaff: http://store.solar-electric.com/solarpanels.html This info may help you decide which PV modules to model in the Xantrex tool.

This model will give you an idea of much energy to expect from a 4,000 W STC system installed in nearby Tuscon: http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/Arizona/Tucson.html

Note that a 4000 W array plus hardware will weigh ~1,000 lbs. The patio roof will need to be able to handle this load, both static and wind. The correct tilt angle for a south-facing PV array in your location is 31.5 degrees up from the horizontal. Check Unirac for mounting racks and hardware. See: http://www.unirac.com and http://store.solar-electric.com/unsoelpamo.html

Finally, and assuming you’re considering a battery-less grid-tie inverter, your solar energy system will most likely not produce and deliver power to your home when the grid fails. This is a required safety feature, called “anti-islanding”, that’s necessary to protect utility workers.

If you want a system that includes battery-backup to produce limited power for your home if the grid fails, then you’ll need a system built around something like OutBack grid-tie inverters and the MX60 controller. See: http://www.outbackpower.com/grid_interactive.htm and http://www.outbackpower.com/MX60.htm

HTH,
Jim / crewzer

booboo · April 2007

Re: Solar panels

A local solar store here suggested Sharp NT-175U1 panels and a Xantrex SW4024 inverter.

This is a sine wave inverter, does it supply power that is compatable with my appliances like the air conditioners, refrigerator, etc. Is there anything that can be harmed or not work with this power?

booboo · April 2007

Re: Solar panels

One more thing. Does anyone have a detailed diagram of a installation like this so I can uderstand all of the equipment needed?

Roderick · April 2007

Re: Solar panels

booboo wrote:

One more thing. Does anyone have a detailed diagram of a installation like this so I can uderstand all of the equipment needed?

Try looking here:

http://briefcase.yahoo.com/bc/rmkey@sbcglobal.net

in a folder called "solar roof"

Do check your rebate terms carefully, it may be that the rebate is invalidated if the installing contractor doesn't have a specific certification. An ordinary roofer could put up the panels, and an ordinary electrician could hook up the equipment, but do they need to be solar-qualified?

I tried the path of calling solar contractors to install equipment that I bought, myself, and was unable to find any that would do it unless they sold me the parts, too. Maybe that's where the profit margin is? Ok, to be completely accurate, no contractor that was rated C-10 (California's all-in-one solar qualification) would do it, ordinary roofers said sure, they'd never done it, but were willing to try.

If you want to seriously consider installing yourself, let us know. I have more information for you.

crewzer · April 2007

Re: Solar panels

A local solar store here suggested Sharp NT-175U1 panels and a Xantrex SW4024 inverter.

The store should have suggested a few more things:

1) A 4,000 W PV array will need three solar charge controllers (i.e., Xantrex C60, Morningstar TriStar 60, or OutBack MX60) for a 24 V system.
2) The Xantrex 4024 needs batteries to operate.
3) When introduced, the Trace (Xantrex) 4024 included a grid-intertie mode. I’m not sure this function is still certified, as Xantrex refers to the “SW Inverter/Charger (as their) most popular off-grid power solution”. This doesn’t sound to me like it’s still supported for grid-intertie applications, and it might be worth clarifying with Xantrex.
4) How to match the SW4024’s 120 VAC output to your home’s likely 120/240 VAC service. The typical solution is to install two inverters stacked in “series” to provide 120/240 VAC.
5) A single 4024 probably can’t run the entire house (in back-up mode), and perhaps even not some big loads. For example, the running load of a 4 ton AC unit with a SEER of 12 would be 4,000 W. A typical solution is to separate critical loads from non-critical loads, and have the inverter power critical loads only.
6) A 24 V inverter is probably not optimal for 4,000 W+ applications. A 48 V inverter would be better (higher DC voltage = lower DC current = smaller wire and, usually, higher system efficiency)

It would be helpful if we had a more complete idea about what you’re actually trying to do.

HTH,
Jim / crewzer

booboo · April 2007

Re: Solar panels

It would be helpful if we had a more complete idea about what you’re actually trying to do.

