Solar Payback

phsci

Not sure where your soil/vent pipe is exactly, but if you wanted to go ahead with this section of roof you might like to look into terminating the soil pipe within the loft space and capping with an air-admittance  ("Durgo") valve. (The vent pipe is primarily to allow air into your soil pipe and prevent waste traps from self-syphoning, rather than letting foul air out.)

Spies

I'm going to stick with the South and West orientation as that fits better with my energy use.

silverwhistle

Exiled_Tyke said:

I don't think I would describe electricity price inflation as 'inevitable'.  

Possibly not, but my current experience of a time of day tariff linked to half hourly wholesale prices is pretty depressing. I'm only continuing with Agile at the moment because I have low usage and solar panels, am curious to see what happens, and can manage a few months with the extortionate prices, which in the current 24 hours only go below 15p for a few half hour periods and are above 30p for 5 of them. I haven't done any modelling over the year but if autumn winds don't bring lower prices I'll be fixing. But the issue of what the fixed prices will be will be giving headaches to the statisticians and mathematicians for the companies as the immediate trend is significantly upwards.

Roll on wind farm roll out!.

Spies

So I've changed a few parameters and this is what I've ended up with, October to Feb assumed 100% of generation used and September and March assumed 50% generation used, all other months are 33%

Petriix

Spies said:

So I've changed a few parameters and this is what I've ended up with, October to Feb assumed 100% of generation used and September and March assumed 50% generation used, all other months are 33%

I've only been recording actual self-consumption data since January when we got our EV (which is regularly plugged in to the Zappi all day as we both work from home most of the time). We managed to use 78% in January, but it's working out between 55-61% for the rest of the months. We have a 3.42kWp South facing array.



It's incredibly hard to get to 100% self-consumption unless you have a constant load of greater than your peak generation. I think you're going about things in the right way, but 18p per kWh is pretty far-fetched right now; I've never paid more than the 12.6p I'm paying right now excepting a couple of summer switches to Bulb to hoover up the free referral credit while consumption was minimal.

If I were you I'd be focussing on getting a better price for the installation rather than trying to make the numbers add up. Our 3.42kWp system cost £4150 in April 2017 and panel prices have reduced significantly since then. A 4kWp array *should* cost about £3500 today accounting for the cost of the parts and labour.

I know it's hard to find an installer willing to only earn a fair wage for the work they do rather than insisting on making a massive markup on the equipment too. Supply and demand dictates the market price, but I think a day-rate of £300 for your work (equating to a £60k income) is pretty fair. Keep shopping around and maybe wait if you can't find a reasonable price. 

Spies

Petriix said:

Spies said:

So I've changed a few parameters and this is what I've ended up with, October to Feb assumed 100% of generation used and September and March assumed 50% generation used, all other months are 33%

I've only been recording actual self-consumption data since January when we got our EV (which is regularly plugged in to the Zappi all day as we both work from home most of the time). We managed to use 78% in January, but it's working out between 55-61% for the rest of the months. We have a 3.42kWp South facing array.



It's incredibly hard to get to 100% self-consumption unless you have a constant load of greater than your peak generation. I think you're going about things in the right way, but 18p per kWh is pretty far-fetched right now; I've never paid more than the 12.6p I'm paying right now excepting a couple of summer switches to Bulb to hoover up the free referral credit while consumption was minimal.

If I were you I'd be focussing on getting a better price for the installation rather than trying to make the numbers add up. Our 3.42kWp system cost £4150 in April 2017 and panel prices have reduced significantly since then. A 4kWp array *should* cost about £3500 today accounting for the cost of the parts and labour.

I know it's hard to find an installer willing to only earn a fair wage for the work they do rather than insisting on making a massive markup on the equipment too. Supply and demand dictates the market price, but I think a day-rate of £300 for your work (equating to a £60k income) is pretty fair. Keep shopping around and maybe wait if you can't find a reasonable price. 

It's not helped by my array having to go on two seperate elevations, two installers now have quoted similar prices, and another one about 1500 higher than the rest, 18p/kwh is currently the cheapest rate in the North West according to uswitch so I don't think thats too unrealistic.

Screwdriva

Have a read of my payback thread here.

I spent considerably more on my system install by opting for top of the line bifacial panels and a 25 year warranty on all Solaredge equipment (optimizers + inverter). The system itself has performed admirably, especially given the orientation of the panels (60% South facing, 40% W/E).

We discovered that, despite our best efforts to consume, we export ~70% of our generation, making export tariff really important to our return on investment. It's looking like 12+ years to pay for itself at today's rates.

That said, electricity prices are rising rapidly, regardless of the comments on these forums, and 19p/ kWh will be the new normal for most. Utility prices rarely come down. We don't own an EV today but that may change the equation substantially in the future.