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Questions re: adding/upgrading Solar PV system

Smiles33

New Member
Jan 29, 2021
2
2
California
Hi all, newbie here.

We had SolarCity (now Tesla Energy) install rooftop systems on 2 prior homes in the past 15 years so I'm familiar with the basics of solar PV systems. Our current home has a 12+ year old ground-mounted system the previous owner installed with a different company. I can't recall how many panels it is, but something like 30+ panels (maybe even 48?) and I think rated around 9 KwH.

We live in a rural area where there's no natural gas service and we use electricity for most appliances (there is a propane tank to power the emergency generator since we have frequent outages). We have no need for a PowerWall given the giant generator. We still pay a few thousand dollars per year during the True-Up period even though we're in CA and they get a lot of sun (south-facing). Since the system is so old, it all is connected to one inverter and is far less efficient (e.g., shade from one nearby large oak trees on a few of the panels apparently reduces production on all the subsequent panels down the line). It's also mounted over a giant concrete foundation on a sloped hill next to our home, so it will look terrible if we tear out the old system and just leave the concrete foundation there.

A neighbor mentioned he's putting in a new Tesla energy solar rooftop system and they are far cheaper than the 4 other companies he got bids from. But I only see roof-top mounted systems. We did put in a new roof after we moved in, so it's feasible, but we have a ton of oak trees closer to the house that we do not want to prune mercilessly to get unobstructed sun to the panels.

I don't see a way to get Tesla to do an onsite inspection. The website seems to imply they only look at aerial photos and then write up your order. Yet I want to talk to someone about our options: 1) keep both systems (will they play nicely together?) 2) tear out the ground-mounted system and install a Tesla roof-mounted system (but then we are left with the giant eyesore of a concrete foundation with nothing on it) or 3) find a company that will install a new ground-mounted system. Are there other options?

Thanks in advance.
 

Ampster

Active Member
Oct 5, 2012
1,779
476
Kenwood, California
Are there other options?
I would start with an assessment of your current ground mount by using PV Watts to compare its output to the model. PV Watts won't be able to take into account the effect of shade. Inverters and panels have become more efficient over the years and are much better at dealing with shade than older systems. I am sure there are companies in your area that would be happy to use your existing infrastructure. One issue is whether a new interconnection agreement would be necessary which may add administrative cost to an install.

Have you evaluated different rates using the PG&E rate tool or your Green Button data? If you are not on TOU rate there may be an advantage based on your usage. Some installers offer to do that evaluation as part of the process. The only company that I have had experience with was three years ago was Sunworks and I know they have done projects in different parts of the state.

Additionally, energy conservation measures are often very cost effective and some have tax incentives like a new solar install would have. For example heat pump water heaters are much more efficient than resistive element water heaters. Also they can be scheduled to take advantage of lower times if you are on a TOU rate.
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,435
2,512
Northern California
I don't see a way to get Tesla to do an onsite inspection. The website seems to imply they only look at aerial photos and then write up your order. Yet I want to talk to someone about our options: 1) keep both systems (will they play nicely together?) 2) tear out the ground-mounted system and install a Tesla roof-mounted system (but then we are left with the giant eyesore of a concrete foundation with nothing on it) or 3) find a company that will install a new ground-mounted system. Are there other options?
After I reserved and sent the required photos they did a rough plan. Then sent someone out to go over everything to make sure and to talk to me about various options in what and how they could back up various circuits. And even after that I had to follow up with a few pictures they requested for some pumps.
 

charlesj

Active Member
Oct 22, 2019
1,140
236
Monterey, CA
Hi all, newbie here.

We had SolarCity (now Tesla Energy) install rooftop systems on 2 prior homes in the past 15 years so I'm familiar with the basics of solar PV systems. Our current home has a 12+ year old ground-mounted system the previous owner installed with a different company. I can't recall how many panels it is, but something like 30+ panels (maybe even 48?) and I think rated around 9 KwH.

....
I would suggest you get all the info about your existing system you can, number of panels, Watt size of panels, what did it generate in the past year/s, orientation, number of circuits, if it has micro inverters or several larger inverters someplace, is there is a backup panel although without batteries, system would be down unless there are generators connected.

While the system is 12 years old, it is still generating without a cent of investment from you. Then comes the question of what will the power company approve if you totally replace it or add on to it. Your roof mounting may have shading with all the oak you mentioned near the house. May want to see if there are shadows on south facing roof surfaces especially now when the sun is low on the horizon this time of year.
Also, what will be your usage or what was the usage by the previous owner for the previous year.
 

arnolddeleon

Supporting Member
Jul 21, 2012
799
864
SF Bay Area
If you are willing to commit $100 you can probably get Tesla to come out.

