What acreage of solar panels...

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What acreage of solar panels...
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mochyn

Joined: 21 Dec 2004
Posts: 24585
Location: mid-Wales

Posted: Thu Apr 03, 08 5:01 pm Post subject: What acreage of solar panels...
Would I need to run a washing machine and three freezers? Photo voltaics, obviously, although I suppose I could have a hot water one for the WMC. Rebuilding the wash house, and might as well go the whole hog.

Helen_A

Joined: 26 Jan 2005
Posts: 1548
Location: MK, Bucks.

Posted: Thu Apr 03, 08 5:20 pm Post subject:

We've been told that we would need about 10sq grid-tied meters to cover our 'permanent' power needs (i.e. fridge, freezer, washing machine and internet, plus occasional lighting). But that it wouldn't do it all year round as we'd also need about 8 hours daylight, and of that at least 3 hours decent sun.....

I'm not so sure that its an accurate survery though... Last summer a 15W solar charger in a case was keeping my laptop nicely charged so.....

Helen_A

Last edited by Helen_A on Thu Apr 03, 08 6:03 pm; edited 1 time in total

dpack

Joined: 02 Jul 2005
Posts: 43816
Location: yes

Posted: Thu Apr 03, 08 5:30 pm Post subject:
imho solar is good for warming things a bit for power you want gravity moving water

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Thu Apr 03, 08 6:02 pm Post subject:

Forget any idea of driving things directly from the panels.
Just think of the freezers. In the dark. Or on a dark January day.

If you are on the electricity mains, it makes massive financial sense to use the grid as your "battery". You can export to the grid in summer/daytime and import from it in winter/night.
Don't get involved with batteries and stuff unless you really must. !!

So, its not really a matter of sizing things against your electricity load.
More a matter of what is financially possible/sensible.

And a lot of the financial viability depends on Grants, subsidies and whatever deal you can make with an electricity company.

Remember "Alternative-Energy"?
He spent something like £17k.
He got a grant for about £8k, leaving him £9k out of pocket.
He's just finished his second year with his system.

Personally, I think his means of calculating payback makes very little sense* - but he has generated 6100 kw/h units of electricity in 2 years in Kent (there may not be as much light energy in Wales - further North and more clouds!).
He seems to actually use very little electricity, hence his bill was minus £200 for the year (they pay him), and he gets a £150 RoC subsidy as well. See how the subsidy is almost half the income?
https://www.alternative-energy.co.uk/Daily%20Outputs.html
And on those figures, it really doesn't look daft.
But miss out on the Grant, take away the RoC subsidy and get a less-good deal out of an electricity company, and it becomes a very different story.

* He's not including the cost of the capital to install the thing. And he's factoring in interest on the income. But he doesn't seem to be recognising that his benefit includes money that he isn't paying out for the electricity that he uses himself - let alone that the saving is of money from taxed income. Or that his new income as a generator presumably ought to be accounted for income tax...

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Thu Apr 03, 08 7:59 pm Post subject:

It's best to get a professional requirements survey done. This doesn't necesarily mean paying professional rates just someone who knows how to correctly size your system against your requirements (on/off grid, reserves required etc.) and the availability of natural resources to do this properly may need a site visit - especially true for solar hot water in order to make best use of the system.

Also don't think about it in payback terms. PV may take 5-15 years to pay back they have a (life of about 25 years to 80% efficiency). Instead think of it from an independance and/or enviromental point of view. Solar thermal hotwater will have a payback time much short than PV perhaps as little as 2 years. Wind turbine can be as little as 5 years or as long as 20 years depending on the size and usage of the system.

Capital expenditure may be high so you may need to factor in interest payments on loans as well.

For solar PV a basic rule of thumb is that your get, on average, at this latitude about 1 peak hour sunshine per day in winter and 4.5 hrs per day in summer. That means for a 60 Watt panel (running at 100% efficiciency) you'll get 60 Watt.hrs per day in the winter and around 250 Watt.hrs per day in the summer. If your needs are 3.5kWhrs per day (average small house) that means 14 PV panels will be sufficient to meet your needs on an average summers day but you'll need a lot more in winter. I haven't taken into account losses in the system. A 60 Watt panel costs around £300 so that's a capital outlay of £4,200 minimum. Just to give you a very broad idea.

Usually you don't try and meet all your energy needs using one system. Wind turbine and solar PV compliment each other well, solar PV supplies electricity during sunny windless days in the summer and wind turbine on cloudy windy winter days. This complicates calculations but can work in your favour.

James

Joined: 11 Jan 2006
Posts: 2866
Location: York

Posted: Fri Apr 04, 08 12:03 pm Post subject:
aren't you on a windy hill in cloudy wales? hmmmm......

