[HN Gopher] Solar on Warehouses
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Solar on Warehouses
Author : ZeroGravitas
Score : 30 points
Date : 2023-04-23 19:52 UTC (3 hours ago)
(HTM) web link (environmentamerica.org)
(TXT) w3m dump (environmentamerica.org)
| Animats wrote:
| Is rooftop solar used mostly to power air conditioning and
| lighting cost-effective for large stores?
| epistasis wrote:
| It's likely far cheaper than buying the electricity from the
| grid, but it will depend on local commercial electricity rates.
| Utilities usually have to set up pretty perverse schemes in
| order for solar to not be an economical choice.
| unixhero wrote:
| Well Duh. Isn't this blindingly obvious?
| Syonyk wrote:
| The short answer is "No, but it sounds obvious if you don't
| know much about it." Similar to Solar Roadways - the less you
| know about solar or roads, the better the idea sounds. The half
| mile gouge down a road near me from a trailer coming free and
| riding on the chains until they noticed and pulled over isn't a
| big deal on asphalt (they'll fill it next time they chipseal
| it), but it would be millions of dollars worth of damage to
| solar road tiles. Among many other issues.
|
| It's the sort of thing that sounds obvious if you don't know
| much about the field, and the more you learn, the more things
| you realize make it a royal pain in the rear to deal with
| unless the structure was designed with solar in mind - and even
| then, it's a pain compared to a ground mount array somewhere
| close.
|
| For a big membrane roof, you don't want a ton of penetrations -
| which means ballasted mounts. Except they weigh a lot, and the
| roof usually isn't built to support them on top of the required
| weight for rain/snow/etc. So you need to screw the stuff down
| to the roof, but now you have tons of penetrations in a
| membrane roof, and if anyone tells you they can do thousands of
| those without a single leak, they're full of crap.
|
| As I talked about in another comment, you can't just run high
| voltage DC strings on a roof - you need per panel electronics,
| so the normal solution is microinverters, but now you're
| pushing 240V around instead of the 1500V you can run on ground
| mounted strings, so wiring cost is higher, and Enphase sure
| makes their money off their handout in the NEC 2017.
| Reliability of microinverters remains an open question as well.
| They're not exactly in a good spot for electronics.
|
| You've got open area, you've got a high current
| interconnection, but the rest of it is just a set of thorny
| problems that makes it quite a bit more expensive than ground
| mount.
| hnburnsy wrote:
| Both Amazon and Walmart have pulled back on solar due to fires
| and electrical issues...
|
| https://www.cnbc.com/2022/09/01/amazon-took-solar-rooftops-o...
|
| https://www.cnbc.com/2019/11/05/tesla-and-walmart-settle-ove...
|
| Might have been a Tesla issue in both cases.
| epistasis wrote:
| Everybody I know that used Tesla for solar regrets it. Cheap
| stuff, but you end up paying for it in the end.
| bufferoverflow wrote:
| When we installed solar, Tesla's was the most expensive out
| of all the proposals. Their solar roof looks very very cool,
| but it's definitely not "cheap stuff".
| epistasis wrote:
| Never heard of anything like that, but most of my
| experience is from 2+ years ago. Is your install recent?
| Are you sure they were equivalent proposals? If you add
| storage, that's no longer just solar, and their storage
| offerings are far more expensive than others.
|
| I couldn't find a local solar installer that wanted to use
| the type of cheap inverters that Tesla wanted to use. My
| neighbor has to have Tesla come out about once a year to
| fix issues.
| Syonyk wrote:
| I've no idea why you're being downvoted, because it _is_ a very
| real issue. You don 't have to burn down many warehouses with
| solar before insurance companies start to have a lot of hard
| questions and rate increases. In tens of thousands of
| connections, it doesn't take a high failure rate on components
| before you've got something high resistance.
| vasco wrote:
| And if you have to evacuate a huge warehouse even once a year
| due to these fires, it immediately is not worth it for the
| operator.
| [deleted]
| photochemsyn wrote:
| Structural design issues are the problem as other comments note.
| If you haven't designed the roof from the beginning to have a
| fairly weighty additional structure attached on top, then all
| kinds of other problems can arise, from leaks to wind-related
| loads and so on.
|
| Over the long term, it becomes something building codes need to
| implement, similar to electrical wiring and plumbing standards:
|
| https://www.nrel.gov/state-local-tribal/blog/posts/solar-rea...
| toomuchtodo wrote:
| NJ has code that requires structural loading on new warehouses
| to be able to support solar on 40% of the roof. It's just a
| matter of getting this into code as soon as possible, so new
| buildings are solar ready as old warehouse space is eventually
| retired at EOL.
|
| https://www.jdsupra.com/legalnews/new-jersey-solar-ready-req...
