Help with large solar installation estimate

One of the members on this forum has worked with a number of Tesla owners: Danny Wang <[email protected]>
He is located in Irvine

I have been so impressed by the knowledge pool on TMC, I'll preface my guesstimate with "I know someone will give a much more detailed response than me" so wait for better expertise than mine.

It has been 20 years since I did off grid power, but today I think $1.50* per watt installed should cover it. At $120K that would be an 80 kW array. In your location (zone 2 at least) count on 5.5 hours average yearly. So 5.5 X 80kW X 0.12 X 365 = $19272 per year production @ $0.12 per kWhr.

* I base this on current solar going for $1 per watt. Last panels I bought 20 years ago were $5 per watt, so with utility rates at $0.12 kWhr it was only viable for remote, off grid homes. Now with the large drop in prices, explains Elon's involvement in solar.

Deckofficer took a reasonable initial approach, but I'm not sure I understand the direction he went with the numbers overall.

If your goal is to match your annual electricity generation, you start with the 5.5 hours average insolation for the region and your average daily use - assuming it moves smoothly from the 166 to the 199 and back, it seems like you need to average about 180 kWh/day. This will produce excess power in april, may, and june, and be short in december and january - but if the power company net meters they'll carry it across.

To average 180 kWh per day in a 5.5 hour area, you need about 33 kW of AC nameplate rating (maximum power production after inverting and whatever losses the orientation induces.)

When I bought my panels a little over three years ago, I paid a little over $4 per watt installed, with the fancy microinverters.
Prices have continued to fall since then - I was thinking you'd be paying more like $2 per watt than his $1.5 - but even then, I'm only talking about $66k to produce as much power as you currently consume. There's also an unlimited 30% of installed cost federal tax credit for individuals that put in solar - I'm not sure if your HOA could benefit from it in some fashion or not.

At ~$1000 per month you aren't paying, you'd make the initial cost back in ~5 years assuming net metering and no rebates.
Walter

You might want to build excess capacity to cover the 10 HPWC Tesla Chargers that you could install for the condo community.....

RubberToe said:

Saghost,
Looks like we crossed in our last two posts. Wow, a 5 year payback time. Almost has me wondering why every condo building in Pasadena isn't covered with solar panels already? Am I missing something?

RT

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Solar prices have only been that low very recently, and it takes time for folks to get around to it. A lot of people probably looked a solar a decade ago and still have those prices and paybacks in their heads.

Also note that this analysis assumes net metering - something that has been common for solar for a long time, but the utilities have been trying to change lately - they end up having to carry a lot of spinning capacity to handle potential changes but can't charge solar customers for it or the infrastructure that you're using (though you're also reducing peak loads and helping them need less infrastructure overall.)

It'll be interesting to see how this evolves - one likely answer which Tesla is betting on is distributed battery storage - one of their 400 kWh pallets at your local transformer would greatly reduce the fluctuation in grid demand, and provide some backup capacity for customers in an outage situation as a side benefit (and if they keep power from the battery to your panels, your panels can keep the neighborhood running for a while longer, too.)

Another piece of it is likely some sort of billing change - in Arizona they tried adding a fixed fee to all solar customers and it was denied by voters. Some additional billing will likely happen eventually - possibly in the form of a demand charge (an item on the bill based on the number of kW used in the highest fifteen minutes of the billing period) or some sort of capacity charge (something I've never seen before, but it would be basically charging for how much of a "battery" they are being for you - it'd aggregate (average? Highest night?) the daily swings in your meter, so that someone who used five kW at night and put them back in the day got one fee, and someone who used fifty at night and returned them in the day would pay 10x as much.)

Of course, if the new fees they eventually decide on become too high, then complexes like yours will just buy their own battery packs from Tesla - if you believe the $100/kWh price some folks have tossed about, one of those pallets would only cost you another $40k now or in the near future, and would let you live almost independent of the grid (but we sized the panels for average use - you'd come up short in the winter months unless you added panels.) With prices of panels and batteries low and falling, it seems like cheap clean power is likely in the future.

More storage and more interconnection is the key to making renewable energy work - but that costs money, which the utility isn't getting from net metered customers, so the current model is unsustainable in the long term as the percentage of solar customers increases - but right now I don't think you're missing anything as the current laws and rates read. Get your panels paid for while the getting is good.
Walter

How much roof or ground space do you have? Building a large solar array requires .. large areas to put the panels...

I just had a 3kw system installed last December. A price of $1.50/watt installed sounds too good to be true. Figuring panels at $1/watt and microinverters about half that, leaves almost no room for racking, roofing work, electrical work, etc. A more likely figure is probably closer to $4/watt range installed. Then if you qualify for the 30% tax rebate, it gets under $3/watt.

How much of your bill is Tier 1&2 vs Tiers 3&4? When sizing the system, it really pays to size big enough to eliminate the higher tier usage to get best ROI. After that, the ROI is much longer.

And yes, net metering is a great thing.

Cosmacelf said:

How much roof or ground space do you have? Building a large solar array requires .. large areas to put the panels...

