Battery or no Battery - Please help me decide!

uk1

Screwdriva said:

Officer_Dibble said:

My payback time if I hadn't had the battery would have been 4.7 years at current rates. With battery (which I did get) it's 6 years.

Isn't the point of a battery to reduce that number (vs. increase it)?

True.  But it seems to me that this simple view might conceal  more than it reveals.  The battery doesn’t reduce the return on the array - it is simply a lower return on that part of your portfolio of solar investment and reduces the overall return on a larger investment.  That in itself isn’t necessarily a bad decision.   I have several fixed interest savings accounts in my investment portfolio and I don’t refuse to buy a new one because the return in the new one is less than the other investments in my portfolio.

In my mind if I have £5k to invest for a 10% return and I can invest and another £5k for a 7% return and the cash is available and makes more investment sense than other options I have, then I can see why it makes perfect rational sense to invest in both and not refuse to do the second because of the better rate you got from the first which might not now be available.  You seem to be saying that because the second investment reduces my return on my portfolio, I shouldn’t do it which to me seems daft.  Also because prices per unit are only going to go up then the battery return is likely going to increase faster than it does today and buying now means you are getting the return earlier than if you simply wait for no better reason.   The solar array is in practice fixed, but you can throw cash at buying more battery as the electricity unit increases in price within the common sense of not buying more than you need.

Your basic approach that investment should be rational I fully agree with but I don’t agree with your over simplistic philosophical approach which ignores the other factors I suggest.  Battery might not be as good as the PV array but it may still be better than not doing it compared with what else you might do with that cash. You should consider them as separate investments although you might buy both at the same time.  

Simplistic arguments can be toxic but can be a danger to making sound and rational decisions. 

Solarchaser

Well there's been a lot of discussion already.

Some of it very relevant and some folk just trying to push their theories in which they have used to make their choices. 

There are several things that are important in deciding on battery or no battery, and they vary with each person.

1. The most important imo, is how much electric energy do you use annually, if its under say 3500kwh, then I'd say there is no point, as the amount you can offset to the battery, bearing in mind you cant offset everything will not make it worthwhile. The caveat here being recent price increases to electricity may make it more borderline than straight no.
Conversely if you use over 6000kwh, batteries will almost certainly save you money unless you undertake a task to deliberately not have them save you money just to make some point on the Internet.

2. How much hassle are you willing to endure?
If you can endure lots of hassle by offsetting most of your use to off peak, then batteries probably won't make sense.
If you don't want hassle but want to save money, then batteries will almost certainly make sense (assuming point 1 is true).

I had solar only for a number of years, and my good lady got *somewhat tired* of my cajoling her to use appliances etc when it was sunny.
Batteries have made married life much less fractious in relation to how the house runs.
I.e. she does what she wants, and I've optimised the house to do that at the least annual cost.

3. How large are your water tanks, and so how much energy can you divert in a sunny day?
If you have a 100l tank then you will only be able to divert say 4-5kwh a day to it, whereas if you have a500L tank then it's more like 20kwh /day.
A component to that is how high is your water usage, as if you consume 3kwh of water a day, then that's all you can really put back in per day over the course of a week.

(In theory 1000l tank will take 1000w in 1 hour to move the temperature 1c.... so 100l tank will move 10C in 1 hour of 1000w. The calculation isn't exactly accurate but it's good enough for quick maths)

I'm sure I had more points to consider when I started typing, but meh.

I have 20kwh of useable batteries, I also have 800L of water tanks.
The Eddi diverter is a cracking bit of kit, and combined with the zappi is a great combo.

In summer the eddi will take a good portion of the solar, but only up to 3kw, my array can produce 7+kwp and so in that case I have a potential 4kw going to the batteries, and so I guess my point here is the size of your array will make a difference in terms of how much you divert to batteries vs water tank.... as well as water tank size I mentioned earlier.

There are weeks in summer that even with my large batteries and large tanks, that I will still export.
Some export is inevitable,  as is some peak rate import.

Round trip efficiency for most battery+inverters seems to be around 80% nominal, so it's a good round figure to make your calculations from.
So charging the batteries with 10kwh, will give you around 8kwh back.
There are different efficiencies for different use rates etc, but really it will likely settle around 80%.
People have claimed up to 98% round trip efficiency, but I've never seen the data to prove this. 