| bjelkeman-again wrote:
| This would seem to be more common from a business perspective,
| but apparently it isn't. This warehouse park, Morgongava, near
| Uppsala in Sweden has at least 2.5 MW installed and installing
| more. This one of their buildings.
|
| https://renewablesnow.com/news/swedish-online-pharmacy-apote...
| rhdunn wrote:
| It's interesting that they are selling the excess to the local
| supplier as they will be able to offset the cost faster, and
| start making a profit from it sooner. That is, the point at
| which the amount of money saved from not paying for the
| electricity and the amount gained from selling the excess
| balances the cost for the installation.
| PaulKeeble wrote:
| This happens in residential solar a lot. During the
| Spring/Summer/Autumn you will produce 1.5x - 2x what you
| consume on any given day but the peak of the power all comes
| at 9-10am to 2-3pm. You need large amounts of battery to move
| that power to cover the house for the other 2/3 of the day
| and that adds a lot of cost and is often similar price to the
| solar array.
|
| One of the best ways to deal with the problem is selling it
| back to the grid but how that is done vastly changes the
| payback period. Some states do it as a unit exchange so you
| sell 1KWh to them then you get that back later when you want
| it for no cost. Whereas many do a sale price with a price
| half or worse. Which price you can get for that power and
| whether its following wholesale (which tends to be peak early
| evening and be more during the day than night) can
| drastically change the pay off period.
| ajsnigrutin wrote:
| So, power when you're not at home, the house is empty, it's
| warm, and your electric car is with you at work, and no
| power at night, when you need to cook, heat and charge your
| car.
| Syonyk wrote:
| Yup.
|
| This is one of the reasons I've argued in favor of "slow,
| at work charging" as the default for EVs. If you put in a
| bunch of 240V/16A chargers (3.8kW), as people show up in
| the 8-9 timeframe, they start charging, and the bulk of
| the charging happens in the ~10AM-2PM window that's after
| the morning peak, as solar is ramping up, and before the
| afternoon cooling/evening peak. You can even restrict the
| chargers a bit more in the morning if needed until off
| peak, though I'm not sure this is worth much over just
| using dumb chargers that are cheap to install. An average
| 35 miles a day driving (in the US) requires ~10kWh, so
| you've got a few hours of charging that can swallow an
| awful lot of power during the time nothing else is using
| much of it.
|
| It's far better than having to deal with evening and
| overnight charging.
| ajsnigrutin wrote:
| But for that you need every parking space in every office
| building equipped by a charger, and somehow have the grid
| strong enough to power all that from solar cells which
| need to be installed somewhere further away, since an
| average office building does not have enough roof space
| to charge all those cars. The hours you mentioned are
| usually spent at work and the cars are parked there (and
| not at home).
| Syonyk wrote:
| Who said every parking space? I didn't. Even at the
| coastal FAANG offices, EVs are still the minority. And
| not everyone will be charging every day. It's still fine
| to have a lot of non-charging spots - some people have
| short commutes and can be perfectly fine charging for
| 8-9h once a week (at 3.8kW, that's around 100 miles in 8h
| of charging). My experience from the early to mid teens
| is that the Leafs fought for charging, and the longer
| range BEVs charged if they could, and otherwise didn't
| get in the (damned near literal) fistfights over
| charging, but if someone showed up early, they'd plug in
| for the day.
|
| If you look at grid demand curves, that "late morning,
| early afternoon" time spot is the mid-day low for _most_
| grids. So there 's excess capacity anyway, and if you
| look at the "duck curve" sort of graphs, there's a ton of
| solar on the grid then anyway. This is only increasing
| with time. So we may as well make decent use of it.
|
| You could also have some lower power, 1440W charger slots
| (15A @ 120V) for those who don't need much power - it'll
| still make up an average day's driving in 8h of charging,
| but since it's literally the same wiring cost and such to
| run 120V as 240V, I'm not sure you gain much with it, and
| it's now perfectly valid for chargers to coordinate
| regarding total circuit demand anyway.
| jpgvm wrote:
| Has anyone done more detailed numbers on costing of roof mounted
| installation vs just putting utility scale solar on the ground?
|
| I would have thought if the economics were super favourable this
| would already be happening by now.
|
| To me it -seems- like a great idea but while I'm pretty versed in
| solar for home scale (diy off-grid setups etc) I have no idea how
| the numbers bear out for this install size, grid connection, etc.
| notatoad wrote:
| we massively under-value land in most cases, which is the
| reason that activists push for solutions like this.
|
| utility scale solar on the ground is economically better, if
| you're looking at "the numbers". but utility scale solar
| probably means repurposing farmland, because that's the
| cheapest land that has enough infrastructure built up around it
| to make a utility install easy. and repurposing farmland to
| build solar isn't a clear win in terms of overall societal
| benefit.
