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Discussion Starter #1
So becuase we are looking to move if we can find the perfect house, I was very wary about getting panels with a long payback time.

I've been given usage percentage from 20 to 85% and with With potentially anything up to 9.8kwp as an option I really needed to know my usage to design the most efficient install.
However up until now my other half has refused to install a smart metre. (don't ask)

However out off boredom I looked at octopus go and was blown away at how cheap it was.

Bulb is 12.99p Go day is 13.75p
Standing charge was 18.75 vs 25p

Meant I just had to make sure I shifted 62kwh a month to break even. (in winter, much less in summer)
My missue does 62kwh driving a month ironicly, I do 110 +, depends on charging at work.
This is a £100 minimum saving.
But I can't have this tariff unless they install a smart metre.
So discussions now insue.
I suspect some off that saving will become a handbag.

So step 1
Set cars to charge on go overnight times to test that's not an issue.
Step 2
Get the Go tariff
Step 3
Assess my usage and size my solar for the fastest payback

Install solar, and two zappis

Step 4
Assess UFH and air to air/water?
 

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If you get a 4kWp array and generate 4000kWh per year, you might just about manage to use 50% of that. You'd be looking at saving maybe £250 per year off your bill (without 'go') and earn another £120 from what you export. I believe that you can't get 'go' and also receive export payments from Octopus currently.

So, best case is a saving of £3700 in 10 years, which is how long the inverter will be guaranteed for. Depending on the total system cost, you might just about break even in that time; and you would likely be in profit if it all keeps working after that. A bigger array would see a higher proportion exported so less savings per kWp.

If you happen to have one or both cars parked at home during the day then you could possibly save a little more. However, at 'go' prices, you will only be spending £10 per month charging them overnight. At that rate, the Zappis wouldn't pay for themselves over their useable lifetimes. In any case I would definitely not install more than one Zappi; just swap the cars around depending on which one needs the charge.

If the numbers add up then go for it, but it's pretty hard for solar PV to be cost effective on a domestic scale since the withdrawal of the Feed In Tariff. Make sure you base your calculations on actual numbers rather than fantasy. Work out exactly what loads you could shift to sunny daytimes; then ask if you could shift them to the 5p overnight period instead. How much would you actually save?
 

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Zappi's don't pay for themselves unless your car is at home when the sun is shinning. When I fitted mine nearly 3 years ago I was able to get them at about £120 each more than a dumb charger and I still don't think they will pay for themselves for quite some time to come as the cars don't sit at home often enough when the sun is shining.
 

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What you also need to factor in is any interest payments, and also the decrease in the value of money due to inflation, which can be significant over 5-10 years, and then also the increase in cost of units bought from the grid over the lifetime of the payback period.

These things however are much harder to predict as you can only guess, or extrapolate from previous data.

You also have ti ask will your energy use go up or down in the payback time? Might you move to a heat pump or other method of heating/hot water, will the cars change and become more efficient, will your job change and access to free charging be gone?

So many questions, the whole payback time thing becomes almost irrelevant and should be done because you want to do it, and the money side of things is very much a secondary concern. :)
 

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To benefit from PV panels it is essential that you can run washing machines, dishwashers and of course car charging when it is sunny. To maximise own consumption and reduce export. In summer my day consumption drops dramatically and so does my night use. All those functions done overnight in winter at cheap rate can now be done during daylight for free. If you have a day job that blows zappi charging on working days. I am lucky, no longer need a day job. I have not bothered with a Zappi because I can monitor by looking at the PV generation and smart meter. Love the smart meter.

Do you have a combi-boiler or a hot water tank? If you have a hot water tank (I have a monster 200 litre tank) you can use a device to use surplus PV energy to heat the tank instead of exporting. Devices such as those made by Apollo Electrics. Thus if I am out on a sunny day my hot water tank is heating up to 70c. There is a mixing valve so the hot water flow is a safer 45c. This also works when you are on holiday, you come home to hot water at no cost.

The solar charger in that case would be better value than a Zappi. You can always set the car to charge at a lower rate or even use the granny cable depending on the PV generation.

I get the maximum feed in tariff and guaranteed export but still enjoy utilising as much as possible of the generation.
 

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To benefit from PV panels it is essential that you can run washing machines, dishwashers and of course car charging when it is sunny. To maximise own consumption and reduce export. In summer my day consumption drops dramatically and so does my night use. All those functions done overnight at cheap rate can now be done during daylight for free. If you have a day job that blows zappi charging on working days. I am lucky, no longer need a day job. I have not bothered with a Zappi because I can monitor by looking at the PV generation and smart meter. Love the smart meter.

