7.2 kw grid-tie system in Rhode Island

RegGuheert said:

AndyH said:

You're missing the point. Talk to the people on the East Coast that make a generator decision based solely on the assumed availability of either a fuel station or a functioning natural gas line.

A battery bank doesn't need an electrically-supported gas line, and keeps the homeowner out of the other electrically-supported "gas line".

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No argument. I'm just pointing out that there is a cost associated with taking this approach.

AndyH said:

My Midnite Solar charge controller is expected to live beyond 20 years.

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By whom? Not by Midnite Solar. Here is their latest warranty statement from the Classic manual:

Warranty
MidNite Solar's Classic comes with a standard 5 year warranty we will repair or replace the Classic at no charge to the consumer during this 5 year period

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Microinverter manufacturers warranty their inverters for 25 years. Not 5 years. 5 years is the length of warranty you offer on a product which you do NOT expect to last for over 20 years. My guess is the MTBF is on the order of 5-10 years like other hand-crafted multi-kilowatt power electronic item like the Midnite Solar Classic Controller.

Your multi-kilowatt inverter also likely has a similar 5-year warranty.

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Actually yes, my expected service life is based on info from Midnite - but not by their warranty statement. It's based on the target set by the engineers that designed the product. Additionally, I understand that each 20°C drop in operating temperature roughly doubles system life where temperature is a limiting factor, that fans are the #1 failure item, and that running the equipment at or over design limits will take a bit out of life. I've designed the system to stay at under 80%, will install the charge controller and inverter in a climate controlled space, and will swap the tiny fan in the Classic before it fails as part of the system PM schedule. Talking with folks using the Classic 150 in similar service suggests the fan won't be working much if at all anyway.

RegGuheert said:

Note that just two years ago they had an additional offer in the manual which is now removed:

End of Warranty tune up
MidNite Solar offers a industry first Tune up / Extended Warranty. 6 months prior to the end of the
warranty period Customers can ship their Classic back to MidNite Solar with a check for $125 dollars and
we will replace any wearable items like the fans and the capacitors and in general tune the Classic up.
This will also extend the warranty by 2 additional years as well.

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If I combine this old statement with recent firmware updates that Midnite has released which aim to reduce fan runtime, I will make the extrapolation that they are experiencing fan failures which of course leads to failure of the electronics.

Finally, I will note that the latest firmware reduces the maximum current for some modes by more than 5% than what was allowed 2 years ago. Again, I believe this is indicative that Midnite Solar is experiencing some warranty failures and is having to reign in their SOA limits on this controller.

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I agree that fans are the weakest link. At the same time, the company has made hardware choices and firmware tweaks that increases component life and reduces the need for the cooling fan. As stated, I'm not concerned about 5% as I'm allowing a bit more than a 20% cushion.

RegGuheert said:

Don't get me wrong, I hope your Classic Controller lasts over 20 years. This controller uses a very innovative power stage design which exceeds all the predecessors. But the manufacturing techniques and build quality are similar to what has been used in renewable energy for many years. I simply do not think there is much chance that it will show a step change in MTBF like has been achieved with microinverters.

AndyH said:

A properly sized bank of industrial batteries in back-up service will do the same.

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Agreed that a battery bank in float service can last 20 years. But I thought I was responded to someone who was using the battery in daily cycling service. I may have understood.

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Maybe I misunderstood as well - I thought the added twist of adding battery to a grid-tied system was solely for emergency backup power.

AndyH said:

Actually yes, my expected service life is based on info from Midnite - but not by their warranty statement. It's based on the target set by the engineers that designed the product. Additionally, I understand that each 20°C drop in operating temperature roughly doubles system life where temperature is a limiting factor, that fans are the #1 failure item, and that running the equipment at or over design limits will take a bit out of life. I've designed the system to stay at under 80%, will install the charge controller and inverter in a climate controlled space, and will swap the tiny fan in the Classic before it fails as part of the system PM schedule. Talking with folks using the Classic 150 in similar service suggests the fan won't be working much if at all anyway.

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I think your approach is a good one, Andy! It should get you close to, if not beyond, 20 years. Hopefully the electrolytic capacitors will last that long. Also, you might want to buy all of your fans within the next few years, as they may not remain available for the full 15 years (assuming replacement every five years).

I installed a Claasic 200 in an off-grid application about 27 months ago. So far, so good! Rightly or wrongly, I took a markedly different approach than you did, partly to reduce installation costs, but partly in the hopes that a higher-power unit would be available at EOL of the existing unit. This charge controller can put out about 70A (limited) into the 48V battery or about 3500W maximum. But I tied it to a 4000W PV array. So it does run at the limits sometimes, but only in cold temperatures when the sun is very near the boresight of the array and there is a significant load on the batteries. It does happen, but not nearly as often as it would if I had done this in an grid-tied application. In that case, the charge controller in this arrangement would run at its limit for a couple of hours for many days each year. But the PV array would also be oriented differently (this array has a 50-degree elevation).

Unfortunately, I do not see an up-rated Classic available yet. In fact, the latest firmware would reduce the peak output current in this application to 65A. I'll have to speak with the owners to see if they want to trade wintertime production capability for longer life. (Wintertime production capability is almost always the limiting factor for off-grid applications around here.)

sling said:

That seems high to me, I did a 1.5k system a little over a year ago for $4.7k before anything. I also did install myself so that might figure into it, but either way, my cost to kw was pretty high as things go - wish I had decided to do a larger system to bring costs down. Helped dad do a 5.6k system at his house for about $13k before anything. Again, we did all installation - obviously theres no labor warranty. And from what I've seen recently, prices on the panels are much less than they were when we bought and installed. After the feds and local incentives we are only going to owe 35% of the total cost. $1.15/kw for me and $0.81/kw for him

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yeah, I have to pay for the labor fee, which includes all the installations and permits needed.


For a person like me, who doesn't have enough $$$ to pay for the whole amount of total solar system...........and doesn't want to get a home equity loan, or a high interest personal loan................having a 3 year zero percent finacing offered by the installer is hard to pass!

thew said:

Don't Forget your Battery Backup~.. !!

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thank you!

But I can't afford to buy batteries

Our area never lost power for the past 4 years, even during hurricanes and the recent blizzard/storms in the northeast.

But I actually just recently bought a 10 circuit transfer switch (30amp), and a 7500watt suge/6000 watt continuous gasoline powered portable generator, so I can power my furnace (propane), GE geospring water heater, fridge, and three rooms during black-outs. I actually don't need to power my fridge, since I can just put my food outside my house during the winter. The furnace and water heater are the essentials for me during winter.

I really need a back-up generator because during winter, I only have central heat (propane)....and no other source of heat to use during black-outs. This is important since my wife and I just had our first born baby girl. She needs heat during winter. And we don't have a family close by to go to, just in case we lose power.

I know that gasoline powered generators are not the most ideal, since gas will not be available at the gas pumps during black-outs, and the shelf life of gas is only good for 3 months. But during winter, if there's a storm/blizzard coming in a day or two, I can always fill up three 5 gallon containers, which will give me power/heat for at least 3 days. And I can always drive to another town to get gas if still needed.

I spent a total of $1000 for a back-up generator system/transfer switch that we might not even use. But its an affordable and good system to have for emergency purposes.