We have some extra money in our budget for our new home and are thinking solar might be a good place to put it. We can install 4KW of solar pretty inexpensively with the rebates. The goal would be to add batteries in the future but I don't see us not being hooked up to the grid. The house is 3300 sq foot Santa Fe style with over 5000 of flat roof. The house is well insulated with good windows. We have Propane tankless water heaters, dryer, cooking and furnace. There are two 13 seer air conditioners one 5 ton and one 2.5 ton. I think a 4KW grid tie system would be a good place for us to start and fine tune it down the road a few years.

crewzer · April 2007

Re: Solar panels

OK. Take a look at the following link: http://www.xantrex.com/web/id/25/learn.asp Were you thinking about something like Figure 1 or Figure 2?

Regards,
Jim / crewzer

mike95490 · April 2007

Re: Solar panels

booboo wrote:

I have a back yard patio cover that has about 1000 sq foot of roof. What would be the best panels and mounting hardware to get for this patio?

My concern would be weight and windload. Patio roofs "usually" can just barely hold themselves up, let alone the weight of the racks and panels, which can be quite substantial.

booboo · April 2007

Re: Solar panels

Why not use a Xantrex GT Series Grid Tie Solar Inverter instead of the one I was quoted?

OK. Take a look at the following link: http://www.xantrex.com/web/id/25/learn.asp Were you thinking about something like Figure 1 or Figure 2?

#2

My concern would be weight and windload. Patio roofs "usually" can just barely hold themselves up, let alone the weight of the racks and panels, which can be quite substantial.

I will run it by my builder but the patio cover is pretty substantial. How much does a typical solar panel weigh? The patio cover is built with trusses and should hold a bunch of weight. Here are a few pictures, should give you a basic idea.

halfcrazy · April 2007

Re: Solar panels

Looks like that patio roof should hold a few pv's :-o the xantrex sw 4024 will require the grid intertie unit as crewzer stated. if you dont need battery backup i would seriously consider the xantrex gt line of inverters

booboo · April 2007

Re: Solar panels

if you dont need battery backup i would seriously consider the xantrex gt line of inverters

No, I want the ability to add batteries in the future.

crewzer · April 2007

Re: Solar panels

#2... No, I want the ability to add batteries in the future.

Given enough money, just about anything is possible. However, deploying a system modeled after Figure #2, which requires batteries to operate, and wanting to add batteries in the future, are pretty much mutually exclusive concepts from a practical perspective.

The only exception I can think of would be to use OutBack grid-intertie inverters with a small battery bank to start, and then add a large 48 V battery bank later. You'd most likely still need to add a subpanel in your home to provide power to critical loads and leave the big loads on the main AC panel. The OutBack inverter(s) would connect between the main- and subpanels. Energy from the PV array would power the subpanel loads. If there was any extra solar energy available, it would feed the the main panel loads and/or the grid. Subpanel loads would be powered through the inverter and from the grid at night and on days with poor insolation.

Adding a large battery bank later would permit subpanel loads to be powered from the batteries and inverter at night and the batteries would be recharged during the day. Once the batteries were recharged, any extra solar energy available would feed the the main panel loads and/or the grid. If the battery voltage fell too low (i.e., at nigh), the charger(s) in the inverter(s) would use the grid to recharge the batteries. In the event of a grid failure, the batteries would supply power to subpanel loads.

You might be able to get away with powering the 2.5 ton AC and other critical loads (fridge, some lights, air handler fan, etc.) using a pair of inverters. The 5 ton unit would most likely have to stay on the main panel.

Does this sort of sound like something that might work for you?

Regards,
Jim / crewzer

booboo · April 2007

Re: Solar panels

In order to get the rebates you can't have any batteries. Maybe the way to do it would be get a Xantrex GT Series inverter for now. Then just swap inverters when we want to add batteries. I am sure the inverter will have some value a few years down the road.

Looks like all you really need is the inverter, solar panels and misc stuff to conect everything. If I were to get the Xantrex GT 5.0 I could add up to 5KW. If I started with 2KW of panels could I add one or two panels at a time when I have extra money to buy them? Or do you have to add them in specific increments?

BB. · April 2007

Re: Solar panels

In general, the cost effective (i.e., cheapest) Grid Tie type inverters need about 200-600 VDC input (depending on brand and model). The battery systems typically need 20-125 vdc maximum VDC input from the solar panels.

So, more than likely, you would need to rewire the solar panels and chuck the Grid Tie inverter if you wanted to convert to battery powered inverters.

