Ground mount vs roof mount

[stallhorn]

Hello all,

I am looking at about 11,000 - 12,000 KWh per year for my energy needs. My roof faces west (and has probably some shade in the morning), so according to PVWatts, it will take a 10KW system to generate that power. But if I do a ground mount, I can get away with a 7.5 KW system. So I am thinking 24 panels @315w or better would give me that. An installer suggested Canadian Solar, which I don't have a problem with. I also like the ground mount for a number of reasons in addition to placing it facing 180 and perfect pitch for my area (Maryland). I don't have to worry if the 15 year old roof needs work. I can clean it anytime. I can replace modules easily if they break.

Even though I can go with any of the inverters, I like the SolarEdge inverters the best, as the company seems to be innovative and more into technology.

So anyone with experience as to what I should be watching for on ground mount?

Thanks.

[J.P.M.]

Ground mounts cost more. Don't know if the smaller array size will take up the diff. As long as space on ground mount is not an issue, less expensive/Watt panels from a quality mfg. may make sense, but panel cost is not the sole consideration. Check local building codes for setbacks, safety barrier considerations and other things.

[TimeOrMoney]

Tough call. You could go to Ironridge or another mount mfg., run their designer for both ground and roof, and compare costs. Also, don't forget all the trenching, conduit, etc. for ground mount. I was going to do ground until I ran the numbers. But I'm SW exposure, so not a lot of power was lost going to roof.

Also, look at PUC incentives, rules, local codes, etc., as there may be reduced or eliminated incentives or other problems for angles too far from South.

[organic farmer]

My PV array is ground mounted. I have 20 panels. I did it all myself, and it cost me around $2,000.

[diogenes]

I have a 10 kw ground mount, my installer told it will perform better than a roof mount because of better air circulation and consequently panels heat up less

[organic farmer]

Depending on mount design it may be easier to make seasonal adjustments of the panel angle with a ground mount.

[radareclipse]

Depending on what you do and choose, ground mount can cost a little more, or a lot more. But don't let "a lot" scare you. There are advantages that you mentioned in your thoughts that I like also. Iron Ridge has a nice solution but will require a whole lot of holes. Since Maryland really doesn't have a worry about tornado's (although 2 tropical storms in 2011 and 2012 - Irene and Sandy), you don't have to get as crazy as making it 90 plus mph proof which can reduce your cost.

I recently came across another ground mount solution that will cost nearly nothing compared to other routes I have gone. Give this a look and consideration.

http://powerssolarframes.com

[bcroe]

I have started a list, about 19 reasons so far to prefer ground mount. But they may not apply to you. Seems like the
driver for roof mount is the lack of affordable space for a ground mount. Bruce Roe

[stallhorn]

Depending on what you do and choose, ground mount can cost a little more, or a lot more. But don't let "a lot" scare you. There are advantages that you mentioned in your thoughts that I like also. Iron Ridge has a nice solution but will require a whole lot of holes. Since Maryland really doesn't have a worry about tornado's (although 2 tropical storms in 2011 and 2012 - Irene and Sandy), you don't have to get as crazy as making it 90 plus mph proof which can reduce your cost.

I recently came across another ground mount solution that will cost nearly nothing compared to other routes I have gone. Give this a look and consideration.
http://powerssolarframes.com

Thanks for the link to the site. They seem to have a good mount system for a really good price.

I agree it doesn't need to be super strong in Maryland, but it all depends on what the county has to say.

One thing I noticed is hat the maximum angle for the mount from the above site (and also on the one quote I have) is ~25 degrees. PVWatts config gives me the best output numbers at ~35 degree tilt. Does anyone know if there is a reason to mount the panels with a shallower angle? It will probably resist wind better, but I don't know by how much.

I am also considering mounting the panels a bit high and use the space under for a car port. Has anyone done that?

[organic farmer]

Ideally you need at least three angles for solar-panels. Depending on your Latitude, the angle of the sun's path at Summer Solstice gives you the summer angle. The angle to the sun during Winter Solstice gives you the winter angle. And a third angle mid-way between the two extremes for use in Spring and Autumn.

My solar panels use these angles.

Summer - 21.7 degrees from horizontal
Spring / Autumn - 46.7 degrees from horizontal
Winter - 68.5 degrees from horizontal

[J.P.M.]

Thanks for the link to the site. They seem to have a good mount system for a really good price.

I agree it doesn't need to be super strong in Maryland, but it all depends on what the county has to say.

One thing I noticed is hat the maximum angle for the mount from the above site (and also on the one quote I have) is ~25 degrees. PVWatts config gives me the best output numbers at ~35 degree tilt. Does anyone know if there is a reason to mount the panels with a shallower angle? It will probably resist wind better, but I don't know by how much.

I am also considering mounting the panels a bit high and use the space under for a car port. Has anyone done that?

Usually the best fixed angle for a mostly south azimuth is about at the local latitude. +/- a bit. As Organic Farmer, and Bruce note, adjustable tilts, seasonally or more often can garner extra production or make snow clearance easier or perhaps less onerous. That adjustable feature does come at some (perhaps cost justifiable ) extra price and design effort however.

[radareclipse]

In order to do an adjustable, your left primarily with a post type mount in the ground. And they go up in price pretty quick, and it can be huge $ in comparison.
A car port can be done, but that might end up being practically custom. I did a quick look up using a Baltimore zip code and the difference between 25 and 35 degrees on a 10kw system might only be 1%.

[TimeOrMoney]

If you have to fix at one angle, you may want to look at your summer/winter usage vs what PV watts gives you each month for different angles. If summer/winter use is similar, you should pick a steeper angle so that you optimize for winter.

[organic farmer]

Usually the best fixed angle for a mostly south azimuth is about at the local latitude. +/- a bit. As Organic Farmer, and Bruce note, adjustable tilts, seasonally or more often can garner extra production or make snow clearance easier or perhaps less onerous. That adjustable feature does come at some (perhaps cost justifiable ) extra price and design effort however.

Not that much