Solar panels and battery - any real world reccomendations?

Journey said:
You not accounting for exported power though in your cost analysis, and given the government and Ofgem announcement that they are going to be increasing export payments then you could be making money back on exported units as well.
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Can you export with Intelligent Octopus? I had assumed you can't.

Journey said:
They are Intelligent which has a 6 hour window.
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Ah so with a single inverter I could only charge 21.6kWh (3.6 x 6).

Could I be charging the batteries and using additional electricity directly from the grid? Or would it all be going through the batteries, in which case I would need a 2nd inverter as at the end of the 6 hour period I would need the batteries to be 100% charged and I will have needed a 4.8kWh during that 6 hour period to keep everything else in the house going.

edit:

batteryfactory.co.uk

GivEnergy Hybrid 5.0kW Inverter Gen 2

9 UNITS IN STOCK - MUST BE COMPLETE AS A PACKAGE WITH BATTERY Part No: GIV-HY5.0-G2 Storage Systems - Hybrid Inverter The second generation of the GivEnergy Hybrid Inverter is a battery inverter and solar inverter in one unit. It can be coupled directly with solar panels to generate usable...
batteryfactory.co.uk batteryfactory.co.uk

@katie279 Looks like there is a 5kW inverter? So that would remove the need for a 2nd inverter as it could charge 30kWh batteries over a 6 hour period?
 
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No, the 5kw inverter only charges at 3.6kwh, and yes you could utilise the grid at the same time as charging, so if you put your dishwasher, washing etc on during that window you'd be removing your need for it from the batteries and so you wouldn't need such a high battery storage capacity, hence you could get away with 2.
 
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SoliD said:
No, the 5kw inverter only charges at 3.6kwh, and yes you could utilise the grid at the same time as charging, so if you put your dishwasher, washing etc on during that window you'd be removing your need for it from the batteries and so you wouldn't need such a high battery storage capacity, hence you could get away with 2.
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Ah yeah the datasheet shows 3.6kWh, I was reading the wrong part, thanks!

We wouldn't be able to swap any of our usage to during the lower tariff window, we can only really use 5kWh during that 6 hour window with the other ~22kWh outside of that time. The extra 400w/hour we use during the day are for things we are using for work etc
 
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tsinc80697 said:
Ah yeah the datasheet shows 3.6kWh, I was reading the wrong part, thanks!

We wouldn't be able to swap any of our usage to during the lower tariff window, we can only really use 5kWh during that 6 hour window with the other ~22kWh outside of that time. The extra 400w/hour we use during the day are for things we are using for work etc
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I still think as mentioned above the full battery approach is not optimum. I said before my suspicion is go for around 60-75% battery (for the bad days) and spend the other on solar.
I was (until it got changed due to supply) getting 2x 6kwh (90% usable) batteries. I played with a third and the ROI for that went to basically 10 years, which happens to be the warranty.

My solar is new so not a great example, but 8/18 days so far in Dec it produced more than 3kw which would be your shortfall. At practically the worst part of the year. Thats a 5.67kw array west facing, although now also shaded by neighbours.

Sometimes its just worth paying for the extra bit from the grid.

I played with various combinations but found that right now (In fact it was based on 28p units) both batteries and solar would likely generate a payback around 5 years. If you take the marginal position of one of top of the other its a bit chicken and egg, but that likely pushes the ROI out some.
However it also bakes in two contributors to the ROI, so your derisking in total.

Summer months I will be still takign some from the grid, but all will the covered by 7.5p units (unless exceptionally bad weather), where as in winter I will be maxing battery usage and taking some peak priced units. But the peak priced units will be far less.
Eg my model says for 7500 units per year, 780 will be peak, 3900 solar and 2800 cheap units.
 
So far this December our original panels of 3.995kw have produced 115kw.
Over the previous 11 years my December figures have been
131
152
132
153
85
133
129
107
145
124
96

The last figure of 96kw is from Last December.

My target for December is 132. The average from the last 11 years is 126kw. The variation in terms of percentage is greater than other months. We have had 7 days of over 10kw/day, but yesterday was just 100 Watts. We might beat our best figure of 153kw but it is as Dirty Harry said " Do you feel lucky Punk?"
 
