Battery size to use off peak power?

[ericmark]

Yesterday for the first time since solar panels fitted with batteries, the battery did not fully discharge before I went on reduced tariff of around 9p a kWh.

Yes produced more than used before, but first time when at midnight I had not gone down to 10% charge, with 3.2 kWh battery.

I suspect I will now see this repeated many times in the summer months, so having more battery capacity will not help.

In heart of Winter the batteries would not charge from solar as solar output to low. So again larger battery capacity would do very little, so in real terms March, April, October, and September are only months were larger batteries will save enough money to be worth while it seems.

But my solar only fitted Sepember and it was Feb before I got split tariff. So for me a little early to judge.

So what do people who have had batteries for longer think, working on a 7 year life, when is it worth increasing capacity?

 

[plugwash]

In heart of Winter the batteries would not charge from solar as solar output to low. So again larger battery capacity would do very little, so in real terms March, April, October, and September are only months were larger batteries will save enough money to be worth while it seems.

What tarrif are you on?

Prices will vary slightly with where you are in the country, but with a postcode of SY21 7EF, "Octopus flux" offers

15.25p import/ 5.8p export between 02:00 and 05:00.
35.59p import/ 26.13p export between 16:00 and 19:00.
25.42p import/ 15.81p export the rest of the time.

With that tarrif it seems like your best strategy would be to fully charge your battery at night, sell any power you generate during the day and then use your battery in the evening.

 

[Why Not Indeed]

when is it worth increasing capacity?

When the cost of doing so is outweighed by the [projected] cost of the electricity you would avoid importing.

 

[ericmark]

I am tied to British Gas so just over 30p 8am to midnight and just under 9 p midnight to 8 am. I have looked at Octopus but swings and roundabouts, may be better but could also be worse, and I don't have enough records to know which over the year which.

My main problem is unless I note power used at 8 am, I can't really work out how much at each rate, an idea yes, but not an accurate reading.

The app from British gas shows in fullness of time kWh, but not £ so a lot of guess work.

So it seems there are two points in each year where storing more energy would save money, but will it save enough to pay for extra battery?

 

[JohnW2]

When the cost of doing so is outweighed by the [projected] cost of the electricity you would avoid importing.

Indeed, but prior to that one probably should have attempted to determine whether the financial benefit of having any size of battery outweighs the cost of having (and maintaining/replacing) it - or, in the case of the older amongst us, whether the benefit is likely to outweigh the cost within one's lifetime (or whether one will be 'worse of' for the rest of one's life because of having bought the batteries/whatever!)!.

 

[hllns]

To work properly it has to monitor import/export which should give you more data. Is there no data in the interface such as on page 6 of this:

https://irp.cdn-website.com/8cc12b47/files/uploaded/Lux%20Power%20Monitor%20SystemUser%20Interface.pdf

 

[ericmark]

Any point on graph will show how much was being used at that point, but the kWh readings are area under graph and near impossible to work out, so I have real time 6.4 kWh imported today, if I look again at midnight I will also see what imported for whole day, so can work out how much at each rate. But need to read at 8 am and midnight. Smart meter seems great switch to £ instead of kWh and will see cost but shows which is useless, before duel tariff got so seemed useful info, but since moving to duel tariff the £ option has stopped working. So there is no real way to work out what is going on, exit fee is £75 so not worth moving supplier, and I have no idea what electric is costing until I get a bill, where the actual meter is would need to stand on a chair to read, so no thank you.

The result is as far as if a battery is worth while or not is a lot of guess work, some indication is given, and the first battery is required to get payment for export so that one is clearly worth while, but as to second to forth as my system can work with up to 4 batteries each 3.2 kWh each then it seems it will not pay for it's self.

Shower will always cost, the inverter can't supply that much, rest could cost nothing but standing charge with extra batteries in summer. But winter solar would never produce enough, so the saving is the use of lower rate power, so looking at 6 months of the year 32p down to 9p approx so battery can save 74p a day per battery without including solar.

I would guess around half of the time, because of solar it can save double that, but only for battery one, and only for around 3 months of the year, so average likely it can save between £270 and £400 a year, life around on 7 years, so around £2k saved, so it is on the edge as to if any saving.

If the figures were saved £4k and cost £2k then OK, but it is so close I can't say if it saves or not. Having one battery OK as it is also an UPS, but having a second, not so sure.

 

[hllns]

Right, I meant the data from the inverter/battery system, the summary graph will show a small amount but it looks like you can inspect and export out the individual elements.

 

[Why Not Indeed]

it is on the edge as to if any saving.

....at today's prices. WW3 is brewing in the middle east, who knows how much you'll be paying in 1, 3, 5 years?

