Musk's Powerwall

[GIThruster]

. . .this one gives 1.2 kWh a day and costs only 1,140 USD.

Yes, but the rating is with strong sunlight presented normal to the panel, and unless you add tracking, the sun is almost never, or never normal to the panel. How much energy you can produce gets modified several times in the standard equation and the angle of incidence is only one such modification. The thing to keep in mind is that a 1kW panel will not generate the same energy in one location as it will in another, so it needs to be rated for the location you intend to install it in.

[pdxpyro]

I'm willing to admit I'm atypical. CNN Money (bastion of truth, I'm sure ) article says:
"The average U.S. household uses 943 kilowatt-hours of electricity in a month and pays 12¢ per kWh, according to the U.S. Energy Information Administration". This equals 11,316 kWh annually.

I have a fairly large home (includes an apartment for my elderly mom) and my annual use is closer to 19,000 kWh / year. A lot, I know, but the old gal has the TV and computer on 18 x 7. It's really about 2 family's worth of use. We've taken steps we can (swapping out incandescents for CFL and LED's, etc.).

So . . . "need"? hmmm. dunno. I'm willing to admit I probably use more than I need.

Anyway "150 by 400 inches" = 416 sq ft. This pretty well packs out my south-facing roof surface.

(I'm willing to end this . . . sorry for drifting OT.)

Do renewables really produce "excess" energy? I've been looking at PV systems for my home (in the Pacific NW of the USA). Even with the roof fully packed, it will only produce a fraction (20-25%-ish) of our total kWh usage. That's my micro view.

How much power does your household need a day?!
Here is an example that I found for a solar panel that is actually pretty cheap. this one gives 1.2 kWh a day and costs only 1,140 USD.
It is only 2.5 by 1 meter, or 100 by 40 inches. An average home needs 5,000 kWh a year. Assuming that you need about that, you should be able to get away with an installation 150 by 400 inches in size. That does not sound all that big to me.
http://www.homedepot.com/p/Grape-Solar- ... /203505963

Edit and here is a solution that produces on average about 5,000 kWh a year and is almost exactly the size I calculated earlier.

[Maui]

"down the drain" - Not quite. As I'm connected to the grid (I realize off-grid folks have completely different considerations), the power generated by PV while I'm at work will flow backward through my meter. Essentially, the grid (someone else using power while I'm at work) is my "storage".

As a little aside, this mandate that the utilities buy back power fed back onto the grid is beginning to threaten the viability of the electric utility industry (or so I have read at one point). Think about it in the extreme-- if everybody bought solar panels that satisfied their daily power needs, fed all that power onto the grid (for $) during daylight hours, then used that power off the grid at night (balancing out power usage and cost) the utility is stuck with the task of generating all that power at night for no net revenue. (EDIT: assuming constant rates, that is. I suppose in a completely free market situation this would drive the cost of power down to zero in the day and to a really high rate at night... sounds like a good reason for a Powerwall)

Why, then (back to what I don't understand), do we need storage?

Back to your original question I'm not sure you are still standing behind, the storage is not about any net excess of energy produced in the long run, it is saving momentary excesses of power for when there are momentary deficiencies of power. Yes, for the moment, from an individual consumer's perspective the grid can serve as this "storage"... but as highly variable renewable energy starts to play a bigger and bigger role, there will come a time where there has to be real storage involved (either the utility's, the consumers', or a combination of both).

Finally, again without really knowing any of the numbers involved, I can't imagine the Pacific NW is a region where solar panels are particularly cost effective...

[choff]

If Musk can pull it off, I'll feel a whole lot better about solar, so long as mass production doesn't drive up the cost and availability of rare earth elements it could work. Pacific Northwest, you have plenty of people living isolated from the grid, you also have lots of rain(at least we don't have to shovel it), not everybody lives on the south face of the mountains. Performance on cloudy days is a big issue, another one is competition for rooftop spaces, people are getting more and more into urban greenhouses, aquaponics, fogponics. Now, if you could somehow integrate solar power with greenhouse farming, that would be a huge plus!

[Tom Ligon]

I'm willing to admit I'm atypical. CNN Money (bastion of truth, I'm sure ) article says:
"The average U.S. household uses 943 kilowatt-hours of electricity in a month and pays 12¢ per kWh, according to the U.S. Energy Information Administration". This equals 11,316 kWh annually.

I have a fairly large home (includes an apartment for my elderly mom) and my annual use is closer to 19,000 kWh / year. A lot, I know, but the old gal has the TV and computer on 18 x 7. It's really about 2 family's worth of use. We've taken steps we can (swapping out incandescents for CFL and LED's, etc.).

So . . . "need"? hmmm. dunno. I'm willing to admit I probably use more than I need.

