Solar Battery - Yes/No?

Screwdriva

ABrass said:

[For 2022 Q1:] Renewables’ share of electricity generation was 45.5 per cent, second only to the record 47.1 per cent achieved in the first quarter of 2020 when the UK experienced exceptionally high wind speed

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1086781/Energy_Trends_June_2022.pdf

We've probably got to the point where we're arguing rather than discussing so we should knock it on the head. But my final word on the topic is: Assuming that good export tariffs will be available indefinitely is a bad idea. We've seen other countries with high solar contribution where excess power is worthless, we will get there at some point.

Oh yes, we got off to a great start in 2022. Sadly, Q2 and Q3 haven't looked very promising, given the ~50% gas we've been burning. I expect this year will be a lower renewables yield than 2021. 

Now, here's where it gets interesting. Our wind capacity in the UK is well funded and planned, where theoretical highs of > 50% of the mix are possible (as you've rightly pointed out) and will occur on occasion, especially after Hornsea 3 & 4 go online in a few years. Conversely, solar is relatively underfunded and unplanned, with theoretical highs of ~22% of the mix yet to be exceeded. Wind and solar are inversely abundant, which makes me wonder if the grid will pay more for solar on sunny low wind days, as this divide continues to grow? Needless to say, that's my final word on this matter. 

Exiled_Tyke

HHarry said:

Exiled_Tyke said:

"We suspect that you have often heard conversations that go something like this: “We are spending $6 a week, or around $300 a year, at the laundromat. If we bought a washing machine for $800, it would pay for itself within three years. That’s well worth it.” You have just encountered the payback rule.

A project’s payback period is found by counting the number of years it takes before the cumulative cash flow equals the initial investment. For the washing machine the payback period was just under three years. The payback rule states that a project should be accepted if its payback period is less than some specified cutoff period. For example, if the cutoff period is four years, the washing machine makes the grade; if the cutoff is two years, it doesn’t.

We have no quarrel with those who use payback as a descriptive statistic. It is perfectly fine to say that the washing machine has a three-year payback. But payback should never be a rule."

I completely agree with this, so I’m not sure why there’s a disagreement - I certainly hadn’t stated that payback was a ‘rule’ and I don’t think Screwdriva had either.

it’s like the Safe Withdrawel Rate on the pensions forum, which is often quoted as a rule, but would leave you in trouble if used as such.

The payback period calculation seems to be a reasonable way of quickly & easily assessing the financial benefit - with the cutoff period being the expected life of the item in terms of a physical thing.  If the washing machine is likely to die before the savings made recoup it’s cost then it probably doesn’t make a lot of sense.

 I also agree with Heed that the calculation should think about factors like repairs or inflation - more so with bigger investments.

As for assessing the payback of a vaccumm cleaner in Reeds post - it could still be financial; it’s bagless so I’ll save £x on bags over it’s lifetime.  But it could be more subjective like time - I’ll save y hours because I won’t have to sweep the floor and my time is worth £x to me.

The term 'rule' isn't especially helpful. However for clarity as soon as you use Payback as the basis for a decision then in essence you have 'a rule'.  Usually (particularly businesses in making investments) will set a  limit on what is an adequate pay-back period.  But this is arbitrary.  Neither is it appropriate to simple assess the entire life of the project and determine that if is pays back eventually that is acceptable.  If say we take a PV project that had a 20 yr FIT plan and we calculated that it would take all those years to get our money back, the chances are that we would have been better off simply putting the money in a savings account (even with the pitiful rates we've been suffering from).   There are many flaws with payback but the key ones are: 1. decision making using payback as a tool is by its nature arbitrary as some limit of acceptable has to be set. 2. If we are using payback in this way then cashflows after the project has paid back are ignored. This would, for example, make it unacceptable to use to compare projects (e.g. two different PV layouts or one with a battery) which have different payback periods.  3. Most crucially it ignores the time value of money. A pound today is worth more to me than one in a year's time. I can find safe investments (e.g. government bonds) which will reward me giving up my rights to my money for a period of time.   

Boffinboy24

Someone needs to build a nice NPV calculator with pricing scenarios in that everyone can input their own personal figures in and use to make solar decision making even more complex  there can be a variable for the monetary value of being able to tinker with your battery system. Then, like most forecasting, our human confirmation bias will tend to lead us to draw the conclusion we wanted deep down after all….but at least the Excel will make us feel better!

sarahbv7

Hello, new to the forum & not sure if this is the correct one.  We have solar panels & are now looking to install a battery, so we can store energy to use in the evenings, can anyone recommend a battery size / brand.  Our system is 3.99kW south facing, installed in 2016, paperwork says with a String inverter & have a 50% FIT.  I've contacted several companies via online enquiries to get a quote for a battery, but to date have had no one contact me, we live in Shropshire.

EricMears

To estimate required battery size you need to have some idea of how much electricity you tend to import outside 'sunshine hours' or if you're on a multiple rate tariff and also intend to charge battery from mains during offpeak hours the figure you'd need is consumption during peak hours.  If you have a smart meter you can probably get that information easily;  if not then you'll need to take a lot of manual meter readings.

sarahbv7

Hi Eric, think you were responding to my post, last year we bought 5,285kWh of electricity & generated 7115kWh.  I don't believe we're on a multiple tariff, so would be looking to charge the battery from generated pv energy during the day.  We have a smart meter & have been logging our energy consumption regularly & at one point twice daily to look at what was using power.

EricMears

sarahbv7 said:

Hi Eric, think you were responding to my post, last year we bought 5,285kWh of electricity & generated 7115kWh.  I don't believe we're on a multiple tariff, so would be looking to charge the battery from generated pv energy during the day.  We have a smart meter & have been logging our energy consumption regularly & at one point twice daily to look at what was using power.

To estimate required battery size,  it's the (highest) daily use you need rather than an annual figure.  Then battery needs to be rather higher than that since you'd not want it completely discharged.

Petriix

sarahbv7 said:

Hi Eric, think you were responding to my post, last year we bought 5,285kWh of electricity & generated 7115kWh.  I don't believe we're on a multiple tariff, so would be looking to charge the battery from generated pv energy during the day.  We have a smart meter & have been logging our energy consumption regularly & at one point twice daily to look at what was using power.

It would be pretty ridiculous to get a battery and not be on a two rate tariff. There is very often insufficient solar to meet demand, especially in winter. The battery would allow you to shift most of your usage to off peak, saving £hundreds. 

Slinky

We are looking at having a 4.1kw system installed, with either a 4.8 or 7.2kwh battery.  At the moment we are with EDF on a single rate tariff through E7 meters (old style).

We don't know whether to keep E7 and load up on overnight rates in the winter (how easy is this?).  EDF rates are currently 52p ish daytime and 7p nighttime in our area. We use about 8-10kwh a day at this time of year and about 3000kwh annually.

Do I need to get a smart meter, if so, should I get an E7 one? What do most people with batteries do?

sarahbv7

Thanks Eric & Petriix, we are still on what EoN put us on when we bought the house, which was new in 2012, as we moved from Australia in 2012, so learning the way the UK does power, which is still obviously new to us. 

Going back over my records in Feb 2022 on a good day we generated between 10 - 20kWh & best day I recorded was 20.66 in Apr 2022, we didn't record over summer but I'm sure there was a higher day.

Looking at our consumption, we seem to use 5 - 8kWh during the day & 7 - 10 kWh at night (although we have now told our son he can't leave 3 gaming screens on when he goes to bed).

Any suggestions on brand of battery, or installers in our area?  Thanks in advance.