Just a question for you guys with panels and an EV...

[NeilBlanchard]

This is my brother's house:



26 panels, 6.37kW, it generated 7.3MWh in the first year they had it. That is about 80% of what they use. Without the incentives, it should pay for itself in under 10 years. They heat with wood pellets, so they are very low carbon.

[KillaWhat]

We should talk... I'm using what's called a "blackout breaker" to trip once the grid goes dark.. then my APC 10kw Smart-UPS backfeeds into the whole house via one of their isolation transformers.

It keeps the micros happy and I can even keep power feeding into the APC with the gen for ext periods if nec (earthquake, etc). I've already tested charging the Leaf and Rav.. no issues.

Best way is just with a big UPS

I figured you would be on top of this with your new PV array.

I'll drop you an email when I'm up and producing.
This sounds interesting, and with the UPS, pretty simple.

Thanks.

[RegGuheert]

Tubes suck. People always think they are better in colder climates because they deliver a hotter temp but they collect more snow in the winter. Flat plates are more reliable in colder temps and thats a fact.

Sorry, but snow is extremely unlikely to collect on any tube system with a 60-degree elevation angle. But the proof is in the pudding. Here is a side-by-side comparison in Ithaca, NY, (Where you live, right?) between a 64-sqft flat panel array and a 51-sqft (46-sqft active) tube collector on the same roof connected to identical systems. (Click on the link at the bottom-left of the page.) Note that the evacuated-tube system collected MORE heat last December than the flat-plate system which has 25% more area:



In January, the flat-plat system only collected 11% more heat in spite of its 25% larger area. But what happens when you have a winter in which we get three-to-four-times as much snow as normal? Here is the plot for the winter of 2009-2010:



As you can see, the smaller tube system produced the same or more energy during the months of November, 2009, through February, 2010.

And this is true for arrays at a 45-degree elevation angle. IMO, both system should preform better in the snow (and in December) at a 60-degree elevation.

So, no, saying

Flat plates are more reliable in colder temps and thats a fact.

is not accurate, even in Ithaca, NY.

All that said, both systems consume about the same number of linear feet on the roof since the flat-panels in the comparison are 8-feet tall versus the tube array which is about 6-feet tall. So if you can handle the much higher wind loads and the worse asthetics of the taller flat panels, then you likely can save some money and produce a similar amount of energy for the same linear roof space.

Edit: Corrected the link since it has changed since I made this post.

[PV2leaf]

The question about not being able to go from the DC that the PV panels produce directly into the batteries of our EVs is valid. The major reason why this is not practical is that the inverters that these systems are designed to use require significantly lower input voltage than a EV battery is configured for.

SMA inverters go on line at 300v and are most efficient at 250v but they can run with higher input voltages up to 480v. A good PV installer will design a system with string size based on panel performance and your local temperature considerations.

When it is hot your voltage has to get high enough to bring the system on-line but when it is -5F on a clear and sunny day your voltage mus stay below the value that will damage inverter. I believe the capacitors used are rated at 600V and you do need a safety margin.

You could always design a system for a much higher voltage and regulate down for both EV and inverter feeds but this would be expensive, create inefficiencies and the high DC voltage created for an input would drive additional expenses as most components are not rated for over 600V

[jimbo69ny]

Sorry man, come to NY almost all of the systems sold are flat plate.

Fact; snow gets stuck in the tubs.
Fact; flat plate collectors get hot and melt the snow off
Fact; flate plate are cheaper

Personal fact; I got a killer deal on the systems I bought. I purchased the remaining inventory from a defunct company so I bought a ton of equipment for a fraction of its value. So for me this was a no brainer. Either way, I never even considered tube collectors for many reasons

[RegGuheert]

Sorry man, come to NY almost all of the systems sold are flat plate.

That's because they are cheaper and many like you believe they are less efficient in snow and cold when in fact they are more efficient in those situations.

Fact; snow gets stuck in the tubs.

Perhaps if you mount them flat on the roof. But not in the tubes in the comparison I showed or any steeper installation. Here is a plot from that system during the Nor'easter on December 18 and 19, 2009. Note that only the flat panel production goes to zero during the storm, but the tubes do not go to zero because the snow does not block the light.



Note again this test is from where you live. In the coldest months, the tube systems are 15% to 25% more efficient per unit area, including when there is massive snowfall.

Fact; flat plate collectors get hot and melt the snow off

This demonstrates how inefficient they are. Better not to accumulate the snow in the first place.

Fact; flate plate are cheaper

Yep, as I noted previously.

Personal fact; I got a killer deal on the systems I bought. I purchased the remaining inventory from a defunct company so I bought a ton of equipment for a fraction of its value. So for me this was a no brainer.

Good deal!

Either way, I never even considered tube collectors for many reasons

...and some of those reasons were flawed.

[Marktm]

We should talk... I'm using what's called a "blackout breaker" to trip once the grid goes dark.. then my APC 10kw Smart-UPS backfeeds into the whole house via one of their isolation transformers.

It keeps the micros happy and I can even keep power feeding into the APC with the gen for ext periods if nec (earthquake, etc). I've already tested charging the Leaf and Rav.. no issues.

Best way is just with a big UPS

is thread is rather old - do you have an update?

I use the APC SURT 6KVA with a Prius as a "generator" and have a variety of APC SUA/SMX UPSs for off-grid use with a 48 volt battery system (hobby of mine). I've often wondered if I could "fool" my SMA grid-tied inverter (4000 TL-US) with one of these pure sine wave inverters?? I worry most about too much PV power trying to back feed the UPS (in off-grid mode) and damaging the UPS. SMA indicated that the GT inverter will simply shutdown if the UPS goes down or no PV power being generated - so no issues there. I do have the option of using one of the larger UPSs with the iso-transformer - but don't know if the iso-transformer would prevent such damage anyway?

Now that I have a Leaf, with the use of level II charging, too much PV power may not be an issue if the Leaf's battery is substantially depleted each day - could possibly put safety shutdown with the APC "EPO" disconnect.

Have you looked into using your APC 10KVA system directly fed from the Leaf's battery (the SURT 8 and 10KVA use 400 VDC as the battery backup source). The big issue is they use +/- 200 VDC (center tapped) with the 4 battery cages.

Feel free to PM me if this is of interest as I've done some testing in this area.