You could plan ahead for this situation by (possibly), for example, bringing down two (or three) lead sets from the solar panels down to a handy junction box where you could rewire the panels from 120 VDC (Max) to 240 or 360 or 480 VDC max -- depending on if you want battery or grid tied inverters...

Also, the question about adding solar panels--you have to watch the current and voltage limits, and match strings (say you have two strings of 10, then you could add two panels for two strings of 12 panels--unless you go over the voltage limits--then, you may have to go from 2x10=20 to 3x8=40 panels)...

That is why it was suggested you go to the Xantrex GT Inverter sizing tool... It does a pretty good job of letting you do what-ifs to see how things play together.

Also, in terms of efficiency, you are better going pure Grid Tie. By adding batteries, you are increasing your losses from ~90+% efficiency down to 60-70% efficiency (more solar panels to power the same appliances).

If you already have reliable Grid Power, you may be better off getting a generator (and transfer switch) to give yourself the occasional backup power. If you need lots of backup power (poor utility reliability) or they don't allow Grid Tie/Net Metering then, perhaps going Battery/Grid hybrid MIGHT make economic sense.

-Bill

crewzer · April 2007

Re: Solar panels

In order to get the rebates you can't have any batteries.

This comment might be worth additional research and clarification. I suspect the system qualification for the rebate requires that the inverter be compliant with UL-1741, which includes “anti-islanding”. The “battery-less” inverters typically meet this spec. Off-grid inverters using batteries typically do not, as the circuitry and testing adds unnecessary cost. However, the Outback grid-interactive inverters, which require batteries, do meet this UL-1741 spec.

Maybe the way to do it would be get a Xantrex GT Series inverter for now. Then just swap inverters when we want to add batteries. I am sure the inverter will have some value a few years down the road.

This might work, but it would likely be a bit more complicated than it sounds. In addition to swapping inverters, you’d have to rewire the array from ~250 VDC-550 VDC down to ~48 VDC-60 VDC. You’d also need to add one or two charge controllers between the array and the new inverter(s). You might also need two new inverters, series stacked for 120/240 VAC, to replace the GT 5.0.

If I started with 2KW of panels could I add one or two panels at a time when I have extra money to buy them? Or do you have to add them in specific increments?

As long as the series string voltage remains within the inverter’s input voltage limits, you could add one or two panels at a time. However, once you max out one series string’s voltage, the next series string, wired in parallel with the first, would have to operate at about the same voltage, and that would likely mean buying a whole bunch of panels at one time.

One solution might be to start with two “short” series strings, wired in parallel, whose design voltage is at the low end of the inverters input range (i.e., ~250 VDC). You could then incrementally add one module to each string and gradually increase the strings' voltage to the inverter’s upper limit (~550 VDC). The Xantrex sizing model I posted earlier can help you sort through this approach.

HTH,
Jim/ crewzer

booboo · April 2007

Re: Solar panels

I think I am starting to get it now. Thanks for all the great advice.

Looks like since the rebate requires no batteries I will have to use something like th GT 5.0. Batteries are probably many years down the road so I will worry about that later. I understand how the panels work with the inverter as far as voltage and watts.

I am a little confused on how the inverters hook up to the electrical panel. Does the inverter only run specific electrical circuts in the house or does it just add power to the power coming in from the grid?

BB. · April 2007

Re: Solar panels

A Grid Tied Inverter is just simply connected to a Circuit Breaker set inside of your main panel. It "back feeds" electricity into your electrical mains--and if you generate more electricity than you consume--it simply spins your utility meter backwards. If you consume more than you generate, it effectively, just slows down your utility meter... From your point of view--there is no change in the power available to your plugs/appliances--it all looks like utility power (including power outages--which Grid Tie inverters cannot help you with).

There are some details to the design (like having a large enough main panel and utility drop) so that you don't accidentally cause a fire (example, a 30 amp utility feed + 30 amps from your solar panels add up to 60 amps in your 30 amp rated fuse box and it could overheat--not likely to be an issue in your case--but is part of the design consideration).

Of course, the reverse spinning of your utility meter can happen--it really depends on how your particular utility company chooses to account for your power (some have separate meters, some use one meter, some prevent meters from turning backwards, etc.).

