Solar PVs - worth the investment?

michaels

Martyn1981 wrote: »

Same as us then on the main roof (6m by 5m). We had 1.3m by 1m panels fitted in a 5 by 3 portrait pattern (but only 13 panels due to a Velux).

You'd probably go for something like 3 by 4 panels landscape, so 4.8m wide (3 x 1.6m) and 4m high (4 x 1m).

12 panels isn't a lot, but 285Wp panels would give you 3.4kWp, which is nice. There are more powerful panels (high efficiency panels) but they cost quite a bit more, but worth pricing up.

Your useage seems very good. The average varies, everytime I look it up as suppliers, OFGEM, DECC vary a bit, but a medium house is somewhere in the 3,300 to 3,800 range, so for 4, you are doing great.

Mart.

Couldn't he fit 4x4 landscape so 16x 250 standard (therefore cheap) panels for 4kwh?

Martyn1981

michaels wrote: »

Couldn't he fit 4x4 landscape so 16x 250 standard (therefore cheap) panels for 4kwh?

4 panels, plus 3 20mm gaps, plus 200mm (or more) each side, would be around 6.86m, but the width is only 6.15m.

Trying to think of a different layout to get more on there. Could have 2 rows of 5 portrait, so 3.2m high, then 1 row landscape of 3, taking it to 4.2m(ish), but the landscape row would be slightly shorter and might look odd. But that's 13 panels, so a tad better.

Mart.

Martyn1981

purple_hamster wrote: »

Now I've booked two companies in to visit next week. They are "assessors". Is that the same as surveyors?

Is it worth having an invertor that can have batteries added in the future (when prices come down)?

I'm trying to think what else I need to ask them!

Hiya. Don't know what an assessor might be officially. Probably just a fancy sounding name for a salesman with a tape measure (laser measure).

Definitely worth asking about the add on battery option, but you need to find out what the price difference is and where the batts will go (physically attached or not) for space. If it's marginal, then great, but if you have to spend a lot more now, perhaps not, as you can have an A/C side battery system added later. This isn't linked to the inverter/PV system, it simply 'steals' leccy that is going to be exported, and pops it into a battery. This is less efficient than a DC batt, since the inverter will have already converted the DC to AC, then the battery's inverter has to change it back to DC for storage again, before back to AC for use.

So for simplicity, an inverter integrated system is better. But we are probably 5 years away from economical domestic batts like this. For my system, generation, usage etc etc, I reckon the battery will need to be close to £1.5k for me to break even over 10yrs. Currently they are more like £3 or £4k.

Do you have a hot water tank? If so then you might want to discuss a diverter that sends spare leccy to the immersion.

Mart.

defaultdriver

purple_hamster wrote: »

Dimensions are:

width of house (ext) 6m15
half of back to front (ext) 3m95
roof height (guess) 3m (I know it's more than 2m anyway!)
google calculator says the hypotonuse is 4m96

We have a chimeny in the middle of the roof at the heighest point.

I've been calling round companies this morning, but most of them either aren't answering or don't do PVs anymore. I've only got two leads so far!

You may also want to take into consideration any possible shading from the Chimeny.
When we had our quotes and surveys, all of them came back as "no shading", but during the summer months we have some shading from the Chimeny in the morning.
My estimate is that I will be losing around 150-200 kWh per year. Not really sure how best to calculate this, but is based on what has been generated by others on a good day.

purple_hamster

We don't have a hot water tank. Otherwise, I'd definitely have the water heated by it too.

purple_hamster

Another question - we have a brick outbuilding next to (detached) from the house. Single storey, SE facing, about 120cm x 240cm (very roughly) with a flat roof. Could we get panels put on that roof, angled to the south? I assume they'd need to be on a stand rather than lying flat. The long side is pretty much south facing. Is that allowed or would we need PP?

tunnel

defaultdriver wrote: »

You may also want to take into consideration any possible shading from the Chimney.

This does need looking at. Although it's stated that the chimney is at the top of the roof(assuming apex) it's not given exactly where on the roof it is and could be a problem. If the chimney is on the right as you look at the roof then it should be ok, on the left or middle then maybe look at solaredge. Solaredge also has the benefit of being future proofed for batteries.

purple_hamster

tunnel wrote: »

This does need looking at. Although it's stated that the chimney is at the top of the roof(assuming apex) it's not given exactly where on the roof it is and could be a problem. If the chimney is on the right as you look at the roof then it should be ok, on the left or middle then maybe look at solaredge. Solaredge also has the benefit of being future proofed for batteries.

Chimney is in the middle. And yes I meant apex, but had a mental block about the word!

What's solaredge?

tunnel

purple_hamster wrote: »

What's solaredge?

Best thing since sliced bread when it comes to shade management.
Seriously though, It's the name of the inverter, difference with solaredge is you then have an equal amount of PO's(power optimisers) to the amount of panels on your roof(one for each panel). It then allows each panel to work independent to each other whereas a string inverter doesn't
In your case, when the morning sun passes over the back(or front) of the property, with your chimney in the middle each panel that goes partially shaded will generate less than the others whereas with a string it only takes 1 panel to go partially into shade to bring all the other panels on that string down to that panels level.
Solaredge shouldn't come with much of a premium either compared to string inverters.
HTH

purple_hamster

Is it best to have mono or poly-crystaline panels? Or does it depend on other factors?

Can anyone answer the question about my outbuilding, above?