Posted By: ScoobyBI read stuff that says PV technology has efficiency up to about 20-25% nowadays

I read stuff that says the Flying Spaghetti Monster created the world. I know which I believe.

Posted By: ScoobyBSame with solar collectors, technology has improved but is it more efficient to heat the water directly or make the electricity to heat the water…..?

It's more efficient to use solar thermal panels to heat water. But as things stand today, it's more economical to use PV because of the huge subsidy that is the FIT. In theory there will be a subsidy for solar thermal next year.

PV efficiency is nothing like 25% yet, more like 16 to 18% at best; less than this when the panels heat up.

Solar thermal is more efficient than PV, as has been pointed out, by a quite significant margin. If you ignore the bias that the FIT subsidy puts into the equation at the moment, then you can get around 3 times as much energy (maybe more) from a solar thermal panel, per m², than you can from a PV panel. What's more, evacuated tube collectors can continue to work in cold weather, as long as there is some solar irradiation. For hot water heating this translates to needing around 1/3 the collector area for a solar thermal installation as would be needed for a PV installation, which may be a significant consideration. The final point is that a solar thermal installation may well be cheaper than a PV installation for a given hot water requirement.

Solar PV + heat-pump (separate or integrated) will take about the same roof space to generate a given amount of hot water as solar thermal would, and any excess can be exported via the grid rather than uselessly boiling water in your system and stressing it. It is more expensive than solar thermal though.

I have lots of PV but an hoping before April to put up a little bit of integrated PV/T (PV + thermal) to get both from the same roof area (though probably a little more space than pure solar thermal).

Rgds

Damon

CW said "but then electricity costs three times more per kWH than say gas."

used to but gas is getting more expensive all the time ( did you mean kWh ?)

How much per m2 is PV?

Thanks for the PV vs Solar comparative advice and i will definately research the Flying Spaghetti Monster's work after i have finished this project.....

qeipl/SteamyTea - agreed, a good gas filled 2G or 3G upgrade for the whole house is also being priced to improve the energy needed in the first place.

My question still stands about todays PV efficiencies and what materials and/or panel suppliers outperform those concieved year sa go but still on the market today?

Does anyone know any worthy suppliers in the SE...?

<blockquote><cite>Posted By: ScoobyB</cite>My question still stands about todays PV efficiencies and what materials and/or panel suppliers outperform those concieved year sa go but still on the market today?</blockquote>

The majority of PV panels that are commercially available today are using monocrystalline/polycrystalline silicon, (with a few using lower efficiency amorphous silicon on glass) which is all pretty mature technology and delivers around the 16 to 18% efficiency mark (a bit less for amorphous cells). There are more efficient technologies available, but they can't yet compete on a "cost per kW" basis.

The nice thing about these silicon technology panels is that they are a known quantity when it comes to performance over their lifespan. We know they degrade only quite slowly, so have a usable life in excess of 20 - 25 years. Some of the newer technologies look promising, but scaling up small, lab-scale manufacturing techniques to the sort of manufacturing volume that current panels are being produced at is pretty difficult, and requires a big investment. It seems that recently manufacturers have instead been concentrating on driving down the production cost of conventional silicon cells, by techniques such as ribbon production of silicon crystals, rather than sliced wafers as used in the semiconductor industry. This promises to make big reductions in cost, because ribbon wafer production is a near-continuous, rather than batch, process. The cells are of similar efficiency to cut wafer cells, so the development is purely a cost-cutting one.

As area isn't too great a limiting factor for the majority of installations, improved efficiency is really secondary to cost per kW. In fact, if you have the roof space, then there is a reasonable argument to support buying the less efficient amorphous cells right at the moment, because panels like the Pramac ones are probably around the best value in terms of cost per kW than the more efficient monocrystalline/polycrystalline ones.

You could go the solar thermal oil route with TEG's to provide DHW, electric on demand and UFH. Linked to thermal oil cooker and thermal oil washing machine most (admit I have only found commercial units as yet which are a bit chunky) of your energy will be catered for.

As I mentioned on the East/West ST thread, if you over generate with PV you can export, if you over generate with ST you can only stop or dump.
I use roughly 5 to 6 kWh a day to heat water (not counting all the tea), so that is about £360 a year.
If I accept that it can deliver 90% of my DHW needs for 70% of the year, I could save £227 a year. On the face of it pretty good (and something I would do if I was not trying to move house). But with loan rates around 8% from my bank, to buy a system that could cope with that would cost around £4000. That would give a ROI of 0.56%. Hardly worth it as I can get 5% on my current account and the same on my saving account at the same bank.
PV/ST may be a good investment if fuel prices rise above inflation, but seems the government want to keep the domestic price down. This is probably why the snake oil salesmen are out, they are selling an impossible dream based on false accounting and faulty logic. Or is that the Banks that only do that

and where to get 5% on a current account, please ST?

