Project Sunroof • Hacker News Board

Re: Project Sunroof

#161

Post by birken » Mon, Aug 17, 2015, 9:04 PM UTC

bmelton wrote: post #147

birken wrote: post #76

Earlier quoted context omitted.

If you are already connected to the grid, then you can simply just feed the electricity back into the grid when over-producing (which is tracked by your meter), and then use electricity from the grid at night. This actually works in your benefit if you have solar panels, because electricity prices are higher during the middle of the day (more demand). So you can "sell" daytime electricity (at high prices) [1], and th…

Except that, as pointed out above, the utilities only pay the wholesale rate for the electricity they buy back from you, and sell the overage to your neighbors for full price. Meanwhile, you're likely losing money selling your peak day electricity for 5 cents and buying it back for 15.

At least with PG&E, my understanding was that those rates only applied to a net over-production over a long period of time (I believe over the course of a year). As long as your power bill is not negative, any over-production during high value times of the day is sold at the market rate and offsets low value electricity you buy at night.

This is important with solar system sizing, because not only don't you want to be a net exporter of energy, the lower tiers of PG&E's energy rates are very cheap so you don't want to generate that power either. You really only want to offset the high-tier, high-demand electricity you use (or plan to use in the future).

For me it didn't really matter because my energy usage is highest during the peak times of the day, but this is my understanding of how it works. I'll know for sure in a couple of months when I see my bill :)

Re: Project Sunroof

#162

Post by rconti » Mon, Aug 17, 2015, 9:09 PM UTC

dkhenry wrote: post #95

andyl wrote: post #21

Fusion of maps, 3d modeling, electricity & lease rates, solar intensity, installers. Easy to use. This feels like something new and powerful. For society: I wonder if it is safe for so much power to be concentrated in one organization. As a technical accomplishment: I'm impressed.

Its not really new, and its not really powerful. From what I can see all this does is give you an estimate based on the square footage of your rooftop. There is a lot more that goes into a real estimate then how big your roof is, namely how can you arrange the panels to cover the roof. That is a neat trick and this company does that http://www.modsolar.net/ I worked with their stack for a bit and from my understandin…

And sun exposure.

Re: Project Sunroof

#163

Post by timcederman » Mon, Aug 17, 2015, 9:12 PM UTC

MRSallee wrote: post #112

Can anyone with more knowledge of solar technology speak to this? I know nothing about solar technology developments. I am interested in adding solar to my house some day, but concerned about spending a lot of money today for solar panels that will either (a) be much cheaper in 5-10 years, or (b) be replaced by much more effective panels in 5-10 years. Assuming that the economics of it are the only motivation for goi…

That's what subsidies are for - to incent you now, and when panels are cheaper and more efficient later, the subsidies go away.

Re: Project Sunroof

#164

Post by birken » Mon, Aug 17, 2015, 9:12 PM UTC

dhess wrote: post #143

birken wrote: post #60

I live in San Francisco and just had a solar system installed last week, so I have a few comments about this. 1) It vastly overestimated how big a solar system that could fit on my roof (by about 5x). It didn't care about chimneys or skylights (which are easily visible through Google maps), nor SF fire code which states that you need a 3-foot empty pathway on both sides of the crest of your roof [1]. So for almost ev…

Which installer did you choose, and would you recommend them?

I used Luminalt [1] and they did a great job throughout the whole process. The installation job was at the highest degree of quality and professionalism that I've experienced.

Though it hasn't been inspected or turned on yet (happens later this week), so I'll see how close their projections were to reality over the coming months as the juice is generated. I did my own projections independently and found that their projections seemed to be on the conservative side, so I'm optimistic.

1: http://www.yelp.com/biz/luminalt-solar-energy-solutions-san-...

Re: Project Sunroof

#165

Post by secabeen » Mon, Aug 17, 2015, 9:15 PM UTC

mikepurvis wrote: post #128

protomyth wrote: post #79

Earlier quoted context omitted.

> Perhaps it should link to a solar installer, and a lumber jack :-) Let's not be cutting down the carbon dioxide remover when we're trying to go eco-friendly. :)

Any gains from PV would be washed away by increased air conditioner usage. If you have a house in shade, be very happy.

That assumes you have an air conditioner. In coastal California, they aren't common in older homes.

Re: Project Sunroof

#166

Post by calciphus » Mon, Aug 17, 2015, 9:15 PM UTC

andyl wrote: post #118

oaktowner wrote: post #108

Earlier quoted context omitted.

But Google doesn't have power over electricity and lease rates or lists of installers -- they're just using publicly available data. There are other sources for maps data, and many people have 3d modeling software. So I'm not sure how this is "so much power" concentrated in one organization.

