California to require solar panels on all new homes

[ggunn]

I'm pretty sure no law of physics says that you can't disconnect from the grid and locally utilize the electricity your solar panels are generating.

Actually, it does if your system doesn't have batteries. It's a pretty long explanation that centers on PV modules being current sources rather than voltage sources, but a PV system cannot provide AC power to loads on demand without being connected either to the grid or a battery bank. Someone may bring up the now discontinued SMA inverters that could power a single outlet with about 1000W without batteries in the absence of the grid, but that was a very small exception.

It isn't the mean old government keeping people from using power from their PV systems. If you want to spend a big pile of money on a standalone PV system with batteries so that you can power your house off grid, no one will stop you.

 

[jaggedben]

Aesthetic concerns, which are already only a big deal to a minority, should be almost completely mitigated with new homes where architects can plan arrays into the overall design. After not too long I think the better architects will get good at it for the better homes.

The motivation for the requirement, of course, is global warming. And jobs.

 

[Strathead]

I'm curious, though. Will the new homes that have all these solar panels actually be able to use the power they produce, or will they be like Florida and not be allowed to? IE, when the grid goes down, you still have no power.

As far as I know, solar requires a minor input voltage to work, so when there is no power, there is no solar power either, unless there is stored energy to produce the power required.

 

[Strathead]

California doesn't have a monopoly on that kind of thing. Here in Texas we needed some new highways, so we built them as toll roads and then sold them to a Spanish company. Our toll fees go overseas. Remember when tolls were collected to pay for roadways and stopped when the roads were paid for? Those days are long gone.

Oh,, I wasn't implying that. In Maine they have one of those toll roads. It was supposed to pay for itself and then be free. It costs a lot more now to ride on than then. They decided they needed that toll money for maintenance.

 

[Besoeker]

What's unaffordable about a negative electric bill?

That's operating cost as opposed to capital cost.
Adding solar panels would increase the the property price and possibly put it out of the reach of some prospective buyers.

 

[drcampbell]

Actually, it does if your system doesn't have batteries. It's a pretty long explanation that centers on PV modules being current sources rather than voltage sources, but a PV system cannot provide AC power to loads on demand without being connected either to the grid or a battery bank. Someone may bring up the now discontinued SMA inverters that could power a single outlet with about 1000W without batteries in the absence of the grid, but that was a very small exception.

It isn't the mean old government keeping people from using power from their PV systems. ...

So you're saying that if I were to put a PV module out in the sun and not hook it up to anything at all, it wouldn't be a source of voltage?
And that the many standalone PV pumping stations installed on ranches don't work because they don't use batteries?
And that SMA inverters provide AC power without batteries. (and, presumably, could be scaled up, paralleled or installed in multiples)
But there's some fundamental law of physics preventing them all from working?

Sounds to me -- after pushing aside all the bovine biosolids -- that what you're really trying to say is that the popular inverters require some 60-Hz energy from an external source for excitation & synchronization and refuse to turn on without it. That's a design limitation of those inverters, not a fundamental law of PV physics.



I don't recall mentioning the government's role in PV installations. It really isn't necessary to provide rebuttals to claims I didn't make.

-

That's operating cost as opposed to capital cost.
Adding solar panels would increase the the property price and possibly put it out of the reach of some prospective buyers.

A mortgage company would need to be really narrow-minded and short-sighted to ignore a revenue stream when calculating affordability. (not that that's inconceivable)

 

[winnie]

Most residential power systems operate on the assumption of a very stiff voltage source (voltage changes only slightly with load), and with the ability to supply much greater load than average (200A 240V service with average consumption on the order of 1-2kW).

It would be very difficult to design a solar power system to meet these requirements without using energy storage. Not physically impossible, but difficult; you would need an absolutely huge array so that you could reliably supply 48kW even when not at full sun. And most of that array would be wasted most of the time.

Now if you design your loads to match the output of your solar panels (pumps that run when the sun is shining, fridges that make ice when the sun is shining, etc.) then you need neither energy storage nor a grid connection. But now we are no longer talking a standard residential system, appliances, or load profile.

FWIW I would also describe a solar panel as a current source. This is not to say that it doesn't produce voltage, it simply means that over its compliance range the output current is pretty much fixed. If you connect a solar panel to something expecting a constant voltage, you might be very unhappy as the voltage will rise or crash depending on the load characteristics.

-Jon

 

[electrofelon]

So you're saying that if I were to put a PV module out in the sun and not hook it up to anything at all, it wouldn't be a source of voltage?
And that the many standalone PV pumping stations installed on ranches don't work because they don't use batteries?
And that SMA inverters provide AC power without batteries. (and, presumably, could be scaled up, paralleled or installed in multiples)
But there's some fundamental law of physics preventing them all from working?
)

Of course pv can power a load directly. It's just not practical for typical premises loads.

 

[jaggedben]

That's operating cost as opposed to capital cost.
Adding solar panels would increase the the property price and possibly put it out of the reach of some prospective buyers.