Posted By: dimengineeryou must be paying around 18.25p per kWh. Which is a lot. - my Gas is around 3p, my Electric is about 12 - 13p.

That is my day rate, though I am on E7 at about 5p a unit. No gas here. Was not thinking when I typed it. So I will save even less then, though will get a hot shower at night some nights.

Posted By: RobinBand where to get 5% on a current account, please ST?

Santander if you put in a grand a month, interest on that rate up to 2.5K and if you transfer from another bank they offer you 100 quid as well. Nice that they are giving my loyal customer money away. They offered me 5% but at a cost of 10 quid a month (plus some useless car breakdown cover and phone insurance) Think that works out at about 150 quid for tying up 3k but with a cost of 120, so that is 30 notes or 1% for loyalty. I did not take up their 'loyal customer' offer.

I have no idea what it would cost to have an installer fit 10m^2 of flat panels (think that is about what I would need to get 1260 kWh of heat (mean sunlight is 135W.m^-2), but would think 4k should do it.
The point I was making was that as a cash investment there are better options.

Posted By: wookey
Still, the point stands that ST is _much_ more efficient per unit area, IMHO it's a real shame the the govt is currently encouaging people to fill their ST space with PV. I enoucarage everyone to try and take a longer-term view and leave some space even if they aren't doing it now.

I don't think that solar thermal is that much more efficient than PV. I used to believe that, but since monitoring my own systems I've discovered that it isn't true. On the best sunny day solar thermal outperforms PV by about 2.5 times, but on a cloudy day PV outperforms thermal by a similar amount. Some days thermal will give no output at all - PV will give some output under all daylight conditions. Overall, since the middle of June thermal has given about 70% more output per unit area than PV.

Of course, that is gross output. Most of the solar thermal energy is wasted, whereas all the energy generated by a grid tied PV system could be used.

Interesting comments Damon and Bill, Some lessons still to be learned on how to use low grade solar thermal heat though!

We use gas to make our hot water, and I can accurately say we use 6KWhr/day gas in the summer. I estimate that 4KWhr/day appears out of the shower- the rest is pipe loses, boiler losses, cylinder losses.
As solar thermal install would replace this for perhaps 200 days/year, so taking away the need for 6*200 = 1200KWhr gas use.
But we could probably use only 4*200 = 800KWhr of electricity to do a similar job for us - i.e. nice showers. Even if we insisted on still using a cylinder, the elec energy use would be less than the gas useage, as elec heaters are 100% efficient and are inside the tank.

I had a quote for a pro solar install - it was £4000* for a guaranteed 1000KWhr thermal energy/year.
The competing technology is a fraction of the full 4KW pk solar PV installed, yielding 3280KWhr/year of electricity for £12000.

So for my circumstance:
£4000 replaces 1200KWhr of gas with solar thermal
£12000*800/3280 = £2930 replaces the same gas useage**

* I am aware that diy is much cheaper, and it is fully my intention to do this *one day*

** assumes we can use the grid as a free battery, and that we don't use a storage tank/pipes etc, ie. have an electric shower, and critically that we get the economy of scale of PV install, for which there is no point doing with solar thermal.

The figs seem to show that I should always get more PV pro installed, rather then get a small domestic pro thermal install. The economies of scale are against small scale thermal, if the alternative is lots of PV. I feel a bit heretic saying this... I'm sure somebody will set me straight soon...

Posted By: JSHarrisWell, being pedantic I'd have to say you're wrong, as 1kWh of energy in one form is exactly the same as 1kWh in another form.

Being even more pedantic, I'll have to disagree.

Firstly, energy isn't a 'thing' that you can have 1 kWh of. Its a property of a system in the real world. So in the same way I can have 4 apples and 4 pears, its true to say that 4 is the same but it doesn't mean that apples are pears.

Secondly, 1 kWh of 'heat energy' as used in this conversation, isn't really energy at all. Its the difference in energies between some arbitrarily defined 'ambient' quantity of energy and the energy of the system under consideration. If you refer the heat energy to absolute zero, it changes the numbers quite a lot.

So I agree that we shouldn't muddy terminology, but I think its also possible to oversimplify concepts.