Solar and PV - week 1

[DrFfybes]

We got our panels installed last Thursday, despite lots of research and prep, it turns out there is a lot to learn once they're in.

First is the true cost, not the financial impact, but the hidden cost. Even at minimum wage I've probably wasted the equivalent of £40 a day watching the output drip up and down on the app, and that excludes 40 min typing this and MrsF's time saying "Are you STILL looking at that *&%*% phone?"

The installer was very efficient - a good neat job, battery kit and brackets installed Weds, then it rained so panels up on Thurs morning and live at lunchtime. Paperwork returned, DNO letter obtained, and I went live on the export tariff yesterday (yup - 2 working days).

Panel output is lower than I thought, 400W panels and none have gone over 375W output, possibly cable losses, or optimiser losses? Also late evening we have the curtains closed because of the low sun streaming in, but the panels facing that direction are not putting much out, I guess the low angle means they're not efficient.

The Huawei dashboard is very confusing, consumption so far today is 3kWh, 5.38kWh of which is from the grid! This is probably due to me using overnight leccy to charge the battery (see later) as yield today is 1.4kWh, so it sort of adds up, but not in a way I can get my head around.

Setting up the battery was also time consuming, there is a Time Of Use mode so you can set it to charge from the mains at set periods, which makes sense if you are on a variable rate (see below).

We use about 9-11 kWh/day, so initially the 5kWh battery was just keeping us going overnight the first day or 2, then 2 cloudy days meant it wasn't full by evening and reached the discharge limit overnight. This is not a problem now we're on the Flux tariff (below).

Other considerations which I had accounted for included charge/discharge rates. We bought a more powerful inverter which allows us to draw 3kW from the battery, and charge at 2.5kW. Some have lower limits. What this means is when the kettle/oven goes on after dark the battery is able to power it, mostly, but anything over that is topped from the grid.

The financial returns on these systems is largely dependant on your export rate, and this is where Octopus have come into their own. Their normal tariff is roughly 30p supplied, 15p exported (compared to the abysmal 5p or so from many suppliers). However there is a very hard to find "Flux" tariff available on a beta test, where it is the same as their variable rate escept overnight you get 3 hours roughly half price leccy which is about the same price as you get for exporting during the day, with the trade off of 4-7pm the rate is 42p import/30p export. Consequently it is a no brainer to charge the battery up overnight at 18p so you start the day almost fully charged, and now the sun is hitting the panels and the battery is full I'm already exporting at 18.5p. More importantly it means that I should end the day with a (nearly) full battery, so as long as the battery lasts until 2am, all our leccy is supplied at the overnight or export rates. The last couple of cloudy days the battery wasn't fully charged by dusk and ran out overnight. However starting the day with a full battery should mean that even in winter it has enough charge to get us over this.

I've had my doubts about the financial viability of batteries, in raw terms they don't make sense as daily payback is restricted to the capacity multiplied by the import/export price difference. However if you consider all the times during the day you draw more than the panel output then actual total draw from the batteries can be more than their capacity each day. Add in cheap overnight charging and they become more viable.

One thing I have little doubt about is these iBoost systems, which measure when you are exporting energy and divert it to the immersion heater. With a battery they make virtually no sense, and with a Flux tariff they make none whatsoever. At circa £300 installed, compared to £20 or so for a timer where the water can come on at cheap rate 4-5am and then say midday from the battery (also charged at cheap rate) then why bother. And that's ignoring the "gas or leccy for hot water" debate which is for another post.

So there we are, no doubt I'll change my mind about much of this in the future, but for now all is looking good

Paul

[BullDog]

Thanks for the update. I find it very interesting to hear.

I had previously thought that heating your hot water from excess PV generation was a given more or less. But thinking about it now, using hot water to store energy or using batteries to store energy is pretty much the same thing in the final analysis. So if you have battery storage it's a waste of £300 for the hot water gubbins. Yes, timed off peak immersion heater use is the better option especially if it's less costly than the income you get for excess PV export.

[UncleEbenezer]

Thanks for the update. I find it very interesting to hear.

I had previously thought that heating your hot water from excess PV generation was a given more or less. But thinking about it now, using hot water to store energy or using batteries to store energy is pretty much the same thing in the final analysis. So if you have battery storage it's a waste of £300 for the hot water gubbins. Yes, timed off peak immersion heater use is the better option especially if it's less costly than the income you get for excess PV export.

For hot water, more efficient to heat it directly than to go via a lossy intermediate (electricity).

Friend of mine has both solar PV and a solar panel heating water on her roof. The latter was installed back in the days when solar PV was prohibitively expensive, and works with a big tank, warming the water in the tank.

I recollect asking about the water heater panel many years ago. She told me ballpark figures for gas boiler use: zero in summer, and roughly halved in winter, compared to life before the panel. Not bad!

Thanks DrF for an entertaining tale!