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This is true. It looks like current generation cheap panels are getting almost 15 W DC per square foot:

http://www.wholesalesolar.com/products.folder/module-folder/Astronergy/CHSM6610P-260.html

Allowing for inversion losses and siting issues, I'll assume 12 W AC per square foot - meaning you'd need something on the order of 2800 square feet covered by solar panels.

(I don't know anything about your building's layout - for traditional sloped roofs they aren't supposed to be near the very top or bottom of the roof, and they usually come in ~40"x~65" panels like the one I linked, so you might need considerably more south facing roof space than that to install the panels (ground/post mounted systems are also options)
Walter

One other thing: In theory, south facing modules may generate the most electricity. But given Time-of-Use metering, you generate more valuable electricity during prime time, then buy it back at night at a lower rate. In my case (E7 TOU) prime time is noon-6 pm, so west facing modules might actually generate a better return dollar-wise. I have a mix of south and west facing modules with microinverters to optimize each module. One can clearly see on the web monitoring software the inverters on the south facing modules turning on and off earlier than the west facing ones. If/when I add on to the sytem it will be on the west facing portion of the roof.

This is the "industry standard" estimator for how much you will generate. Factors in your location. Better to show you where to fish than send you a fish, as you will be able to point to a real source (rather than some guy on the forum) when you pitch to your board.

PVWATTS

And, here's a good article on per watt installed prices. There are many sources, but make sure you only look at 2014 studies or reports. There's lots of old stuff that shows up on google.

It really does not take long to become conversant on this stuff, good luck.

PS, The two major components are panels and inverters. There are many different capacity of panels... generally the higher power ones cost more, but also generate more (in same space). Be realistic about how many you can fit on your roof... it would probably make sense to have a pro take a look before you get to tied up in numbers. There are two options for inverters (that is, DC to AC conversion). One is string inverters... large boxes, usually inside building, that handle a string of panels. The other is micro-inverters, which attach to back of each panel. There are a number of advantages to micro inverters: there's less loss between the panel and your use, they allow monitoring of generation by panel (which is useful for troubleshooting), and they allow you to expand the system easily (even to the point of using different types/capacity panels in future). They cost a bit more, but I personally would recommend.

See RT, I told you wiser minds would drop by, listen to them, not me, my knowledge is dated 20 years and off grid. Some of my old installs were rather interesting and a learning curve.

tomas said:

And, here's a good article on per watt installed prices. There are many sources, but make sure you only look at 2014 studies or reports. There's lots of old stuff that shows up on google.

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Huh. My installation was cheaper than the 2012 listing in 2011, despite the installer specifying US made panels and the more expensive micro-inverters. I guess I was luckier than I realized.
Walter

Saghost said:

Huh. My installation was cheaper than the 2012 listing in 2011, despite the installer specifying US made panels and the more expensive micro-inverters. I guess I was luckier than I realized.
Walter

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A lot depends on the specific site challenges. Electrical Panel upgrades, how long the thick cable runs need to be, how awkward the roof is, etc.

So it is a flat/level roof? Then you can use the entire roof. The racking will be tilted to optimize collection.

Also, since you say the primary electric load is hallway lighting, changing to LED was a great idea. The difference in efficacy/power usage over incandescent can be a factor of 7 or more. Are the monthly power costs you quoted earlier before or after switching the lighting? If before, you should look at the usage afterwards - since that will drive the number of PV modules you need downwards.

Net metering is a function of the power company, not the city. Once the system is installed and the city building inspector signs off on it, there is a simple application process to e-file at the utility company. (Your solar installer will help you do this.) In my case (PG&E) it took about two weeks for them to approve and enable net metering. Up until that time, the power usage would floor at zero kwh used. After they enabled it, the meter can run backwards. There is also a reconciling process where if you generate more than you use on some days/months it will balance out other days/months of lower production.

Solar hot water heating for the pool is a great idea too.

I skimmed this, but don't see any mention of depreciation and maintenance expense impacting payback. A hurdle for single family residences (not the OP's case, of course) in my mind is mobility = why pay upfront cost of installation if I may not be here. Are people seeing part of installation cost reflected in higher selling prices to minimize that concern?

CHGolferJim said:

I skimmed this, but don't see any mention of depreciation and maintenance expense impacting payback. A hurdle for single family residences (not the OP's case, of course) in my mind is mobility = why pay upfront cost of installation if I may not be here. Are people seeing part of installation cost reflected in higher selling prices to minimize that concern?

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A properly done modern array shouldn't have meaningful maintenance expenses - the panels and inverters are solid state devices that just sit there and generate power, and the rain is usually adequate to clean them off.

I'm not sure what you have in mind for depreciation - I guess a business could possibly take credit for the depreciation as a tax offset?

I'm not even an expert in my personal taxes, let alone all the business tax rules.

For the mobility aspect, I was promised that the reduced utility bill would result in higher home selling prices, but I have no experience with that. A real estate agent said that for every dollar saved on monthly bills a house was worth an extra hundred dollars on the market?
Walter