Solar Panel: battery ratio

[sizbut]

The answer is really that there is not a ideal amount (not useful I know). All I can do it speak from experience on my own system based on its 3 years of operation.

So I have 3kW generation and 7kWh storage, so roughly a 1:2 ratio. No EV.

For 6 months of the year it is almost perfect with less than 5% of my electricity coming from the grid. The batteries fully charge during the day and any excess* goes to the grid.

However, for the other 6 months, the batteries rarely fully charge and it can be as low as 10% depending on cloud cover, though there will be exceptions where they reach 60% on a cloudless day.

My conclusion: (I struck my original conclusion, it was total tosh) If I had more storage it wouldn't benefit me in any way. Over the summer it would be storage that would just remain charged without being drawn. It the winter is would just remain uncharged. There might be some odd times as we transitioned between full sun and low sun days where it might finally charge and then discharge the next day but they would be few, so the benefit and return on investment would I suspect be close to never.

* I also have a solar diverter on my immersion tank which cuts in when the grid export is over 100W. It cost £300, I was fortunately able to fit it myself, and if my spreadsheet is correct it has already 80% paid for itself though obviously it only really works well during the summer, the traditional gas boiler is doing the rest.

An additional thing to look at is, if I understand correctly as I've not done this, the likes of Octopus can charge batteries from the grid at low cost hours for you to use when you need the power. That is one way to make the batteries be of use during winter months. However they only do that with certain models of inverter (presumably those that they sell).

[Cugel]

In principle yes, but in practice no.

Very few cars are "Vehicle to grid" (V2G) capable, and likewise, inverters.

V2G was being promoted by National Grid as the future to enable grid balancing. Why aren't all vehicles capable now.

Good question.

Because vested interests don't want you to have independence of supply but still be totally dependent on the (functioning) grid?

Maybe "full facts" state otherwise?!

Who knows what shenanigans, from which lobbyists acting to preserve what vested interests in the energy supply field are going on? There seems little doubt that there'll be some, given the ever greater corruption of politicians being revealed day after day.

Even if V2G and other facilities were encouraged and made that allow individual home and business electricity generators and storers to suck far less at the grid and its power generators, the grid is likely to remain a necessary part of the energy-using infrastructure.

But its evolving nature could be greatly improved if the old model of huge central supply and long distance transmission of electricity was amended to include multiple pathways and numerous e-storage facilities of many types and sizes to easily interoperate between millions of those with solar panels, house batteries, car batteries, small windmills and any other local/small-owner potential elements of the grid. A sort of internet for electricity.

For example, I'd like to see a significant e-storage and distribution facility in our village or parish, one able to take in excess solar energy from households and businesses generating it all around and distributing it at low cost and peak demand times to the whole village/parish. This in turn could be connected to a larger and similar (but still relatively local) network; which in turn can all be connected also to the national grid.

It would reduce overall costs and be very quick to implement even piecemeal; but could also distribute those costs (and any income from generation/storage and provision) amongst a huge number of participants. It would also make the national grid far more resilient than a system with most power produced and stored by just a very few huge, expensive and difficult to built/decommission facilities that are also very vulnerable to failure, sabotage, military attack or other disaster that would affect the whole nation.

But there's a lot of profit to be made from building, operating and decommissioning nuclear power stations and the like. However, there's just as much to be made from installing solar panels and batteries, I would have thought. It'll probably come down to which lot of lobbyists can afford to buy which politicians, then. Or browbeat them with various threats.

[Carlton green]

Update: booked for installation in a couple of weeks time.

11 panels, 5kw nominal output, 10kwh battery plus EV charger and immersion heater input.

Thank you for the update, I hope to hear both how the installation goes for you and whether it ends up living up to your expectations of it.

[roubaixtuesday]

Update: booked for installation in a couple of weeks time.

11 panels, 5kw nominal output, 10kwh battery plus EV charger and immersion heater input.

Thank you for the update, I hope to hear both how the installation goes for you and whether it ends up living up to your expectations of it.

I shall try to give an update post installation and perhaps at the end of summer.

[wheelyhappy99]

Even if V2G and other facilities were encouraged and made that allow individual home and business electricity generators and storers to suck far less at the grid and its power generators, the grid is likely to remain a necessary part of the energy-using infrastructure.

But its evolving nature could be greatly improved if the old model of huge central supply and long distance transmission of electricity was amended to include multiple pathways and numerous e-storage facilities of many types and sizes to easily interoperate between millions of those with solar panels, house batteries, car batteries, small windmills and any other local/small-owner potential elements of the grid. A sort of internet for electricity.