Mercenary Keyboard Warrior said:
I still think as mentioned above the full battery approach is not optimum. I said before my suspicion is go for around 60-75% battery (for the bad days) and spend the other on solar.
I was (until it got changed due to supply) getting 2x 6kwh (90% usable) batteries. I played with a third and the ROI for that went to basically 10 years, which happens to be the warranty.

My solar is new so not a great example, but 8/18 days so far in Dec it produced more than 3kw which would be your shortfall. At practically the worst part of the year. Thats a 5.67kw array west facing, although now also shaded by neighbours.

Sometimes its just worth paying for the extra bit from the grid.

I played with various combinations but found that right now (In fact it was based on 28p units) both batteries and solar would likely generate a payback around 5 years. If you take the marginal position of one of top of the other its a bit chicken and egg, but that likely pushes the ROI out some.
However it also bakes in two contributors to the ROI, so your derisking in total.

Summer months I will be still takign some from the grid, but all will the covered by 7.5p units (unless exceptionally bad weather), where as in winter I will be maxing battery usage and taking some peak priced units. But the peak priced units will be far less.
Eg my model says for 7500 units per year, 780 will be peak, 3900 solar and 2800 cheap units.
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The only exception to this is you could go 'full battery' like I do if you have EVs, we've got a Tesla and a Leaf charging to around 80% in the overnight load and then excess solar can charge them - given they've got 100kwh of battery between them, then that's plenty!
 
HungryHippos said:
Same advice I always give when this comes up, combo batteries and panels is best.

In your example you wouldn't even need the 3rd battery though, you just need it to last the day, and I'd wager 20kwh or so of batteries would do that, assuming the inverter is capable of charging them in the off peak window.

Money you theoretically save on battery VAT would go some way to adding panels, but depends on installer passing on the kit saving.
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This is pretty much what I'm doing with the solar and batteries, two inverters and 2 batteries. I'm on Go, not intelligent, so have the 4 hour window to also heat the kitchen/diner floor and also dishwasher, washing machine and dryer and car when needed.
All of that can be done without drawing from the batteries which then takes me through to the next charge.
 
I’m looking for advice on battery storage and, whilst I’m sure my scenario is covered in the 250 odd pages of this thread, I’m struggling to find the answers! My questions are:
  • What is a fair price for supply & installation of a 3kW AC coupler with 2x 9.5kWh batteries? All GivEnergy & excl. VAT. I've been given a quote of £11k, which feels high given no VAT. This is just outside London.
  • Presumably about £1.5k more to add a second 3kW AC coupler so there's 1 per battery?
  • How does having 2x AC couplers work? When the house is importing energy which battery decides to start outputting to compnsate? How do they interact and work things out? Is this built in?
Background information is:
I plan to get an ASHP installed soon. I’ve gone through the heat loss survey etc. and I’m now just looking at minimising running costs.

I’ve already covered reducing demand - I’ve added as much insulation as possible (cavity wall, suspended floor), added wet underfloor heating downstairs and upsized all radiators upstairs (which will let me run at a marginally lower flow temp and therefore reduce electricity demand with the same heat output). The final step in the jigsaw is reducing the ongoing cost of the energy I will use.

From the design calculations, the heat pump is expected to use around 7.5MWh per year for space heating (& output around 20MWh) and around 1.5MWh for water heating (outputting around 4MWh). Excluding my EV (which is charged in the Octopus Go window), my other annual usage is around 4MWh per year. My solar panels generate around 5MWh per year (although obviously all in the wrong months!).

The ASHP installer provided me with a very handy table of indicative ASHP usage by month, which I've broken down for my HP usage. It's quite interesting so I thought I'd share:
MonthAverage proportion of
annual energy use		Avg. Monthly use (kWh)Avg. Use per day (kWh)
January19%1,42546
February17%1,27545
March12%90029
April7%52517
May4%30010
June2%1505
July1%752.5
August1%752.5
September4%30010
October6%45014
November12%90030
December15%1,12536
 
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Water heating, although presumably you use a solar diverter. I guess you can still get rubbish days.

That said I expect they will just be using a standard model as it’s hard to predict and factor in all the variables such as solar.

It’s the same when considering PV. If you have a BEV, your electricity usage profile looks very different to just a house with the same consumption. Likewise a BEV can make no impact on PV or a huge impact depending on how and when it’s driven.
 
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