sort of an add on to the CA thread

[analog8484]

just curious. If I understand things correctly, the vast majority of installed residential solar PV can't be used if the grid is down. so people are going to have all these PV modules in full sun when the grid craps out, but can't make power from them.

Is there some relatively simple way to get around this limitation of residential PV systems?

I am thinking if there is, someone is going to make a ton of money installing such modifications in CA.

It depends on what you mean by "relative simple". What's your reference point?

 

[synchro]

You may want to consider an inverter generator for clean power. Recent prices have dropped significantly.

I recently made the mistake of looking at the specs for my CyperPower 1500VA UPS. THD of 40%!!!

A square wave has a THD of about 48%, so the waveform of your UPS probably looks almost like one.
Inverter generators typically use PWM and therefore the distortion can be quite low depending on the amount of filtering used to attenuate the carrier and other high frequency content.

 

[gadfly56]

A square wave has a THD of about 48%, so the waveform of your UPS probably looks almost like one.
Inverter generators typically use PWM and therefore the distortion can be quite low depending on the amount of filtering used to attenuate the carrier and other high frequency content.

Yes, I think there was other mention of the output being a square wave. IIRC, the distortion happens at the corners, on the top of the "up" side edge and bottom of the "down" side edge, and if you look closely enough, it's really ugly. "Square wave" being a very bad approximation of the actual output. But I'm remembering from..well, a really long time ago.

 

[petersonra]

It depends on what you mean by "relative simple". What's your reference point?

How about it takes 15 minutes or less and costs less than $15

 

[jaggedben]

But even then most of the PV+storage systems do not have a backup mode, they only perform time-shifting, storing energy during the day and releasing it in the evening. ...

I belive that is a very incorrect statement. I mean, I don't have stats handy, other than my personal ones. But of the several dozen systems I've had a part in, every one of them has off-grid operational capability.

 

[jaggedben]

How about it takes 15 minutes or less and costs less than $15

Is $15 a typo? I mean, one would think that the cheapest portable generator would be a point of comparison.

The systems I install transfer from on-grid to off-grid in 100 milliseconds. They do cost more than $15 though.

 

[analog8484]

How about it takes 15 minutes or less and costs less than $15

Yeah ... that's a non-starter and why I asked

If your value for not having to deal with power outages for hours is only $15 then it's not really a worthwhile problem to solve.

 

[petersonra]

Yeah ... that's a non-starter and why I asked

If your value for not having to deal with power outages for hours is only $15 then it's not really a worthwhile problem to solve.

So what is the number? $1000?

 

[winnie]

For the residential PV that I am investigating for my own house, it looks like a hybrid inverter that would do battery management and off grid backup will cost about $5K more than a basic grid tie inverter.

This doesn't include the batteries.

As previously mentioned the SMA Sunny Boy inverters already include a receptacle that is directly powered by the PV array. But it has no energy storage to stabilize the output (they take the cheap approach of limiting the output to a fraction of array capacity) and doesn't work if rapid shutdown is required. This is probably the closest @petersonra 's '$15' addon, a cheap use of capacity where the manufacturer simply doesn't bother solving the issues of stability.

Jon

 

[ggunn]

How about it takes 15 minutes or less and costs less than $15

Then no.

 

[ggunn]

So what is the number? $1000?

My dad's usual response to a question like that was "how long is a piece of string?" The cost to convert a grid tied only PV system to one which will power a home during an outage is dependent on many variables with very wide ranges, but it boils down to "how much power?" and "for how long?".

 

[winnie]

The other potentially 'cheap' approach to using PV _without energy storage_ is direct coupling of the PV array DC to loads specifically designed to use the variable DC.

I believe that there are some EV charging systems that can do this, and I know that you can buy mini-split systems that are designed to connect directly to PV panels.

This sort of approach gives up a huge amount of flexibility as compared to a whole home system where fixed voltage fixed frequency AC is distributed to everything, supplied either by the grid or by local power. But by eliminating that flexibility you get significant cost savings.

-Jon

 

[jaggedben]

For the residential PV that I am investigating for my own house, it looks like a hybrid inverter that would do battery management and off grid backup will cost about $5K more than a basic grid tie inverter.

This doesn't include the batteries.

That's a great price if it's a contractor's price to install the equipment and includes rewiring backed up loads. If it's just for equipment you could do muuuch better, like $1-1.5k more than for grid tie.

 

[ggunn]

That's a great price if it's a contractor's price to install the equipment and includes rewiring backed up loads. If it's just for equipment you could do muuuch better, like $1-1.5k more than for grid tie.

But as he said, the cost doesn't include the batteries, which leads back to the how much power and for how long questions. Battery capacity is expensive.

 

[winnie]

That's a great price if it's a contractor's price to install the equipment and includes rewiring backed up loads. If it's just for equipment you could do muuuch better, like $1-1.5k more than for grid tie.

This is just for equipment without batteries. If you are saying that a hybrid inverter that handles the grid tie for normal operation and also battery management and island operation can be had for less than $3K, then I for one am very interested.

-Jon

 

[jaggedben]

The other potentially 'cheap' approach to using PV _without energy storage_ is direct coupling of the PV array DC to loads specifically designed to use the variable DC.

I believe that there are some EV charging systems that can do this, and I know that you can buy mini-split systems that are designed to connect directly to PV panels.

This sort of approach gives up a huge amount of flexibility as compared to a whole home system where fixed voltage fixed frequency AC is distributed to everything, supplied either by the grid or by local power. But by eliminating that flexibility you get significant cost savings.

-Jon

I don't think you get any real cost savings that way. Not if you place a reasonable value on the time involved in researching the ways to convert loads to DC and installing wiring and such for that. So, if you're a DIYer with nothing else to do, then yeah maybe you can save some cash. But as a business proposition to sell to others you work with the loads they have, which and AC. Also, none of the PV systems these days with rapid shutdown are designed to deliver raw DC anymore, so the supply lines for that are not streamlined, and it could violate code.

 

[jaggedben]

This is just for equipment without batteries. If you are saying that a hybrid inverter that handles the grid tie for normal operation and also battery management and island operation can be had for less than $3K, then I for one am very interested.

-Jon

Well for example for Enphase Ensemble you just need the Enpower switch, which I would think you could get for $1500 somewhere. We get it for less. When I was doing Solaredge the difference in inverter cost was at most about the same, depending on the power of the non-hybrid inverter that would have otherwise been used.

 

[ramsy]

So, if you're a DIYer with nothing else to do, then yeah maybe you can..

Install NREL's silicon carbide inverter, in your house.

 

[analog8484]

So what is the number? $1000?

Not sure if you have solar or know the cost of a typical solar system. It's generally $3-$4/watt unless you DIY. Using a typical 5kW example that's $15-$20K which is a significant sum for most people. So, if you own that system and you get a power outage where your wife finds out solar doesn't work and ends up spending hours to throw out bad food, clean refrigerator and restock the refrigerator. Now, your wife is yelling at you for spending all that money on the solar system that doesn't work when you need it the most. What's your value now? For some, the value is high enough to go spend another $15-20K for a home battery. Many more people don't see the financial justification and just bought generators. You can look at the sales and stock price trend of Generac to get a sense of the demand surge. For most of solar owners, 10-20% of their solar system cost is likely the practical value for broad adoption.

 

[ggunn]

Now, your wife is yelling at you for spending all that money on the solar system that doesn't work when you need it the most. What's your value now?

Your wife doesn't understand why you bought the PV system in the first place, which was to offset part or all of your utility bill. It's like buying a car and complaining because it doesn't fly. You can buy a helicopter but it will cost a lot more.