My own lux system with pylon batteries worked out as 82% iirc last year using battery power import vs battery power export from the inverters 

Screwdriva

uk1 said:

Screwdriva said:

Isn't the point of a battery to reduce that number (vs. increase it)?

True.  But it seems to me that this simple view might conceal  more than it reveals.  The battery doesn’t reduce the return on the array - it is simply a lower return on that part of your portfolio of solar investment and reduces the overall return on a larger investment.  That in itself isn’t necessarily a bad decision.   I have several fixed interest savings accounts in my investment portfolio and I don’t refuse to buy a new one because the return in the new one is less than the other investments in my portfolio.

In my mind if I have £5k to invest for a 10% return and I can invest and another £5k for a 7% return and the cash is available and makes more investment sense than other options I have, then I can see why it makes perfect rational sense to invest in both and not refuse to do the second because of the better rate you got from the first which might not now be available.  You seem to be saying that because the second investment reduces my return on my portfolio, I shouldn’t do it which to me seems daft.  Also because prices per unit are only going to go up then the battery return is likely going to increase faster than it does today and buying now means you are getting the return earlier than if you simply wait for no better reason.   The solar array is in practice fixed, but you can throw cash at buying more battery as the electricity unit increases in price within the common sense of not buying more than you need.

Your basic approach that investment should be rational I fully agree with but I don’t agree with your over simplistic philosophical approach which ignores the other factors I suggest.  Battery might not be as good as the PV array but it may still be better than not doing it compared with what else you might do with that cash. You should consider them as separate investments although you might buy both at the same time.  

Simplistic arguments can be toxic but can be a danger to making sound and rational decisions. 

Ah but therein lies your flawed assumption. You assume that others have the £5K+ of liquidity readily available to spend on an entirely optional, and in many use cases, unnecessary piece of kit. In doing so, you ignore the opportunity cost inherent in such a purchase. As an example, spending £5K on insulation will likely save the average household more than a battery. (And that doesn't factor in the replacement the battery atleast once during the life of the system).

As you rightly shared, simplistic arguments can be toxic but can be a danger to making sound and rational decisions.

Solarchaser said:

1. The most important imo, is how much electric energy do you use annually, if its under say 3500kwh, then I'd say there is no point, as the amount you can offset to the battery, bearing in mind you cant offset everything will not make it worthwhile. The caveat here being recent price increases to electricity may make it more borderline than straight no.
Conversely if you use over 6000kwh, batteries will almost certainly save you money unless you undertake a task to deliberately not have them save you money just to make some point on the Internet.

Entirely valid and should be factored into any calculation. The majority of PV households in the UK are < 4kW/ 3.68 systems. 

uk1

Screwdriva said:

uk1 said:

Screwdriva said:

Isn't the point of a battery to reduce that number (vs. increase it)?

True.  But it seems to me that this simple view might conceal  more than it reveals.  The battery doesn’t reduce the return on the array - it is simply a lower return on that part of your portfolio of solar investment and reduces the overall return on a larger investment.  That in itself isn’t necessarily a bad decision.   I have several fixed interest savings accounts in my investment portfolio and I don’t refuse to buy a new one because the return in the new one is less than the other investments in my portfolio.

In my mind if I have £5k to invest for a 10% return and I can invest and another £5k for a 7% return and the cash is available and makes more investment sense than other options I have, then I can see why it makes perfect rational sense to invest in both and not refuse to do the second because of the better rate you got from the first which might not now be available.  You seem to be saying that because the second investment reduces my return on my portfolio, I shouldn’t do it which to me seems daft.  Also because prices per unit are only going to go up then the battery return is likely going to increase faster than it does today and buying now means you are getting the return earlier than if you simply wait for no better reason.   The solar array is in practice fixed, but you can throw cash at buying more battery as the electricity unit increases in price within the common sense of not buying more than you need.

Your basic approach that investment should be rational I fully agree with but I don’t agree with your over simplistic philosophical approach which ignores the other factors I suggest.  Battery might not be as good as the PV array but it may still be better than not doing it compared with what else you might do with that cash. You should consider them as separate investments although you might buy both at the same time.  