To me, what makes it powerful is the ubiquity - the 'full take' ness of it all. Sure the app is solar-related data, just for a few regions. But could include whatever data Google chooses, expanded to the whole world, for whatever audience Google chooses. I've worked with aerial surveillance systems, the types used on police choppers. Put the crosshairs of the flir camera on a house and it will tell you all kinds of s…

But if the data is already public, surely making it more widely available devalues it as a means of control or coercion?

You can blackmail me if you know something no one else does. You can't if you know something everyone else does.

Services like this fix asymmetric access to information. They're not revealing anything new.

Re: Project Sunroof

#167

Post by JoeAltmaier » Mon, Aug 17, 2015, 9:20 PM UTC

thrownaway2424 wrote: post #160

JoeAltmaier wrote: post #158

Earlier quoted context omitted.

Turning electricity into heat isn't all the work you can get out of the energy. Heat pumps get even more, by using the energy to move heat from one place to another (e.g from ambient outside air to the volume to be heated), and the heat from this process also heats the volume.

If the air outside my house is warmer than the air inside my house, I'll just open the windows. Generally when one needs a heater it is because the system surrounding the house is colder, sometimes much colder, than the house itself.

Cold makes it harder on the heat pump, but not impossible. Heat pumps use a compressor (just like AC unit). If the pump can create a mass of gas colder than the outside air, then that mass will be warmed by the outside air (no matter what the absolute temps are).

In the limit of course (too cold outside), a heat pump is just as efficient as using the electricity for heat directly.

Re: Project Sunroof

#168

Post by gregable » Mon, Aug 17, 2015, 9:21 PM UTC

Navarr wrote: post #48

pilom wrote: post #43

Other than the "buy now" aspect, this doesn't seem any better for calculating solar savings than http://pvwatts.nrel.gov/ I used PVwatts when sizing my home system in Denver and thought it did a great job.

It's "easier." I just logged into PvWatts, knowing practically nothing about solar, and I'm confused at Step 2. There's a billion variables that it wants me to fill out instead of trying to calculate them for me for optimal results.

Agreed PVWatts is more accurate, and it's what a solar installer is actually likely to use when doing a roof assessment. But to use PVWatts you need to input things like the tilt and orientation of your roof, the size of the system you want to build, the cost of power from your provider, inverter efficiency, etc. This asks for your address and your monthly electricity bill to give you a rough estimate, both of which homeowners are much more likely to know.

Re: Project Sunroof

#169

Post by timcederman » Mon, Aug 17, 2015, 9:22 PM UTC

jvm wrote: post #63

Forgive my ignorance, what does one do during non-insolated hours? Do solar cells typically come with battery packs or does one just pull from the grid? If the latter then the cost savings are a bit less impressive than stated. Also can you put power back into the grid in San Francisco? Is that benefit included in the cost savings estimate?

Very few installations use batteries.

Right now in the Bay Area, almost everyone is using net energy metering (NEM). You get a bill once per year, and they balance out your usage vs generation, and any extra usage is charged.

There is a minimum you have to pay each year, so most installers aim for 85-95% of your usage to be generated by your system. As other folks have stated, it's not advantageous to sell back to the grid given the low price - as such, very very few people actually sell back to the grid, and instead make a small purchase each year, and mostly at off-peak rates.

Re: Project Sunroof

#170

Post by jsprogrammer » Mon, Aug 17, 2015, 9:36 PM UTC

ZeroGravitas wrote: post #125

_delirium wrote: post #98

Earlier quoted context omitted.

I suspect you'd fare pretty badly in a market, even if a better one existed. In Texas's deregulated electric marketplace, the market price for large-scale solar installations selling into the grid has fallen to around $0.05/kWh. Power from a single small-scale residential installation with less reliable delivery is probably worth less than that.

Depends on how much "better" the market is e.g. if it priced in the greenhouse gas externalities, the avoidance of transmission losses and grid upgrades etc then solar may be worth triple the residential rate. I believe a couple of states have calculated "value of solar" to use as part of their grid regulation, though specific factors like mix of gas and coal production and projected grid expansion factor into this.

Any reasonable grid would also be wired such that the power you generate will first go to your neighbors, if they need it, instead of 'round-tripping' to the utility and back. So, the utility is taking a huge cut even though it isn't really a factor in the transaction.

There are of course large-scale infrastructure costs (you get to fail-over to nuclear/coal/gas/wind/other), but it seems like all of those things should be accounted separately instead of all being lumped into two line items on a monthly bill from your local monopoly.