I have a current Tesla order for additional PV. I have two existing PV systems, an 18 year system from a defunct company and 12 year old Solar City system. I added Powerwalls 3 years ago.

Multiple PV system can be made to play with each other pretty easily.

Tesla did a design based on the satellite photos. Then they came out for a site visit to take more detailed measurements and look inside the attic. You can also modify the order after you initially place it.

I've since modified the order to add another Powerwall.
 

BGbreeder

Member
Jun 19, 2020
236
132
Bay Area
I hear you about not wanting to trim trees near your house. It is part of the beauty of living in a rural area.

FWIW: lots of solar companies will decline to build ground mounts because of the complexity of the required engineering for wind and earthquake resistance, and the resulting permitting complexity.

However, you are looking at either an additional solar on the roof, which is cheap compared to a new ground mount, or an upgrade to your ground mount (microinverters, optimizers, or new panels), which is much easier from the permitting side of things. I'm with @charlesj that step one is to figure out what you do have, and how the production is compared to an ideal, and go from there.

If your house is heavily shaded from a solar perspective, your best bet may well be to renovate or extend your ground mount.

Now for a different thought: you don't say where you are in California, but I am guessing that your fire risk is non-zero based on the fact you are in a rural area. Given that, trimming your oaks may be a good call for very different reasons.

All the best,

BG
 
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h2ofun

Active Member
Aug 11, 2020
2,464
423
auburn, ca
I hear you about not wanting to trim trees near your house. It is part of the beauty of living in a rural area.

FWIW: lots of solar companies will decline to build ground mounts because of the complexity of the required engineering for wind and earthquake resistance, and the resulting permitting complexity.

However, you are looking at either an additional solar on the roof, which is cheap compared to a new ground mount, or an upgrade to your ground mount (microinverters, optimizers, or new panels), which is much easier from the permitting side of things. I'm with @charlesj that step one is to figure out what you do have, and how the production is compared to an ideal, and go from there.

If your house is heavily shaded from a solar perspective, your best bet may well be to renovate or extend your ground mount.

Now for a different thought: you don't say where you are in California, but I am guessing that your fire risk is non-zero based on the fact you are in a rural area. Given that, trimming your oaks may be a good call for very different reasons.

All the best,

BG
I know I removed a number of oak trees around my house. Do I miss the "look"? I do NOT miss having to deal with all the leaves around my house, especially on my roof!! It is nice not having the shade on my panels. I love I now have a clear west view across the lake with amazing sunsets. Did I say I do not miss dealing with all the leaves. :) And yep, I am in fire country so I have made my home safer
 

Smiles33

New Member
Jan 29, 2021
2
2
California
Thank you all for your very detailed and helpful replies. It's such an old system that it does not have a monitoring system or an app to monitor it. I have to walk out to the inverter and check to make sure its status light is green once/month and then watch the utility meter to make sure it's going "backward" to confirm the system is producing. This only started after it took more than 6 months to notice the old inverter failed (I handle the bills don't check the utility bill every month since we're on an annual True-Up model). But I can pull old utility bills to see what we generate on an annual basis.

And I think $100 is totally worth the cost to have Tesla come out to evaluate my options (including how to make the existing system play nicely with a new system). Thanks for the reassurance that other homeowners have had multiple systems by different vendors work together. I am uncertain how to enter the data in their calculator since my monthly bills with the PV system vary so widely. I guess I can try to "average" it out rather the use the "outlier" winter or summer bills.

Yes, we have a TOU plan, so I charge my car at night. I will look up PV Watts and see what info (if any) is on the panels themselves once I ask my husband to climb up there to look (we have rattlesnakes and other unpleasant creatures in the hills!). There was no other info left to us by the seller, but I just checked on-line and a permit was pulled in 2008 for an 8.4 KwH ground-mounted solar PV system. It was final'ed, so that's presumably accurate.

We already have a 22 kwH propane-powered generator wired to the house with an automatic transfer switch (especially useful during our regular power outages due to wildfire risks). It's sized large given the extra demand of pumps and gates (i.e., when the power is out, we don't get any water and have to manually open the heavy motorized gates keeping the cows out). I don't think it makes sense to add PowerWalls/batteries until the price comes down more. I assume the only reason to do it now would be to keep us in the Tier 1 rate. It's cheaper to add more panels than to pay for the PowerWalls to store the electricity.

As for the oaks, yes, we live in a wildfire region and all the insurers have already refused to cover us so we're stuck with the state FAIR plan (that's a whole other tangent!). I have a crew come annually to inspect all the oaks on our property for safety and they've already removed the heavy branches that might have led to damage below. We are in the dry California hills, so there's no avoiding wildfire even if I severely pruned the 8-10 trees closest to the house.

Thanks again!
 
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