Well, at least you're not as bad as Al Gore. The last figures I saw on his home said he had $50k of PV equipment installed, and it produced something like 5% of his power needs. I was flabbergasted. Then I saw his household energy use and had to suspect he has a multi-level basement running Gro-Lux lights to produce medical MJ on a huge scale. Or else has a medium industrial manufacturing plant somewhere on the lot.

You need an energy audit. I'd start with your refrigeration and air conditioning. I've had a refrigerator try to eat me out of house and home, and the replacement had a very rapid payback, under a year I think if I remember the impact that lemon was having on the bill. A neighbor recently got a sudden increase of about $700 a month in her electric bill on her old home (on the market) due to a defective AC system.

I've done some back of envelope calculations on PV for the 1440 sq ft log cabin. I believe we could run whole house air conditioning on it with six of those big panels mentioned by someone above ... the ones I've looked at are about $300 each and 300 W, a dollar a watt (the holy grail of PV cost for years). That would give 1.8 kW in full sun, for about 4 hours a day, the period when air conditioning is most needed. This assumes a high-efficiency air conditioning unit (25 SEER units are available now).

Adding cooling loops behind the panels would make them double as heat collectors in the winter. Excess power in the winter would be far beyond our present needs, and in the summer we are outdoors most of the time.

[Tom Ligon]

I was just up at the cabin and went down to check the stream. I'd guess it was running 3 gallons a second, or about 24 pounds of water a second. I've estimated I could put in a plastic pipe down to a turbine with roughly a 100 ft drop. That's 2400 ft-lbs/sec, or 3.2 kW, and it runs all day and night.

But, alas, it doesn't run all year. We've had a wet spring, but if we have a drought this summer it may reduce to a garden hose flow of a few gallons per minute, or even dry up to dripping faucet rates.

So while this particular stream really tempts me to toy with small-scale hydro, the Tesla battery is not nearly enough to get me through months of drought. But for someone with a good stream, hydro has great $/W, and less storage problems. If the stream is small, one could use a Tesla battery for load leveling, particularly providing surge capacity for well pumps, power tools, etc. And the nighttime generation would charge the battery on your Tesla roadster.

[Tom Ligon]

. . .this one gives 1.2 kWh a day and costs only 1,140 USD.

Yes, but the rating is with strong sunlight presented normal to the panel, and unless you add tracking, the sun is almost never, or never normal to the panel. How much energy you can produce gets modified several times in the standard equation and the angle of incidence is only one such modification. The thing to keep in mind is that a 1kW panel will not generate the same energy in one location as it will in another, so it needs to be rated for the location you intend to install it in.

Indeed. I don't use trackers, though. At present panel prices I'd be inclined to have a couple of extra sets facing east and west instead, if you have the space. But with the present panels set to the sun's vernal equinox high noon elevation, I figure 4 hours per day of full useful power, and anything else on the sides is a bonus. Trackers can squeeze out marginally more but the intensity is reduced by more atmosphere, and this is at a cost of capital equipment, wind damage, etc.

And no tracker will correct for clouds. My rule of thumb for my area is that one day in three gives decent sun. In the absence of hard numbers, budget on that unless you live in Arizona. And if you live west of the Cascades in Washington or Oregon, give up.

All, please remember that the household energy use numbers above are not the real issue. Homes CAN run on a lot less ... try to go solar and you will worry about every watt-hour, and will conserve like crazy. But industry is already highly conscious of energy costs. The bean counters have been trying to pinch energy pennies for years, especially in energy hog industries. I came to the conclusion long ago that solar is hopeless for heavy industry in most areas.

[paperburn1]

This last post also highlights the other problem with solar. Each and every installation is or should be custom made for each home. This makes a true mass production solution problematic. Dollar for dollar conservation measures pay back very quickly and should be the first projects undertook. Where applicable for the end user it can be made to work but will never support heavy industry. we need fusion or a fail-safe fission to proceed to the next level of our civilization. I truly believe we are at one of those tipping points in human development excess power is required to make that step.

[Skipjack]

. . .this one gives 1.2 kWh a day and costs only 1,140 USD.

Yes, but the rating is with strong sunlight presented normal to the panel, and unless you add tracking, the sun is almost never, or never normal to the panel. How much energy you can produce gets modified several times in the standard equation and the angle of incidence is only one such modification. The thing to keep in mind is that a 1kW panel will not generate the same energy in one location as it will in another, so it needs to be rated for the location you intend to install it in.

That is not what the website said! It says

This system will provide approximately 1,200-Watt Hours or 100-Amp Hours of charge per day.

, which suggests to me that they are factoring in some of the issues, you are discussing. The panels have a 400 Watt rating. 1,200 Watt Hours would be 3 hours at maximum intensity a day.

[Skipjack]

I'm willing to admit I'm atypical. CNN Money (bastion of truth, I'm sure ) article says:
"The average U.S. household uses 943 kilowatt-hours of electricity in a month and pays 12¢ per kWh, according to the U.S. Energy Information Administration". This equals 11,316 kWh annually.

