Yet another battery / no battery system

Solarchaser

For me, utilisation is the wrong way to look at it.
You want to look at how many days in the year you will have excess solar from your daily production,  and multiply that by the batteries kwh capacity and then multiply that by the cost of electricity.
Take the cost of the batteries and devide that by your figure and you have your payback.

Now in truth that's not the true figure as batteries will do better than that because in a day with 20kwh of solar it won't (most of the time) be constant sun, and so batteries fill in the parts that the clouds cover iyswim helping to better utilise your solar power for things like running your washing machine when it's sunny, that's no good if you get cloud cover on its heat cycle, but batteries will help that.
Worth considering imo.

Also there really is an immense satisfaction at powering your own house from your home made power, it's a satisfaction you can't really understand until you do it, it surprised me how rewarding it felt 

EcoScruples

You've nailed it there, 
The satisfaction of the battery filling the gaps is why I'm so glad I went the whole hog.
I wish I'd  have went bigger on my inverter now too, and panels.

Alnat1

Agree with Solarchaser and Eco, no need to go outside and check how big the blue bit of sky is when you have a battery. Also it's a great feeling when the battery powers the house through the night and there's enough left for toast and a cuppa in the morning.

I already wish I'd got a bit more battery (March 22 install, went with 4.8kWh) and I'd prefer to have enough for 24 hours. 

Reed_Richards

Here is a cloudy day in July with a 6.5 kWh battery. 

• I only got full sun very briefly around 11:30.
• Negative Meter readings mean I am drawing power from the grid, despite the fact that the battery State of Charge never drops below about 25% (reached at around 07:00)
• When we are cooking at around 18:30 the battery cannot match the power requirement so we have to draw some power from the grid.
• Starting at 16:00 the battery is fully charged so I run the immersion heater for 20 minutes.  The combined output from the battery and the panels is not quite enough so I draw a small amount of power from the grid.  And the battery cannot respond instantaneously to the demand so there is a spike in power drawn from the grid until things adjust.

The point I am trying to make is that even with solar panels and a charged battery I am still likely to draw some power from the grid. 
     

ABrass

That is an interesting graph, thanks @Reed_Richards.

I've decided to go for the battery option. I'll probably put more details up and respond to the posts above when I've got access to a computer instead of my phone.

Thanks for the consult.

mickyduck55

Reed_Richards said:

Here is a cloudy day in July with a 6.5 kWh battery. 

• I only got full sun very briefly around 11:30.
• Negative Meter readings mean I am drawing power from the grid, despite the fact that the battery State of Charge never drops below about 25% (reached at around 07:00)
• When we are cooking at around 18:30 the battery cannot match the power requirement so we have to draw some power from the grid.
• Starting at 16:00 the battery is fully charged so I run the immersion heater for 20 minutes.  The combined output from the battery and the panels is not quite enough so I draw a small amount of power from the grid.  And the battery cannot respond instantaneously to the demand so there is a spike in power drawn from the grid until things adjust.

The point I am trying to make is that even with solar panels and a charged battery I am still likely to draw some power from the grid. 
     

I have the same issue but my import is very low.. I find the 2 kWh kettle makes a significant difference .. I rarely need more power than the battery and solar can provide at any one time

Alnat1

I'm willing my 3kWh to break.

I really want a 2kWh kettle but ditching a perfectly good one.......I just can't make myself do it to save the occasional 1p cost.

ccbrowning

Interesting graph! Looks like the Quooker this house came with is just 1.6kW.  I'm considering a battery mainly since my largest roof is east-facing. However I'm worried that there won't be enough output for the heat pump with a givenergy 9.5

EcoScruples

Alnat1 said:

I'm willing my 3kWh to break.

I really want a 2kWh kettle but ditching a perfectly good one.......I just can't make myself do it to save the occasional 1p cost.

I received a 1kw kettle for my birthday, that way I avoided feeling like I'd wasted a good kettle.
It really doesn't take that much longer to boiler a litre of water and I find myself using less water too.

ABrass

Heat pumps run during winter when there's insufficient solar power to power them. They just don't work well together. @Reed_Richards has been trying something similar in practice and can confirm.