Maximizing south orientation - does that make a lot of sense?

**J.P.M.** · 05-18-2020, 12:34 AM

To your last paragraph: If you haven't done so already:

1.) Download a slightly dated but free PDF of : "Solar Power Your Home for Dummies", or buy an updated version for $ 20 or so at bookstores/Amazon.
2.) Download/get familiar w/ something called PVWatts. It's a PV design model from NREL. User friendly and an easy learning curve. Read all the help screens a couple of times, use 10 % system losses and get the inputs close to reality and make a few runs. GIGO applies.
3.) Call your POCO and find all that's required for NEM. Do it now and avoid surprises.

Don't cram too many panels on a roof. Think long term: How will you get at a panel in the middle of an array ? Besides, building and fire codes probably won't let you pack things as tight as you might at first want.
Get your annual load in kWh from the POCO.
With net metering, PV systems are usually sized to your annual load in kWh, not instantaneous loads in W.
Adding a 2d PV system is possible, but may not be practical. Consider future loads carefully and realistically and consider maybe adding some capacity at initial install. Just be more sure of future needs be careful of the economics.
If a relatively low slope for the E-W roofs like the 20 deg. south slope, You may find PVWatts might indicate an off south penalty that's not quite as severe as you might think. Also, between east and west slopes, because of T.O.U (Time of Use) pricing, west facing panels will probably be more cost effective than east facing panels. However, and in spite of what you may think or hear, south facing panels will probably be more cost effective than west facing panels. It gets a bit complicated. Read up and get preliminary sizing, then come back and get details after you get more informed.

You seem to have some idea what you're writing about, but not much. Get the book, get familiar with the model, study up and then come back here and ask informed questions to fill in knowledge gaps your education creates.

Do all the above before you call any vendors. Your education will help avoid getting taken to the cleaners by vendors who prey on customer's solar ignorance. Do the homework and you'll wind up with a safer, more fit for purpose and more cost effective system for the effort.

Welcome to the neighborhood.

**Mike90250** · 05-18-2020, 02:20 AM

If you have lots of high power gear running, you might need a main panel upgrade too, to handle all the solar you are going to throw at it.

There is something to be said for a west biased array, unless you are in a area with afternoon marine layer like El Segundo or Redondo Beach. If your inverter has 2 inputs, one can be fed from a south facing array, other from a west facing.

Batteries are a BIG expense, with little payback in a major city. You would likely be better off with a 10Kw generator, propane or diesel. Gasoline goes bad too quickly, unless you are attentive and rotate it. Big earthquake - loose power, you are likely to loose natural gas pipeline too = no generator.

**drivefast** · 05-18-2020, 11:44 AM

Thank you guys, that's exactly the kind of guidance i was looking for. Except for the "for dummies" book, i have pretty much done all the rest. I used the NREL tool for a quick calculation, and bookmarked it - i'm pretty sure it will see more use pretty soon. I know i will have to call and ask my questions to the utilities, and city, and so on: that part i hate the most, and i try to be all prepared so i minimize the time spent with them. In terms of planning for the future - frankly, i don't even know what other major consumer i could add in the house anymore. If anything, things i may need to replace in the future, like HVAC, will end up consuming less. I'm not considering pushing solar power back into the grid, or prep for outages and long downtimes - there's nothing so critical in our house that can not be sourced from a 2000VA UPS. If anything, these last few weeks taught our family we *can* live humble with whatever disasters life would throw at us.

In terms of servicing the installation, there would be no panels "in the middle" - i only have room for 2 rows. There's also not much reason to "save" space on top of the house, i would start with maximizing the part with best effectiveness. What else is ever gonna be there anyway?... The only thing i can think of would be more efficient panels in the future.

Our area doesn't suffer from morning marine layer, and gets really hot during the summer. I do have some trees around, but i wouldn't mess with them because their shade is also good for reducing the roof temp. In terms of electrical panels, i have a 200A for the house, and an extra 100A for the garage (the one i was telling you is awaiting for the inspection). I'm pretty handy myself, i didn't need to call a contractor in years, and i'm an electrical engineer, but only did software my whole life. I will for sure call a couple of friends, both electricians, for most of the installation part, but for the project - i would have to build it myself. Kinda hard these days to get people to sit around the table and discuss a project. Quotes i asked for in the past, from local vendors, were more than 3x the price of the most expensive parts, and none of them was able to tell me what they will use or how they will do it. I think only one of them came to see the house. They were asking for my electric bill, and poof! they would tell me the total price in 5 minutes

I'm off to figure out from the permitters about how many panels i can install on my south-facing roof. That seems to be the first thing i will have to decide. I'm gonna call it "a high density installation", maybe they will be more lenient with a catch-phrase

Thanks again everyone, and i would still appreciate further comments. I'll keep this going with information i get, that may be applicable for others.

**J.P.M.** · 05-18-2020, 12:47 PM

Originally posted by drivefast

Thank you guys, that's exactly the kind of guidance i was looking for. Except for the "for dummies" book, i have pretty much done all the rest. I used the NREL tool for a quick calculation, and bookmarked it - i'm pretty sure it will see more use pretty soon. I know i will have to call and ask my questions to the utilities, and city, and so on: that part i hate the most, and i try to be all prepared so i minimize the time spent with them. In terms of planning for the future - frankly, i don't even know what other major consumer i could add in the house anymore. If anything, things i may need to replace in the future, like HVAC, will end up consuming less. I'm not considering pushing solar power back into the grid, or prep for outages and long downtimes - there's nothing so critical in our house that can not be sourced from a 2000VA UPS. If anything, these last few weeks taught our family we *can* live humble with whatever disasters life would throw at us.