I have to admit that my 5,000 kWh were wrong. I saw them on a website and they were clearly being super optimistic. 11,300 sounds a lot more likely. Mine is about 9,000 a year and my house in small. But then I live in Michigan, where I have the heat on 6 months a year. Unfortunately, this is also one of those places, where solar is the least useful. So these solar panels would be below the average of 1,2 kWh a day for my region, I am sure. On the other hand places like California, Texas and Arizona would be over the 1,2 kWh.

[Tom Ligon]

If Musk can pull it off, I'll feel a whole lot better about solar, so long as mass production doesn't drive up the cost and availability of rare earth elements it could work. Pacific Northwest, you have plenty of people living isolated from the grid, you also have lots of rain(at least we don't have to shovel it), not everybody lives on the south face of the mountains. Performance on cloudy days is a big issue, another one is competition for rooftop spaces, people are getting more and more into urban greenhouses, aquaponics, fogponics. Now, if you could somehow integrate solar power with greenhouse farming, that would be a huge plus!

A former Talk-Polyweller and I are in touch. He bought a country place near here a few years ago. It has a pool inside a greenhouse, and he is converting it to aquaponics. Maybe I could get him to drop back in for a discussion of this.

[paperburn1]

I am in my second year of playing with hydroponics. I have a 4 x 8 bed and it seem to be working wonderfully. We harvested literally bushels of greens from the garden. From everything I have read and my own personal experience this will seem to be the third agricultural revolution. with an insulted tank and a simple solar heater I think we will be able to extend our system to year around growth.
https://www.facebook.com/photo.php?fbid ... 070&type=1

[pdxpyro]

Northern Oregon is about same latitude as Michigan. "least useful" is probably an apt description, but ROI (especially with tax incentives at Fed and OR level) is still reasonable.

I'm willing to admit I'm atypical. CNN Money (bastion of truth, I'm sure ) article says:
"The average U.S. household uses 943 kilowatt-hours of electricity in a month and pays 12¢ per kWh, according to the U.S. Energy Information Administration". This equals 11,316 kWh annually.

I have to admit that my 5,000 kWh were wrong. I saw them on a website and they were clearly being super optimistic. 11,300 sounds a lot more likely. Mine is about 9,000 a year and my house in small. But then I live in Michigan, where I have the heat on 6 months a year. Unfortunately, this is also one of those places, where solar is the least useful. So these solar panels would be below the average of 1,2 kWh a day for my region, I am sure. On the other hand places like California, Texas and Arizona would be over the 1,2 kWh.

[pdxpyro]

Yes! Your comments really get to the heart of my thoughts about viability (now) of storage proposals.

You're one observation ("if everybody bought solar panels that satisfied their daily power needs"), though, is problematic. I just don't know if there's enough roof real-estate on a single family home (let alone apartment complexes) that could make this true. At least, not until efficiency of panels increases by multiple of what's currently (pardon the pun) out there.

Finally, see my post immediately above. Solar is cost effective in the NW, especially with tax incentives factored in. What we lose in insolation (compared with sunnier climes), I think we gain in lowered draw (less AC year-round).

"down the drain" - Not quite. As I'm connected to the grid (I realize off-grid folks have completely different considerations), the power generated by PV while I'm at work will flow backward through my meter. Essentially, the grid (someone else using power while I'm at work) is my "storage".

As a little aside, this mandate that the utilities buy back power fed back onto the grid is beginning to threaten the viability of the electric utility industry (or so I have read at one point). Think about it in the extreme-- if everybody bought solar panels that satisfied their daily power needs, fed all that power onto the grid (for $) during daylight hours, then used that power off the grid at night (balancing out power usage and cost) the utility is stuck with the task of generating all that power at night for no net revenue. (EDIT: assuming constant rates, that is. I suppose in a completely free market situation this would drive the cost of power down to zero in the day and to a really high rate at night... sounds like a good reason for a Powerwall)

Why, then (back to what I don't understand), do we need storage?

Back to your original question I'm not sure you are still standing behind, the storage is not about any net excess of energy produced in the long run, it is saving momentary excesses of power for when there are momentary deficiencies of power. Yes, for the moment, from an individual consumer's perspective the grid can serve as this "storage"... but as highly variable renewable energy starts to play a bigger and bigger role, there will come a time where there has to be real storage involved (either the utility's, the consumers', or a combination of both).

Finally, again without really knowing any of the numbers involved, I can't imagine the Pacific NW is a region where solar panels are particularly cost effective...

[GIThruster]

I just don't know if there's enough roof real-estate on a single family home (let alone apartment complexes) that could make this true.

Not by a long shot. I would guess the national average home would be lucky to put 30% production in. Businesses are the opposite as you can cover the parking lots.