/ Domestic solar.. is it a good idea?

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mullermn - on 11:08 Wed

Wifey and I have been having discussions around whether we’re likely to move house again or stick in the current one for the long haul. If we commit to staying long term that opens up discussions about more substantial investments in the place - maybe a bit of remodelling, and I’ve also been considering getting solar installed. 

Not sure where to start on this. Does anyone have any experience or previous research to share?

I’m aware that the government has killed off the feed in tariff as of this month (typical that I start thinking about this a month too late!), so financial payback may be harder to achieve, but my understanding is that the net environmental benefit comes much sooner. 

I’ve also been of the opinion for a while that our next car is likely to be electric, so I’m viewing this as a step that would deliver benefits when that happens.

Given the abolition of the feed in rate I’m wondering if there will be a drop in consumer demand over the next couple of months, possibly resulting in discounts or offers from the solar retailers, so this might be something to look at sooner rather than later. 

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summo on 11:17 Wed
In reply to mullermn:

There are a vast range in variables. Basics like where in the UK you are and what direction your roof faces. Too more complex; age of house, heating system.. if you want to just add to the grid, or have a solar water heater. Or use solar towads running an air source heat pump, or heat recovery system. 

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mullermn - on 11:30 Wed
In reply to summo:

I think my incentives are:

1) environmental; I’m too lazy and selfish to be much of an activist, and I like bacon too much to be vegan, so this is somewhere I can use money to buy some karma. 

2) geekery. More technology! Graphs! Who doesn’t like that? Also, If we do have the house remodelled we might end up with electric underfloor heating in part of it due to lack of wall space for radiators, and given the vague plan to move to an electric car there’s a neatness about all these things supporting each other that appeals. 

So it’s more a case of how much is this costing and does it work in reality rather than expecting to make money from it. 

We have an almost exactly south facing roof, sadly not the largest part of it but probably big enough (not done any calculations yet) and we’re in Bristol to fairly southern as the UK goes. 

Edit: Oh, and having just noticed that the feed in rate has just ended I’m wondering if we might see a bit of a crash in the solar market with associated discounts on offer as companies fight for customers. Might be a very opportune time to get involved - if any future govt reintroduces the feed in rate then we’d be quids in. 

Post edited at 11:32
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daWalt on 11:38 Wed
In reply to mullermn:

you could look into solar water heatign rather than PV. This technology has been around for domestic application for decades.

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daWalt on 11:45 Wed
In reply to mullermn:

might see a bit of a crash in the solar market with associated discounts on offer

future govt reintroduces the feed in rate then we’d be quids in. 

The "deals" on offer were always tied up with FIT and some were quirte frankly a bit dodgy. e.g. your contract being passed on to another company, you being liable for repair and maintenance for 50 years with masive termination fees...

personally I think the latter is very unlikely.

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MeMeMe - on 11:51 Wed
In reply to mullermn:

We fitted PV solar to our house when we bought somewhere and it turned out it needed half the roof replaced so we did it at the same time, the panels are part of the roof rather than being on top of the roof (if you know what I mean).

We got in there while there was still some incentives left (although not that much) and I think it cost us about 6k all in. It's worked pretty well for us, we live in Cumbria so not the best place for solar and our roof is SW facing rather than due south but despite that we're looking to pay of the investment in about 6 years (we're halfway though that now). Don't quote me on this but I think half our payback was the feed in tariff and half was savings from using the electricity. Panels should be cheaper now so you may to pay less for a system.

Our system is setup so we use all the electricity we generate, when the sun shines we either use it directly for electrical appliances or if that's not using it all it gets directed to an immersion heater in our hot water tank. A sunny day will generate enough hot water for our hot water use and for our heating.

We also recently bought an electric car but that's not linked to the system as such, it'll draw 7kw when charging where as at best our solar outputs 3.6kw. We can link it up so that it will draw only what the solar produces but we don't have enough panels to produce electricity to heat our hot water and charge our car so we've not done that. We're considering putting up more panels to charge the car but that obviously relies on the car being plugged in when the sun is shining when really we mostly charge it in the evenings.

In winter the solar doesn't produce anything worth having, the difference between summer and winter is dramatic. In winter we heat our water with a back boiler on our wood burner.

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steveriley - on 12:11 Wed
In reply to mullermn:

I love ours - work from home and time the washing/dishwasher for when the sun's out. The metrics you get from Solaredge are great. The thing that's hard to quantify is the saving you would make in not drawing power from the grid when you're generating. That's only ever going to go up as unit costs rise.

