On-grid domestic battery storage

zeupater · 20 March 2017 at 8:41PM

ASavvyBuyer wrote: »

This may be a daft question and not even sure if this would work, but has anyone tried using a UPS (Uninteruptable Power Supply) normally used for PC equipment, as "Domestic Battery Storage" for alternative relatively low power equipment?

For example; charging it up during the day, (from solar power) and then using it to power a LED TV or LED lighting during the evening, with power switched off at the socket.

The payback time may make it not worth it, but there are some smaller UPS's available for under £100 which may store enough power.

Hi

The issue is that UPS systems aren't normally based on deep cycle usage - they're usually designed to be continually topped up so as to be available for occasional power outages ... as for 'enough power', well that depends on what you want to power and for how long, for example for ~£100 you may just be able to provide ~700W for around 2 minutes .... a decent capacity UPS which is capable of supporting an IT server environment at (say) 11kVA for ~60minutes would cost considerably more than a 13kWh Tesla Powerwall battery system.

HTH
Z

ASavvyBuyer · 21 March 2017 at 10:21AM

zeupater wrote: »

Hi

The issue is that UPS systems aren't normally based on deep cycle usage - they're usually designed to be continually topped up so as to be available for occasional power outages ... as for 'enough power', well that depends on what you want to power and for how long, for example for ~£100 you may just be able to provide ~700W for around 2 minutes .... a decent capacity UPS which is capable of supporting an IT server environment at (say) 11kVA for ~60minutes would cost considerably more than a 13kWh Tesla Powerwall battery system.

HTH
Z

As mentioned, was not thinking of using anything that took a lot of power ("a LED TV or LED lighting") so maybe less than 100 watts for the tv, or less than 15 watts for the lighting, on for 3-5 hours, so a maximum of 500 watts for the TV or 75 watts for the LED lighting.

However, it seems that the batteries used in UPS's, are the type that do not like being discharged & charged up on a regular basis, so may not last that long.

ASavvyBuyer · 21 March 2017 at 1:13PM

ASavvyBuyer wrote: »

As mentioned, was not thinking of using anything that took a lot of power ("a LED TV or LED lighting") so maybe less than 100 watts for the tv, or less than 15 watts for the lighting, on for 3-5 hours, so a maximum of 500 watts for the TV or 75 watts for the LED lighting.

However, it seems that the batteries used in UPS's, are the type that do not like being discharged & charged up on a regular basis, so may not last that long.

Done a quick count on the figures for payback time, and it does not seem worth it. Max could save with a low power LED TV, is about £20 a year; so would take at least 5 years to cover it's cost and batteries probably would not last that long.

zeupater · 21 March 2017 at 6:36PM

ASavvyBuyer wrote: »

As mentioned, was not thinking of using anything that took a lot of power ("a LED TV or LED lighting") so maybe less than 100 watts for the tv, or less than 15 watts for the lighting, on for 3-5 hours, so a maximum of 500 watts for the TV or 75 watts for the LED lighting.

However, it seems that the batteries used in UPS's, are the type that do not like being discharged & charged up on a regular basis, so may not last that long.

Hi

Using a 500W on a £100 UPS may give you around 3 or 4 minutes of off grid usage, with a decent LED TV you may get 15-20minutes whilst the batteries are still in good condition ...

Regarding the battery types (highlighted in red) ... Correct, that's why I mentioned you'd need a deep cycle battery system ...

HTH
Z

zeupater · 21 March 2017 at 6:47PM

ASavvyBuyer wrote: »

Done a quick count on the figures for payback time, and it does not seem worth it. Max could save with a low power LED TV, is about £20 a year; so would take at least 5 years to cover it's cost and batteries probably would not last that long.

Hi

Using a standard UPS on a deep cycle basis will kill your batteries in next to no time, you'd be lucky if you'd save anywhere near the first year's £20 before the system stops accepting charge or delivering power for any acceptable time ...

HTH
Z

Martyn1981 · 23 March 2017 at 2:19PM

I've just been watching an oldish interview on WA's (Western Australia) roll out of PV and storage.

I thought it worth mentioning on here as the speed is catching everyone out, and WA's energy minister has stated a couple of things.

Firstly that by 2025 Perth would get all of its daytime electricity from solar, and secondly, that also by 2025 that Perth would get 70% of its electricity from solar and batteries. [Edit: Further reading seems to suggest his claims relate to the whole of WA, not just Perth. M.]

