System Design and Consulting Services?

marks · September 2006

After having conducted a tremendous amount of research into the PV arena, I've come to realize how the small nuances can have a dramatic effect on the performance of a system and its bottom line. The info published by the CEC, SEI and others is extremely helpful, however after thoroughly reviewing this forum, it's apparent and imperative, that a system be thoughtfully engineered.

Being that I'm located in a semi-rural area on the Central Coast in California, there isn't too much competition amongst the PV installation companies. Hence when the numbers are broken down, their combined margin for profit and labor is in excess of 40%. Since the idea is to install a 6-8 kWh system, this margin goes a long way in impacting the return on investment, or increasing the size of the system.

The general parameters of the situation include 1,000 kWh of usage per month, most of which is consumed by pumps for water treatment, irrigation and so forth. The roof is 44' by 24' with cement tile, two of the four vent stacks are within two feet of the perimeter and the other two are within four feet of the edge and can easily be moved. It faces SSE with a pitch of 10:12, I have a manlift with which I can access all parts of the roof. There is another 200 sq. ft. of roof available on a SSW exposure. The 400 amp main panel is located almost directly below the 32 foot roof peak. It seems that 6kW is the trigger point for a two inverter system, thus that marginal increase would be considered in calculating the expense of a larger system. Our latitude is 34.90 degrees, with an average solar radiation value of 5.9.

On the economic side, I've estimated that a 6.5 kWh system will meet 80% of our needs and the remainder will be provided by PG&E at the baseline usage rate. At this time I don't forsee a battery back-up to this grid tied-in system. A gallon of propane is $.50 cheaper than the equivalent electricity, measured at the baseline level of $.12 kWh. Five years ago, while constructing the home, I plumbed both gas and 220v to the water heater and clothes dryer. Also the CA rebate of $2.60 kW will again be reduced this coming January.

Lastly I enjoy being a hands-on type of person, and the skills necessary for the most of installation process is well within my scope. Thus what I'm in search of; is obtaining assistance in the engineering and design portion of this project, does anyone have any ideas???

niel · September 2006

Re: System Design and Consulting Services?

marks,
i see you have indeed come over here to post and i hope those in california can also pipe in on this, but all can pipe in. in actuality there are many that install in california and the west has quite a bit more going for solar installers in general than here in the east. we are catching up slowly though. there isn't anything wrong with self installs, but the laws have to be observed with permits and inspections. you may wish to talk to your local inspectors about their requirements as this can vary from town to town. even if they say there's nothing special you should follow the nec guidelines and maybe even consult a construction company to inspect the roofs you intend to place the pvs onto that the structures themselves can handle the added weights and wind loads presented by and to the pv's installation. if installing portions yourself you can have those in the electrical and construction fields (or even the local inspector) advise you on how to properly do this yourself. much of this is planning and preparation and you did figure that out on your own. the forum here also has alot of reading available for your enlightenment.
as to your system do you roughly have some equipment in mind? as to the mounting it would be better if you were to split the pvs so that half are on the southeast facing roof and the other half on the southwest facing roof so 2 inverters minimumly would be needed regardless of the power produced. the roof pitch you may not want to be a fixed angle for the pvs and there are mounts that can adjust. this is an added expense in having an adjustment but may afford you more power collected over the seasons. a permanent angle of that of your roof could be used though just not as well as if it were to be aimed. one advantage for you is that the sun is slightly lower in the sky when aimed more sw or se. this is much more pronounced in the winter as the sun can go so much closer to the horizon during the winter solstice.
you would also need to feed the power from both roofs to the main box so poles may have to be used if the distance is too great, but underground cabling could also be used. check local laws or go with nec requirements.
i've been up all night so i don't know if i'm leaving anything out at this point, but i want to hear more from you and others here on the forum. we can make recommendations to you as well, but the final decisions are yours for we aren't there and individual tastes in equipment vary.
speaking of something else, i have to ask if you will have any shading problems even in the se and sw as this could determine if a roof will not be utilized if bad enough. when using grid tie, the shading is a severe problem when encountered for it will affect the entire string the shaded pv is in. ideally you should have a perfect view of the sky from the e to the s to the w, but less than perfect is sometimes ok depending on circumstances.

marks · September 2006

Re: System Design and Consulting Services?

Neil,

Your insights and analysis is greatly appreciated, and I'll try to respond to your observations:

The idea of having an adjustable rack system makes good sense. After crunching the numbers I realized there is a 12% gain if the angle is reduced by 15 degrees during the summer, and an additional 2% gain by increasing it in the winter.

Regarding the racking I'm considering the Fast Jack components. Their foot print is smaller than Unirack thus providing for an easier installation. Yes, I do need to check the truss calculations however my assumption is that it is not a limiting factor.

There is no shading on the roof, with the exception of two vent pipes that I could move if necessary.

I've recalculated the numbers, and it would be best to build a system that operates with only one inverter. Either the Fronius IG5100, or Xantrex SW5548. Regarding the PV choice, I'm open to recommendations. Sharp is here locally, I've seen Schott 250w panels for $1,000, however price and convenience are not the deciding factors. Reliability and performance carry more weight.
Intrestingly, the CEC basis its rebate according to different performance test, which generally is 10%-12% lower than the rated wattage.

Regarding the install, I'm confortable with most everything and could bring in an electrician for the final connections. I'd like to be as knowledgable as possible prior to meeting with the Planning Dept. in order to address their concerns.

If anything else comes to mind, please ask. Thus far this has been a wonderful learning experience into a new arena.

