How to live without heating - save £000s

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There's a cold snap incoming from the end of the week onwards 

QrizB

HertsLad said:

Perhaps this will generate almost 3kwh, even on a cloudy day in December. If not, I will increase the number of panels until it does. 

I'd like to state now - that seems a trifle optimistic.

I have 11 ~250-watt solar panels on my roof, facing ~south.

Today, a cloudy day in December, they generated 0.3 kWh.

To generate 3kWh would require 110 panels.

Now, let's assume that you've bought recent panels rated at 500 watts rather than my rather elderly ones. You'll only need 55 panels. Each 500-watt panel is however going to cover about 2.2 square metres; to fit 55 of them on the roof, you'll need 121 square metres of roof space.

That would take the whole of my roof, both north and south aspects, plus the entire other semi that I'm attached to.

To get 121 square metres of south-facing roof would need four semis like mine.

HertsLad

QrizB said:

HertsLad said:

Perhaps this will generate almost 3kwh, even on a cloudy day in December. If not, I will increase the number of panels until it does. 

I'd like to state now - that seems a trifle optimistic.

I have 11 ~250-watt solar panels on my roof, facing ~south.

Today, a cloudy day in December, they generated 0.3 kWh.

To generate 3kWh would require 110 panels.

Now, let's assume that you've bought recent panels rated at 500 watts rather than my rather elderly ones. You'll only need 55 panels. Each 500-watt panel is however going to cover about 2.2 square metres; to fit 55 of them on the roof, you'll need 121 square metres of roof space.

That would take the whole of my roof, both north and south aspects, plus the entire other semi that I'm attached to.

To get 121 square metres of south-facing roof would need four semis like mine.

Thanks for the reality check! You may be correct. I just looked back at history on my two present Victron controllers. 10 days ago, so almost on the shortest day, they collected 1kwh of energy from my existing panels. Since then, I disconnected my 24v freezer in order to avoid needing too much energy. The power collected is now about 0.2kwh per day. I probably charged other batteries 10 days ago, in order to need 1kwh of energy. This was with 2 panels facing south on stands in the garden, but mostly in shade at this time of year. Plus 10 panels laying horizontally, wholly in shade, on my flat roof. And 3 panels not connected at all. I am hoping for a huge boost in power when I fit 10 panels on my house roof, facing SE and in a good position for morning sun, all year round. Four of my panels are 320w. The others are 420w, bought about a year ago.

QrizB

I know you want to DIY this, but there's a reasonable economic case for having panels installed on your roof professionally, with MCS certification, and claiming the export payments in the summer months when you will be generating far more electricity than you need.

As an example, for £5500 you could have 10x500W panels installed (link) and set up for export. That would generate something like 4500kWh a year; on a bad day in the winther you might only get 0.5kWh, but a good day in summer would make 30kWh.

If you need 3kWh a day, that's ~1000kWh total for the year. The 3500kWh excess you'll generate you can then sell back to the grid; export prices seem to be stable at present, and have been around 15p/kWh (some minor variation between suppliers) for the last 2-3 years. At that rate, 3500kWh would earn you £525 a year, a 9.5% return on your £5500 expenditure.

And that's all ignoring whatever contribution your existing off-grid system will make; if you only need to use 200kWh a year from the rooftop system, that's another 800kWh to sell and an extra £120 per year of income.

HertsLad

QrizB said:

I know you want to DIY this, but there's a reasonable economic case for having panels installed on your roof professionally, with MCS certification, and claiming the export payments in the summer months when you will be generating far more electricity than you need.

As an example, for £5500 you could have 10x500W panels installed (link) and set up for export. That would generate something like 4500kWh a year; on a bad day in the winther you might only get 0.5kWh, but a good day in summer would make 30kWh.

If you need 3kWh a day, that's ~1000kWh total for the year. The 3500kWh excess you'll generate you can then sell back to the grid; export prices seem to be stable at present, and have been around 15p/kWh (some minor variation between suppliers) for the last 2-3 years. At that rate, 3500kWh would earn you £525 a year, a 9.5% return on your £5500 expenditure.

And that's all ignoring whatever contribution your existing off-grid system will make; if you only need to use 200kWh a year from the rooftop system, that's another 800kWh to sell and an extra £120 per year of income.

Many thanks for the suggestion. It's something for me to consider - running two systems in parallel - my existing 24vdc system and a 240vac grid tie system. Reasons why I haven't considered it so far are: 1. The cost which I thought would be higher than £5500. Do you have a supplier in mind, please? 2. Needing to pay the electricity standing charge; 3. An expensive grid tie inverter which might not last long; 4. Consumer type battery units in smart cases, costing more than I am currently paying. I recently bought two more 100ah 12.8v lithium batteries for £100 each. But if the investment has a near certain return, and to increase the appeal of my house, the conventional approach you suggest may be worth thinking about. I might be able to get the cost reduced by pointing out the hooks and rails are already fitted. Have you considered upgrading your panels from 250w to 500w?

QrizB

HertsLad said:

1. The cost which I thought would be higher than £5500. Do you have a supplier in mind, please?

If you drop a PM to @Screwdriva he can put you in touch with a supplier that covers your area (the East of England?) and can provide a system at that price, more-or-less.