Given the scale and speed of rollout needed to meet these claims/assumptions, I though it was worth mentioning on this thread as it seems to confirm thoughts that Australia will be a major driver of storage, and will hopefully help to bring prices down fast / faster.

Distributed Solar and Storage: Disrupting Australia's Energy System

The Perth claims are in the last 5 minutes, and relate to statements made in 2015.

Ectophile · 24 March 2017 at 2:02PM

I've just had a visit from the guy who sold me my solar panels back in 2011. He's running a different company now, after the solar industry collapsed, so the new one does other sorts of building maintenance as well as solar.

He says he can fit a new Solax inverter and battery unit for around £5.5K. The battery has a capacity of 4.8kWh, of which 3.85kWh would be usable. That's with a 10 year warranty on the inverter and 5 years on the battery (expected life 10 years). Apparently, it can even operate in islanded mode if there's a power cut.

My old inverter is about to go out of warranty (5.5 years), so I need to consider that as well.

I haven't done the maths yet to work out what the payback period is likely to be.

ASavvyBuyer · 24 March 2017 at 2:53PM

Ectophile wrote: »

I've just had a visit from the guy who sold me my solar panels back in 2011. He's running a different company now, after the solar industry collapsed, so the new one does other sorts of building maintenance as well as solar.

He says he can fit a new Solax inverter and battery unit for around £5.5K. The battery has a capacity of 4.8kWh, of which 3.85kWh would be usable. That's with a 10 year warranty on the inverter and 5 years on the battery (expected life 10 years). Apparently, it can even operate in islanded mode if there's a power cut.

My old inverter is about to go out of warranty (5.5 years), so I need to consider that as well.

I haven't done the maths yet to work out what the payback period is likely to be.

If you estimate the inverter to be worth about £1k, that leaves £4.5k's worth of electricity to import over the next 5-10 years. With already having Solar Panels, is it likely that you would import that much during the lifetime of the battery?

Since we had Solar Panels installed, we import less than £250 worth a year (including standing charge), so it would take over 18 years to break even.

Martyn1981 · 24 March 2017 at 4:19PM

Ectophile wrote: »

He says he can fit a new Solax inverter and battery unit for around £5.5K. The battery has a capacity of 4.8kWh, of which 3.85kWh would be usable. That's with a 10 year warranty on the inverter and 5 years on the battery (expected life 10 years). Apparently, it can even operate in islanded mode if there's a power cut.

My old inverter is about to go out of warranty (5.5 years), so I need to consider that as well.

I haven't done the maths yet to work out what the payback period is likely to be.

Hiya, having a ponder here, ASavvyBuyer has broken it down sensibly, so let's say £4.5k for the battery.

Loads of negatives I'm afraid.

Firstly, 5yr warranty isn't enough, and 10yr life expectancy is too short too.

Secondly, 3.85kWh useable, let's go super optimistic and assume you get 5kWh out of it each day, and it lasts 10yrs, that's 18,250kWh, which at 12p import would be worth £2,190, so half the cost of the battery. £4,500 / 18,250kWh gives you a cost of nearly 25p/kWh stored.

Thirdly, Tesla PWII installed is £6.3k, I now that's £2k more but it has a useable 13.5kWh ..... just for comparison.

Fourthly, also for comparison, I got quotes, including install from Powervault, which are approx:
4kWh useable (8kWh) lead acid - £2.7k 5yr warranty
4kWh useable (4.4kWh) Li-ion - £3.8k 10yr warranty
6kWh useable (6.6kWh) Li-ion - £4.9k 10yr warranty

So, still far too expensive, prices still falling, and a good chance that prices will fall faster each year, than current savings, so even if it was questionably viable today, it would probably still be worth waiting for a few years till we see where the market is going, and if prices are stabilising.

Lastly, you mention it can operate in Islanding mode during a power cut. Worth double checking that. Islanding allows the inverter to keep working even if the grid is down, some can do this, but they are usually more expensive and 'meatier' inverters.

You may be absolutely correct, or he may have meant that the battery has a dedicated socket for you to plug essentials into during a powercut, such as freezer, laptop, battery charger (flashlights) phone etc. Lots of the batts seem to have one of these, but the PV system would be shutdown.

Islanding is great if you need it, with lots of powercuts, but otherwise it probably adds a lot of cost.

Ectophile · 26 March 2017 at 8:21PM

I was told that the islanded mode was a matter of flipping a switch, so presumably it's a mode that the system can be put into when disconnected from the mains.

But I rarely get power cuts here, in an urban area.

It's not looking very cost-effective when you do the maths.

On-grid domestic battery storage

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