PV with ASHP Self Use vs Export

[jayc89]

22 minutes ago, joe90 said:

No, if you DIY (like I am going to) you cannot claim £ fir the generation to the grid, it’s just used as a dump fir unused lecky. So use as much as you can, if you had an EV you could dump to this.

 

So in a DIY installation, unused energy still goes back to the grid, you just don't get any payment for it? Heh. 

[Dillsue]

26 minutes ago, jayc89 said:

 

I was thinking a DIY installation where, as I understand it, you're not legally allowed to export back to the grid?

Technically you cant 100% do a DIY install as you need a qualified spark to test and certify the install. You can do all the work but you need a spark to test before you connect up to the mains. That said, theres lots that dont do that.

[Carrerahill]

33 minutes ago, joe90 said:

No, if you DIY (like I am going to) you cannot claim £ fir the generation to the grid, it’s just used as a dump fir unused lecky. So use as much as you can, if you had an EV you could dump to this.

This is what I did too.

 

 

 

 

[PhilT]

Thanks everyone for your help which gives me some confidence it's worth doing. Are there any other key issues and watchouts, when appraising supplier quotes, and generally?

[JohnMo]

Just watch your not getting taken for a ride with pricing.  To buy the parts you are looking circa £1k per kWh, the bigger the array the more economical it becomes.

 

If you any risk of shadow that includes clouds you need optimisers on each panel.

 

You need an external DC isolation switch even if the inverter has one.  It is likely the inverter could fail before the panels, the additional DC isolation allows the inverter to be removed safely.

[Dillsue]

28 minutes ago, PhilT said:

Thanks everyone for your help which gives me some confidence it's worth doing. Are there any other key issues and watchouts, when appraising supplier quotes, and generally?

As I understand things, the PV industry is running flat out and seemingly install prices have gone up noticeably this spring/summer. I know personally theres been material shortages.

 

If you get a quote now youll likely be asked to pay more than you would have 6 months ago so it might be worth putting things on ice for a few months hoping that things calm down in the autumn/winter?? That said the October price cap hike might fire up the industry further????

[joth]

17 hours ago, ProDave said:

However Octopus do seem to be offering a tariff now that actually pays a decent rate for export, not the insulting rate of 5p per kWh so that may change the equation.

Not listed on https://solarenergyuk.org/resource/smart-export-guarantee/ yet?

 

They have "Agile outgoing" which pays market rates like for Agile import, which in general is a crapshoot but it means right now is good - they're paying around 40p/kWh around the times of day ppl are likely to have excess solar generation 

Snag is to get this tariff you can't be on Octopus Go for import. My "Go" fixed tariff is very favourable so i don't want to cut it now. It ends in Sept, so I could switch then, but that's just as solar generation starts to tail off 😕

 

[PhilT]

On 17/08/2022 at 20:52, JohnMo said:

Little confused.

 

In Jan your output from PV for the month will be around 150kWh, some days the output will be zero, but if we average to 31 days of equal generation, 4.8kWh per day.  Even getting a CoP of 4, that less than 2 hours of running the heat pump.  So full use from PV without any other loads.

 

In summer you are generating circa 400kWh per month, 13kWh per day, a couple of hours doing hot water, would 5.6kWh, other background uses, washing machine, dishwasher etc plus immersion to bump up cylinder temp to max, all the PV is used.

Still mulling this over and struggling to understand how I could replicate the the high % usage figures achieved by others.

Jun-Sep I'm using c. 6kWh/day total, of which 1kWh/day is ASHP doing DHW - could be replaced by PV 3kWh but that will have virtually no impact on usage or cost.

So from the biggest 4 months PV output of c. 1,600kWh I will only be able to use around 600kWh.

The months of Mar/Apr/May & Oct/Nov are potentially more promising, but during those months the ASHP uses most energy before 9am and after 6pm.

Would appreciate some help identifying anything I might be missing, and any other opportunities.

 

[JohnMo]

Just size the array to suit your needs, make it smaller

[joe90]

2 minutes ago, PhilT said:

ASHP uses most energy before 9am and after 6pm.

Not if you put a timer on it! With UFH and a large DHW tank you should have enough of a buffer to get you over the “off” period. Like @ProDave I plan to have my  ASHP timer set to 11am 4pm when I get round to installing PV. I guess it will take a little while to tinker with it to get optimum usage and you can always have an override switch or another room stat set to a lower temp to override the timer. Many ways to skin a cat 🤔

[joe90]

2 minutes ago, JohnMo said:

Just size the array to suit your needs, make it smaller

But for what time of year?, I would go max 4kw to cover winter, I would rather give away the excess in summer than be short in winter!

[JohnMo]

You can also change the angle.  Vertical mounted panels flattens the output curve, a more flat mounting position, decrease winter output in favour of summer production.

 

Best idea is mess with tool linked to previously, to get a system that suits you and your available mounting positions.

[joe90]

2 minutes ago, JohnMo said:

You can also change the angle.

Difficult on a roof, my garage is about 25’ which is not ideal, especially in winter. I once considered a ground array and one that I could change the angle a few times a year but shading/cost etc stopped that idea.

[JohnMo]

None of options are easy.  I want to install some more panels on a wall on the drive, no shading, but wife says no.

[PhilT]

16 minutes ago, JohnMo said:

Just size the array to suit your needs, make it smaller

good ideas - limit the array to less panels mounted horizontally at the highest possible position on the roof (which has a couple of gables anyway so makes even more sense) and my roof is already quite steep at 42deg. I like joe90's idea but don't have UFH unfortunately, and my house is a 30 year old self build, but I could try running the ASHP heating more during the day to make a kind of 'air thermal store' to cover the evening period.

[JohnMo]

You may be better running in weather compensation mode anyway, so it runs at very low flow temps, so get a better CoP. Run in day and overnight in set back mode (2-3 degrees lower temp), and normal mode when your home.