Replacing concrete interlocking tiles with solar roof

frozen_wastes

I've long considered installing solar panels on my roof, with a goal of doing so by the year 2020.
















But rather than limiting the rated output to 4KwP which seems to be the popular rated size, I'm considering longer term electricity demands for my house with a need to accommodate an electric car in the future. So my thought's are that I want a solar panel array to be maxed out to occupy the predominantly sunny sides of the roof (roof edge to edge edge).

I'm not wanting a panel array that sits on top of the roof tiles, but I'd rather take the tiles off the roof, and make the solar panels an integrated part of the roof.

Several advantages that I can think of:
- Maximum electrical output
- Aesthetic quality
- Leaves, pine needles, seedlings etc don't have nooks and crannies to fall into.
- Reduced static load on underlying structure.

Biggest design constraints:
- still need roof access so I can sweep my chimney (stainless steel circular cross section), and clear leaves and debris (trees to the west of my house)
- Bungalow is L shaped, and I'm looking to build panels into the valleys of the roof. Do triangular panels exist?

So my question is:
- Who can supply integrated roof mounts / systems?
- Is it worth employing an architect / surveyor to design and supervise such a project?

I thought I'd ask here before consulting any companies. I live in Aberdeenshire.

Martyn1981

Hiya, triangular panels exist, Google trienergia, here's there brochure.

Integrated panels also exist, and again you should find a lot on T'internet, though they don't come up so often on here.

Another option might be to wait (you said by 2020) and see what develops with the Tesla roof tiles. These will start to be deployed this year, and the toughened glass tiles look great and are supposed to be 'tough as hell'. I think Musk even joked about offering an infinity warranty on them.

If you can go bigger, then definitely go bigger. The 4kWp popularity was that the old tariff dropped down after 4kWp, but now the first band is upto 10kWp (and 10-50kWp gets slightly more). But you will need to ask your DNO for permission to export more than 3.68kW, otherwise the system will need to be capped, or employ some clever storage to take excess. If you are on 3 phase then the limit is triple that.

frozen_wastes

Martyn1981 wrote: »

But you will need to ask your DNO for permission to export more than 3.68kW, otherwise the system will need to be capped, or employ some clever storage to take excess. If you are on 3 phase then the limit is triple that.

Very interesting to note. The long term thought going through my head is to tie the PV panels to a high voltage DC bus on to which a battery storage unit and electric car charger could be connected. Then there could one inverter to couple the DC bus to the existing 240V AC distribution. The objective is to strive towards grid neutrality for as many months of the year as possible.

Objective with a DC bus is to minimise conversion losses from panel array to battery, and from stationary battery to DC car charger. It's also to boost the available current needed to charge any future electric car. I read somewhere that 80A is needed to future proof your car charging requirements. My main incomer is rated at 100A - I've got no intention of needing to upgrade this connection. So I need to achieve 80A in house using the battery and PV array.

I'd think about doing this project in phases - solar PV first, then stationary battery storage, and then electric car. Timescale depends on economics.

I discussed a calculation with a colleague to see whether PV was worthwhile without subsisdies. I reckoned that in terms of my existing £300 annual electricity bill, it wasn't worthwhile. But in terms of a £1600 annual diesel bill, a PV array could pay for itself within about 5 years if it could generate 5000kwh annually to cover 20000miles of electric driving (based on performance figures from Model S 100D). That got me excited, so now I'm investigating options.

Martyn1981

I think you are on the ball, and your timeframe helps as there are a number of issues:

1. Domestic storage is still early and expensive, so it needs a few more years to come down in price and start to standardise.

If you're interested there's a thread on it here

On-grid domestic battery storage

2. PV subsidies, are very low, but the good news is that they don't drop much more over the next 2yrs (from 4.04p/kWh today to 3.55p/kWh in qtr1 2019) so no rush, and maybe ..... just maybe ..... probably not though ....... the government may do something to boost them a little bit!

More info on PV in the FAQ's (see my autosig).

3. There are DC battery systems that work with the inverter to divert to storage on top of the 3.68kW export. I think these are called battery inverters, but a good installer will be able to advise, and I think many more DC systems will operate this way (be able to operate this way) as we move forward.

So, imagine a great big 10kWp PV system, that in good sun will probably hold around 8kW of generation. If the inverter and batts are big enough, then you might be able to charge the batts at around 4kW, whilst 'only' exporting 3.68kW, and working within all of the DNO rules.

4. PV panel efficiencies are rising slowly, but steadily. 17%+ efficiency 'normal' panels of about 285Wp are now common, and more powerful 'normal' panels (before going into high efficiency panels) are available. This means you can squeeze a greater and greater amount of kWp into the same roofspace, and for the same amount of labour, roof rails, scaffolding etc.

