Solar - real-life experience of investment vs return

1961Nick

Spies said:

My system has generated 3307kWh over the year, of which I used 42% of it (no battery).

I 'saved' £361 vs importing that same energy from the grid and earned £457 from SEG.

This leaves 5 years before I 'break even' assuming that prices stay the same but we are going to be looking at moving house before then most likely.

If we do, the new house will need to have panels and a battery installed from day one.

As others have said in the past, treat it as more of a home improvement rather than trying to justify it based on payback period, you don't buy new windows and then work out when they will payback for themselves do you?

The advantage of batteries is that you can easily take them with you when you move house.

new_owner

Spies said:

As others have said in the past, treat it as more of a home improvement rather than trying to justify it based on payback period, you don't buy new windows and then work out when they will payback for themselves do you?

I do when replacing things 

I think solar needs to be considerably cheaper for me to add this to my house. It certainly makes sense to roll it out in car parks and anywhere that you can get business to deploy. 

Screwdriva

silverwhistle said:

I wouldn't assume too high a price per kwh to justify any investment. If you look at the half hour variable price tariffs you will see that at times recently that they have been negative (they pay you!) and whilst this has only been over the holiday period there will be another 2.5GW (? from memory) of more wind installed in the UK by next winter and more to come in the subsequent years. 

Couldn't disagree more. While the UK is definitely over indexed in wind generation, we have yet to benefit from plunge pricing (where they pay you) during peak solar generation hours. Reason: there is an imperfectly inverse relationship between wind speed and solar irradience, and this that forms the core of any off-grid system design.

Said another way, the UK will benefit greatly during the cooler months when turbines are spinning happily and the sun shines less. But we will be burning alot of gas during the warmer months when they aren't. This is when I expect solar returns to be disproportionately favourable, as they were this past year. Given our government's recent myopia on investment in Solar PV generation, I don't expect this will change. 

Ethics and geopolitics aside, I am yet to see a positive ROI case for investing in large batteries (without higher than normal consumption involving a heat pump and/ or EV) but a solution like the 5 kWh Myenergi Libbi (with built in inverter) may make some sense, given the savings inherent with not purchasing a separate inverter and the bonus of Myenergi's excellent customer service for when the batteries age.

This is why we don't own a battery and yet managed a total return of > £900 p.a. for our 4kW system. We will be investing in Ripple Energy's next project instead, to bring the purchase price of electricity lower, closer to a 1:1 ratio with the PV generated energy exported to the grid via Octopus Agile. 

Martyn1981

Screwdriva said:

silverwhistle said:

I wouldn't assume too high a price per kwh to justify any investment. If you look at the half hour variable price tariffs you will see that at times recently that they have been negative (they pay you!) and whilst this has only been over the holiday period there will be another 2.5GW (? from memory) of more wind installed in the UK by next winter and more to come in the subsequent years. 

Couldn't disagree more. While the UK is definitely over indexed in wind generation, we have yet to benefit from plunge pricing (where they pay you) during peak solar generation hours. Reason: there is an imperfectly inverse relationship between wind speed and solar irradience, and this that forms the core of any off-grid system design.

Said another way, the UK will benefit greatly during the cooler months when turbines are spinning happily and the sun shines less. But we will be burning alot of gas during the warmer months when they aren't. This is when I expect solar returns to be disproportionately favourable, as they were this past year. Given our government's recent myopia on investment in Solar PV generation, I don't expect this will change. 

Ethics and geopolitics aside, I am yet to see a positive ROI case for investing in large batteries (without higher than normal consumption involving a heat pump and/ or EV) but a solution like the 5 kWh Myenergi Libbi (with built in inverter) may make some sense, given the savings inherent with not purchasing a separate inverter and the bonus of Myenergi's excellent customer service for when the batteries age.

This is why we don't own a battery and yet managed a total return of > £900 p.a. for our 4kW system. We will be investing in Ripple Energy's next project instead, to bring the purchase price of electricity lower, closer to a 1:1 ratio with the PV generated energy exported to the grid via Octopus Agile. 

I think you are only looking at the supply side, so yes when solar is higher wind is lower. But on the demand side, we also see a reduction in those high solar periods, that's why wind is so useful for the UK, as it generates more when demand is higher, and vice versa. But it still generates year round.

In the future, the demand difference will grow, as space heating moves to leccy.

But I do agree with you that solar investment/encouragement by the Gov should have been much higher, but for the UK it will be a lower source of generation, by far, than wind.

Screwdriva

Martyn1981 said:

In the future, the demand difference will grow, as space heating moves to leccy.

As temperatures warm and more households in the South of England continue to adopt air-conditioning, the same could be said for PV in the summer? 

ABrass

All models for a renewable based UK assume some level of over provision. That means there will be periods of over production. Some of them assume huge amounts of over provision.

we should expect to see periods of excess supply on a frequent, but not regular basis.

Air con might make a difference to reduce the peak for Solar but I'd be amazed if it were significant.

Martyn1981

Screwdriva said:

Martyn1981 said:

In the future, the demand difference will grow, as space heating moves to leccy.

As temperatures warm and more households in the South of England continue to adopt air-conditioning, the same could be said for PV in the summer? 

TBH I don't think there is any comparison. Space heating is required for around 6 months of the year. I've found with our A/C (installed for the heat side), that it gets used for around 10 part days of the year. Also, the days when it's needed are the days that the PV is peaking well above average, so even with its use, PV export will be average to above average.

As I said, I agree that PV rollout could be better, a lot better, but I still don't think your conclusion that gas consumption will be boosted is correct. In fact, consideration to fit A/C could come hand in hand with the decision to fit PV too, resulting in a net benefit for each such property, spilling over to balance several non-PV households getting A/C.

Edit - But to be clear, I would of course love to see much more PV being rolled out, and its generation curve tends to be nicely complimentary to wind.

Screwdriva

Martyn1981 said:

As I said, I agree that PV rollout could be better, a lot better, but I still don't think your conclusion that gas consumption will be boosted is correct. 

Time will tell. I'll be the first to admit I got it wrong but for now, my prediction is that Outgoing Agile will remain much higher (2-3X) than 0.15p during the summer, assuming winds don't appear out of thin air.

ABrass

Screwdriva said:

Martyn1981 said:

As I said, I agree that PV rollout could be better, a lot better, but I still don't think your conclusion that gas consumption will be boosted is correct. 

Time will tell. I'll be the first to admit I got it wrong but for now, my prediction is that Outgoing Agile will remain much higher (2-3X) than 0.15p during the summer, assuming winds don't appear out of thin air.

That's exactly what they do, but this thread has gone way off topic.

silverwhistle

At the moment I'm not worried about A/C usage, although demand might be increased for the badly designed flats we see. On the South coast with a south facing window I just added some bodged passive shading for a few days at the peak last summer and it was very effective. If the problem gets worse I'd install a more permanent solution.

We could do with more solar, no doubt, but I wouldn't expect to see plunge pricing as a result although prices did soften a bit, but as I've got my own PV didn't pay that much attention. I didn't use any gas domestically for 7 months from March to October and I don't think there was much demand for electricity generation? Somebody may have the figures to hand.