Mains backup from PV

[mutleybones]

Hi,

the storms in France last night have knocked out the overhead power cables and my better-half is without power, with a couple of defrosting freezers and a dead batch of eggs in an incubator that were due hatch Tuesday   Then she went outside to find that the 36ft polytunnel had survived the battering from the elements, but is was no match for a 30ft walnut tree  

Anyhoo, I'm stuck in the UK working at the moment and feel a bit helpless. As part of our renovation I was thinking of wiring up a backup generator for this sort of situation, but an now wondering if it is possible using PV. I'd like to be able charge up a battery bank when the sun shines and export the surplus to the grid, when (not 'if')  the grids fails I'd like to automatically switch to the batteries to power essentials only - freezers, heating controllers and pumps (wood and solar powered), incubators, satellite broadband (no phone ) and torch chargers, etc - for maybe 3 days, assuming no further sunshine.

I'm guessing I'd need panels, batteries, inverter, magic boxes, ... please fill in blanks.

We're near Cognac and PVGIS website estimates 3,300 units a year for a 3kWp system.

French gov do a similar scheme to FITs paying €0.57 per kWhr if the panels are roof integrated. Would need to be installed by artisans unfortunately (payback period just doubled).

Steve.

[EccentricAnomaly]

It seems to me that you are really talking about two almost separate systems:

1. Batteries and inverters to provide backup power (big UPS).

2. PV panels to provide grid-tied electricity.

Using the PV to charge the batteries is almost incidental, you could just charge them from the mains when the power is on.  Of course, having the PV fed to the batteries would mean they last longer if there happened to be a long power cut in sunny weather, but somehow the world doesn't seem to work like that.

I.e., do the batteries if the need for interrupted power justifies them.  Do the grid-tied PV if the economics (interpreted broadly, maybe not just directly financially) justifies it.

[Paulh_Boats]

1) how often are the power cuts?
2) how long are the power cuts?
3) run round with a power meter to work out the kWh per day of the essentials

Then you can calculate the size of the battery bank from 2) and 3)

Then 1) lets you calculate how much solar power you need to keep the batteries recharged.

However you will find it is 100 times cheaper to buy a smart mains battery charger for 100 Euros - job done in about 30 minutes.

PV is sexy, but will you get enough sunshine in January to charge batteries after a long power cut? Maybe not so you will need a mains charger as backup, so start the system simple.

Also one small PV panel is enough to keep batteries charged after mains charging - so you can turn off the mains charger which is probably a good thing as many are not recommended for permanent connection.

Automatic changeover:
This is complex so often it is done manually. For the incubators I suggest a computer UPS because it will work automatically when you are asleep; the better UPS models can use external batteries to last much longer.

cheers
Paul

[dhaslam]

When I was building   I put   in  three UPS for the bedroom and utility  room  end of the house.    This means that there are  bathroom and bedroom lights, heating  and hot water when  the power is off.    Computers and  satellite box also on UPS.  Power cuts are usually only  for an hour or two.   The UPS don't last that long but it gives a chance to sort out alternatives.    There is probably a bit of overhead with the UPS but  my wife has advanced dementia and  needs constant care.   

[SteveH]

 Have a look at these links billi posted for me on another thread.

steve  found interesting  documents  and a new product on the victron website

http://www.victronenergy.com/upload/documents/multi%20with%20grid%20connected%20converter%20for%20solar%20and%20or%20wind%20turbine.pdf

http://www.victronenergy.com/upload/documents/Brochure%20-%20Solarswitch%20-%20rev%2000%20-%20EN.pdf

Billi

 Possibly quite expensive, but you would have an intigrated system that maintained all the functions you would need...

 Steve.

[knighty]

for the cost.... if it's only for during power cuts.... he is not going to be better off with a small generator ?

[billi]

Steve

another Steve in Greece is close to a set-up like you are thinking off ....

A lot to read and a bid hard to understand due to the technical side
http://www.navitron.org.uk/forum/index.php/topic,6834.0.html

There are "off the shelf " systems  like Sunny Backup from SMA , but expensive

So the "self  made  option"  would be  cheaper . Something like that

In addition to your grid tied PV , you need a Off grid inverter and a battery bank  and that switch perhaps http://www.victronenergy.com/upload/documents/Brochure%20-%20Solarswitch%20-%20rev%2000%20-%20EN.pdf

You are looking for extra costs like the system  in the document  for a 3 kw  with a decent second hand forklift  battery   for about 3500-4500 Euro on top of your Grid tied

Do you not have more roof than for 3 kwp ?  at 57 cent per unit and complete package prices down to 2500 euro/ex vat per installed kwp , if my budget or the bank allows i would go for as much as possible  

have a look at  grid tied Package from Germany  quite low prices there available  , and i estimate they will even get cheaper  cause the feed in tariffs there  are declining  ( will save you a few thousand euro   )

Perhaps you could live then completely of the Off grid inverter (perhaps a 5 kw unit then required) and just use the night time tariff from france ( is it 7.3 cent ?) to recharge your battery during the night , if you want

Billi

Oh  i see SteveH was here as well  

[mutleybones]

Hi everyone, thanks for the replies, power's still off, hundreds of thousands and one homes without at mo, according to Aunty Beeb. She's got plenty of logs, candles and wine, sounds romantic - shame I'm not there  

Agree with everything said, in essence it is two distinct functions, but it would be lovely if it all 'just worked' together, like a big, never-ending UPS that switched over automatically and produced €50 notes for the rest of the time.