You can't wait forever, obviously, but you do have time to plan and plot and research.

You might also be interested in a thread on adding a small ASHP, as batts would work well with this, and provide supplementary heating and efficient use of a large PV system.

Discussion ... ASHP(Air/Air) with Solar pv ....


[Edit - Forgot to mention, certainly worth comparing PV costs to diesel fuel savings, but in fairness you should max savings out at leccy import prices (not diesel equivalent value per kWh). I have seen estimates of the PV being worth around 40p/kWh, but this isn't really true since there is a natural cap on savings ..... just buying the leccy instead. M.]

EricMears

frozen_wastes wrote: »

I'd think about doing this project in phases - solar PV first, then stationary battery storage, and then electric car. Timescale depends on economics.

Possible snag with this is that if you fit a lot of solar tiles without the supporting power usage items you'd need DNO permission to export far more than they might happily allow.

frozen_wastes

EricMears wrote: »

Possible snag with this is that if you fit a lot of solar tiles without the supporting power usage items you'd need DNO permission to export far more than they might happily allow.

If I could get a time of day electricity tarriff, then it may be worthwhile to invest in a stationary battery before a PV Array, however I do note that batteries are very expensive right now, but I'm anticipating large price drops.

EricMears wrote: »

You might also be interested in a thread on adding a small ASHP, as batts would work well with this,

I've long considered heat pumps, but have steered away from them on the grounds of cost and hassle. At the moment I have an LPG boiler (upgraded 2011). The received opinion is that I need to achieve heating with a low water temperature (e.g. 45 degrees instead of the present 65 degrees) in order to achieve a good Coeffient of Power with a heat pump. Achieving that would be tricky with my existing steel radiators. I've long thought that underfloor heating systems would be needed to achieve this. That's too much trouble and cost. However I've noted that replacing steel rads with aluminium might be a viable path, since they have higher BTU ratings for a given volume. My main concern with aluminium though is electrolytic corrosion. I've got copper pipes, which I think would react with aluminium.


My ideal path to ASHP would be a straight boiler swap out, and possibly the radiators. But I'd need to consider whether this on its own is possible without further interventions.

EricMears

frozen_wastes wrote: »

The long term thought going through my head is to tie the PV panels to a high voltage DC bus on to which a battery storage unit and electric car charger could be connected. Then there could one inverter to couple the DC bus to the existing 240V AC distribution.

There's also a possible snag there. Any generation you use before the inverter (and hence before the TGM) will not count towards any FIT payment. Unless of course you can find some way of measuring the DC output that is acceptable to the FT scheme regulator.


BTW it wasn't my suggestion to add a heat pump - that was Martyn's

Martyn1981

Martyn1981 wrote: »

Another option might be to wait (you said by 2020) and see what develops with the Tesla roof tiles. These will start to be deployed this year, and the toughened glass tiles look great and are supposed to be 'tough as hell'. I think Musk even joked about offering an infinity warranty on them.

Looking at the Tesla GB site, it turns out that Musk wasn't joking after all:-

Infinite Tile Warranty

Made with tempered glass, Solar Roof tiles are more than three times stronger than standard roofing tiles. That's why we offer the best warranty in the industry - the lifetime of your house, or infinity, whichever comes first.

No prices yet, as far as I can see.

Martyn1981

frozen_wastes wrote: »

My ideal path to ASHP would be a straight boiler swap out, and possibly the radiators. But I'd need to consider whether this on its own is possible without further interventions.

If you are considering going the whole hog, then again something to ponder over time, however the ASHP thread on here is about just adding a small aircon type unit to maintain the temp in just one (or two) rooms, and avoid running the whole house central heating.

By using a small system, and cherry picking the better COP times (daytime and warmer months) you could get a good return/balance v's changing the whole house system over ..... unless that's on the cards anyway.

Exiled_Tyke

Is there a significant difference in the performance of integrated panels? I know that without the airflow behind them they get hotter than the more usual over-roof panels, but how much difference does this make to the output?

groovyf

Martyn1981 wrote: »

Looking at the Tesla GB site, it turns out that Musk wasn't joking after all:-

No prices yet, as far as I can see.

Going via the US site, there's a calculator that can be used to determine cost, etc. I randomly put in 650 square feet (I'm guessing at the size of both roof faces I have - a very vague estimate!)
The roof tile cost (installation, etc included I believe) would be $17,200.
I would expect a similar cost in £ (as we always get stiffed on conversion rates)