greido

Should I Install Solar Panels on the Flat Roof of my Extension?

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Hi, I’ve recently joined and looking for some real-life experience on Solar panels; I’m building a flat roofed extension onto my house and the flat roof will essentially be dead space, therefore, I thought I could possibly utilise this with Solar Panels?

I know very little about these and I’d be very interested to get peoples view on the value of installing them now or as a measure to future proof the house? – The way things are going, electric cars are going to become the norm and as I understand it the country currently cannot produce enough electricity to cope with future demand which will inevitably lead to increases in prices (simple supply and demand) therefore, should I be creating my own electricity in anticipation of this and also potentially running electric underfloor heating rather than gas powered plumbed heating?   

Any thoughts or opinions on the above would be most welcome.

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My suggestion would be yes, but run the numbers carefully wrt orientation, usage pattern etc and your conscience.

 

AIUI domestic feed in tariffs are gone, and instead you are paid for exporting electricity. But otoh solar panels are now cheap, and there may not be much you will miss out on in the next few years by buying now. IMO batterIes have much further to go in overall efficiency gains per £.

 

However, the rates are low (5p per unit ish?), so now the thing is to use your own generation for max advantage which might be washers or charging cars or hot water or a heat battery, but that we still need evolution in the gubbins to let you use that effectively and easily on a single home scale, and that commercial solutions are not quite there yet to make it a no brainier from a financial point of view.

 

Some people are doing it, but there are still elements of home brew involved for maximum effectiveness aiui.

 

That gap may be bridged by eco-conscience (sometimes I do that with extra insulation) plus expecting the tech (particularly battery tech, but also interface-to-car tech  and 2 way meter tech, and perhaps tariff offers) to evolve.

 

So my answer would be provision for it at the least (routes to run wires, install space etc) to avoid butchering anything later, and take.a look. If it adds up, do it.

 

I am not clear whether Sunamp (heat battery) have sorted out their previous problems yet, or whether on demand charging interfaces to cars are here yet, r on the cost effectiveness of batteries.

 

One option is to setup with secondhand panels.

 

Potentially a complex decision as to how far to go.

 

The heating with solar is a bit of a red herring imo because the seasonal time of needing it is directly the opposite of the output from your solar system mostly, and domestic heating has been very successfully addressed by passive approaches. Heating water for your ablutions is a far more fruitful thing to consider there.

 

Ferdinand

 

 

 

 

 

Edited by Ferdinand

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Welcome

I would check to see how much shading the flat roof gets first.  And then what angles you can get panels at to get the most appropriate generation levels to suite your lifestyle.

There is a lot of nonsense talked about the national grind not being able to supply enough capacity.  It is not going to be a problem for the foreseeable future.

As for price, probably not an issue as new generation is coming on stream at under half the price of new nuclear and 20% below current wholesale prices.

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I sourced and installed my own. I got a 4KWp ground mounted system for £1500 with a lot of searching to find everything at the cheapest price.

 

On the basis (reasonable assumption) I can self use £250 worth of electricity in a year, it will have a payback time of about 6 years.

 

Personally I would forget the export payment thing.  If I had been able to claim that, I would have been paid less than £10 this year.  And in order to claim it, yo must have had the panels installed by an MCS contractor, which would add considerably to the cost.

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Welcome.

 

There's a pretty useful website that allows you to put in your location, the orientation of the panels and the number of panels and will give you the estimated generation over the course of a year, month by month, PVGIS:  https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

 

For example, this is the estimate it provides for our PV installation, which is pretty close to what we actually get in practice (we tend to get a few percent more than PVGIS indicates, our average is very close to 6,000 kWh/year over the last five years):

 

image.thumb.png.9d36ca520e4f69080e535715f80120b4.png

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1 hour ago, ProDave said:

I sourced and installed my own. I got a 4KWp ground mounted system for £1500 with a lot of searching to find everything at the cheapest price.

 

On the basis (reasonable assumption) I can self use £250 worth of electricity in a year, it will have a payback time of about 6 years.

 

Personally I would forget the export payment thing.  If I had been able to claim that, I would have been paid less than £10 this year.  And in order to claim it, yo must have had the panels installed by an MCS contractor, which would add considerably to the cost.

