Solar system advise

Jibber123

Krakkkers thats what I was after, real world figures, what you get out of a certain size installation. I don't plan on going completely off grid but with what's going on at the moment I can't see a sustained future for the national grid. All the government is doing is stop gap measures. Several other developed countries are currently shedding loads and having planned power outages. I think it's only a matter of time. If I'm going to invest in solar, I might as well invest in a system that can hopefully do the bulk of what I need, we're noting talking about a few £100 after all. I know a change in lifestyle is needed, we already have solar thermal so get free hot water for 9-10 months of the year. Log burners provide a warm place in the house but we still need background heat in the house to prevent damp and mould and keeping long burners going 24/7 in the winter uses a huge amount of wood and time. Unfortunately we've got 2 freezers running during the winter for produce we grow and rear, together with the one in the kitchen for day to day use, this is a big chunk of our energy usage. Apart from the electric cooker, kettle, toaster. All the loads are quite small background usage. Router, charges LED light etc, but as the old saying goes a ton of feathers still weighs a ton. And it all adds up. Krakkkers, do you have any info on the system you've got installed and monthly kwh for a couple of years. 

QrizB

You've got some good answers above (and I realise this reply will appear on page 2, where you might not read it). But here are a few additional things to consider:

Jibber123 said:

...they seem more interested on selling you what everything they can and getting the government grants

There are no government grants for domestic solar PV systems. You'll be paying every penny yourself.

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 ...

Others have answered this for you, but (assuming your electricity use is spread evenly througfhout the year, 500kWh per month) I would expect that to generate 500kWh in December on a relaible basis (so 9 years in every 10, say) you'd need 40kWp of solar panels - around £40k worth, and covering at least 80 square metres - backed up with 50kWh of batteries - around £30k worth.

So yes, £70-80k sounds a reasonable estimate.

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've had solar panels for a decade now. Over that period they've averaged just under 1kWh generated per watt of panel. To generate 6000kWh a year you'll need at least 6kWp of panel, probably a bit more (depending exactly where in the country you are and how close to ideal your site is).

Also if I decide to go with an electric heat pump to replace the gas this will make a huge difference.

Yes. Swapping from gas to a heat pump will add 4-5000kWh/yr to your energy use, biased towards winter. You could easily end up needing twice the amount of solar I've calculated above - 80kWp - plus three times as much battery - 150kW - which pushes the price up to £170k.

To my knowledge the only person oj this forum who is close to being fully off-grid is HertsLad. You should read his two threads:

1. How To Live Without Heating
2. Should I Go Off-Grid

You can spend a lot more than he has without being all that much more comfortable.

QrizB

Jibber123 said:

Krakkkers, do you have any info on the system you've got installed and monthly kwh for a couple of years. 

Not Krakkers but here's 11 years of data from @JimJames system:

http://solar-panels-review.321web.co.uk/index.php/yearly-comparison-of-solar-pv

JimJames is in pretty much the best place in the UK for solar power. I would expect almost every other system in the country to do worse than that.

Here's a system in Sheffield, which might be more typical:
https://pvoutput.org/aggregate.jsp?id=66193&sid=58867&v=0&t=m

...we already have solar thermal so get free hot water for 9-10 months of the year. Log burners provide a warm place in the house but we still need background heat

If you have solar thermal plus log burners and are still using 12000kWh/yr of gas, you're using much more heat than the average property. 6000kWh/yr of electricity is also double the average.

Have you tried to reduce these? Do you know where all the electricity goes, for example?

Krakkkers

Use this for your own estimate...JRC Photovoltaic Geographical Information System (PVGIS) - European Commission (europa.eu)

Jibber123

It's a detached bungalow. And the building is a Y shape so most of the rooms have 2 or even 3 outside walls. It's also got single glazed crittle windows, which we can't change as we're in a conservation area, I've installed secondary double glazing inside where possible but I've only done about 1/2 the house so far, time and money permitting, to give you an idea of our buildings heat losses we've got a 48Kw boiler that only just keeps the house at 18C on a very cold winters days hence the log burners. Like I said we've got 2 extra freezers running 6 months of the years which is about 800 kWh from memory, plus running a few things like egg incubators and electric fences for the animals all adds up too. We've got LED bulbs throughout the house, and occupancy sensors on some rooms as well. The electric cooker uses a fair bit and the OH does a fair bit of cooking and baking too. We did do through our energy usage about 4-5 years ago and got if right down from £180 a month to just over £85, but with current prices per kWh it's sky rocketing again. Hence the interest in solar PV.

Krakkkers

If you use the calculator above it can bring your house up on maps to give you the alignment, lat. long.
For me it overestimates winter generation and underestimates summer generation.
Predicts about 3850 kwh a year for me but generally i get 4100 and this year 4300.

Jibber123

Great tool Krakkkers, and good to know it's a little under in its estimates. Worrying that I may need a lot more kWp that I initially thought tho.

Krakkkers

Sounds like you are running some kind of smallholding?

Jibber123

It's just over an acre, couple of pigs, couple of sheep, chickens, ducks, turkeys and fruit and veg so yes a small 'small holding'. Just spent 2 days apple scrumping, and got 60l of apple juice in the freezer and 150l of cider fermenting now! We've got space for solar ideally on the roof of the house but we could put them on the ground in the corner or an outbuilding and run cabling back. The bungalow is fairly well in the trees so might be an issue with shade but that's the finer details. I'm trying to work out if its basically worth the outlay? I'm thinking the saving are going to be fairly small even with the current electricity prices.

QrizB

Jibber123 said:

I'm trying to work out if its basically worth the outlay? I'm thinking the saving are going to be fairly small even with the current electricity prices.

For a well-sited system the savings are potentially decent. I've just modelled a typical system in Excel and payback takes about 11 years and the 25-year internal rate of return is about 6.5%. (This is assuming that the current high energy prices subside after a couple of years and drop back to 14p/kWh import, 5p/kWh export. If prices are higher, payback is sooner and returns are better.)