Have Solar Feed in Tariffs run their course?

EricMears

Ectophile wrote: »

A competent DIYer should be able to meet the requirements of BS7671, provided that they know about electrics. But they would need to read up on how to install it properly, as there are specific requirements for PV installations.

I couldn't agree more. However, part P of the Building Regs severely limits what DIYers are allowed to do these days and I doubt fitting an inverter would come into that category.

zeupater

MFW_ASAP wrote: »

I'm currently looking at a combination of PV and thermal panels, so I don't have an axe to grind in the PV vs Thermal debate. I just thought it was an interesting discussion because I was like the earlier chap and pretty much thought it was cut and dried in favour of thermal.

Now that you've reminded me, I think the FITs skewed the figures quite a bit towards PV, plus the argument was that the area used by the panels would be irrelevent unless you had a small roof and could not fit 4kw of PV on it (and therefore would not qualify for maximum FIT). The argument I guess was that if you had a large enough roof for PV and only put smaller thermal panels on it, then you were wasting roof generation space.

On the point about preventing stagnation, is that achieved by correctly sizing the cylinder, panels, average water usage and average sunlight hours? I'm not sure how you could do this effectively as we generally have grey skies in most of the UK, and so the system would be designed for that, but if we have a glorious summer your design would be compromised. Whereas, the PV would just benefit more from the clear days?

I guess what I'm thinking is that if you size a thermal system to not stagnate on an average day, then you can't change the design if we have well above or well below average?

Hi

You have correctly identified the main issue with heating water with solar, that being periods of grey skies. There are only really two solutions ... have a backup (probably non-renewable) heat source, or create a buffer through considerably increasing the storage volume.

Don't get me wrong, our thermal system does stagnate, but it doesn't do it very often and certainly not on an 'average day'. When we have a period of consecutive really sunny days the water is stored at a considerably higher temperature than the norm, therefore the system heat-loss is considerably higher and conversely, when gain is lower, heat-loss is also lower ... the trick is to (simply ) match the collector size, orientation, storage volume, relative heat-loss & typical usage.

When it comes down to the 'pv' -vs- 'thermal' debate, it doesn't bother me ... you should consider me neutral as we have both, it's just really a consideration of offsetting efficiency & flexibility. However, taking the viewpoint that electricity has far more potential for 'added-value' applications, I believe that the full potential of the energy collected is not being realised when simply dumping through a resistive heat-source on a long-term (/permanent) basis.

If you are considering a pv/proportional power solution you really should consider the volume of water to store, in which case it could also be a good idea to look at a dual element solution. Priority should be given to the higher element and the lower one cutting in when there is sufficient power, or the upper element has reached it's thermostatic set-point ... that way you will allow stratification to form within the cylinder and increase the likelihood of having some hot water even if the weather has been dull.

Regarding maximising the use of available roof-space, I agree. We have all of our collectors on a single roof plane and represents around 1/4 of what is available & ~1/3 of what is suitable(ish) for solar collection, so there's plenty of scope for expansion, if necessary ... the reason for this simply being that it looks good (in my view, and it's my roof ) and makes best use of the sun's arc for our orientation and energy consumption profile ... ie, heavily weighted after midday than before -

HTH
Z

silverwhistle

zeupater wrote: »

However, taking the viewpoint that electricity has far more potential for 'added-value' applications, I believe that the full potential of the energy collected is not being realised when simply dumping through a resistive heat-source on a long-term (/permanent) basis.

I think even those of us who use PV for hot water - in my case only from mid August - would'NT deny that. From a personal economic point of view though, it makes sense to use it for hot water. My ex-council terrace has just enough space for 4kw PV, and very neat it looks too. Thermal would not make any sense. To be honest, once my tank gets to temperature it doesn't use much energy, although I was a terrible wastrel and had a lovely bath after footie training last night.. My gas boiler is still off and it'll be a little while before I need to use it for heating, so it certainly doesn't make sense to use it for DHW. You'll be aware that we all _try_ and use as much of our generation as possible: washing machines, dishwashers, vacuum cleaners, drills, sanders, bread making, fast freezing, slow cookers, pizza makers and so forth. I'm proud to say though that, since I've been here I haven't yet used my £4 Wilko iron.

I appreciate that I'm getting a subsidy, but don't feel particularly guilty given the fact that I'm actually investing in infrastructure rather than consumption, helping the BoP and thinking ahead to my retirement.

MFW_ASAP

zeupater wrote: »

When it comes down to the 'pv' -vs- 'thermal' debate, it doesn't bother me ... you should consider me neutral as we have both, it's just really a consideration of offsetting efficiency & flexibility. However, taking the viewpoint that electricity has far more potential for 'added-value' applications, I believe that the full potential of the energy collected is not being realised when simply dumping through a resistive heat-source on a long-term (/permanent) basis.

Great post Z. The above really hits the nail on the head with my deliberations about whether to go PV or Thermal. We only have so much roof space and so I want to maximise the energy that I generate with it. Thermal is more efficient at heating water, but as you pointed out, PV has more flexibility. I certainly wouldn't hard-wire the PV to an immersion heater, but rather divert any excess power that we are not using. If it means that the tank is not completely hot when the sun goes down at least it will have raised the temperature and taken some of the load off the gas boiler. Alternatively, if thermal panels provide hot water even on overcast days and it means that our gas boiler is off for the late spring/summer/early autumn then that too has great benefits.

I was looking at PV-T panels which seemed to give the best of both worlds, but unfortunately after looking into them I realised that they are compromised and would require a heat pump. I'd still consider these if we were looking to go down the GSHP route, but with mains gas, it just doesn't work out financially.

I guess I'll have to continue the research before I decide.