[scrumpyjack]

Does your battery system enable power to stay on during mains cuts? I'm thinking of getting a Powerwall. The economics of a battery are vary marginal but, as we quite often have power cuts, the Powerwall facility to keep everything going automatically in the event of a mains failure is a big plus.

[Dicky99]

Not everyone has your capability to analyse the performance in such a detailed manner which makes me wonder how many people who've made the same financial commitment don't have a scooby what the cost benefit is to them

[servodude]

Panel output is lower than I thought, 400W panels and none have gone over 375W output, possibly cable losses, or optimiser losses?

You wouldn't really expect 100% of rated output unless under test conditions; sounds like you are > 90% efficient which is very good (I'd normally use 80% on my back of fag pack calcs)

[BullDog]

Does your battery system enable power to stay on during mains cuts? I'm thinking of getting a Powerwall. The economics of a battery are vary marginal but, as we quite often have power cuts, the Powerwall facility to keep everything going automatically in the event of a mains failure is a big plus.

Same thinking here too. I have a UPS running my home modem, telephone and router because of power cuts. We don't have much suitable roof area for PV. Maybe about 2 or 2.5kw worth. But we could install that to get a VAT free battery storage unit that we would charge every night on off peak electricity. I think a 10 to 12kw battery unit would almost eliminate day time power tariff use for us.

Simple payback is daft numbers really. But it's not the whole story as you point out.

[DrFfybes]

Does your battery system enable power to stay on during mains cuts? .

No. Standard UK domestic systems must shut down when the grid supply fails. This is to avoid someone coming to work on the supply getting zapped when the sun comes out and everyone's panels kick in.

You can get switchover units like hospitals etc use, not sure of the cost but I gather that are coming down now. If poewr supplies become an issue then we will look at that.

You wouldn't really expect 100% of rated output unless under test conditions; sounds like you are > 90% efficient which is very good (I'd normally use 80% on my back of fag pack calcs)

Maybe I was naive, but then again my 10L bucket holds 10L, my 8m tape measures up to 8M, and my 110 dB smoke alarm frightens the living daylghts out of me

We don't have much suitable roof area for PV. Maybe about 2 or 2.5kw worth. But we could install that to get a VAT free battery storage unit that we would charge every night on off peak electricity. I think a 10 to 12kw battery unit

Might work - prices are coming down slightly as well, about 5% off a panel, our installer said demand has dropped off a cliff the last 3 months, partially as everyone wants them before Summer, but this time last year he had a 43 month order book, now it is half that. Any system needs an inverter, battery controller is just over a grand then about £3500 per 5kWh battery (for a 'branded' one). Effectively you'd be spending circa £15k to halve your electricity bill and secure your supply. That buys a very large Genny

[BullDog]

Does your battery system enable power to stay on during mains cuts? .

No. Standard UK domestic systems must shut down when the grid supply fails. This is to avoid someone coming to work on the supply getting zapped when the sun comes out and everyone's panels kick in.

You can get switchover units like hospitals etc use, not sure of the cost but I gather that are coming down now. If poewr supplies become an issue then we will look at that.

You wouldn't really expect 100% of rated output unless under test conditions; sounds like you are > 90% efficient which is very good (I'd normally use 80% on my back of fag pack calcs)

Maybe I was naive, but then again my 10L bucket holds 10L, my 8m tape measures up to 8M, and my 110 dB smoke alarm frightens the living daylghts out of me

We don't have much suitable roof area for PV. Maybe about 2 or 2.5kw worth. But we could install that to get a VAT free battery storage unit that we would charge every night on off peak electricity. I think a 10 to 12kw battery unit

Might work - prices are coming down slightly as well, about 5% off a panel, our installer said demand has dropped off a cliff the last 3 months, partially as everyone wants them before Summer, but this time last year he had a 43 month order book, now it is half that. Any system needs an inverter, battery controller is just over a grand then about £3500 per 5kWh battery (for a 'branded' one). Effectively you'd be spending circa £15k to halve your electricity bill and secure your supply. That buys a very large Genny

Thanks. That's kind of what I was thinking. Simple payback makes zero sense. I have invested the equivalent amount of money into renewable generation and battery storage instead. Doesn't help with the power cuts but it does help with the bills.

Meantime my UPS keeps the phone and internet working through the power cuts. Pretty much essential now if you have digital telephone that needs power to dial 999.

[scotview]

We got our panels installed last Thursday, despite lots of research and prep, it turns out there is a lot to learn once they're in.

Thanks for taking the time and effort for your interesting post.

I suppose the million dollar question is : from your very early experience of powering the kettle/oven with your system, what's your thoughts on off-peak/solar/battery systems providing whole of home, continuous power input. In particular, replacing the heat output of a gas boiler during mid winter heating demand.

[scrumpyjack]

The Tesla Powerwall does include automatic switchover in the event of mains failure.

https://www.tesla.com/en_gb/support/ene ... power-cuts

[DrFfybes]

I suppose the million dollar question is : from your very early experience of powering the kettle/oven with your system, what's your thoughts on off-peak/solar/battery systems providing whole of home, continuous power input. In particular, replacing the heat output of a gas boiler during mid winter heating demand.

