Solar Panels with Batterys

[steelman99]

Have had solar pannels for a while now , and after getting a smart meter , we realised how much electric we were sending back to the grid even in winter.
Therefore we decided to splash out and get a battery storage system fitted , its a 4.8Kw system that can have extra batterys fitted if we want.

Much to wifes annoyance Ive been monitering things over the last month and for most of the time we are running the house off solar/ battery power. even in the morning after running things like tv/ fridge/freezer lights ect all night the batterys are still at 40-50% capacity.
When I put the kettle on it used to draw around 3KW , but since the batterys were fitted its around 1-1.2kw we are pulling in from the grid (figures from smart meter display & the app that connects to the battery system). Im guessing the batterys can only be discharged at a certain rate , therefore with a 4.8kw system using 2 batterys , each battery will only give up about 1kw at a time.
Otherthing we are noticing is that the batterys are fully charged again by 2 or 3pm, after that we are just giving back to the grid

Thoughts are to add another battery or even 2 to the system so that we can be as indipendent as possible for electric , and not draw anything in from the grid for most of the year - guess the question is would adding more batterys give us this , or is the ammount that can be drawn from the batterys limited by what can go through the inverter

If it helps its an AC coupled system & a lux power system

 

[JohnD]

Do you mean the battery is 4.8kWh?

What did the battery and controls cost?

What month were they installed?

 

[steelman99]

Battery is 2X 2.4kw batterys giving 4.8kw storage in total , can be scaled up to take more bttery if we want
Were installed in Feb , and have managed to keep everything other than the kettle and the oven supplied with power - even the toaster dosent pull in anything from the grid - the whole battery system cost 3k to install , but electric costs have dropped by £30 per month , so at pre April prices should pay back in 10 years , of course if the cost of electric gos up should pay back sooner

Solar system was installed back in 2011 , so we get just over 60p per KW we generate and then another 4p for half of that as deemed export, the panels paid for themselves in FIT payments in under 10 years.

 

[JohnD]

When you say 4.8 "kW" for the batteries

You mean "kWh"

Right?

 

[bernardgreen]

kW is the rate of using electricity, kWhr is the quantity of electricity used or stored ready to be used.

 

[SpecialK]

Is your inverter not powerful enough?

 

[SFK]

Another vote from me ffor you think also consider the invertor. Invertor size needs to match your power requirements and battery size.

 

[Agile]

It is all very well talking about a benefit for 10 years. However most batteries have a very limited life and are expensive to replace. Similar questions come up with electric cars. Many may not last 10 years or 3650 deep cycles.

Can anyone come up with any calculations which give useful information on the benefits ( if any ) of a battery system and what is the optimum battery size.

The battery drain cannot exceed the inverter power !

Can anyone point me to specifications for batteries offered for this purpose?

 

[ericmark]

I did read a report by some one in Australia on fitting solar panels and batteries, and his conclusion was it depended where you lived in Australia with varying amounts of sun light and varying grants, but in essence it was unless there is a government grant not worth doing to save money. Unlike UK it was regional government who gave grants not central government so it varied.

The main problem is maintenance, if you have 1000 solar panels and one goes wrong your likely to have the tools and expertise to fix it, but with 8 solar panels on a roof if some thing goes wrong it costs a lot to fix, sitting in a brown field site where no ladders or scaffolding required great, but roofs in UK are not designed for solar panels, Turkey OK they have flat roofs and internal access to roof, so easy to fix, and the angle can be set spot on for max power.

I am sure for many the solar panels work, and with the original set-up even if they didn't you still got paid, they assumed how much they produced, it was not metered. And guaranteed payment for 25 years I seem to remember, that has all now gone.

I tried to set up a narrow boat with inverter and lead acid batteries, and we had two inverters fail, it is a case of sticking a pin in yellow pages to select the hardware, everyone claims theirs is the bees knees.

As to kWh it is really a silly unit, as there is not time involved, the watt is a Joule per second, so the hour cancels out that second, so 3,600 seconds in an hour so a watt/hour is 3,600 Joules. What it does is make the numbers smaller, and easier to work out what power an appliance will use, but it is hard to make people understand that a kilowatt/hour has no time.

 

[EFLImpudence]

but it is hard to make people understand that a kilowatt/hour has no time.

Well, it does.

It is using (the equivalent of) 1kW for an hour (half a kW for two hours or 2kW for half an hour).

You might be better saying a kWh has no power.

 

[ericmark]

Well, it does.

It is using (the equivalent of) 1kW for an hour (half a kW for two hours or 2kW for half an hour).

You might be better saying a kWh has no power.

Oh dear, seems I have not explained, if you multiply some thing but x then divide it by 3600x the x cancels out, and the thing is 3600 times smaller.

So a Joule per second = a watt, so a watt/hours equals 1/3600 Joules. There is no time, a kWh = 3,600kJ.

 

[EFLImpudence]

Oh dear, seems I have not explained, if you multiply some thing by x then divide it by 3600x the x cancels out, and the thing is 3600 times smaller.

Yes, but why did you choose 3600 and what is 'x'?

There is no time, a kWh = 3,600kJ.

So a Joule per second = a watt, so a watt/hour equals [1/] 3600 Joules.

Yes, a Watt for an hour equals 3600 Joules.

Actually a Watt for a Second is a Joule.



Is it an unbelievable coincidence that exactly one Watt for exactly one second is exactly one Joule?

 

[flameport]

Similar questions come up with electric cars. Many may not last 10 years or 3650 deep cycles.

Old generation EVs from 10+ years ago (mainly the Nissan Leaf) had batteries which were rated for 3000 cycles, which is at least 10 years in normal use, as that's still using the vehicle 6 days a week and for the full capacity of the battery every day.
Also note that even after that, it doesn't mean the battery is useless, just that it's capacity has diminished by a certain percentage.
For the Nissan Leaf from 10+ years ago, that degradation can be as much as 50%, which makes the vehicle range an unusable 30 miles or so. However that vehicle only had a range of about 70 miles when new.

Batteries today are rated typically 6000+ cycles at full charge/discharge, which for an electric vehicle in normal use represents at least 20 years and in many cases a lot more, as plenty of people do not use their car every day, and even when they do, most journeys are short and do not use the full capacity of the battery.
Even with 50% degradation after that time (which is unlikely as modern batteries do not degrade at anything like the rate of those from a decade or more ago), that still means a typical EV with an as-sold range of 200 miles could have over 100 miles of range remaining even after 20 years use.
It's already the case that for the majority of EVs the batteries will last longer than the car.

Specifications are readily available from battery manufacturers, one example: https://en.byd.com/wp-content/uploads/2017/06/b-box-eur-spec.pdf

 

[aptsys]

It is all very well talking about a benefit for 10 years. However most batteries have a very limited life and are expensive to replace. Similar questions come up with electric cars. Many may not last 10 years or 3650 deep cycles.

Can anyone come up with any calculations which give useful information on the benefits ( if any ) of a battery system and what is the optimum battery size.

The battery drain cannot exceed the inverter power !

Can anyone point me to specifications for batteries offered for this purpose?

We already lost around 80 miles range in 3 years on our Model S, though it has mainly been supercharged every other day rather than the current limited charging methods. The batteries also seem to be reducing in efficiency also, with similar energy in resulting in fewer miles. Not great.

 

[Mr Chibs]

We already lost around 80 miles range in 3 years on our Model S, though it has mainly been supercharged every other day rather than the current limited charging methods. The batteries also seem to be reducing in efficiency also, with similar energy in resulting in fewer miles. Not great.

Out of curiosity, what was the range 3 years ago and today?