In terms of servicing the installation, there would be no panels "in the middle" - i only have room for 2 rows. There's also not much reason to "save" space on top of the house, i would start with maximizing the part with best effectiveness. What else is ever gonna be there anyway?... The only thing i can think of would be more efficient panels in the future.

Our area doesn't suffer from morning marine layer, and gets really hot during the summer. I do have some trees around, but i wouldn't mess with them because their shade is also good for reducing the roof temp. In terms of electrical panels, i have a 200A for the house, and an extra 100A for the garage (the one i was telling you is awaiting for the inspection). I'm pretty handy myself, i didn't need to call a contractor in years, and i'm an electrical engineer, but only did software my whole life. I will for sure call a couple of friends, both electricians, for most of the installation part, but for the project - i would have to build it myself. Kinda hard these days to get people to sit around the table and discuss a project. Quotes i asked for in the past, from local vendors, were more than 3x the price of the most expensive parts, and none of them was able to tell me what they will use or how they will do it. I think only one of them came to see the house. They were asking for my electric bill, and poof! they would tell me the total price in 5 minutes

I'm off to figure out from the permitters about how many panels i can install on my south-facing roof. That seems to be the first thing i will have to decide. I'm gonna call it "a high density installation", maybe they will be more lenient with a catch-phrase

Thanks again everyone, and i would still appreciate further comments. I'll keep this going with information i get, that may be applicable for others.

On roof panel loading density: Most CA jurisdictions require set backs from roof ridge of 3 ft. as well as side setbacks for at least one side of an array. Like it or not, that's for whatever else will be up there anyway (i.e., fire fighters and first responders). Pack it as you will, but add/think serviceability to your design plans.

My guess is you won't get too much of an advantage with the powers that be calling it a high density installation.

I'd also respectfully suggest in your search for getting as much annual output/area from a roof as possible, that you not get sucked into the "most efficient panel" game vendors play. Higher eff. panels - ones with greater output per sq. area - do indeed wring more power out of a m^2 of panel/roof area, but do so at an increase in installed cost/STC W that usually exceeds the life cycle savings brought about by the increased output.

Plan for future needs realistically. Batteries are possible, but maybe not ready for prime time just yet. Besides, things are in developmentally early stages and storage prices will drop as events develop. also, 5 years ago a lot of folks said they'd be getting an EV within 5 yrs. What %age of currently registered vehicles in CA are EV's ? Just sayin'.

**bcroe** · 05-18-2020, 01:48 PM

You need to check on possible efficiency upgrades on your HVAC and water heating equipment.
The state-of-the-art mini split heat pumps swapped in here cut those loads by more than half.
good luck, Bruce Roe

**drivefast** · 05-18-2020, 02:22 PM

Well, i'm pretty sure there will be a difference between what i wish to have, and what i will end up with

and i dont think someone would close an eye on the building codes because of a wise-ass definition, that was just a joke. Three feet from the ridge is quite a bit of real estate though, it appears i'm gonna have to do the math and the geometry again.

I was actually surprised to find 400W panels for only 15% more $ than the 320W, for a 25% gain, with about 3sqft extra. Since my first concern was to optimize space, it seemed to make sense. I'm gonna continue to keep an eye on the balance of power - efficiency - square-footage - price while recalculating, and see what comes up optimal. But recalibrating the whole system would for sure throw me into panels on top of my detached garage, with some sort of bringing over the power lines over to the house panel, giving up the idea into driving everything with a single inverter and probably getting into microinverters, and so on. Those were the kind of costs i was trying to avoid by cramming everything, er, i mean increase the density and efficiency

on the best roof side i have. We'll see.

It's mind-boggling for me that in 2020 there is no intelligent switch, or per-consumer circuit source selector, that would optimize the cost based on each source availability and price. Your solar panels are giving you 4.5kW right now? use them to power up everything. Your AC kicks in and now you need 5kW? get a few circuits from the house moved over to the grid feed. Too much solar energy produced? fill up the battery, or if it's full, pump it back into the network. Is it 7PM, or whatever time the TOU kicks in? switch over everything to the TOU feed. This would probably require relay switching and some short term batteries to make everything smooth, but hey, it's feasible, and it's the holy grail of what everyone's discussing here.

**bob-n** · 05-18-2020, 04:19 PM

Yes, a turn-key purchase optimizer would be very useful. One thing that makes such an optimizer difficult is that the market is constantly in flux and vendors are shy to publish their lowest price. Some people have had luck getting lower prices by showing vendor #2 a quote from vendor #1.

Another thing that confounds decisions is that you can't predict the future. You don't know what power will cost 5 years out and don't know net-metering terms 5 years out, but you can be confident that it will be different than today.

In my opinion, you're optimizing a system with a relatively broad peak. In other words, if you don't make the optimum decision, you'll still be close to optimum. You may find a panel putting out 350 watts and another putting out 400 watts. You won't be considering panels putting out 250 watts or 500 watts. Make some assumptions, do the math, and see if it makes sense. If so, then optimize at the exact moment that you're planning to buy.

I'm not recommending for or against any vendor, but for your first estimate, you will appreciate the open-pricing policy at the website of www.altestore.com Other vendors are harder to deal with. If it doesn't make sense with their pricing, you know to stop.

Maximizing south orientation - does that make a lot of sense?

Maximizing south orientation - does that make a lot of sense?

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