Sticks in my throat slightly that the latest change means new consumers are effectively subsidising Big Energy if over-production is sent back to the grid.

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Rigid Raider - on 12:31 Wed
In reply to mullermn:

If you wanted to feel virtuous and enjoy a simple DIY project, do as I did and buy a basic solar water setup from this supplier near Bolton: http://www.solarproject.co.uk/

The whole setup cost me around £800, including an unused 160 litre copper cylinder off Eblag. It's very simple, twenty evacuated tubes (like elongated Thermos flasks) on the roof collect solar energy, which is carried to a coil in the 160 litre cylinder. Cold water flows through that cylinder so it is pre-heated before flowing down into the old cylinder in the airing cupboard where the gas boiler finishes the job. The hardest bit was mounting the frame for the tubes on the roof; the plumbing and electrics were easy and it runs off a 12v transformer plugged into the mains. At this time of the year the top of the attic cylinder is hitting 35c and by July we will be seeing 60c every day, meaning "free" hot water. After eight years I reckon it has paid for itself. It is maintenance-free. The carrier from manifold to coil is water with 25% car anti-freeze and happily I seem to have got the debit balanced quite well.

Post edited at 12:32
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Philip on 19:47 Wed
In reply to mullermn:

Feed in for PV has gone but RHI is still going. I get £1500 / year for ASHP + Solar Thermal for 7 years. (£600/year for 25 years for my Solar PV). And benefit from lower heating costs. The solar PV is more useful as I have an electricity demand for many months.

Planning to replace roof and considering going for a big solar array ~18kw and some batteries. Once I have the electric cars to charge.

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wintertree - on 20:07 Wed
In reply to mullermn:

I think you’ll find some installers dropping their costs a bit but the available potential for reduced install cost isn’t going to make a big difference on top of the panels and the inverter.  Unless they do a really crap job of the roof work to save costs - which you don’t want.  Some real cowboy installers on the “we rent your roof” type jobs where you get free power and they got the feed in.   I don’t think the disappearance of the feed in tariff will affect panel or inverter costs as the UK isn’t a large part of the global market.

The generation tariff is still available, if not the feed in tariff.  I’m currently trying to figure out how to just register for the generation tariff.

Our new 8-panel array is putting out about 12 kWh per day, and we are using about 1/3rd of that on weekdays and most of it on weekends - our EV charges evenings during the week and afternoons at weekends.  

I was happy to spend the money because it chips away at decarbonising supply.  If everyone with the roof space did this it would make a mahoosive difference.  Apart from our boiler and one day a week with the diesel 2nd car, we are now net carbon neutral for ~7 months of the year.  Next up is insulation on the remaining walls, more solar and a heat pump.

There is I think going to be government funding (feed in) for battery load shifting which goes naturally with solar.  I’m building a load shifting system with a Victron Multiplus-II and cheap AGM batteries.  The intent is to move 6 kWh from day time to charging the EV at night and to provide house scale grid backup supply; it also allows the mains connected panels to function and augment battery supply in a grid outage.  Only 30% of the batteries will be used for load shifting so they last, key to this is using a 6 A charge inlet - cheap and custom length and high visibility cables from “Zencar”.

Battery load shifting is obviously not so green compared to shifting when you use the power or using the grid to virtually load shift by exporting then importing again.  

If you’re planning a re-roof, talk to a decent installer about in-roof panel mounting.  Done with an “all black” panel they look great and save money on roof tiles.  My array is all-black on an asphalt shingle outbuilding.  Looks pukka.

In terms of cost recovery, any estimate is very tied to your own financial situation, the aspect of your roof, future interest rates and energy costs.  Maybe it’ll make money maybe not.  Hard to tell!

My personal calculation is that the panels are no worse a place than FSCS protected savings, do more for the environment and give me some piece of mind.

Beware small minded planning (permitted development) limits in conservation areas.  

Also watch out for trees - any growing outside your control that will end up shading your roof?  There is no legal protection for the light environment that you installed panels for.  Likewise future developments.

Post edited at 20:08
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wintertree - on 23:07 Wed
In reply to Philip:

> Planning to replace roof and considering going for a big solar array ~18kw and some batteries. Once I have the electric cars to charge.

I’m considering going from 2.4 kW to about 16 kW over the next few years.

