Ground mount vs Roof mount?

[peakbagger]

IMO, to a DIYer a ground mount is a lot easier to DIY. If you do not value your time, then DIYing a ground mount can offset paying someone to do a roof mount. Most people are very uncomfortable about working on roofs, some arent (like myself). If you are paying for either option, no way will a ground mount cost less. Panels are relatively cheap and if you have room on the roof a couple of extra panels can make up for less-than-optimal orientation now that roof mounted systems have to have panel level optimization. If you are in snow zone, a ground mount properly designed is lot easier to keep the panels clean. I am a fan of adjustable tilt angle which boost year-round output but is more complex. I am also an engineer and a DIYer so I may have skills you do not have. I have installed three arrays at my home over the years, One small wall mount, one pole mounted ground mount and one roof mount. In all cases I did the install completely solo with the exception of digging a hole and trench. I am in no rush when I do it and think out the work in advance and this included lifting the panels up on a second floor roof solo. I am planning a future array for new home and expect it will be ground mount DIY.

Generally, in snow areas having to put a fence around a ground mount is not an issue as the wiring behind the panels in "inaccessible" due to elevation. Unless the AHJ is going above and beyond code, and requiring a fence specifically, its not that difficult to install hardware cloth behind the panels in areas where wiring is exposed.

There is a downside to a ground mount and that is foreign objects tend to be thrown inadvertently at panels located near the ground, potentially damaging them. Could be from kids playing, lawnmowers or snowblowers. The upside is design an array right and they can be a nice shady area. There are some slick designs out there of arrays integrated into pergola type structures and garages. In most cases these are also DIYs.

[bcroe]

I have a list of 52 reasons to prefer a ground mount, but lower cost
is not one of them. The ground mount will get the most performance
by allowing optimum orientation and snow removal. Here I get a lot
more out of my inverters by using strings in parallel facing east and
west, but this needs to have an angle generally steeper than roofs.

Bruce Roe

[J.P.M.]

1.) Have you figured out what your current annual kWh load is ?
2.) Have you estimated what your furure annual load(s) might be ?
3.) Have you determined how much of your current and future electrical load you want to offset with a PV system ?
4.) Have you done your own preliminary sizing yet using PVWatts ?
5.) If so, have you run the models for the roof orientations and for an optimally oriented ground mount ?
6.) Do you have net metering from your power provider ?
7.) Have you checked local building codes etc. yet ?
8.) How many vendors have you contacted so far ?
9.) How much do you know about solar energy and PV ?

Ground mounts are more expensive than roof mounts. How much ? hard to say. It depends on your application, how much you know about PV and how good your negotiating skills are - among other things. But the same can be said about roof mounts.

However, ground mounts offer advantages in siting, accessibility for servicing and cleaning that roof mounts don't have. But, they also may require more hoop jumping when it comes to your building dept. Be prepared to maybe put a fence around it among other requirements. On the other hand, a ground mount may not need rapid shutdown capabilities. Also, if shade free (and given the better placement/orientation options a ground mount offers, it ought to be), a ground mount can make better use of string inverters which make for an inherently more reliable system (fewer parts to fail) and, because string inverter systems are usually less expensive than micros or optimizer systems, they can slightly mitigate the added cost of a ground mount that uses optimizers or micros.

Depending on shading and orientation of your roof areas, and the suitability of a proposed area for a ground mount, the advantages of a ground mount may make up for some of the extra cost.

Also, if you haven't done so already, I'd check with your local building dept. for what they require for PV in general. Do not treat them as an afterthought. If building permits are required, they can be your best friend if you involve them or your worst enemy if you ignore them.

As for roofs, That's a tough call. If you feel a new roof under a rooftop array is in your best interest, that would seem to me to make a ground mount a better choice.
How long to you expect to keep the house ?

You state all the vendors you've contacted are proposing a roof mount. That may be because most arrays are roof mounted so vendors assume that's what you want.
Do the vendors you contacted know you might be interested in a ground mount ?

Bottom line: If it was me, I'd first get more educated and then do a ground mount, but I'd get more quotes from better vendors.

At this time and place, your likely lack of knowledge about PV is your worst enemy. If you haven't done so already, get and read a copy of "Solar Power Your Home for Dummies". Not a perfect tome, but a cheap investment that pays big dividends. Customer ignorance is the red meat vendors thrive on.

Then, set your project goals, get your current and future loads, do your preliminary sizing with PVWatts, figure out whether you want a ground or roof mount (or PV at all for that matter) before you get more quotes from local vendors who are also established electrical contractors who will be around in the future, and will do a ground mount if that's what you decide is the best fit for your project goals.

[vnatale]

I am looking at a solar installation of somewhere between 6 and 7 kW.

All vendors are proposing a roof mount.

However, my house is almost 100% un-ideally situated with a west / east orientation.

The proposals are to put it on the east side because of no trees blocking like there would be on the west side. However, I think the sun efficiency is 78% on that east side (slight tilt) as opposed to 100% if facing south.

So thinking about a ground mount on my property which would face straight south.

I'd need about 20% less panels to do the same electricity production with a ground mount than a roof mount? That could be an initial savings of 20% with a ground mount?

But then I'm reading that ground mounts are more expensive because you need to build some kind of foundation to put them on, requires more labor to do so, and you have to dig a trench at least 18" deep to get to my electrical panel?

Does all of that outweigh the initial 20% savings I reference above so that to that same 6 or 7 kW it'd cost more for a ground mount installation than the roof situation?

Let's say the cost of the roof installation before credits is going to be about $25,000.

The other factor here is that I had my entire roof done in December 2005 with 30 year shingles. Therefore at this point they could go another 13 years. However, no solar company wants to put an installation on a 17 year old roof. If I went ahead and did have them install it on the existing roof somewhere in the life of the installation I am going to have to pay to have the installation taken down and re-installed at the time when I do have to re-roof.

It pained me to no end to have to rip off a perfectly good roof and throw away somewhere between 8-13 years of remaining life. But it seemed like I should do it now so that the life of the roof matches the life of the installation and I avoid the future cost of taking down / putting back up the installation.

I decided I'd only have the east side of the roof done. Cost? $5,400. I'd not be having this cost absent the decision to go solar. Therefore I'm assigning part of that $5,400 to the cost of going solar (and not eligible for the 30% federal tax credit). I have to assign at least 1/3 - $1,800 - as an additional necessary cost to go solar. I'm looking at the rest of the cost as giving me an extended life of the roof.

So the only answer I'm looking for here is if you think it would cost me more or less for a ground mount than what I'm looking for for a roof mount.

Use $25,000 for the roof mount plus the $1,800 for the roof (not eligible for the 30% federal credit).

Could a ground mount come in at less than that taking into account the reduced panels necessary for the same production but with the other associated costs for a ground mount that you don't have with a roof mount (plus not having any additional costs related to the roof)?