-Bill

booboo · April 2007

Re: Solar panels

Thanks, this helps as I need to make sure I have a blank slot in my electrical panel for the breaker for the inverter. I have a 200 AMP panel on the outside of the house and a sub panel inside the house because there was not enough slots for breakers in the exterior box. My guess is the electricians were planning on filling up the exterior box completely.

crewzer · April 2007

Re: Solar panels

I need to make sure I have a blank slot in my electrical panel for the breaker for the inverter.

There are two hot outputs from the 120/240 VAC inverter, so make sure you leave a "double" slot, like that for a double breaker for an A/C, an electric water heater, an electric dryer, or a range.

Regards,
Jim / crewzer

BB. · April 2007

Re: Solar panels

Someone here can help with the exact numbers... But it may matter where you install the inverter breakers... Say, for example your outside box is 200 amps and your internal box is wired with a 100 amp 240 VAC breaker pair and a 100 amp rated box...

If NEC allows 20% (may be 25% or so--don't remember) of the box rating to be used for solar generation--your outside box would allow:

200 amp x 240 VAC * 20%= 9.6 kWatt maximum inverter output

While your inside box would allow:

100 amp x 240 VAC * 20%= 4.8 kWatt maximum inverter output

It is a bit more complicated than that (you are usually only allowed to run a circuit at 80% of rated current, so those numbers above would even be derated by another 0.8 )--As you can see, depending on how everything is wired, you may end up hitting limits on the amount of solar power you can connect to your house depending on where you make the solar grid tie inverter connection.

Try to make sure that the electricians never fill a box completely--it makes it so difficult down the years to add simple little stuff (say a camper connection, pool, workshop, or exterior outlets) if the box is 100% stuffed full. Now is the time (while the walls are not finished and you still have the electricians there) to make sure you have what you want and allow for possible further expansion.

-Bill

4/17 edit by crewzer to change 0.8) to 0.8 )
Thanks Jim! -Bill

lukey · April 2007

Re: Solar panels

I have a buddy of mine that purchases from a dealer out on the eastcoast in New Jersey. He recently purchased Suntech 170W panels for $4.00 a watt and GE 200W panels for $4.20 a watt. I asked him why he purchased the panels in New Jersey and he replied that even with the shipping costs he is still saving money on the panels. He received his panels in perfect condition and is very happy dealing with that company. The only stipulation is that a minimum of 2 panels must be purchased he said and that was because it makes the shipping and handling easier and safer. If any one is interested let me know and I can ask my buddy what the name of the company is. I think I will contact them also even if they are from New Jersey! lol

Luke

BB. · April 2007

Re: Solar panels

Wind-Sun is selling 160 watt SunTech panels at $730 per panel--or $4.50 per watt...

http://store.solar-electric.com/su175wasoelp.html

(just a plug for the folks who kindly provide this forum).

-Bill

System2 · April 2007

Re: Solar panels

You might want to watch what type of panels you buy. Some grid tie
panels produce high voltage and are not suitable for off grid usage

brad

booboo · April 2007

Re: Solar panels

I have a buddy of mine that purchases from a dealer out on the eastcoast in New Jersey. He recently purchased Suntech 170W panels for $4.00 a watt and GE 200W panels for $4.20 a watt. I asked him why he purchased the panels in New Jersey and he replied that even with the shipping costs he is still saving money on the panels. He received his panels in perfect condition and is very happy dealing with that company. The only stipulation is that a minimum of 2 panels must be purchased he said and that was because it makes the shipping and handling easier and safer. If any one is interested let me know and I can ask my buddy what the name of the company is. I think I will contact them also even if they are from New Jersey! lol

I am interested.

booboo · April 2007

Re: Solar panels

The installer I am talking to quoted me $7.00 a watt for sharp NT-175U1 panels. I told him that was too high and I could get panels for $4-4.5 per watt. He told me that the Sharp were really good panels and he suspected that the others would not be as good quality and that is why they are $7 per watt.

Now I think this is BS but is there a quality difference between panels? If so how much of a difference? Would it be smart to pay $7 per watt for sharp over $4.2 per watt for GE?

System2 · April 2007

Re: Solar panels

It's my opinion that the GE and Sharp panels should be about equal in quality. Check the warranty on both. I have 8, GE110 panels and am very happy with them. Someone would have to give me a VERY good reason why I should trade them for Sharp. Would I buy GE again? Yes, in a flash!
Wayne

Solar panels

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