Predictions and Insights into the Default Tariff Cap - Cornwall Insight

Predictions and Insights into the Default Tariff Cap Cornwall Insight is a trusted provider of forecast models for the Default Tariff Cap, commonly known as the price cap. Here, we present our latest predictions for the upcoming cap periods and address frequently asked questions regarding the...

www.cornwall-insight.com

I don't know if prices are going up or will stay the same but I think it's safe to say that they won't be going down.

 

[ericmark]

....at today's prices. WW3 is brewing in the middle east, who knows how much you'll be paying in 1, 3, 5 years?

Predictions and Insights into the Default Tariff Cap - Cornwall Insight

Predictions and Insights into the Default Tariff Cap Cornwall Insight is a trusted provider of forecast models for the Default Tariff Cap, commonly known as the price cap. Here, we present our latest predictions for the upcoming cap periods and address frequently asked questions regarding the...

www.cornwall-insight.com

I don't know if prices are going up or will stay the same but I think it's safe to say that they won't be going down.

Yes we have no idea as to future, we have seen duel tariff, reduce and increase the diffrence between night and day rates.

We have seen the whole idea of storage heaters move from being the best idea since sliced bread, to a system everyone is trying to get rid of.

Oil and gas have never as far as I know had duel tariffs, we had huge gas holders to try and balance out supply and demand.

We have electric mountain to try and do the same with electric, and there is a huge debate as to heat pumps. However storing enough power to run heat pumps is not going to happen, so we can only work with what we have today, to try and work out future changes is pointless.

We have seen the U turn on Diesal cars, we may see the same with heat pumps and batteries. There is no reason why we can't have a sterling engine driving a heat pump, which could be multi fuel. So all we can do is look at today's prices.

 

[Harry Bloomfield]

I don't know if prices are going up or will stay the same but I think it's safe to say that they won't be going down.

They just did, exactly that?

Me personally, with so many tariffs available, I don't really see the point of buying batteries. They are expensive, and will not stand many cycles being deep discharged. The only good point, might be keeping them as backup, for power outages, which is something a small generator could better manage, and without the limitation of capacity.

 

[Why Not Indeed]

They just did, exactly that?

I'm talking about the future, you're talking about the past. That's cheating!

 

[Diver Fred]

Neighbour has 14kW on his roof with 7kW battery. He's also on Octopus 'Agile' for electricity. I've seen his figures and his electric costs for the last 3 quarters is zero and he also as not paid any standing charge on his gas, only what he uses for heating. That is all through what his house exports.
He expects to be moving into surplus this next quarter.

 

[ericmark]

There have been some good points made, since no option as to first battery, it is needed for a few reasons, one to be eligible for payment for export, my panels were fitted to late for grandfather rights, two it stops have to check state of sun shine, and three gives some UPS function, so only debate is if a second, third or fourth is worth while.

It seems likely not, depending on time of year and weather, the time between 4 pm and midnight may be covered or not with battery supply, this is between 1/3rd and zero of the hours in the day, so average is likely around 2 hours per day, so it does seem a second battery is not worth it.

Pre-solar I had considered a generator for emergency supplies, but the main point is if one is home one can do things, but if not home at the time there is no one to start the generator, with solar the supply to non UPS supplies is lost when grid is lost, so the solar is only supplying the battery and those items on the 3 kW UPS supply, which is my central heating and freezers, so likely it can maintain that load for weeks without anyone needed to start a generator or refuel it, so it with solar panels does seem the better method, but without them the generator would be better option.

I did consider having more on the UPS supply, like the lights, however we can get around lights, I do have a spare 13 amp socket to charge phones etc, and so limited it to freezers and heating.

 

[JohnW2]

Pre-solar I had considered a generator for emergency supplies, but the main point is if one is home one can do things, but if not home at the time there is no one to start the generator, with solar the supply to non UPS supplies is lost when grid is lost, so the solar is only supplying the battery and those items on the 3 kW UPS supply, which is my central heating and freezers, so likely it can maintain that load for weeks without anyone needed to start a generator or refuel it, so it with solar panels does seem the better method, but without them the generator would be better option.

Whilst that is all theoretically true, power cuts of long enough duration to impact on the contents of a freezer are 'almost unknown' - I certainly have not experienced one in the 60 or so years for which my household has had a freezer.

I do have a small generator, but primarily to run the CH and broadband router (and phone/laptop chargers if necessary) as well as lights (although that's not crucial, given torches etc.) - but even that has been used very very rarely ';in anger'.

In any event, even if one considers the ('almost unknown') worst-case scenario, I imagine that the cost of loss of a freezer's contents would fade into insignificance in comparison with the capital cost of technological means of avoiding that (very unlikley) event.