Simplistic arguments can be toxic but can be a danger to making sound and rational decisions. 

Ah but therein lies your flawed assumption. You assume that others have the £5K+ of liquidity readily available to spend on an entirely optional, and in many use cases, unnecessary piece of kit. In doing so, you ignore the opportunity cost inherent in such a purchase. As an example, spending £5K on insulation will likely save the average household more than a battery. (And that doesn't factor in the replacement the battery atleast once during the life of the system).

As you rightly shared, simplistic arguments can be toxic but can be a danger to making sound and rational decisions.

You are clearly wrong on both counts. I made no such “flawed assumption”.

1.  You were rubbishing the choice of having batteries for someone who presumably could resource the purchase of the batteries.  Why was it wrong to assume that someone contemplating purchasing a battery had the resources to buy it?!?

2.  I was responding to your specific comment that adding a battery reduced the return on the total investment and not whether roof insulation is better.  Roof insulation should of course be a greater priority than investing in batteries. My point was a simple one and that was just because the return on the battery might be less attractive than the return on the PV array that in itself is not a good reason to not consider the investment on it’s own merits and that there is an alternative way of considering the investment than yours as extremely well illustrated in Solachaser’s post. 

Boffinboy24

Whilst there is disagreement on the thread, overall the point is that it is not simple to decide.

Before spending the money you need to consider your own usage (higher usage “helps”), uncertainties around prices of the various tariffs that make up the likely savings (if important to you), other factors such as convenience of not having to time appliance use with solar, and the fun of tinkering. Battery size makes a difference too. A smaller battery fully utilised every day may be a better choice than a large one that isn’t. 

When considering financials - especially if you don’t have cash going spare - you need to critically look at the opportunity cost, ie what if you put the 5k in a savings account (which reduces the relative cost benefit of the battery), pension, S&S ISA, something like Ripple etc. based on your own attitude to risk.

For most people, I believe the risk adjusted benefit of the battery will be borderline at very best (especially as many arguments rely on certain tariffs and pricing assumptions that create uncertainty). That said, for my personal circumstances I have finally ordered one, and part of that is not because it makes the best “investment” case (only a bit better than cash savings over predicted lifecycle) but because of some of the other reasons. 

I suspect few people have modelled their battery purchase to the degree a business would to inform the decision by looking at a Net Present Value, Return On Invested Capital, or whatever assessment you pick. That’s fine, as it’s not a business decision and most of us have other non financial interest in it (myself included). But if the OPs personal reason for wanting one is solely financial then you need to do a proper analysis of your own circumstances. 

EcoScruples

ggmf said:

EcoScruples said:

Hmm, if your main aim is payback then at the moment everything screams no to a battery.

Disagree, define ROI or 'payback'? As above my ROI on our 'whole' system is 5 years for electricity only, and this will reduce, when further increases in unit prices are applied. This then reduces again to approx. 4 years or less currently if I include savings due to reduction in gas usage and SEG payments are taken into account.

Everybody's utilisation and requirements will be different, need to look at the while installation.

Yes I ran my calcs again and got 6 years so as long as rates stay high then a battery makes sense but only if you can afford it as its still a big outlay.

For it boils down to the fact I wanted a battery, if I had the choice again I'd buy one again.
It wasn't a loss maker when I bought it and it's even less so now. 

And I get to poor over stats and feel a big smug at not paying the energy company so much money.

uk1

Thanks so much - very much appreciated.  

As I am fairly old and I learn every day and I owe a lot to this forum about my hoped for journey into solar.  It is the friendliest forum I’ve seem on MSE and help and opinion given generously.  

As a more general point, I have learned that I only learn from people that hold different opinions to my own, as those that hold the same opinion as my own have little new to offer with help to see an alternative side and view of an issue. I love changing my mind about things if a better view is logically presented.   That implies that for those that are healthily open-minded and capable of learning from others that they should read and listen and think about what others write and say.  It is the breadth of opinion that enriches and helps those wishing to continue to learn and benefits all and that is why it is much more useful to welcome opposing or even contra-opinion when expressed with good intention. Those that choose to contort and shut down alternative opinion harms fora for all and are simply demonstrating that they have weak argument that they cannot tolerate being challenged. 

