Question on battery outlets

Caspero

A question for members who have installed batteries with their PV systems.


I'm looking at a PV system installation at the moment which will power my house, with most of the excess production going into my electric vehicle's battery using a Zappi EV charger which can divert excess PV production to the car.

There won't be much excess production after the above two items are catered to so a battery wouldn't get much use.

However, I do have a server in the house and need an uninterruptible power supply for that when the grid goes down.

I know that standard PV systems become generally unavailable to the house when the grid is down as a safety feature so the server would die in that situation. However some batteries have a local socket at the battery which you can plug into when power is down.


Would the sockets on the batteries function like a UPS (uninterruptible power supply) as long as the battery has charge? i.e. when the grid is up, do they work, and then they just continue to work when the grid goes down until the battery dies? Or do they only kick in when the grid goes down? Is there a few seconds of time while power switches from grid to battery for the sockets where any connected server would die?



Also does the battery in a system need to be placed near the fusebox or connected to the inverter? My server is in the attic so if possible I'd place the battery there.

KCross

How long do you want/expect the server to run when there is a powercut?

Standalone UPS systems are not that expensive and will run servers for a few hours (depends on the server of course) and provide surge protection also and gracefully shut down servers before they run out of juice.... which is a key requirement.

Hybrid inverters do have the ability to feed the battery power to an isolated circuit which could run your server when the power is on and off but if you care about your server losing power without a graceful shutdown you should really be using a proper UPS which would be cheaper and have more safety features than just installing a battery system on your Solar PV to act as a UPS.

Caspero

KCross wrote: »

How long do you want/expect the server to run when there is a powercut?

Thanks KCross, most of my power cuts are no longer than 30 mins...if we could even last that long that'd do. It's not a massively critical server...but would be nice not to have it die.

KCross wrote: »

but if you care about your server losing power without a graceful shutdown

Are you saying this because the isolated circuit takes a second to kick in and the server would lose power during that time? Or because it'd shut down when the battery dies?

I'm not too worried about the latter because that would be quite an infrequent occurrence.

KCross

Caspero wrote: »

Are you saying this because the isolated circuit takes a second to kick in and the server would lose power during that time? Or because it'd shut down when the battery dies?

I'm not too worried about the latter because that would be quite an infrequent occurrence.

The latter.
Servers dont like the rug being pulled out from under them. Doesnt really matter if its infrequent. That one time it happens could/will be the time you lose the contents of your drive... in a past life I supported many a customer who suffered that fate.

Also bear in mind that you could get a power cut while the battery is also dead giving you no "UPS time" so you could easily find your "30min requirement" not being satisfied if you are relying on just the Solar battery to keep it alive. i.e. Its not in a constant state of fully charged waiting for a power cut like a UPS is.

Caspero

KCross wrote: »

The latter.
Servers dont like the rug being pulled out from under them. Doesnt really matter if its infrequent. That one time it happens could/will be the time you lose the contents of your drive... in a past life I supported many a customer who suffered that fate.

Also bear in mind that you could get a power cut while the battery is also dead giving you no "UPS time" so you could easily find your "30min requirement" not being satisfied if you are relying on just the Solar battery to keep it alive. i.e. Its not in a constant state of fully charged waiting for a power cut like a UPS is.

Got it thanks. OTOH...I have no UPS now and this would effectively be free ex grant...so yes I hear you it's not as good as a UPS but it's better than nothing

KCross

Caspero wrote: »

Got it thanks. OTOH...I have no UPS now and this would effectively be free ex grant...so yes I hear you it's not as good as a UPS but it's better than nothing

If you are getting a SolarPV system with a battery anyway then fine, but dont decide to go for a more expensive battery based Solar PV system just for that requirement as its a waste of your money, imo.

Get a non-battery, standard inverter system (should be a good €1500 cheaper after grants for the same 4kWp) and buy yourself a €150 basic UPS with the spare change and you'll be better off financially and your server will thank you for it!

Caspero

KCross wrote: »

(should be a good €1500 cheaper after grants for the same 4kWp)

Thanks KCross, is this 1500 difference comparing against an inverter that has a battery built in?

Or does adding a battery to a PV system effectively result in 2 increased costs:
i. The battery and
ii. A more expensive inverter?


The way I had been thinking about it was that a 2kwh battery (the min size to get the grant) is c. 1k and there is an extra 1.2k grant for a system with a battery. Maybe I'm not considering all the moving parts?

Hard to get answers from the installers....I emailed 12 from the SEAI list...only got replies back from 3....requested quotes from them all plus a few referrals people PM'd me, and only 1 has so far sent a quote...and he doesn't really answer questions like this one. I'd be lost without boards.

KCross

Caspero wrote: »

Thanks KCross, is this 1500 difference comparing against an inverter that has a battery built in?

Or does adding a battery to a PV system effectively result in 2 increased costs:
i. The battery and
ii. A more expensive inverter?

Correct and add extra labour and profit to that also.

A non-battery system has a cheaper inverter and obviously no battery. If you add batteries you HAVE to get a hybrid inverter.

Caspero wrote: »

Hard to get answers from the installers....I emailed 12 from the SEAI list...only got replies back from 3....requested quotes from them all plus a few referrals people PM'd me, and only 1 has so far sent a quote...and he doesn't really answer questions like this one. I'd be lost without boards.

Whatever kWp system you plan to get you need to get quotes with and without batteries. Only then will you know what the real world price difference is.

Be sure that the non-battery quote does NOT include a hybrid inverter and you need multiple quotes as you will have installers who will want to sell you the more expensive battery system and will hike the non-battery quote to make it look like the battery quote is worth while.

As a reference, best quote I got for a non-battery system was ~€4500 (after grant) for a 4.3kWp system on a slate roof with two orientations.

Caspero

KCross wrote: »

Correct and add extra labour and profit to that also.

A non-battery system has a cheaper inverter and obviously no battery. If you add batteries you HAVE to get a hybrid inverter.

Ah ya that changes the equation so! Thanks for the guide on system price too!

unkel

KCross wrote: »

Hybrid inverters do have the ability to feed the battery power to an isolated circuit which could run your server when the power is on and off

This very much depends on the inverter. With many the emergency power supply only works when the grid is down

KCross wrote: »

Servers dont like the rug being pulled out from under them. Doesnt really matter if its infrequent. That one time it happens could/will be the time you lose the contents of your drive... in a past life I supported many a customer who suffered that fate.

OS are far more robust these days. A sudden power cut rarely leads to problems starting up and never really affected loss of data apart from a file being written to at the time of a crash

KCross

unkel wrote: »

OS are far more robust these days. A sudden power cut rarely leads to problems starting up and never really affected loss of data apart from a file being written to at the time of a crash

That exactly. I’ve had to recover systems as a result of that. The OS itself generally survives as it’s just a lot of static files.