Do you have a combi-boiler or a hot water tank? If you have a hot water tank (I have a monster 200 litre tank) you can use a device to use surplus PV energy to heat the tank instead of exporting. Devices such as those made by Apollo Electrics. Thus if I am out on a sunny day my hot water tank is heating up to 70c. There is a mixing valve so the hot water flow is a safer 45c. This also works when you are on holiday, you come home to hot water at no cost.

The solar charger in that case would be better value than a Zappi. You can always set the car to charge at a lower rate or even use the granny cable depending on the PV generation.

I get the maximum feed in tariff and guaranteed export but still enjoy utilising as much as possible of the generation.
Presumably, if you have a smart meter, you only get paid for your actual exports rather than the deemed 50%. You'd be better off getting paid to export the surplus and then paying to heat your water at 5p/kWh overnight.

Solar diverters are almost always a false economy. They have the appearance of giving free energy. However, the installation costs are significant and the potential savings are small. Worse still is that you end up wasting lots of energy by heating water that you don't need rather than exporting the electricity to power your neighbours' fridges. That demand is instead met by gas power stations, which is ironically worse for the environment.
 

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Presumably, if you have a smart meter, you only get paid for your actual exports rather than the deemed 50%. You'd be better off getting paid to export the surplus and then paying to heat your water at 5p/kWh overnight.
GO isn't allowed with the Outgoing tariff at the moment. But there's plenty of cheap hours overnight with Agile currently..

 

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Presumably, if you have a smart meter, you only get paid for your actual exports rather than the deemed 50%. You'd be better off getting paid to export the surplus and then paying to heat your water at 5p/kWh overnight.

Solar diverters are almost always a false economy. They have the appearance of giving free energy. However, the installation costs are significant and the potential savings are small. Worse still is that you end up wasting lots of energy by heating water that you don't need rather than exporting the electricity to power your neighbours' fridges. That demand is instead met by gas power stations, which is ironically worse for the environment.
No, I still get paid the deemed 50% export rate even if I succeed in using 100%. Thats the 25 year deal I signed up for 8 or so years ago.

Installed the solar charger myself, not difficult. I have had it 3 years now. I rely on my woodburning stove in winter for hot water (back boiler). In summer I rely on electricity either off peak or solar PV so in my case it is cost effective. The heat store is super insulated, I only use kiln dried wood or wood briquets in the wood-burning stove.

if I do not use much hot water then it takes less energy to heat and then yes surplus electricity is exported to the grid. Quite happy to export it if I can not use it, it would be churlish when I am paid the export tariff not to.
 

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Discussion Starter #10
Make sure you base your calculations on actual numbers rather than fantasy.
This is why I want a smart meter.
This point is that I have a east west roof that would produce 12% less than a south facing roof but could allow me to consume about 80% off that. I just dont trust my averaged numbers to be the basis off thousands ££ off outlay though.

Do you have a combi-boiler or a hot water tank?
Both

I signed up for 8 or so years ago.
Thanks...good to hear that.. :(


Yeah Zappis...prob right about one. at 65kwh/month @13.76p thats an £8.93 return a month.
And that prob only sunny months.
 
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I have just started my production, it's been running since the beginning of January, and I am very happy with it so far. I can't help you with your tariffs since I live in Sweden, but just to give you an idea...

We had a consultant who did the calculations and after his calculations he recommended a solution which we thought would work well. I am an engineer, so of course, I checked out before (without telling him) just to see what his and my calculations would give, and we were very near. Anyway, we use about 22MWh per year (2019) and our panels are calculated to produce 12MWh per year (11,895kWp) so it will cover about half of what we use. As of this year, we will use more because of my car, which is a PHEV and I got it at the end of last year, so it did not effect last year that much. Anyway, this is the February production so far.

127946


As you see, we have some good days, but also some really bad ones. I think your climate is about the same as mine, I live in the souther part of Sweden, so we are comparable. OK, February so far only saved us the same as we consume in two days, but I expect the figures go up dramatically during the lighter period of the year. Still, I am surprised how much we managed to produce during this bad weather period, with a lot of clouds and rain. What we don't use up is sold back to supplier (though we use every drop of it during winter), so a smart meter is necessary, but we had that already before. I don't know if you have to pay extra for that in the UK. In any case, unless it is sold back, it would not be possible to get any return for the investment, because during the summer we only need half, or even less, compared to the winter use. Our cars are charged outside the most productive solar hours most of the year, except maybe three-four months, so most benefit would be if we would always be able to charge our cars (one EV plus one PHEV) during middaytime, but that's not possible, except perhaps during the weekends. Payback time is calculated to be between 8-10 years. We have 39 panels, divided in two groups, twenty facing south, 19 facing west. The roof angle is 27 degrees. The inverter is a 10kVA three phase inverter and the system is Solar Edge system.