Charging batteries from the mains with an inverter would be the simplest option and quite cheap to run overnight as and when. For extended outages, perhaps a generator could provide direct power and recharge batteries for evening/quiet use.

The FIT-equivalent still sounds attractive, €2000 a year income tax-free, we've reduced our living expenses (and working) to £6k a year, so that would go a long way. In which case the solarswitch device would at least mean the panels would be producing for us if the grid went down. I can imagine the conversation with my wife that we can't get power from the panels because the mains are off.

I think the problem lies in the fact all of the supply lines are overhead, just after Christmas ice brought down the cables for a few days. In August/September a nearby lightning strike will shut us down for a few hours quite (as in 'too') frequently.

For the moment, I'm off to get a small genny to take back with me, along with the new polytunnel hoops. Anyone any experience of the screwfix or wolf jobbies?

After the storm has passed, there's bright sunshine and panels would be great.

Billi - just read your post, will look into that, thanks for the info, maybe get the ferry via Germany, got the ivor williams with me 

Steve.

[mutleybones]

An aside: Billi, I've just seen your avatar, is it Le Petit Prince? We did a comprehension exercise in my french class, it got me so confused. Afterwards, I read the english version and it made my head hurt even more! Steve.

[billi]

Le Petit Prince

   

I think the book was present to me three times so far in my life , the first one from my mother , the second and third from Girlfriends 

I took my ifor williams (3.5 ton tipper)  from Ireland down to Bordeaux/Bergerac full with plants and tools
 2.5 years ago  for a landscaping job , i told the client that we arrive at 8 in the evening , we managed to be there at 2 in the morning  .
Driving is fine in France , but i did not expect  it goes so much up and down  with my heavy trailer .

Anyhow came home 10 weeks later with 500 bottles nice red wine .

Anyhow let me know how you are getting on . Ebay Germany is quite good for second hand batteries , or other stuff i can assist with my degenerating mother language (German) 

Billi

[Paulh_Boats]

Anyone any experience of the screwfix or wolf jobbies?

Not directly but I did a lot of research. The Screwfix jobbies are noisy and 2-stroke, so lots of smoke.

The best home generators seem to be the Hondas - quietest on the market (52db at 7m), Eco throttle that adjusts to load automatically, 4-stroke so they meet EEC emission guidelines, pure sine wave inverter output.

They aren't cheap though!
http://ww1.honda.co.uk/power/generators/detail.html?code=EU10i

http://ww1.honda.co.uk/brochure/download/portableEnergy.pdf

cheers
Paul

[HalcyonRichard]

Hi All,
         I had a few power cuts. maximum 1/2 hour while building work on nearby barns was going on. I thought about minimum requirements to keep fridge/freezer , central heating boiler and a few lights going. In all about 350 Watts. So battery + inverter or generator. Trouble was power cuts stopped as soon as barns were converted. My simplist backup idea was to have a 500 Watt inverter @ £30 + extension lead. Then run this off the car battery when required - 3 hours plus on a fully charged car battery. Then in the unlikely event of a prolonged cut run the car engine to re-charge the battery. Remember to check operation every so often as you don't want to find out it doesn't work when you actually need it. I haven't had a power cut for two years. If I was expecting longer more frequent power cuts the Honda looks very good, reliable and designed for long running times. PV is good but sods law says a power cut will happen in midwinter with least sunshine.

Regards

Richard

[Justme]

There is probably a bit of overhead with the UPS

Thats an understatment.

We found that the ups (a 600va I think) when just on standby used more power than the pc did when it was on.
When the pc was on the power was about 20% more than just the pc alone.

We then started to turn the UPS off when the pc was not on but had to disable to audible no mains alarm buzzer.

[mutleybones]

Thanks for that Paul, you're right, not cheap, but the mutt's.

Billl, could you give me a phrase to search for on ebay.de, I'd like to narrow down my results somewhat.

A million and one homes now without power, in the grand scheme of things its no big deal compared to the 22 people that have died, except perhaps for the two poor sods that survived the storm and then died from CO poisoning from their (indoor) generator.

Cheers all.

Steve.

[billi]

steve  what are you looking for on Ebay.de ?
generator?, Batteries ?

Richard   thats a way of doing it as well  I have a 500 ah Battery 12 volt connected to my car alternator via an automatic switch (charges starter battery first )  and a 3 kw inverter ( for building site tools )  or a 300 watt true sinewave  one  to connect to my home battery via the inbuilt charger of my off grid inverter 

But a 3 kw PV in Mid france  will do something in winter surely  , about 4-6 kwh on an average wintersday

Billi