The changeover from both of the quoted systems is fast. Fast enough for you not to realise you have a grid outage. A friend of mine specifically bought the Tesla Powerwall 2 rig to effectively act as a UPS. Now, it is never going to be a proper “no break” /guaranteed supply, but it is quick enough that their internet router does not drop out.
For me, if having spent a large sum of money on solar and batteries….to still have no power in an outage……would be unacceptable.
At least you now know to ask for this before ordering a system.
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I had an outage early this morning! A very unusual event for us. My NC kit was in network standby but doesn’t appear to have suffered any harm.
Ironically, I am in the process of getting quotes for a solar/battery system. I hadn’t thought an EPS capability would be worth the extra expense, but I’m giving it some more thought now 
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Thank you. Yes, I have read that it is “nearly” instant and have seen the videos where the lights don’t even flicker. As I said I rarely get power cuts and these gateways are an extra cost option but if it protected Naim kit would be worth it. Good to hear the NC didn’t cut out
Sorry, I think you misunderstood. The power cut was about 2 hours. So the NC kit lost power when in network standby. When power came back the kit worked fine again once switched on.
You need to think carefully about how you want the batteries to work for you, and how large (and expensive) they need to be.
Basic battery setups start at around £3k on top of the PV/inverter costs. My friend recently had one installed, and had a single socket added which is OK for basic stuff like keeping the router working during a power cut. If you want to run whole ring mains, heating or cooking you’ll obviously need more than that.
In order to effectively use the battery to store PV power and/or off peak grid power you will want to run it low, ready to benefit from the next recharge opportunity. At that point it’s of little use for backup in a power cut unless you add additional capacity. A bank of Tesla Powerwalls at £10 to 15k each is going to have a fairly long payback time compared to the cheaper options.
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Two years (or so) on from first puzzling about how large a battery I needed… I think I have two answers; the financial one and the other one.
I went for a 5.8kWh battery (options were this or for an extra £2k 11.6kWh) which is probably about a third or so of my daily average use (excluding car charging). Based on my data over the last couple of years since the system went live, the larger battery size would have probably meant that most days I wouldn’t have needed to use any peak time electricity.
With the smaller battery I only use any significant peak time electricity during November-March and in those months I might have saved around £200 a year.
So it’s a ten year pay back ignoring cost of money.
Frankly I think, for my use, that around a third of my daily average domestic use was about the right battery size, financially.
Having said all that… I do wish I’d bought the larger battery when I had the system installed just because I like having small ongoing bills. I can’t be bothered with the hassle of dealing with another supplier to get the second battery fitted; I tried twice with the original supplier/installer and they weren’t really that interested in doing the job.
Of course… in a few years when the system needs some components replaced I will have the opportunity to get a larger battery I suppose.
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Discharge power rates may also be worth considering here. A Tesla Powerwall is pretty good at a peak output of 5kW. I’ve seen others much lower than this. If you are busy cooking dinner (probably a common time for a power cut) with the car plugged in, then I guess you would question what happens when you are drawing more that 5kW and a power cut occurs. Would the battery trip itself?
I’ve done the sums. For me it’s more about using the battery for load shifting on smart tariffs to make/save money. EPS would be a bonus, albeit at a little higher cost.
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The new Powerwall 3 can do double that.
My most optimistic calculations for batteries is a 15 year pay back, by which time they will be shot….
So for power cuts, we have a wood fire and a gas BBQ. We keep batteries charged on the torches.
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Load shifting and batteries make a lot of sence. I only buy electricity of the grid at a cheap rate at night. The PV set up is nice and means i dont use my battery until the sun goes down. In winter the worst generation i saw was just under 1kWh a few times, but often even in december, it can be 5 to 7 units. In summer it is often well over 35 units per day. I sell my excess at 15p/ unit and buy in at night at 7p/ unit. So, this year my net bill will be £0 and that includes charging my EV.
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What do you mean by this term?
If you mean that they will be broken or have no storage capacity left, then this is most unlikely for over 90% of them.
If you mean that their storage capacity will have fallen by 20-30% after 15 years but will otherwise carry on, then that would be fair enough.
Best regards, BF
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I’ve just moved from oil to air including replacing the 7 year old solar panels for the latest to treble the previous output together with a 5 Kw battery.
The calculation is for a 9 year payback. If the worst happens I’ve instructed my wife not to let them turn off the life support until the end of year 9!
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Interesting. So presumably you have had to leave the government FIT scheme.
What number and power output were your old ones, and you new ones?
Did you get backpack on your old panels? I’m in year 6 of mine, and will make payback in the next few months.
My old panels 2.3 Kw were on the house when I bought it as a new property.
I decided to decommission them as I needed at least 6 Kw and new panels are around twice as efficient.
I shall now apply afresh for payments with my current electric provider.
I didn’t really consider payback on the original panels as I needed to upgrade to 6 Kw plus. I could have kept the old system going and added a new system but I’d have two inverters and roof space taken up by less efficient panels.
Thanks. Interested to know what was the wattage rating of your individual panel before and after are. My 6 year old ones are 300W - not sure how that’s improved, but hope they are a lot better in the winter these days
230 to 440 nearly double. Early reading from the inverter confirms these figures.
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420 or 440w dc is standard issue from pv panels now. 10 years ago it was 200w dc. It might appear a dramatic change but panels are about 20% efficient now.
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