PV's vs Tubes?

pwurple

Hi all, just started looking into this, we have our planning permission for a small extension, including installation of solar panels, so I'm here to ask for your experiences in both

Which to go for is the question....

For hot water, we have a 150litre tank, located on the ground floor, which is barely used as our showers are electric. I'm assuming if we put in tubes, this also means adding a pump somewhere and changing our showers and associated plumbing costs. So it's going to be more expensive to install. We had a pumped system in a previous house, and honestly the noise of it in the internal hotpress nearly broke my heart waking the baby. Where do you guys keep your pumps? We don't have an attic, the house is bungalow, which will become dormer.
We use one tank of oil per year for heating (price has dropped recently to about 500 euro for that), and the house is well insulated.

Electricity, we already have a night rate meter, we use roughly 500 day units and 450 night units per billing period.

So because our electricity bill is double our heating bill, and would be less expensive to install because I don't need to replace showers or replumb, I'm leaning towards PV's. Looking at pricing for a 3kWp system, with an immersun for any overage, it looks like it would cover it's cost in about 8 -9 years. (I'm assuming it would cover half my day units)

Can i get some PV usage experiences, maintenance problems, anything I shouod look out for, or am I being crazy in the reasoning above?

Or is there yet another option, does anyone do both together?

I've two options on the roof, 45 degree incline due south, and / or flat roof on our planned extension. No overshading on either.

Calahonda52

My pump in a dormer is in the garage, seated on an acoustic rubber pad, with qualplex pipes fixed along the wall to kill the vibration and flexies at the pump and its not a bother.
Its a top quality Wilo pump, 25 years running and only one repair job: the hot press install was always a noisy option.

I also have a with near the alarm panel to turn it off if needed at night, the toilets are dual flush so unless you get a dodgy takeaway or a bad pint.....

Can u get planning for a 3kWp system?

I would go PV and not thermal.

Does you payback calc include storage, inverters etc and what assumptions have you for PV generation vs demand.

I am not an expert but I think the math is flawed with that payback which seems overstated.

pwurple

Payback does not include storage, because I'm not getting any battery pack installed, overage will be going to the hot water tank.

3kWp system is 12 panels. I put it in the planning drawings and application along with everything else. No mention was made of it, planning was granted. I don't know whether I needed to or not, but I have it now anyway.

Explain to me what is included in "inverters etc. "... That's what I'm trying to determine, whether something is missing from my quotes, and whether the stated generation rates are overstated. I've been told to expect 800-850 kwh year for 1kWp. So, 2400 per year for 3kwp. Is that acceptable

This is what I want to know, I can't tell if the information I'm getting from the suppliers is overstated.

Where do I get real world info?

Calahonda52

Re
overage will be going to the hot water tank
how is this going to work?
what voltage is from the panel array?
If its not 240v then what kit have you got that will run on the panel array output?

At the risk of incurring the wrath of Zorro , my rule of thumb for PV without any feed in tariffs has been that payback is equal to panel life, c 25 years.

I am just a layman here but am trying to elicit from you the math behind the proposals you have so as the experts can help you with having to do any "dental extractions" for the relevant data:D

pwurple

Calahonda52 wrote: »

Re
overage will be going to the hot water tank
how is this going to work?

Immersion Heater in the tank

I am just a layman here but am trying to elicit from you the math behind the proposals you have so as the experts can help you with having to do any "dental extractions" for the relevant data:D

Don't really know what you mean here. No teeth involved. :0)

Calahonda52

yes in the tank but if the tank is at 60 already what happens?
also overage suggests that u will use some in the rest of the house so I am asking what and how

as asked already
what voltage is from the panel array?
If its not 240v then what kit have you got that will run on the panel array voltage output?

the math is pretty simple
Input calc
Solar radiation at your location: maybe 800kWh/meter squared / annum
ditto at ur location at 45%, adjusted for daily movement of the sun
conversion efficiency factor of the panels, maybe 8% to 10%

output math, before cylinder
daily demand profile,
does it match input?
It most lightly wont so....

If you lay out the math and underlying assumptions from the proposals we can comment

pwurple

Sorry, the word "math" is like nails on chalkboard. It's maths, or mathematics, or really, since this is completely trivial, plain ould sums!

There is no panel array to give voltage, because there is nothing at all in existence except an empty roof and planning permission for the very open-ended 'solar panels'. The very literal blank slate!

I've given you the family usage, and the roof orientation. That is all that exists. The rest is imaginary, to be planned, data to be gathered. I am at the start of this investigation. I've got some back of the envelope numbers done from what two providers suggested would be performance, but I have no way of knowing if that's overstated or not.

Would you care to describe any real world example, or a best-case recommendation for a retrofit rather than a new build? That's what I'm looking for.

Examples of existing systems that the posters here may have, where I don't need to build a whole new house to incorporate them, and what performance do they experience with their specs.


If you have nothing to suggest, fair enough.