We're talking roughly a 0.2 percent increase in sales price or mortgage payment. Not likely to be decisive.

 

[jaggedben]

So you're saying that if I were to put a PV module out in the sun and not hook it up to anything at all, it wouldn't be a source of voltage?
...

No he is saying if you take a typical PV inverter (i.e. grid-tied) and hook it up to PV modules but not to the grid, it will not be a source of voltage. And he is correct.

 

[jaggedben]

... FWIW I would also describe a solar panel as a current source. ...

Might as well be more accurate. It is a semi-conductor with an I-V curve that varies according to irradiance.

 

[ggunn]

So you're saying that if I were to put a PV module out in the sun and not hook it up to anything at all, it wouldn't be a source of voltage?
And that the many standalone PV pumping stations installed on ranches don't work because they don't use batteries?
And that SMA inverters provide AC power without batteries. (and, presumably, could be scaled up, paralleled or installed in multiples)
But there's some fundamental law of physics preventing them all from working?

Well, I wasn't going to dive that deep into this, but yes, of course, you can use the DC from solar modules as long as the consumption of the load is free to vary with the insolation on the array, i.e. the brighter the sunlight, the harder the pump (or whatever) works. That's very different from supplying power on demand. Current source vs. voltage source.

The SMA inverters you mention are no longer in production (I don't know why), but no, you cannot parallel their single outlet outputs that work (worked?) without the grid. Even the largest ones could only supply about 1200W to a single outlet.

Sounds to me -- after pushing aside all the bovine biosolids -- that what you're really trying to say is that the popular inverters require some 60-Hz energy from an external source for excitation & synchronization and refuse to turn on without it. That's a design limitation of those inverters, not a fundamental law of PV physics.

It's not just the popular GT inverters, it's all of them. Don't you think that if it were possible for a PV inverter without batteries to work with a transfer switch and go on supplying power on demand to a dwelling in the absence of the grid, someone would be doing it? The problem is that PV modules are current sources in the linear range of their operation and therefore the inverters for which they are the only power source are as well. The demand curve and the supply curve will never match precisely, so in order to run off grid it is necessary to have a battery bank to provide a buffer between supply and demand. When an inverter is connected to the grid, the grid is the buffer. This is indeed a fundamental of PV physics.

If you think you can get around this, well, do it. You'll be very wealthy.

I don't recall mentioning the government's role in PV installations. It really isn't necessary to provide rebuttals to claims I didn't make.

It was the absurd assertion that the reason PV systems in Florida shut off when the grid goes down is that that PV owners there were "not allowed" to use their PV systems in the absence of the grid that started this line of discourse. I wasn't necessarily replying specifically to you.

 

[Besoeker]

We're talking roughly a 0.2 percent increase in sales price or mortgage payment. Not likely to be decisive.

That surprises me.

 

[jaggedben]

Ggunn, SMA's new line of residential inverters still has the 'secure power supply' outlet. That feature is not out of production.

 

[winnie]

It's not just the popular GT inverters, it's all of them. Don't you think that if it were possible for a PV inverter without batteries to work with a transfer switch and go on supplying power on demand to a dwelling in the absence of the grid, someone would be doing it? The problem is that PV modules are current sources in the linear range of their operation and therefore the inverters for which they are the only power source are as well. The demand curve and the supply curve will never match precisely, so in order to run off grid it is necessary to have a battery bank to provide a buffer between supply and demand. When an inverter is connected to the grid, the grid is the buffer. This is indeed a fundamental of PV physics.

A small disagreement, but I agree that the above is correct as a practical matter.

You can always run the PV module as less than its maximum power point, which means that a smart enough inverter could match a small enough load to the PV array even without energy storage. This means that your array has to be capable of producing more power than you need (give current insolation) and the inverter has to be willing to sacrifice output to match the load.

Since PV systems are generally sized around the _average_ power consumption of the residence (at least where you have grid tie and net metering) the array will likely be quite undersized for actually running the home without the buffer of the connected grid.

-Jon

 

[Galt]

California seems to have a surplus of folks who like to tell other folks what to do.

 

[drcampbell]

... PV systems ... will likely be quite undersized for actually running the home without the buffer of the connected grid. ...

That same could be said of portable engine-driven generators, but with a little bit of intelligent load shedding, it should be possible to power the fridge, furnace and a few essentials during a blackout.

 

[electrofelon]

California seems to have a surplus of folks who like to tell other folks what to do.

Im still mad at them for ruining the gas can :rant:

 

[ggunn]

Ggunn, SMA's new line of residential inverters still has the 'secure power supply' outlet. That feature is not out of production.

Good to know and I stand corrected.

 

[ggunn]

A small disagreement, but I agree that the above is correct as a practical matter.

You can always run the PV module as less than its maximum power point, which means that a smart enough inverter could match a small enough load to the PV array even without energy storage. This means that your array has to be capable of producing more power than you need (give current insolation) and the inverter has to be willing to sacrifice output to match the load.

True enough, but how would you get the inverter output to track the load?