For example, I'd like to see a significant e-storage and distribution facility in our village or parish, one able to take in excess solar energy from households and businesses generating it all around and distributing it at low cost and peak demand times to the whole village/parish. This in turn could be connected to a larger and similar (but still relatively local) network; which in turn can all be connected also to the national grid.

It would reduce overall costs and be very quick to implement even piecemeal; but could also distribute those costs (and any income from generation/storage and provision) amongst a huge number of participants. It would also make the national grid far more resilient than a system with most power produced and stored by just a very few huge, expensive and difficult to built/decommission facilities that are also very vulnerable to failure, sabotage, military attack or other disaster that would affect the whole nation.

https://energylocal.org.uk/

Energy Local Co-ops link renewables generators with consumers, providing they are within an area served by a grid primary sub station. Several of the levies and tariffs fall away as the main grid infrastructure isn’t used/doesn’t need upgrading. Generators can be as small as householders selling the excess from their roof to commercial scale PV or turbine operators contracting to sell a % of their output to the Co-op. Generators can expect around 25% more for the spill sold to the Co-op than they get from the grid, consumers using locally generated power pay less per kWh, typically saving 10-30% on their total bill.

But there's a lot of profit to be made from building, operating and decommissioning nuclear power stations and the like. However, there's just as much to be made from installing solar panels and batteries, I would have thought. It'll probably come down to which lot of lobbyists can afford to buy which politicians, then. Or browbeat them with various threats.

Big engineering companies like big projects. And the big nuclear projects suit the fossil fuel companies because the 10-15+ years lead time means they’ve more time not being undercut by cheaper energy from renewables. Worth remembering that the taxpayer is on the hook for decommissioning costs. We still haven’t found a way to dismantle the row of old nuclear powered subs, currently I think at Faslane.

[slowcyclist]

I am having just the same conundrum, though massively less usage than the average home, as just a small off-grid setup of what most would consider the very basics. Only constant power is, cooking (not electric to cook but to run it), heating, in winter, and laptop.

Not sure if it has been discussed in this long thread but there is a theory of 'overpanelling' to get far more panels for the winter months than one would normally require in average solar weather.

So I have around 1100W for charging a 100Ah battery. My usage I am not sure in watt hours but the battery depletes if not getting charged after about 2 days. Not totally so I could make a guess at around 400Wh per day.

The overpanelling worked a treat when there was even a small break in the clouds for a couple of hours, which was enough to give a full charge but this past couple of weeks has been horrendous with next to 0 solar at all.

Just the constant blanket of thick clouds and/or mist.

I had been considering getting another battery so that the bank can charge on those good days to give a longer buffer for bad days, as there is a huge surplus, with the battery topping up rather quickly with just 100Ah but even 1 more I don't think would cut it as it has been like this for 8 days or more.

This has been exceptional though this winter and I had been fine almost all through it, bar perhaps a day here and there where I was bottoming out, even on the shortest days. Ironic that the days are longer now but this is actually the worst period.

I read an article yesterday that stated that this is the wettest it has been for however long with rain every single day since new year so I don't think it is worth it spending however many hundreds on more kit just for these few days although I do recall the same happening around exactly the same time last year, of many weeks of cover, so it is an issue but it is acute and only for a couple of weeks.

Going to ride it out I think and just plan things to do which don't use electric.

[Cugel]

I am having just the same conundrum, though massively less usage than the average home, as just a small off-grid setup of what most would consider the very basics. Only constant power is, cooking (not electric to cook but to run it), heating, in winter, and laptop.

Not sure if it has been discussed in this long thread but there is a theory of 'overpanelling' to get far more panels for the winter months than one would normally require in average solar weather.

So I have around 1100W for charging a 100Ah battery. My usage I am not sure in watt hours but the battery depletes if not getting charged after about 2 days. Not totally so I could make a guess at around 400Wh per day.

The overpanelling worked a treat when there was even a small break in the clouds for a couple of hours, which was enough to give a full charge but this past couple of weeks has been horrendous with next to 0 solar at all.

Just the constant blanket of thick clouds and/or mist.

I had been considering getting another battery so that the bank can charge on those good days to give a longer buffer for bad days, as there is a huge surplus, with the battery topping up rather quickly with just 100Ah but even 1 more I don't think would cut it as it has been like this for 8 days or more.

This has been exceptional though this winter and I had been fine almost all through it, bar perhaps a day here and there where I was bottoming out, even on the shortest days. Ironic that the days are longer now but this is actually the worst period.

I read an article yesterday that stated that this is the wettest it has been for however long with rain every single day since new year so I don't think it is worth it spending however many hundreds on more kit just for these few days although I do recall the same happening around exactly the same time last year, of many weeks of cover, so it is an issue but it is acute and only for a couple of weeks.