Our inverter can supply 6kW, but our battery output is capped at 3kW. That is either a kettle, immersion heater, small oven, but not the main oven nor a combination of high current appliances. Electric showers in particular need a lot more, and would need a grid supply or bigger inverter. If it is sunny then the solar adds to the available power. A Powerwall can supply more, 5 or 7 kW, still not enough for an electric shower.

An electric boiler uses 10kW or more, so you'd be capped by your battery output. Better to use ASHP in that circumstance, air to water or air to air (we've got the latter in commonly used rooms).

So you would probably time shift/export as much as your batteries can handle for much of the year, but there will be peaks of use where you need to import. With a gas boiler then I'm expecting to import very little 'non offpeak' electric, and be a net exporter over a year, but I'll find out in winter

Paul

[88V8]

Panel output is lower than I thought, 400W panels and none have gone over 375W output, possibly cable losses, or optimiser losses? Also late evening we have the curtains closed because of the low sun streaming in, but the panels facing that direction are not putting much out, I guess the low angle means they're not efficient.

Whilst testing some panels, years ago this was, we noticed that even a thin film of cloud dropped the output significantly.
Presumably yours will need at least an annual clean?

V8

[scrumpyjack]

Panel output is lower than I thought, 400W panels and none have gone over 375W output, possibly cable losses, or optimiser losses? Also late evening we have the curtains closed because of the low sun streaming in, but the panels facing that direction are not putting much out, I guess the low angle means they're not efficient.

Whilst testing some panels, years ago this was, we noticed that even a thin film of cloud dropped the output significantly.
Presumably yours will need at least an annual clean?

V8

We have never cleaned ours in the 12 years we have had them and the output is still fine.

[DrFfybes]

Whilst testing some panels, years ago this was, we noticed that even a thin film of cloud dropped the output significantly.
Presumably yours will need at least an annual clean?

V8

Yes - even in the brightest bit of today some panels peaked at 300W. Being East/West facing they probably never get direct light at exactly 90 degrees, it will always be slightly incidental to the panel face, which could account for it.

So far today we are a net exporter, imcluding replacing the battery we charged off peak. Even better between 4pm and 7pm export is paid at 30p, same as the standard import, so we're coining it in at about 10p/hour Of course come winter the likelyhood of exporting after 4pm drops somewhat, but as we tend to start to make tea about 7pm anyway then we shouldn't import much peak power even then.

[Tedx]

The entertainment value alone must be worth thousands....nothing on the telly? No problem. Let's see how much I save be turning off the box.

Low on power? Reroute the energy from the phaser banks to the dylithium crystals and escape on impulse power.

The imagination has no boundaries

[DrFfybes]

The entertainment value alone must be worth thousands....nothing on the telly? No problem. Let's see how much I save be turning off the box.

Low on power? Reroute the energy from the phaser banks to the dylithium crystals and escape on impulse power.

The imagination has no boundaries

Oh, now there's an idea.

Rewrite the monitoring software so you can rename the components.

[GoSeigen]

Not everyone has your capability to analyse the performance in such a detailed manner which makes me wonder how many people who've made the same financial commitment don't have a scooby what the cost benefit is to them

And this is the main indictment of home solar installations IMO: huge losses in terms of scale. The difficult decisions should be in the hands of experts with access to better information and data doing it on a large scale for lots of customers.

GS

[Dod101]

The entertainment value alone must be worth thousands....nothing on the telly? No problem. Let's see how much I save be turning off the box.

Low on power? Reroute the energy from the phaser banks to the dylithium crystals and escape on impulse power.

The imagination has no boundaries

Oh, now there's an idea.

Rewrite the monitoring software so you can rename the components.

Plus the fact that life is for doing other things besides monitoring solar and PV systems. Anyway very interesting and it would be even more interesting to see how things are going after a year's use.

Dod

[servodude]

Not everyone has your capability to analyse the performance in such a detailed manner which makes me wonder how many people who've made the same financial commitment don't have a scooby what the cost benefit is to them

And this is the main indictment of home solar installations IMO: huge losses in terms of scale. The difficult decisions should be in the hands of experts with access to better information and data doing it on a large scale for lots of customers.

GS

I'd agree if home solar/storage was necessarily at the expense of grid and delivery improvements
- but it's not, it doesn't stop a coherent energy transition plan at a higher level
There's a really very good argument for distributed generation and storage from the engineering point of view of the traditional energy suppliers in that it makes the distribution network stronger; reducing the instantaneous base load requirement because it doesn't have a single point of origin, and making blackouts less likely/common.
The difficult decisions are in the financial and regulatory parts of the market because new renewable sources are significantly cheaper to install and run but the big players are almost exclusively profit driven (depending on your region)