In our case, my other half wanted it for a long time (several years) but I was against it. However, now finally prices are acceptable as well as the efficiency of panels are much higher than before, so I said yes last year, and I am very pleased so far, considering the bad weather.

You can check some online calculators before, or contact a consultant (or both, as I did) before making the decision. It is a big investment, and local conditions play a huge role as well, so don't just jump in without carefully considering as much as you can. Here is one to start with.
 

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If you have a gas boiler then remember to base any potential savings for heating on the price of gas per kWh (typically 3p) rather than the electricity price. Also, it's not how much energy you divert but how much you reduce your import by. It seems like you're asking the right questions. Accurately understanding your usage is a sensible first step. Smart meters and Go or Agile will likely save you a fair bit.
 

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Marli - we are on Octopus Go for the 5p overnight charging, and have our export tariff with Bulb. They pay 5.38p export compared to Octopus’ 5.5p. As mentioned above you can’t have Go and export with Octopus, so you either have to opt for Agile, or take your export to Bulb or elsewhere. Go is best for us as can’t avoid the 4-7 spike on Agile as family with kids. There is no issue having your SEG export with someone different to your consumption tarrif.

We installed solar in September, so are not on deemed export. It seems better to just charge on Go at 5p and get paid export at 5.38p than use solar to charge the cars or heat the water with a diverter (gas being 3.2p). Again, hard to see a Zappi ever paying for itself. I would imagine it breaking long before it pays for itself. We installed 6.2kW of solar at a cost of £6,000.

If you need an Octopus referral code - ours is Warm-Burn-664.

James
 

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Discussion Starter #14
Thanks for the advice on export.
If I could use all my power overnight I like the idea off storing it in the grid at minus point 38 pence :)
 

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Consider getting solar and switching to economy 7 - the two go together rather well. You get the cheaper rate overnight, when you want to charge the car, and the solar helps offset the higher cost daytime units. Bulb do E7.

Counter intuitively, you end up using more units this way as you import a lot overnight at the cheaper rate. I use more overnight units than daytime now - 3000kWh v 2000kWh peak. I only export about 1200kWh as much of the surplus from PV is going into the diverter and heating water - the gas can be turned off from the start of May.
 

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To benefit from solar panels, just sit back and accept that every kWh of power you generate, 1kWh of CCGT power is not used and the closer we get to being carbon neutral.
Whilst I agree with those sentiments, most people need a system to at least "wash its own face" on the costs front.
 

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Whilst I agree with those sentiments, most people need a system to at least "wash its own face" on the costs front.
While I agree with you, I think if you ever get solar panels you must consider it as a financial loss with some limited, but not guaranteed return. My panels are calculated to "wash it's own face" after 8 years (maximum 10) but what if... one or two "bad" years and that calculation is no longer valid... or my consumption changes and will need much more electricity (for example I would buy an EV with a large battery). So if return of investment must be guaranteed, or is critical for me, then I would not have them now. I take the risks because I want to and I am ready to risk the costs. Though I am not a green fanatic, I feel I must do what I can do, and see it more like "return of investment" for my kids and their kids.

I think for people who can't afford that view it is best to sit tight. The costs of solar panels will go down even more, so it will be cheaper (and probably also better, more efficient) later on.
 

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While I agree with you, I think if you ever get solar panels you must consider it as a financial loss with some limited, but not guaranteed return. My panels are calculated to "wash it's own face" after 8 years (maximum 10) but what if... one or two "bad" years and that calculation is no longer valid... or my consumption changes and will need much more electricity (for example I would buy an EV with a large battery)....
I can't understand that. A bad year isn't that much different to a good year. Increasing consumption would ensure that you have more chance of using your own power and help guarantee the return. I was lucky in getting the early FIT, so mine are already paid for and into profit.
 

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Whilst I agree with those sentiments, most people need a system to at least "wash its own face" on the costs front.
Possibly, but looking at the expense of many things people buy, cars in general, holidays and much else, little of these are claimed to be cost effective. At least solar panels have good cost efficiency credentials.
 
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