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Fri Apr 04, 08 12:09 pm Post subject:

James wrote:

aren't you on a windy hill in cloudy wales?

hmmmm......

Oh yes, rarely cloudy though. I qualify that by saying where we live is often cloudy due to being very close to the mountains but where we're building has a martime climate and is clear for a lot of the time. Great thing about this area is the huge variety of microclimates in such a small area.

Northern_Lad

Joined: 13 Dec 2004
Posts: 14210
Location: Somewhere

Posted: Fri Apr 04, 08 12:09 pm Post subject:

dougal wrote:

Forget any idea of driving things directly from the panels.
Just think of the freezers. In the dark. Or on a dark January day.

She lives in Wales - they don't need to switch their freezers on in January.

Jb

Joined: 08 Jun 2005
Posts: 7761
Location: 91ï¿½ N

Posted: Fri Apr 04, 08 12:13 pm Post subject:

Basic figures are that solar radiation delivers about 1Kw / m2

Half of the time it's night
Half of the day your solr panel isn't square on
Depending on where you can site it it may be even less efficient
Solar panels are not 100% efficient
It could be cloudy
Over winter you could get even less solar radiation and fewer daylight hours in which to capture it.

So at best you could only use solar power to supplement other power sources, unless you were willing to use a large storage system and cut your power usage dramatically over winter.

I looked into this a while ago and unfortunately it worked out that by the time I had accounted for all the above the payback time was longer than the solar panel lifetime! Having said that there are these guys who have come up with cheap PVs that bring the cost down dramatically. If that starts producing in any quantity then PV will certainly be worth installing. Alternatively if you are willing to accept that it will only supplement it and don't need to fit it to a roof then it could be viable but wouldn't be a complete solution.

mochyn

Joined: 21 Dec 2004
Posts: 24585
Location: mid-Wales

Posted: Fri Apr 04, 08 12:30 pm Post subject:
Why I thought of solar was because we're having the wash house rebuilt, which is where all those machines are and the roof gets a reasonable amount of sun. I'd also just saved us quite a bit of the cost by getting slates from Freecycle, so was going to use that saving to offset the cost of the panels. I'll have a rethink.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Fri Apr 04, 08 12:39 pm Post subject:

If you are having roof work done (or need to change your hot water tank) then installing solar *thermal* (ie water heating) can be done for even less extra cost than it would cost to do the job entirely on its own.

Navitron (last time I checked) would supply evacuated tube (ie good) solar collector, controller/pump/gubbins kit and a super-insulated replacement hot water tank for about £1000 total. Installation extra, and up to you.
This is pretty fuss free, and nowhere near as major an investment decision as solar ("PV") electricity.
It should also be possible to organise the bits quite quickly.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Fri Apr 04, 08 12:52 pm Post subject:

dougal wrote:

Navitron (last time I checked) would supply evacuated tube (ie good) solar collector, controller/pump/gubbins kit and a super-insulated replacement hot water tank for about £1000 total. Installation extra, and up to you.

That sounds like excellent value.

mochyn

Joined: 21 Dec 2004
Posts: 24585
Location: mid-Wales

Posted: Fri Apr 04, 08 12:57 pm Post subject:
Now, that sounds an even better idea, Dougal. At the moment the washing machine heats its own water, albeit only to 40*, but having that done through solar would make a lot of sense. It only works that way because the wash house is 'outside' and it would be difficult to pipe hot water from the Rayburn to it. More thinking needed now...

Jb

Joined: 08 Jun 2005
Posts: 7761
Location: 91ï¿½ N

Posted: Fri Apr 04, 08 12:59 pm Post subject:
Bear in mind that if you replace your washing machine many washing machines now only take a cold water supply so if you connect that to a solar heated water tank you might no longer have the option of a cool wash.

vegplot

Joined: 19 Apr 2007
Posts: 21301
Location: Bethesda, Gwynedd

Posted: Fri Apr 04, 08 1:00 pm Post subject:

mochyn wrote:

Now, that sounds an even better idea, Dougal. At the moment the washing machine heats its own water, albeit only to 40*, but having that done through solar would make a lot of sense. It only works that way because the wash house is 'outside' and it would be difficult to pipe hot water from the Rayburn to it.

More thinking needed now...

Do you have a budget? I think it's important you set yourself one then see what you can acheive within that budget then revise if necessary. You can make resaonable effective solar thermal hot water collector and storage out of an old radiator, hot water tank and some plumbing. Not as effecient as a evacuated tube collector but could be a lot of fun.

Last edited by vegplot on Fri Apr 04, 08 1:01 pm; edited 1 time in total

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