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.