HertsLad said:

2. Needing to pay the electricity standing charge;

Your're already paying that, though, and from what you've said you want to continue with a grid connection.

HertsLad said:

3. An expensive grid tie inverter which might not last long;

Experience on the Green & Ethical forum has shown that grid tie inverters last a decade or more. Most come with a manufacturer's warranty too.

HertsLad said:

4. Consumer type battery units in smart cases, costing more than I am currently paying.

Personally I don't think on-grid battery storage makes any sense for your use case. Stick with the off-grid batteries you already have.

HertsLad said:

... I recently bought two more 100ah 12.8v lithium batteries for £100 each. 

I like a bargain as much as anyone, but a lot of those cheaper batteries are very poorly put together and the only way to know it to take them apart and look.

Watch some of eg. Will Prowse's videos and you'll see what I mean.

HertsLad said:

Have you considered upgrading your panels from 250w to 500w?

My FIT is paying £2k a year, should continue to do so for a decade yet, and I don't want to do anything to prejudice that!

HertsLad

QrizB said:

HertsLad said:

1. The cost which I thought would be higher than £5500. Do you have a supplier in mind, please?

If you drop a PM to @Screwdriva he can put you in touch with a supplier that covers your area (the East of England?) and can provide a system at that price, more-or-less.

HertsLad said:

2. Needing to pay the electricity standing charge;

Your're already paying that, though, and from what you've said you want to continue with a grid connection.

HertsLad said:

3. An expensive grid tie inverter which might not last long;

Experience on the Green & Ethical forum has shown that grid tie inverters last a decade or more. Most come with a manufacturer's warranty too.

HertsLad said:

4. Consumer type battery units in smart cases, costing more than I am currently paying.

Personally I don't think on-grid battery storage makes any sense for your use case. Stick with the off-grid batteries you already have.

HertsLad said:

... I recently bought two more 100ah 12.8v lithium batteries for £100 each. 

I like a bargain as much as anyone, but a lot of those cheaper batteries are very poorly put together and the only way to know it to take them apart and look.

Watch some of eg. Will Prowse's videos and you'll see what I mean.

HertsLad said:

Have you considered upgrading your panels from 250w to 500w?

My FIT is paying £2k a year, should continue to do so for a decade yet, and I don't want to do anything to prejudice that!

Thank you very much for your helpful comments and suggestions. But all this solar chat is probably better suited to my other thread on living off grid. Are there moderators who can move posts from one thread to another?

I will contact Scewdriva, thank you, but after I return from a 2 week ski holiday towards the end of January. I need to turn my attention to getting ready. Today, I noticed the solar power seemed lower than it was, on a very clear, blue sky day. Perhaps some electrical joints need looking at. But it will have to wait until after my holiday. There is still enough power for very low consumption while I am away.

I seldom subscribe to the idea you get what you pay for. That's why I buy the cheapest lithium batteries and they seem to work perfectly well. I did take a 36ah lithium battery apart after the voltage dropped to 2v and the BMS prevented normal charging. Tips on youtube failed, before I opened it up. The build quality seemed perfectly OK, even if the BMS exhibited quirky behaviour. I have watched several of the Will Prowse videos and they didn't alter my thinking.

No, I have not paid a standing charge or used any mains electricity for several years.

I looked at Octopus deals. They would charge about £7500 without batteries. Yet they imply batteries are almost essential for export at peak times for public consumption. It might push the installation cost up to £10K, an astronomic and totally non-viable amount. Hopefully Screwdriva can point to better deals.

wrf12345

Just to add, recent changes mean that the roof fixings have to be an MCS approved install. can't recall if that is just to get the export and/or to comply with permitted development (MCS is now needed for external heat pumps otherwise you have to get planning permission, talk about locking down the country and big State).

HertsLad

wrf12345 said:

Just to add, recent changes mean that the roof fixings have to be an MCS approved install. can't recall if that is just to get the export and/or to comply with permitted development (MCS is now needed for external heat pumps otherwise you have to get planning permission, talk about locking down the country and big State).

Outrageous, if your warning is correct. The brackets have a line of screw holes to line up with joists in various places. My joists and tiles are probaably similar to many houses. The bracket for the rail mounting lines up with a low point of the tile, which still has to be ground down. But the screw can't line up with the bracket. It's to one side. I didn't think this seemed sturdy enough so I glued and screwed extra blocks of wood to the joists from inside the loft. I then use one screw into my new block of wood and one screw into the actual joist. I can't see MCS contractors going to all that trouble. I was thinking probably the entire line of brackets is OK when linked with the rail. Perhaps my approach is a bit OTT. But it's crertainly stronger; not weaker.

QrizB

HertsLad said:

wrf12345 said:

Just to add, recent changes mean that the roof fixings have to be an MCS approved install.

Outrageous, if your warning is correct.

MCS-certified installers have enough structural engineering training that you don't need separate Building Regs sign-off for the modifications.

If you DIY, you need to make your own Building Regs application to your local authority, supported by structural engineering calcs.