Solar panel placement.

[Dmitry]

I'm looking into option of getting solar panels since tax break is still going on and Im interested in improving my property in a green way.
The house roof is relatively flat gable, but oriented west/east. I have 3,5 acres and there is some land I can give up for panels. How far panels can be installed from the house? and does it affect performance if it's further from the house?.

 

[Dmitry]

Here is snap shot of the map, , it's not exactly west / east orientation , may be its ok to install it on a roof . What do you think ?

 

[Dmitry]

Here is bird view

 

[Where2]

How far panels can be installed from the house? and does it affect performance if it's further from the house?.

There are online wire voltage drop calculators available. Use 240V, toss a 50A load on it (12kW system), and don't forget to use the total wire length, not just one direction out to the location from your meter. Aim for a voltage drop under 3%, and weigh the added expense of upsizing the wire one additional gauge versus 25 years of heating wire for no benefit.

 

[jebatty]

A good source would be your solar system designer and electrician. We have the 50A PV system and relied upon the solar design consultant and the electrician to install an appropriate wire size for the 220' underground run from our ground mount system to the meters on the house. Our system also has microinverters and they report their total output at the panels, and we have a production meter at the house. The production meter reports 99.1% of the watts that the microinverters report, so I suppose that translates to a 0.9% power loss.

Solar designers have a globe-like device they can place at the proposed panel location and it will show likely shading from trees and other objects. Shading on a string inverter panel array affects the whole string and can materially reduce production. Shading on a microinverter array only affects the panels being shaded and can result in materially greater production.

You can do your own estimates of shading potential by determining the sun position at various times of the year and then using some geometry to determine shading from distant trees and objects. This website shows the sun position at various times of the year for a location your insert.
http://suncalc.net/#/25.7617,-80.1918,12/2013.12.29/20:12

This website shows the sun zenith (height above the horizon) and other sun location info at various times of the year for the location you insert.
http://www.solartopo.com/solar-orbit.htm

You can then use this website to determine how far your panels need to be from various trees/objects to be free of shading based on the sun zenith and your panel tilt.
http://www.cleavebooks.co.uk/scol/calrtri.htm

I wish you success on your PV installation.

 

[5654684]

You need to determine the cost/benefit on each approach:

Roof solar: less cost on racking, more shading in your location, probably microinverters if feasible

Ground mounted solar: Higher costs with the mounts and wiring, still need to do solar analysis.

PVWatts is a great tool, especially with your orientation.

How many watts are you looking at?

 

[DBoon]

My 5.3kW installation is pretty similar to jebatty's (before his upgrade) - but he used microinverters and I used a string inverter with two parallel lines of 300V. Higher voltage = less current (for given power rating) and less resistive loss in the cable and ability to use a smaller diameter (and less expensive) copper conductor for a long run (mine is also about 250 feet). Performance is not really impacted either way, you just pay more for the longer cable run.

To answer your second question, I think the premium is about $1 to $1.50 per watt of installed DC capacity for a ground mount located ~250 feet away. If your roof is a non-ideal east/west, then you may come out roughly even since you will get less production out of an east or west facing array and will therefore have to upsize it and pay the premium for more capacity.

 

[peakbagger]

If you go pole mount, you would most likely have the inverter indoors and the wire run would be at a higher voltage so the wire loss is lower.

The bigger issues are the difference in performance and local incentives. You can use PVWATTS to model two fixed roof mounted arrays versus one ground mount fairly quickly. While you are at it, you may want to look into modeling the ground mounts for seasonal tilt. If your roofs are fairly shallow, winter snow is not modeled by PV watts and can reduce your output.

Many incentive programs are based on nameplate watts of panels installed while some incentives are production based (feed in tariffs). With production based you generally want the array that puts out the maximum power and you may end up with a tracked pole mount.

 

[semipro]

The ability to permanently or seasonally adjust the angle of a ground mount installation may offset any line losses you have. Many roof panels are set at the same angle of the roof whether optimal or not.
A few other advantages of ground-mounted arrays that attract me:
- You can more easily clean the panels of dirt of snow
- You can shade your house with trees for summer cooling and not affect the panels
- Your roof can be replaced/repaired without removing the panels
- Roof access is improved should your house catches on fire. Through roof access complaints by firefighters about PV equipped houses are rising.

 

[woodgeek]

If pole mounted at an adjustable angle....you can set the angle in winter such that they will shed snow. Adjusting the angle 2x a year will be easier than cleaning them off many times (or just losing the power).

 

[jebatty]

I understand the advantages of adjustable pole mount, and I can see how this would work for a small array. But for a large array, this could be difficult and involve multiple poles, and then there would seem to be an issue of the poles shading each other, especially in the early sunlit morning and later sunlit afternoon.

 

[begreen]

We've got 10 panels on our pole mount. I thought it was going to be a bear to rotate south westerly after winter, but it turned out to not be a big deal. I can do it by myself. Haven't changed the angle yet, but then again we don't get a lot of snow. The good thing is that it's 10 ft off the ground and is not ever going to get buried in a snow drift.

 

[tmarch]

Assuming you get snow I would defiantly go with a ground mount of some sort. Pole mounts are simple and less expensive, but more difficult to wire than a standard ground mount.

 

[peakbagger]

I spent 10 minutes yesterday at lunch changing my pole mount angle. Five of them were walking back and forth for hardware and a wrench. I have another wall mounted array, that take about 20 minutes as I need a hydraulic jack and a pole to lift it up. I could install permanent jacks but have been doing it 4 times a year for 12 years with the current set up.

I don't see much difficulty wiring a pole mount, I have disconnect mounted on the pole and flex cable running the area under the panels. Not very difficult. The biggest limitation is large pole mounts tend to be sails, the VT tracking pole mount has a anemometer and goes into a park mode when the wind get too high. I just have two sway braces to the lower corners of my array that I hook up in the winter and then leave one in place during the rest of the year.