Going to ride it out I think and just plan things to do which don't use electric.

The most cost effective use of a battery in winter, when solar is low, is to download much cheaper overnight electricity from the grid to store and use during the next day time, rather than using expensive grid electricity during the day. We can download enough, if necessary, in the 6-hour overnight period to fill 30 KWH of battery whilst also charging the e-car at the cheap overnight rate.

The overnight rate is 6.5p per KWH whilst the day time rate is 26p per KWH so the saving is 75% on the grid cost less the extra consumed as inverter losses as the voltages and phases involved are changed. This loss is not one I have a figure for but for most domestic inverters the figure is usually between 5 - 10%.

A larger battery also provides for solar storage so that any dull days can be traversed without having to use the grid. Typically we download nothing from the grid for several months, from some time in Spring to some time in Autumn. We're all electric, including the car, so we use 9000 KWH per year ..... but generate 10,000 from the solar panels.

As e-cars and overnight charging become a norm, overnight cheap rate electricity might become more expensive. But not yet.

[slowcyclist]

...from the grid...

You missed the part where I stated it is an off-grid setup?

[Cugel]

...from the grid...

You missed the part where I stated it is an off-grid setup?

I did! Apologies.

[Carlton green]

...from the grid...

You missed the part where I stated it is an off-grid setup?

For those that are off grid then there’s a significant problem with solar and the winter months. iirc there was a thread - maybe a year ago - about a guy in a camper van who has similar issues. Over-panelling and / or a larger battery might be one solution, but (assuming local conditions allow) I’d be tempted towards pragmatic use of a small fossil fuelled ‘standby’ generator.
YMMV.

[PDQ Mobile]

...from the grid...

You missed the part where I stated it is an off-grid setup?

I am curious.
240v?

Not 12v with inverter?
A 100ah battery could be a largish vehicle battery.

"Cooking but only to run it", what source needs electric control?
And ditto "heating".

Lighting and power tools?

400 watts a day is super low.

[slowcyclist]

...from the grid...

You missed the part where I stated it is an off-grid setup?

I am curious.
240v?

12V only

A 1000 ah battery could be a largish vehicle battery.

It is a lithium 100Ah leisure battery not 1000Ah.

"Cooking but only to run it", what source needs electric control?
And ditto "heating".

You have not heard of diesel heaters? Very popular. They run on fuel but require small amounts or electric to operate. Likewise with gas.

Lighting and power tools?

Lighting = 2 LED lights. Probably about 0.2A, can't recall, but low.

No power tools - all hand.

400 watts a day is super low.

It is what it is.

I had thought about my setup initially having on no electric at all. I did consider it but a little system for those modest purposes above made more sense when I considered options and largely because having a laptop I decided was a must, to do research and such to further my knowledge of practical skills I use.

It is just a single space 'tiny home' type of thing.

[Carlton green]

I had thought about my setup initially having on no electric at all. I did consider it but a little system for those modest purposes above made more sense when I considered options and largely because having a laptop I decided was a must, to do research and such to further my knowledge of practical skills I use.

It is just a single space 'tiny home' type of thing.

This thread is probably the wrong place for further discussion on your home but I’d love to hear more about it. Might you, please, be willing to start a new thread telling us about your ‘eco’ home?

[PDQ Mobile]

You missed the part where I stated it is an off-grid setup?

I am curious.
240v?

12V only

A 1000 ah battery could be a largish vehicle battery.

It is a lithium 100Ah leisure battery not 1000Ah.

"Cooking but only to run it", what source needs electric control?
And ditto "heating".

You have not heard of diesel heaters? Very popular. They run on fuel but require small amounts or electric to operate. Likewise with gas.

Lighting and power tools?

Lighting = 2 LED lights. Probably about 0.2A, can't recall, but low.

No power tools - all hand.

400 watts a day is super low.

It is what it is.

I had thought about my setup initially having on no electric at all. I did consider it but a little system for those modest purposes above made more sense when I considered options and largely because having a laptop I decided was a must, to do research and such to further my knowledge of practical skills I use.

It is just a single space 'tiny home' type of thing.

I correct the "1000" to 100ah, but you were too quick for me! (Typo)

Yes I have heard of diesel heaters mostly in campervans.
(Heating oil is often cheaper than any diesel if bought in quantity?)
Gas doesn't often need leccy except for ignition spark?

Anyway always interested in off-grid, you are saving a lot on standing charges these days.

[Jdsk]

Might you, please, be willing to start a new thread telling us about your ‘eco’ home?

I'd be interested in that. But I wouldn't describe space heating or cooking with fossil fuels as 'eco'.

Jonathan