What rate do they pay the export tariff at for new installs these days? I just got £27 export for the last 3 months on my 4kwp system

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9 minutes ago, MikeGrahamT21 said:

What rate do they pay the export tariff at for new installs these days? I just got £27 export for the last 3 months on my 4kwp system

per @Ferdinand up thread -- about 5p/kWh

 

There's a league table of 1 here:

https://www.solar-trade.org.uk/resource-centre/advice-tips-for-households/smart-export-guarantee/

(more will appear in Jan when the SEG legislation comes into effect)

 

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So, for us the export payment would be a bit less than the current export payment we get under the FiT scheme (that's currently 5.38p/kWh).  Assuming we export 50% of our generation, then at 5p/kWh we'd get around £150/year for our 6.25 kWp PV array.  The value of our self-consumption is a lot more, as it's all at peak rate, so, again assuming 50% of generation is self-consumed, that's worth about £472/year.

 

Adding the two together gives a net benefit of around £622/year, so not bad.  That's still enough to recover the net cost of our in-roof PV installation after about 10 years.

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12 minutes ago, JSHarris said:

So, for us the export payment would be a bit less than the current export payment we get under the FiT scheme (that's currently 5.38p/kWh). 

Oh,  currently the league table has Octopus offering 5.5p on their fixed tariff, so actually beat your current FIT export rate  - I didn't quote it exactly as it's liable to change between when anyone looks at it and when you go to claim it :-) and not realizing that 0.5p would make all the difference.

 

Also Octopus offer some sort of time-of-day variable rate, I assume that only makes sense if you have battery storage and can cleverly time when you export (on the assumption that on sunny days the rate will plummet exactly when everyone else is generating), but I haven't actually researched that at all.... again very liable to change between now and when I eventually get connected to it

 

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1 minute ago, joth said:

Oh,  currently the league table has Octopus offering 5.5p on their fixed tariff, so actually beat your current FIT export rate  - I didn't quote it exactly as it's liable to change between when anyone looks at it and when you go to claim it 🙂 and not realizing that 0.5p would make all the difference.

 

Also Octopus offer some sort of time-of-day variable rate, I assume that only makes sense if you have battery storage and can cleverly time when you export (on the assumption that on sunny days the rate will plummet exactly when everyone else is generating), but I haven't actually researched that at all.... again very liable to change between now and when I eventually get connected to it

 

 

 

I've been following the Octopus variable rates, Go tariff, etc for a while, but can't get the sums to add up for our pattern of use.  I also suspect that these tariffs are very much an inducement to get more people to have "smart" meters, so that tariffs can be made more complex, and harder to compare in terms of value for money.

 

One problem is that we need most of the 7 hours E7 off peak period in order to charge up the floor slab, and this isn't something that can be speeded up by just increasing the power input, as doing that increases the flow temperature, which then tends to cause a temperature overshoot.

 

Battery storage helps a tiny bit, but not as much as might be thought at first, as the cost of re-using the stored cheap rate electricity is about 1.2 times the unit cost, because of round-trip losses.  That makes the 8.148p/kWh E7 off-peak rate really 9.78p/kWh for us.  The Go tariff is marginally better, but again the 4 hour time slot is tight, allowing for the slow down in charge rate of batteries during the balancing phase (a 10 kWh battery storage system may only charge at a mean rate of around 2 to 2.5 kW in practice) and allowing for the 30 min period of uncertainty in timing at either end of the 4 hour period (makes the 4 hour slot effectively around 3 hours, until such time as some means of accurately syncing meter 30 minute tariff rate change periods with loads is implemented).

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Remember, the new export payment only pays actual export, metered via smart meter, not deemed 50% of your generation as with the present FIT system.

 

That is why our export payment would be so low, because we self so much of it.  It is far better to self use it and save in the order of 14p per KWh than export it and only get 5.5p per KWh

 

I find a 4KW system is about optimum if you are relying on self usage. By dumping excess power to an immersion heater you can use most of what you generate if nothing more useful is consuming it. It is really only in the mid day peak that we can generate more than we can use at times.  Larger systems than 4KW and it will become harder to self use all of it, and that I feel is where battery storage will become more important.  My first years assessment is battery storage with only 4KWp would not have been particularly useful. 

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