Thanks again.

niel · September 2006

Re: System Design and Consulting Services?

i'm glad i'm helping you some here and sent you a pm while you had posted this. that 1 inverter will mean you have limited the system to the 5100watts rating of that 1 inverter. i was thinking 1 inverter per roof, but that depends on exactly how many pvs you'll fit on each roof. these will of course be series strings of pvs to feed in the 275v-500v voltage range of the inverter. if more current and or wattage is wanted the series strings have to be paralleled. this fact could influence the pv you'll buy for your system as you want to fit the most you can within the specs of the inverter. if you say use a string of pvs and they total 3400w then you won't be able to parallel more as it would exceed the 5100w rating of the inverter. you also want to stay away from using different kinds of pvs or mixing and matching unless you really know what you're doing so stay with 1 pv make and model. in the series string voltage it's better to stay more towards the lower voltage end for efficiency, but high enough from the bottom end to allow better operations during cloudy periods or that little extra during sunrise/sunset. in going to the online store for northern arizona wind and sun(naws) you will see the many pvs they carry and each will have their own working voltages(do not use open circuit voltages except to avoid exceeding the maximum inverter voltage) and their physical dimensions. pv voltages do vary widely as 12v pvs you'd need twice as many of the pvs as compared to 24v pvs, but the 24v pvs often will occupy a slightly smaller space than 2 of the 12v pvs due to the extra area for frames.
as to the pvs themselves there is much you'll have to weigh in on. ist there's the cost or price per watt stc. 2nd is the warrantee offered. thin films go 20 years and mono and multi crystalines go about 25 years. 3rd is the tolerance that they guarantee like +/-5%. that means a 100w pv could be at 95w stc and not 100w. on the other hand it may be 105w too, but i doubt it. you may see something like +2/-10%. this is obviously an overated pv, but is legal to say and sell it as a better one because they list the tolerances to cover their butts. 4th would be the reputation and service offered by the manufacturer. i trust you have read wind-sun's responce on i believe it your initial thread. http://www.wind-sun.com/smf/index.php?topic=1796.0
5th would be the efficiency of the pvs as more efficiency means less space needed for mounting and a lesser number of mounts needed.
i hope i'm not forgetting anything here. the more you know the better of an idea of what you want or need will be realized. once you've got it in your head what the system will appear as, put it on paper and see if it works out that way too and keep the paper as you may think of something else you didn't originally factor into your thoughts of the system visuallized.

Roderick · September 2006

Re: System Design and Consulting Services?

It sounds like you've done construction work, before, so this is probably no surprise to you, but the biggest surprise to me was that roofs (rooves?) aren't uniform. It may not be flat, it may not be square, the rafters may not be straight, and they may not even be evenly spaced. It helps if you're re-doing the roof, anyway, and can see exactly where the rafters are, because you will want to anchor your panels to them in some way.

I put up our panels on the assumption that the rafters would all be evenly spaced, and now, it looks like crap, all unevenly spaced. Works fine, though. If I had just mounted everything in one or two very long rows horizontally, a wealth of sins would have been covered, and the whole thing would have looked much nicer. However, it would be a bear to change the angle of such a large structure, and if you wanted to adjust the angle for the seasons.

Professional installers refused to design a system with adjustable angle, saying it would be impossible to give a warranty on a system that the user moved all the time, flexing the wires. I don't know if they were just being lazy, but I can also see a point about an array that isn't parallel to the roof being much more vulnerable to wind.

One final tip is to check the specs of everything you buy, even if it's sold together as a "kit". The kit I bought came with no instructions, whatsoever, not even a topology (1 string of 18 vs 2 strings of 9). The included materials suggested that all the panels should be wired in series (only a single MC patch cord included), but that would have exceeded the maximum input voltage of the inverter at cold. I called the seller, and they said oops, we'll send you another cord so you can wire two strings of 9. I also found out too late that the wire they supplied for bringing power down from the roof was THHN/THWN rated #10, which would have enough ampacity (current carrying capability) in dry conditions, but not wet. The wire was rated for 90 C dry / 75 C wet, and conduit is considered a wet location, since it could fill with water. The inspector called me on it, and I will have to pull new wire through the conduit. The wire supplied with the kit would have been fine if the panels had all been in series, giving just half the amperage. I would suggest that any wire you put in conduit be THWN-2 rated. This insulation rating is hard to get at Home Depot in gauges 10 and smaller, but easy to find in 8 and larger. You could, of course, go to an electrical distributor or solar store and get THWN-2, or even USE-2, in #10, but it would cost more.

If you do it yourself, DO insist that you get a plan review from your jurisdiction, if they offer it. They will put a stamp of approval on your plans, which will save you time at inspection, and give you some leverage, if some small thing is found wrong. I was surprised to find that in my area, there are enough solar installations to have one inspector that has a lot of experience with it, who could have quickly pointed out flaws in my design at plan review. Unfortunately, I didn't get that guy, and the person who looked at my plans was only interested in size and weight.

marks · September 2006

Re: System Design and Consulting Services?

Thanks again for your insights, and in the past few days things have really come together. I've rechecked the numbers, and the most efficient sized system is a 6kW system. It's within the budget, and provides for the greatest return on investment as the remainder of the usage would be within the baseline rate. SMA has a fantastic site for doing the calcs and so forth, it and others were very enlightening. I have no intention of mixing equipment, or doing anything out of the ordinary.

Your points are well taken, with respect to equipment configuration, wire type and usage, and the roof's structural components. Since I was active in the framing of the home, I don't expect too many surprises. After having just reviewed the CEC docs once again things are making more sense, and the electrical schematics seem self explanatory. Since all indications for this project are positive, I plan to enroll in a two day Basic Residential Installation Class that is sponsored by Sharp Industries next month in So. Cal. It's a 200 mile drive and $400, however it should be time well spent. In the meantime, I'll focus the research and discussions with the industry and planning officials. I'll keep you guys posted as things evolve.

System Design and Consulting Services?

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