Power From Solar During Grid Power Failure

[MarineLiner]

Has anyone heard anything about the TerraWatt Power ecoJoule 2500 inverter?
It supposedly solves the problem that was being discussed on this thread.
In a power outage, it prevents solar power from going into the grid but does NOT prevent solar power from going to your house.

[MarineLiner]

... when the grid power goes the solar will be shut down.
... how to keep the solar generating power for my house while cutoff from the grid during the power failure.
Is the cutoff done purely as a safety measure for the power companies or is it something ...

[greenHouse]

You realize, when you add batteries to a system, you have oodles more maintainance, unless you are expecting week long outages in clear summer weather. A small gas genset will easily keep you going for a couple days. If an ice storm comes through, and it's 2 weeks to get power on, your PV may not make much power in bad weather, and you still have to run the genset.

Yup, and when the Texas PUC changed the feed-in tariff and wasn't paying me for exported power, I was able to stop giving away several hundred KWh a month. Whenever time-of-day / tiered billing becomes available, I can time-shift my consumption to exploit whatever differences in rates exist.

Battery maintenance in a grid-interactive system is next to nothing compared to battery maintenance in an off-grid system. They just don't get worked as hard.

[Mike90250]

You realize, when you add batteries to a system, you have oodles more maintainance, unless you are expecting week long outages in clear summer weather. A small gas genset will easily keep you going for a couple days. If an ice storm comes through, and it's 2 weeks to get power on, your PV may not make much power in bad weather, and you still have to run the genset.

[greenHouse]

I just read about an Grid-tie/battery backup set-up. It didn't list the inverter by manufactor, but apparently they exist.

Having an automatic switch to cut-off the Grid would be necessary though. I know locals that have those switches installed when they use their gas generators, during an extended outage. It may even being required here.

Good luck
Jeff

Well, yeah, once you add batteries to the equation all sorts of things are possible. I have a pair of OutBack GVFX3648's and they run without the grid just fine. Them and 25KWh of batteries

[netttech]

I just read about an Grid-tie/battery backup set-up. It didn't list the inverter by manufactor, but apparently they exist.

Having an automatic switch to cut-off the Grid would be necessary though. I know locals that have those switches installed when they use their gas generators, during an extended outage. It may even being required here.

Good luck
Jeff

[greenHouse]

I'd have serious doubts about how well that product can work in real-world scenarios. Cloud passage will drop all DC input and cause an AC power outage. A few seconds later, AC power returns. Then another cloud and another AC power outage.

If you want to ride through an AC power outage, battery backed is the only way to go. If not, pure grid-tie. But batteryless AC seems like it would be far more trouble than it is worth.

[Arthur]

TerraWatt Power ecoJoule 2500 inverter

Has anyone heard anything about the TerraWatt Power ecoJoule 2500 inverter? It supposedly solves the problem that was being discussed on this thread. In a power outage, it prevents solar power from going into the grid but does NOT prevent solar power from going to your house.

Arthur

[slade1977]

I sometimes forget that the electrical systems I work with are usually at an industrial capacity, so I regularly see inverters capable of going from 400VDC to 220VAC aren't hard to come by, but do run around $1000.

[Mike90250]

I got a 5 pack on ebay a couple of years ago, 200W each, $50 lot. Still have to make
a heatsink plate for them, and wire it up, but I "could" downconvert my array voltage
to something useable.

[JustinSolarGuy]

That's good to know. That's a lot of dough for a few hundred watts. You won't be able to run your whole array on one of those. You would need to run a bunch in parallel or use a small inverter. This just illustrates how things sound easy until you actually try to implement them. If you don't have a lot of experience building things and putting projects together you will seriously underestimate what is really involved getting something put together that seems so simple.

[Mike90250]

There are Industrial DC-DC converters that will convert 400VDC to 48VDC. You can charge batteries from that, to keep a fridge going off a small inverter.

Expect to pay about $300 for a 200W converter

[JustinSolarGuy]

That is nearly identical to my first solution except that you forgot to address the voltage issue. Most off grid inverters are 24 or 48 volt input. A grid tied SMA will probably be running 250-350 volts. Good luck finding an off grid inverter that will take that kind of voltage. If someone on here knows of a high input voltage off grid inverter please let me know. I would recommend this option to my customers as something they could add on later if desired. You may be able to find some way to step that voltage down using a Charge controller or DC to DC converter. But you will probably have to get creative and usually those are also designed for 24 to 48 volts.

[slade1977]

There is a relatively simple way (and safe and legal) way to accomplish this.

Go get a manual bus transfer switch. It's the same kind of switch board used for generators that are attached to houses on the grid. You can get an automated one, but I've had no problems with my manual one on my generator.

Since I don't know exactly how your system is wired, I'll try to be vague enough to give you ideas where to put it.

First, you'd need to install an A/B switch upstream of the gridtie inverter. Then you'd need another, non-gridtie inverter. That would then need to be tied into the manual transfer switch. When the lights go out, you would have to switch the A/B switch, and then the manual transfer breakers.

The way a manual transfer switch works for home systems is this. It basically replaces the breakers in your circuit panel. You wire the actual home circuit to the transfer switch. The transfer switch has two power inputs, one from the gridtie system and one from the non grid tie system. It is completely safe and legal. What happens when you switch the breaker from gridtie to nongrid tie, it completely isolates the circuit from the grid and there is no way power will flow out of your house to the grid and possibly killing a lineman somewhere when your 110VAC becomes 440VAC going upstream through the transformer.

When the switches are in the grid tie position, power is coming from the applicable circuit breaker in the main panel into the transfer switch, and then powering the home circuit.

When you throw the switch into the non-grid position, power is drawn from the non-grid source and then into the home circuit.

And then, for added insurance, kill your main breaker until you see your neighbor's lights go on. I only do this because my best friends dad is an electrician and I wouldn't trust his life on a $200 bus transfer switch.

I know it may be hard to understand how I wrote it out, but if you look at a wiring diagram for a generator transfer switch, it'll make it perfectly clear (as mud). Basically, the bus transfer box acts as a bunch of A/B switches. You'd need to identify 'vital' circuits you'd want to keep running when off the grid. They make some really large boxes that can power the entire house, but you'd likely be better served to identify only those circuits you truly need.

[woltnj]

Thank you for a very thorough explanation.