Solar system advise

Jibber123

With the current situation I'm starting to think solar seems to be the way forward but none of the companies I've spoken to over the phone seem to instil any confidence when you start talking about details, they seem more interested on selling you what everything they can and getting the government grants. What I'm after is to know basically how many kW of panels I'd need to be completely non reliant of the grid.
We use just under 6000kWh of electricity a year and 12,000 kWh of gas. Assuming just the electricity for starters, and 12hrs a day of sunlight avg across the year. that's 6000/365/12= 1.4 kW of panels plus a bit for losses so say 2kW and a good size battery bank to ride out the overcast days etc. The companies are talking about 6-8 kW of panels which seems a lot higher, but they don't seem to offer any reasoning. I understand in the deepest darkest winter months you will need more kW's of panels to generate enough electricity to meet your demands, and then you will have surplus in the summer to sell back to the grid, but is 3-4x the yearly average really needed?  When you read all the manufactures literature they recon they still generate 80% of there rated output in winter. Also if I decide to go with an electric heat pump to replace the gas this will make a huge difference. One company said I would need 35-40 kW of panels to run the heat pump in the winter and with the battery bank the quote was £79,000! I know energy prices are going up but it will still take 15 years to recoup the installation costs, and that is without anything going wrong and needing to be replaced.

pfpf

you better ask Prof Brian Cox.

Krakkkers

I am afraid you have completely misunderstood how much power is generated by the panels.
To generate 6000 kwh a year would require at least 6 kwp of panels and even then you would likely be able to use less than half of that without serious battery back up.

victor2

You might get more information looking here:

https://forums.moneysavingexpert.com/categories/green-ethical-moneysaving

However, without a drastic change in lifestyle, plus a very significant cash outlay, you will not be able to go totally off grid and hope to capture and store the energy you need from the sun.

Edit:

We have friends who are off grid. They have 8 panels south facing, batteries (which only last a few years) and run a large American style fridge freezer plus LED lighting from it. In the winter they have to switch off the fridge overnight to prevent it running the batteries down. They buy calor gas for cooking, have no TV, no washing machine, no internet routers or any other electrical devices apart from a "camping" shower driven by a 12V battery and calor gas to heat the water, which is captured from their guttering. The battery is charged up when they have a sunny day and can plug in a charger. Showers are short and not daily!

Krakkkers

To replace your gas usage for heating over winter is an impossible task as that would be an additional 12,000 kwh by your figures which in the winter might take an additional 25 kwp of panels and battery storage?
The reality is no one uses solar in the way you have imagined.

Ectophile

My rough rule-of-thumb when it comes to solar panels and the weather is that in full sun, you should get close to the rated power.  Light cloud can reduce it to a tenth of that.  Heavy grey cloud may reduce the output to hundredth of the rated power.  My 3.4kWp of panels can produce less than 100W in bad weather.

In the winter it's not unknown to go for days with no sun.  And even when the sun does come out, the days are short.  If you want to go completely off-grid, you're going to need a very big battery that will power all your needs for several days, and several kilowatts of solar panels.

Petriix

I have a 3.42kWp array facing nearly due south. I average about 3500kWh generation per year. However this varies from around 80kWh in the worst months to 500kWh in the best months. On a cool but sunny spring day we can generate up to 24kWh whereas on an overcast winters day it might be less than 1kWh.

As well as the seasonal variation, it's common to be generating more than you can easily utilise or require a top up from the grid. Unfortunately most big appliances use a powerful heating element for a short period in their cycles. Ovens oscillate on and off etc.

I have an EV which is often plugged in all day ready to use any surplus. But I still export at least half of what I generate. I could reduce this at the expense of importing more to supplement the solar. However, that would actually cost more than simply waiting for the Octopus Go Faster cheap rate.

With a battery I could shift almost all of my usage to off peak, but the savings wouldn't be sufficient to recoup the battery cost within its usable life. I've got plenty of smart meter data to analyse when that might change with rising prices.

Running an air source heat pump from solar is unlikely to be possible as the vast majority of your demand will be when you're not generating much. 

At 6,000kWh per year you're still likely to make a decent saving. But it would be pointless to try and become totally self sufficient. You'd need so much redundancy to cover the periods of low generation. Each extra kWp you add would be less useful than the last. 

[Deleted User]

Really really roughly, treat 1kWp installed as generating 1000kWh in a year.  Without a battery, you will use 30% and with a battery you will use 50%, unless you make drastic lifestyle changes.

And you'll need a battery the size of your house to store excess summer production to run appliances in winter - particularly if you're going to try and run a heat pump too.

[Deleted User]

Off grid: not a hope. I have a 6.35kWp array that generated 110.3kWh last December: my worst day was 350Wh.

Krakkkers

Basically the info the installers gave you was correct, it was your understanding that was incorrect.
Solar panels are still very much a worthwhile investment.

Krakkkers

4Kwp installed in Lincolnshire, south facing, Jan and dec about 100kwh, peaking in May at 600kwh.
This year has been unusual, 500kwh in Apr, May, June, July and Aug.