| epistasis wrote:
| Converting farm land into solar, or even fallow land, seems
| like a massive societal benefit. Most farmland is
| fantastically unproductive, used for excess corn, soy, or
| sugar that we struggle to find uses for.
|
| Taking even a fraction of the land used for ethanol and using
| it for solar would give us enough energy to power the US. And
| the ethanol business is a complete make work program.
| Syonyk wrote:
| > _... but utility scale solar probably means repurposing
| farmland..._
|
| Great. Let's start by repurposing the land that grows the
| corn we turn into ethanol at somewhere around or below unity
| EROEI, as a political handout to the midwestern states.
| "Burning a megajoule of diesel, to grow enough corn to make
| something slightly less than a megajoule of gasoline," is
| _not_ a winning solution to any problem but "How to best
| hand money to states that happen to have early Presidential
| primaries." It's not a bad gig for Iowa (I lived there for a
| decade), but neither is it a particularly good use of energy,
| fossil fuels, or money. Let's put solar up there, and work
| out.
|
| Once we've gotten rid of the ethanol debacle, we can see
| where things are and discuss from that point, but there is a
| _lot_ of farmland right now that doesn 't grow human or
| animal food, it grows corn that we process rather
| inefficiently into ethanol.
| algo_trader wrote:
| > Has anyone done more detailed numbers..
|
| This is usually under "C&I" (commercial and industrial), as
| opposed to rooftop or utility scale.
|
| Try Lazard LCoE report, NREL Solar reports, IRENA renewables,
| or use google.
| Syonyk wrote:
| > _Has anyone done more detailed numbers on costing of roof
| mounted installation vs just putting utility scale solar on the
| ground?_
|
| You're far cheaper on the ground, for a variety of reasons (at
| least in most areas). A good ground mount install should be
| able to come in around $1/W, and you'll have a hard time
| getting roof mount below closer to $1.50 or $2/W installed, and
| if you get $2/W, you're getting a great deal.
|
| If you're doing the work yourself, ground mount for around $1/W
| is doable (including the frames), but roof mount I've not been
| able to get below about $1.25/W, and that's hard - $1.50/W is
| more typical.
|
| The main difference is that the roof mount system requires
| rapid shutdown on (in NEC 2017 and later) every panel, and
| you're limited to 600V (though with rapid shutdown
| requirements, this is less relevant). For a ground mount system
| that's isolated away from random people (fenced area), you can
| run up to 1500VDC to the inverters, and this rather reduces
| your costs in wiring. You also don't need rapid shutdown, so
| you can just run strings of panels (20 or 25x 72 cell panels in
| series, depending on the environment).
|
| Also, if those strings have an arc fault somewhere, you're not
| going to burn up much that matters for a big ground mount
| install. You'll cook a couple panels, and that's about it. A
| fire under the panels on a warehouse is a much bigger deal.
|
| The main problem you run into with warehouses, though, is that
| there's just no good option for mounting. For a flat roof,
| they're generally built to exactly the loading requirements for
| the area. You don't have the spare PSF capacity for a ballasted
| mount, which means that assuming you've got the weight rating
| for the panels, you're looking at a _lot_ of roof penetrations
| on a flat membrane roof to hold stuff down - and the odds of
| some of those leaking is basically 100%.
|
| Plus it's a royal pain to work on roof mount systems.
| jpgvm wrote:
| Thanks for the great writeup! The root loading makes perfect
| sense when you think about it and in that context makes the
| equation much more expensive unless the warehouse could
| feasibly use all the power generated (which seems unlikely).
| hijinks wrote:
| ya till solar hits a tipping point like it is in California right
| now. Then the utilities want to set a flat rate based on wages to
| stay connected to the grid.
|
| This will 100% work but we also need battery tech to hit like
| 250-300 a kwh for storage is my magic number to get a 40-50kwh
| backup and detach from the grid.
| krasin wrote:
| > we also need battery tech to hit like 250-300 a kwh for
| storage is my magic number to get a 40-50kwh backup and detach
| from the grid.
|
| Here you go, a 30kWh 48V battery for $9k ($300/kWh):
| https://signaturesolar.com/eg4-lifepower4-lithium-batteries-...
| hijinks wrote:
| wow thanks.. looks perfect
| epistasis wrote:
| The storage market has been revolutionized in the past few
| years thanks to LFP chemistries, and it's only going to get
| better soon. There are massive new US production facilities
| coming online, and Bloomberg is estimating that US cell
| costs will be $83/kWh, just a few dollars more than Chinese
| costs. Add in the IRA tax credits, and the cost will be
| less than $50/kWh. Packs will be more expensive than cells,
| of course, but the future looks very rosy. I always chuckle
| when I encounter the sweet summer children that think that
| battery tech is stagnant...
|
| (Subscription required) https://www.bnef.com/shorts/16235?e
| =Insight%20Alert:sailthru
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