One can only grid connect ~3.7 kW per phase (up to 3 phases *if* you stump up for a 3-phase feed) under the simpler EREC G83/2 route.

More than that and it’s EREC G59 which involves DNO consultation and approval *in advance* rather than the “sure do it just get the installer to tell us” regime of G83/2.

I’ve not had definitive advice on what the power power is taken to be for a battery + solar system; some installers say the DNO consider “worst case” where the battery also feeds the grid in a fault condition.

Would be very interested if you’ve got any feedback or pointers.  

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Jamie Wakeham - on 11:47 Thu
In reply to mullermn:

Now the FiT is gone, making a standalone PV system pay for itself is hard.  There is talk of re-introducing an export payment this summer (there are a couple of energy suppliers already offering it - Bulb and Eon).  If it does get widely reintroduced, it'll be something like 5p/kWh for every unit you actually export.

On the back of a fag packet, if you simply export every unit you generate, a decently sited South facing system will pay for itself in something like 30 years!  The good news is that it will probably last that long, but that is an enormous payback time. 

If you self-consume a good amount, then payback will be shorter.  One third self consumption would mean a payback of 20 years; one half self consumption would give about 16 years.  If you could use every single unit yourself you'd pay back in 11 years.

Clearly the thing to do is increase self consumption - an electric car you charge at home in the daytime is one way to do this.  Electricity driven heat pumps are another (expensive to buy but as Phil says, eligible for RHI payments).  Commercial home battery systems are currently too expensive to be worth it but are coming down in price all the time.

Worth noting that a diverter to push PV energy into an immerison heater won't help you.  You're displacing a unit of gas (probably abut 5p) with a lost unit of electrical export (probably about 5p).  They only ever made economical sense for those on unmetered export.

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mullermn - on 12:28 Thu
In reply to Jamie Wakeham + all:

> Clearly the thing to do is increase self consumption - an electric car you charge at home in the daytime is one way to do this.  Electricity driven heat pumps are another (expensive to buy but as Phil says, eligible for RHI payments).  Commercial home battery systems are currently too expensive to be worth it but are coming down in price all the time.

This was basically the conclusion of my day of research. I love the concept of the Tesla Powerwall (and similar) but currently it's simply cheaper to buy the electricity from the grid than it is to store your own and use it later, bearing in to account the cost of the batteries and the expected lifetime of the unit.

Our decision point for staying in the current house or moving will probably be in about 4-5 years, so I might revisit it then. If a few more Tesla Gigafactories have come online and pushed down the cost of the batteries, or if we're a generation forward in the Powerwall concept then the equation might be different.

Thanks for all the info on this thread everyone, I know a lot more about this than I did yesterday.

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Jimbo W on 13:30 Thu
In reply to mullermn:

A neighbour just installed a 6kw system (20 panels) with a 10kw battery for £10k included. On Monday, which was overcast all day (I know because I was out all day digging the veg patch), with the North East aspect they have their solar panels, they generated 11kwh. They expect very little in winter, but that is looking potentially worthwhile even without the FiT.

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Jamie Wakeham - on 13:39 Thu
In reply to Jimbo W:

That's a bloody good price.  I paid £10k for my 5.7kW system (with no battery) four years ago.

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neilh - on 13:46 Thu
In reply to mullermn:

Be casreful if  you may want to sell the house at some stage.It surprising what information you have to provide on solar panels when sellinga house fitted with them and it may not be as attractive to buyers.

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wintertree - on 15:53 Thu
In reply to Jamie Wakeham:

> Worth noting that a diverter to push PV energy into an immerison heater won't help you.  You're displacing a unit of gas (probably abut 5p) with a lost unit of electrical export (probably about 5p).  They only ever made economical sense for those on unmetered export.

Ecologically it’s probably better to export and displace fossil electricity generation than to displace local gas heating, as the later is a much more efficient use of gas so you save emissions by exporting.

Diverting to water heating only really makes sense when you’re off grid and are otherwise loosing the power.

Post edited at 16:02
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Jamie Wakeham - on 17:25 Thu
In reply to wintertree:

Oh, absolutely. Diverters have never been green; they've only ever been a way to somewhat cynically game the deemed export system. 

Thinking about it, in the last few years there have probably started to be periods in midsummer (bright windy days) when the grid CO2/kWh is actually lower than burning gas in a decent boiler. At those times, a diverter would be a net CO2 saving. Sadly those periods are not that common just yet...

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