Thanks again. And for the forum generally in providing a place for people to ask and learn. 

🙂

2nd_time_buyer

To be fair on @Screwdriva, whilst I have often been infuriated by his anti-China view on components, I have started to come to the same conclusion. But maybe not for the same reason.

Unlike him, I have seen little evidence that Chinese solar components are inferior in terms of quality and reliability or are even less well supported. However, the ethical considerations of our reliance on China are beginning to weigh on me a bit more. Although, I am reluctant to discuss it, despite "ethical" being in the board title.

Anyway, my general sentiment is that, Solar as with life, is not black and white and there can be more than one right answer. To misquote Orwell  "Solar good, Solar and Battery better!" (Or maybe not).

uk1

I have absolutely no issue with what anyone says and I share your agreement concerning caution with respect to trade with China.  Not on the quality issues per se but I’m particularly concerned about using anything from China that might give China unforeseen technical access to something we do and rely on eg phones, power, internet etc.  The frailty of some is that when they decide that they do not like what another poster has said then they cannot agree with anything they say. They will never progress or learn because they already know everything. 

I am for reasons that no one else need trust, have an unusual level of trust that I place on instinct and intuition, and I find myself thinking that where we are today is not where we are more likely be heading and the way forward might be completely different from what we see today. We spend our time discussing and trying to understand choices we confront today but the trajectory might be different and we should consider them when deciding what path to take today. 

It seems to me that with a finite level of UK electricity production that cannot be increased rapidly and a rapidly increasing demand of  24 hour electricity demand that varies considerably over 24 hours that the Octopus approach  of incentivising and encouraging  load to move away from high demand day hours (which could be sold at a premium unit rate) to low demand night hours (which could be reduce in price or even given for free if it releases daytime units that can be sold at extortionate daytime rates) is something that can be achieved extremely rapidly.  

However solar kwh panel improvement seems slow compared to the increase in this demand - but battery although expensive and still not yet as reliable as it need be is readily available.  So I can see a situation where battery could be an increasing share of the overall investment because it is an attractive way to rapidly shift load from day to night to store extremely cheap power.  I can also see an argument where delaying installation of PV arrays until they are meatier in generating self-sufficiency  but battery taking up more of the load because you can do it quickly. 

To head off any anger, I’m not saying this view is “right” it just seems to me to be the more likely trajectory of the different ones that we could choose from.

silverwhistle

Screwdriva said:

 Clearly, cost is a factor for many. Just because you can afford a suboptimal investment, as you highlighted, doesn't mean it makes sense for others. 

This is the second time you've chimed in about PV/ battery returns (based on your ownership experience I presume).  Next time, do us both a favour and resist the urge to make it a third when you see my posts. 

  I think most people on here are posting from their own experience and are not being prescriptive, so I think you may be misreading some of the posts on here and drawing the wrong conclusion.

There seems to be plenty on here with an accounting background and certainly better spreadsheet skills than I have but in any CB analysis there is still an element of value judgement and what weighting you put on various factors. Some people here clearly give a value to the element of autonomy or environmental considerations or peace of mind regarding future bills and other such aspects more difficult to quantify.

For what it's worth batteries wouldn't make sense for me. It's a fairly safe assumption on here that the alternative of roof insulation (or whatever) has already been done, although it's no doubt worth mentioning occasionally that it's something that should be fairly high up on people's priorities.

In my own case as a single low user batteries don't make sense much as I'd like to have one for some of the more emotionally based reasons mentioned above. It's seems even less rational when I have around 50kWh of battery parked on my drive. Perhaps I'll splash out on a V2L cable. Will there be a return? Possibly not, without a deal of faff, but how do you cost the benefit of a power source during a blackout? The cost of your freezer contents, for example?

The best benefit for myself having a battery would be, without going into the full investment of a myenergi controller, to act as a buffer when I use the granny charger. The odd cloud wandering past the sun would no longer be an issue, and I could extend the amount of granny charging I do without risking paying intermittently full rate electricity. I'm not sure how to cost that though..