Solar Power - Definitely Green but is it affordable

MWT

Petriix said:

We managed to use 58.5% of our generation in 2021 with an EV but no home battery. With the Givenergy 8.2 kWh battery we're adding this month, I anticipate getting that above 80%.

With the EV it is certainly possible, the doubt expressed above is with a large array, no EV and not being a high electricity user in the first place.

007apm

tim_p said:

Has a salesman told you that 80% self consumption is possible?

Salesmen are typically constrained by industry standard quotes and strangely from Eon whose quotes are easier to compare, show no increase in 'own use' with the battery size.  They did suggest ~60% own use which must be an average.  It must be possible to perform better than average! The wisdom that i seek is how to achieve this and to push that 60% upwards...  All help is  most useful...

Reed_Richards

007apm said:
...Various references suggest that Summer months produce more than we can sensibly use but it may be that say installing an electric shower and if all of us take morning showers it would move our energy use from gas to self generated electricity and hence put less back to the grid. 

That's not a good idea; an electric shower will use more power than your solar panels can provide.  If you are lucky enough to have a hot water tank then you can use the immersion heater to heat the water in the tank.  Immersion heaters typically require 3 kW which is a better match to the output from a typical solar array that the 7.5+ kW requirement of electric showers.    

Petriix

If you want to maximise self-consumption then you need something which can utilise between 1-4kW constantly over a long period of time. Appliances tend to use their heating elements in short blasts rather than constant demand.

There is, however, little point in using the energy for the sake of it. If you can switch that demand to the cheaper overnight period then you're better off exporting the power for the SEG payments. It's different for those of us on the old FIT system because we get paid for the 'deemed' exports regardless of how much we use ourselves. 

QrizB

007apm said:

tim_p said:

Has a salesman told you that 80% self consumption is possible?

They did suggest ~60% own use which must be an average.

60% own use sounds like an extreme, not an average. Having had a fairly modestly sized solar PV system for ten years I would suggest that 30-40% self-use is more typical, in the absence of a battery.

Most generation is in the summer when you don't need it. In my case, my system will generate 300kWh in a summer month but we might only use 150kWh that month (and some of that use is when it's dark) so we end up exporting a lot.

Take a look at the "my generation" and "how low can you go" threads in Green & Ethical to get a feel for what's achievable in practice.

[Deleted User]

There needs to be a reality check here. Yes, last month was poor for solar as graph below shows: however, a c.25% loss of a predicted output of 108kWhs for the total month was no big deal. All of the solar energy generated was used in my home - either for domestic use or to recharge the PW2. In addition, we had to take more than 75% of our monthly energy needs from the Grid. What is not shown in the graph below was the fact the output at times was less than that required to meet the baseload requirement for my home. If May turns out to be a poor month then lost output is clearly more significant.

The other part of the reality check is that solar can only be used to charge an EV if it is sitting at home all day. If it is sitting at home then it is not accruing many miles. An 8.6kWh battery might give you at best 25 miles of increased range but it leaves the home on the Grid overnight. 

It is also worth researching a few things before committing to a battery. Firstly, the relative positions of the battery and EVSE in the power circuit are critical. Get it wrong, and even with Octopus Go, the battery may discharge as the EV charges. Secondly, do you want a battery which you can manually choose to discharge to the Grid when demand exceeds supply? Some people have been making a lot of money on Octopus’ Agile Outgoing tariff by exporting during the 5 to 7 peak period. Finally, do you want a battery where the supplier takes over control? For example, the Tesla Energy Plan offers an import/export price of 11.7p/kWh and Octopus/Tesla use the battery to support the Grid. Don’t trust installers as they are there to sell you a product: do your own research.

tim_p

007apm said:

tim_p said:

Has a salesman told you that 80% self consumption is possible?

Salesmen are typically constrained by industry standard quotes and strangely from Eon whose quotes are easier to compare, show no increase in 'own use' with the battery size.  They did suggest ~60% own use which must be an average.  It must be possible to perform better than average! The wisdom that i seek is how to achieve this and to push that 60% upwards...  All help is  most useful...

If you think about the actual generation of the months between April and Sept, then you will need to think of some practical way of using the generation. My 4 kWp system generates around 15 kWh per day throughout that period with a lot of days being well over that average amount, often averaging 20kWh per day for the month. Where will you use 80% of that, particularly if you envisage a larger system on an optimal roof (mines split over 3 different orientations, none ideal). An EV can only use it if it’s sat on the driveway charging, but then it’s not using it to need charging the next day. A battery of typical size, say 10kWh, can only be filled once if it isn’t being used so exactly where do you imagine sinking 20+ kWh per day, most days throughout those spring and summer months. 

spurdog1

always seems "vague" these prices. No one can say hown many panels needed, how much each?
Makes you feel they are made up prices.

MWT

spurdog1 said:

always seems "vague" these prices. No one can say hown many panels needed, how much each?
Makes you feel they are made up prices.

You have to complete a survey to say exactly what will fit onto a roof and there are calculation to make depending on the direction the panels face, location of the property and to account for any shading, so it isn't easy to be definitive without a lot of work, hence the vague feel to some rough quotes.

You also have to take the VAT rules into consideration which can have an impact on how the installer will split the cost between labour and materials.

Also factor in that the panels come in a few different sizes and in different kWP ratings even in the same size, but you can see prices for individual panels easily enough online, you just can't be sure what will be the best fit for the array and your roof without more work.

[Deleted User]

One final thought. As a homeowner you can have as many panels on your roof as you like without asking your DNO for approval provided the maximum output (controlled by the inverter) does not exceed 3.68kWs per phase (most homes are single phase). Any output above this - and in all cases where a battery is fitted - prior DNO approval is required. The DNO will take at least a couple of months to review the submission and technical documents and it may - depending on your local electrical infrastructure - impose a max export limit. I was lucky and my export is not limited but there are reports of some people not being so fortunate. It just means that even if your array is capable of producing say 7 kWs max, your export may be limited to 5kWs.