Calahonda52

Before I put you on my ignore list, did I read that while you come on here looking for advice, which I gave in good faith, you want to lecture me on my choice of words?
Have a nice day.

pwurple

Whoops! I didn't realise the ego's were quite so delicate around here! Sorry if I offended Calahonda.

quentingargan

I don't think you are being over-sold. According to SEAI, whose figures for DEAP software are conservative and are the same from Wexford to Donegal, a 3kw array on a south facing roof with 30 degree pitch will give you 2578 KwHrs per year. If (and I think this is a big if), but if you use half of this displacing electricity purchased at 18c and the other half heating water which would have cost you 9c from oil or gas, or night rate electricity, then your savings are €348 per annum.

The industry is waiting for the introduction of a feed in tariff which might pay you for surplus power exported. Or it might, like in the UK, pay you for power produced. Either way, you don't know if the new scheme will apply to existing systems. It would be very unfair if it doesn't but there is no guarantee.

If you would like a more precise simulation of what your system would produce based on your geographical location, as well as your roof orientation and pitch, there are a few simulation packages that can produce a fairly accurate report. PM me if you want one.

Bear in mind when considering tubes that when your cylinder is at 60, there are stresses on the system. You also need to factor in the cost of changing antifreeze every two or three years, which takes a fair chunk out of your savings. You may also have other component failure with pump stations and expansion vessels. PV by comparison is quite trouble free. The only thing I have ever seen fail is the inverter which could be knocked out by a power surge on the grid if there is a direct hit by lightning, but that is very rare.

I have tubes and PV myself and am happy with both, but I think that with the fall in prices of PV, it has gone well ahead of thermal in payback etc.

Life expectancy of your average inverter is 10 years.

Daharmaster

I installed a 3 kWp array (18 X 280W) panels + Immersun hotwater controller in Nov 2014. Location is Cork SSE facing roof at a 35 a 40 slope. First year operation exceeded 3,100 kWh. I would say that last year was an above average solar year. Our total electrical on site demand was around 3700 kWh.

58% of total generated was used , with remainder exported. Of that 58% Hot controller used about 29%, with 29% displacing electrical usage. Total cash saved / earned 430.
For the first 6 months of the year no-one at home during the day, second 6 months 1 person with a baby


Original Expected pay back was15 years assuming 25% export (optimistic!) based with export tariff of 9 cent - assuming it stays in place........if not lucky to get 25 years on this basis.

Hot water tank was around 170 l which was too small for our needs. I have upgraded to 300 l tank before Xmas.
Also replaced OFCH with air source heat pump + insulation up grade. I try to heat the house during daylight hours primarily
I hope to get on site usage up to 80% with this approach.


Safer'sunpublic is a site with real time recorded data from various PV installations including my own.


I ruled out solar thermal in favour of PV based on maintenance concerns and pure payback grounds.


Today I was at home with the baby did a dishwasher load two clothes washes + cooked the dinner + all the hot water on solar power. Obviously that won't happen every day, but it does give me great enjoyment out of the system.

quentingargan

Daharmaster wrote: »

I installed a 3 kWp array (18 X 280W) panels

Thanks for this info. Just not clear about the size of your array. 18X280w would be just over 5kw. Is that a typo?

Daharmaster

Sorry its 18m2 of panels with 11X280W giving 3080 Wp installed

pwurple

Thanks, that website is great, exactly the real world info i was looking for.

How did you arrange feed tariff?

Daharmaster

I applied to ESB networks for a generation license, then applied for an import/export meter. Once installed then applied to Electric Ireland Microgeneration scheme. This is now closed to new entrants since the end of 2014. It's not clear how long this scheme will continue. It may come to an end this year with the announcement of a feed in tariff.
I would not install a new oversized system in the current environment and given what I know now about extent of export requirement until the Feed In Tariff rules are clear, as the gov might decide to use a grandfathering rule to exempt older installations, or ones that previously received supports. This is what happened in the UK.

quentingargan

pwurple wrote: »

How did you arrange feed tariff?

There was an export tariff available from Electric Ireland. It was closed to new applicants in January 2015, but existing customers are still getting their export tariff.

The industry expects a new incentive to be introduced later this year which would be available regardless of which utility company you buy your electricity from.

pwurple

Interesting. Maybe i will hold so until that plan is made clearer. I have been looking at the year-round generation against our year round usage, getting the balance right will be interesting.

In summer, or usage is far lower. Less lighting, less devices, less kettles boiled, less oven, more salad... Picnics, tents and bbqs in the garden with the kids, maybe out of the house more on holiday.

In winter, when usage is high, the generation of the system is much lower due to the short days. So if I specced to cover my winter usage, i would be overpowered for the summer.

quentingargan

pwurple wrote: »

Interesting. Maybe i will hold so until that plan is made clearer. I have been looking at the year-round generation against our year round usage, getting the balance right will be interesting.

In summer, or usage is far lower. Less lighting, less devices, less kettles boiled, less oven, more salad... Picnics, tents and bbqs in the garden with the kids, maybe out of the house more on holiday.

In winter, when usage is high, the generation of the system is much lower due to the short days. So if I specced to cover my winter usage, i would be overpowered for the summer.

Yep - it is really impossible to match consumption to supply and you will always be importing or exporting - it is only fair that you get paid for the exports. You could fit an OWL monitor in the meantime - this stores data every minute of your consumption which is useful. If you buy the solar version now, it will give you really useful data when (and if) you do fit a PV system.