throwaway3334

Are these solar tiles (solar shingles) or a traditional air-gaped panel?

I was looking at installing a very small solar array, just to offset the AC costs. The quote for the solar kit that could produce ~1.5kW (2170W Solar Kit: 7xURE NSP 310W - Mono 60 Cell - All Black Panels + 7xEnphase IQ7 60-Cell Microinverters w/QCables + 1x Enphase IQ Combiner 3 + Wireless Monitoring) was $6.5k.

But, I was also considering having a 10kW battery to store that energy and to have a backup power, like Tesla Powerwall - $10k. And then there was work to install, permits, my time. Overall my estimate was, realistically it'd be ~$25k. Maybe I was wrong.

On my house I have two sections of roof that are flat/horizontal. Roof is pretty thin there and although there is insulation, on hot days ceiling was getting worm in the 2 rooms under these sections. I also was hoping that an extra layer of solar would insulate my roof a bit more. So I wouldn't have to run AC that much. So the hope was to stop wasting annoying $400 on AC in the hottest months. But the cost of installing solar felt prohibitive. So I've made a quick calculation and spent $100 on the reflective roof paint instead...

You can look at how much space roofs cover in the suburb in the Bay Area. It'd be roughly 25% streets, 40% roofs, 30% backyard, 5% front-yard. Adding white reflective coating increases "Solar Reflectance" and decreases "Thermal Emittance" and absorption. Most dark roof materials reflect 5 to 20% of incoming sunlight, while light-colored roof materials typically reflect 55 to 90%. A white roof coating that you can purchase at your regular home improvement store would do that 90%.

So effectively, in the suburban area there is an opportunity to change our average solar reflectance by ~32% [(90% - 10%) * 40%]. If we just abandon the idea that a good house should look like a house in Normandy and have a black roof.

[edit: I've opened a section of sat map (in Sunnyvale, near Reed Ave/Sequoia Dr.) and estimated roof/street/backyard/front-yard by area, for a lot of 2 houses and adjacent street. The numbers above are from that estimate. Heat and noise of ACs is somewhat local (urban heat island effect, etc), so that local estimate is what counts. It is not surprising that we can have 40% roofs. Land is expensive in the suburb like that.]

As per: https://en.m.wikipedia.org/wiki/Reflective_surfaces_(climate... - "If all urban, flat roofs in warm climates were whitened, the resulting 10% increase in global reflectivity would offset the warming effect of 24 gigatonnes of greenhouse gas emissions, or equivalent to taking 300 million cars off the road for 20 years. So it seems, there is not only local/urban heat island effect, but even some global effect. To put this into perspective, Tesla sold 2 million vehicles. No idea, if the Wiki numbers are correct...

For now, everyone is free to pump out kilowatts of heat with their roofs, parking lots, air conditioners into the surrounding air. It is not considered pollution, even when it is already 100 °F outside.

On the days when there is an inversion in the atmosphere, the hot air stays trapped. People have to run ACs in their houses, stores and offices. And that results in even more heat routed to the place, with ACs units, literally pumping energy from the solar arrays somewhere in the desert into the city.

Actually, I was looking into installing solar, to offset $400/month of air-conditioning costs, during the summer. I could have had around 1.5kW of solar. But the cost of this is north of $25k, plus all the hassle to get the permits, plus all the extra complexity. While the cost of painting the roof is $100 + work. And now it is very rare that I have to run the AC.