Usage verses what's generated

DebLong

Ok, help please, am I being too simplistic?
My 6 bed household uses approx 9000 kw electric a year.
My FIT system generates approx 1790 kW less 500 going to grid, a year.
If I buy 3x2.4 batteries =7200 kw
and connect to system, alongside the FIT, do I only have to pay for the 528 kw (approx)?
Thx 

Ectophile

It's unlikely to be that simple.  Solar panels generate more electricity than you can use in the spring and summer, but much less in the winter.  So you're likely to find the battery is never run flat in the summer, but barely charges in the winter.

Also, the "3x2.4 batteries =7200 kw" doesn't make sense.  3 x 2.4kWh = 7.2 kWh.

And make sure you don't mix up kW and kWh.  They are different things.

Reed_Richards

The standard units of electricity usage are kWh (kiloWatt hours)

So your annual electricity usage is 9000 kWh of which 1290 kWh is generated yourself, leaving a shortfall of  7710 kWh.  Unfortunately the batteries you are looking at will have 2.4 kWh capacity so 3 of them will give you 7.2 kWh of storage, one thousandth of what you stated.

Also, if 500 kWh spare electricity that you export is instead used to charge a battery or batteries then the most extra electricity you can ever possibly get to use is that 500 kWh so you still face a shortfall of 7210 kWh which you have to pay for.

And also 500 kWh per year is 1.37 kWh per day.  In actuality you will be able to store more in summer and less in winter but 7.2 kWh of storage seems excessive in this context.  

Reed_Richards

If you did have 7.2 kWh worth of batteries that would actually give you a maximum of 6.5 kWh of usable storage.  If you charged these each day from your solar panels but topped them up each night from cheap night rate electricity that would give you about 2365 kWh of cheaper electricity per year that you could use during the daytime.   That would bring the shortfall for which you pay full price down to 5345 kWh.  

Alnat1

DebLong said:

Ok, help please, am I being too simplistic?
My 6 bed household uses approx 9000 kw electric a year.
My FIT system generates approx 1790 kW less 500 going to grid, a year.
If I buy 3x2.4 batteries =7200 kw
and connect to system, alongside the FIT, do I only have to pay for the 528 kw (approx)?
Thx 

I think the OP put a comma in the wrong place. 

My FIT system generates approx 1790kW less, 500 going to the grid a year.

Reed_Richards

Alnat1 said:

DebLong said:

Ok, help please, am I being too simplistic?
My 6 bed household uses approx 9000 kw electric a year.
My FIT system generates approx 1790 kW less 500 going to grid, a year.
If I buy 3x2.4 batteries =7200 kw
and connect to system, alongside the FIT, do I only have to pay for the 528 kw (approx)?
Thx 

I think the OP put a comma in the wrong place. 

My FIT system generates approx 1790kW less, 500 going to the grid a year.

I don't agree but it doesn't make any odds. If they export 500 kWh per year then the most extra electricity they can possibly use with even the biggest batteries is that 500 kWh.

DebLong

Thx for your replies, yes me being too simplistic. The salesman nearly persuaded me to buy 3 batteries, costing £5500 (mats and labour) , lucky I said I needed to check figures first. 
So how do I generate more electricity? I have 12 panels already and room for more. Thx

QrizB

DebLong said:

So how do I generate more electricity? I have 12 panels already and room for more. Thx

Let's get back to basics.

My 6 bed household uses approx 9000 kw electric a year.

Even for a larger-than-usual house you're using a lot of electricity. Do you have electric heating, or are you using gas / LPG / oil etc for that?

DebLong said:

My FIT system generates approx 1790 kW less 500 going to grid, a year.

You say you've got 12 panels. Do you know the rated power, in kWp, for your system? I'm going to guess that it's less than 2kWp based on your generation numbers but I could be wrong.

How confident are you with your "500 going to grid" number? Do you have an export meter (possibly as one function of a smart meter)?

So how do I generate more electricity?

If the numbers and my assumptions are correct, then yes you probably need to add more panels. Quite a lot of them, given your 9000kWh/yr use.

If you use your 9000kWh at a constant rate throughout the year, that's almost 25kWh/day. I suspect that a case could easily be made for increasing your installation to 5kWp, and possibly as high as 10kWp (or more).

In practice you'd probably do this by adding a second (and possibly third) system, independent of your current one so you don't compromise your FIT payments.