use PV during blackout

[Steffen595]

Hi again,

how is the current legislation during blackouts, PV is switched off? Would be nice if it still would drive my fridge.... Suppose there is more blackouts to come, if I look whats going on in the neighbourhood in term of new buildings and what is not going in terms of the rotten grid.

edit:
afraid not ........ Cross Forum Link Removed...........they are not allowed.
whoch is weird, couldn't it just disconnect itself from the grid and feed into my house. Would switch the AC off and only run the fridge...

Cheers,

Steffen

[SilentButDeadly]

PV panels alone can not supply sufficient stable voltage and current to run appliances safely and without risking appliance failure..

It is certainly a requirement for your PV system to automatically disconnect from the grid in the event of a blackout otherwise your PV will energise the local area of the grid....and you could kill a lineworker as a result.

However, there are a couple of brands of inverters (Oz made too) that allow you to run a battery backup so that in the event of grid failure the PV are disconnected from the grid and house current is drawn from the battery system. Of course it costs a heap more (batteries and the inverter) but that's the price you pay if you don't want to rely solely on the grid....

[Steffen595]

fridge would need 150 or so W to run, PV should whip that up easily in summer.

Battery bank sounds trouble, well, just empty the fridge before summer is on its worst then.... Last time I covered it in wet towels.

[sundancewfs]

You need some sort of storage and delivery device (batteries, capacitor bank) to be able to provide and maintain a constant voltage and current. If you didn't have them, every time the sun went behind a cloud, your fridge would freak out and die very quickly.

[Steffen595]

fridge off, backyard tomatoes then....

[Draffa]

If you've got access to The Grid, the financial cost of adding a battery bank is a no-goer, if you want to look at it from a $ POV. Also consider the the typical blackout here in Oz only last about an hour (iirc), and if all this years blackouts happened at once you'll only lose power for about 8 hours. Financially, it's better to just toss a fridge full of food once a year than install the batteries.

However, if you want to do it anyway, take a look at what the homebrew Electric vehicle community do for batteries: if they use PBa, they'll generally go for sealed, 6V batteries. By the time you've got enough batteries to get to 240V (40), you've got enough Amps to kill a bull elephant, and enough capacity to run the house on typical night-time drain (roughly 1/3rd daytime consumption) until the power comes back on (you'll be draining the batteries at a 10h rate, rather than 1hr. Puekert's effect). A homebrew EV will typically use about 200Wh/km, and for a typical 40km commute, this is a bank of 8kWh +reserve (you don't actually want to drain the batteries to 0% of capacity. keep them above 80% and they may well live for a decade. Treat 'em mean and you'll be replacing the bank next year).
Basically, a EV built for a 100km commute will need as much battery capacity as a house uses in a 24-hour cycle.

You could go totally ghetto and make you own Edison Cells, if you wanted and have the time and patience, although these are one of those 'lost' technologies, and I don't know how many you'd need or what the charge/discharge curve is like. Lithium is total overkill for household-level batteries. I don't know what the Patent statue os NiMH is these days. Looks like it was transfered back to ECD Ovonics (formerly owned by GM, then Texaco, then Chevron), but who owns them?

All that said, I'd ask a specialist in RAPS systems to work it out for you. You're talking about a house full of electronic equipment and people, and you don't want to take the advice of some idiot (looks in mirror) on the internet. :)

[Smurf]

To be perfectly honest, if you really want a back-up power supply then for daytime use a small petrol generator is going to be an awful lot cheaper and simpler than trying to do it with solar. And for the 2 hours each year that you might end up using it you're not going to be using enough petrol to worry about.

If you want to use batteries, then again it ends up being simpler to just charge them from the mains unless you're wanting to guard against a long term failure (more than a few days) of the grid. In a city that's tin foil hat stuff and you're going to have far more problems than your household appliances if the city loses power for a prolonged period. On the other hand, if you're in a rural area at the end of a long power line with few consumers (ie not a priority for the utility to restore following storms, fires etc) then it could be worthwhile having a decent backup. But unless you're planning on regular use, petrol / diesel is still going to work out a lot cheaper than doing it with batteries and solar.

If you just want a short term back-up, for example to keep computer gear running etc, then an off the shelf UPS is the way to go. But realistically, unless you are running a business or otherwise likely to suffer a significant problem in the event of a power failure (or you've got cash to spare...) then it's just not worth worrying about for most parts of Australia. How many blackouts do you actually get? And how much of a problem really are they?

[Bruiser]

Woops - Draffa, connecting 6V batteries to get 240V doesn't change their current capacity. That's done with a parallel connection, which doesn't improve the voltage (but does double the number of batteries each time). Worth mentioning I thought.

As for a fridge that keeps things cool when the power goes off, mine has a special storage device to achieve this - the icemaker!

[Smurf]

Perhaps worth noting in all of this that it is generally accepted in the electricity supply industry that any blackout less than 4 hours should not result in any real harm - fridges defrosting, problems with water supply etc.

[Steffen595]

its just, there will be more blackouts in the future. 4 new rabbit boxes to be built next door, all blyck FC sheet and some plywood am afraid, all will rely on aircon. The power grid is from post WWII suppose, when majority got away with a 16A connection to their homes....

[chrisp]

There are many trial/experimental systems being tired to support/augment the grid using locally produced energy. Most schemes, as noted by other here, rely on some form of energy storage. For most, the cost and bother of buying and maintaining a battery bank isn't worth the effort.

However, in the future, many of us will have an electric car with a reasonably sized battery pack (typically 20 kWh). We'll, in effect, will have a battery pack sitting around most of the time doing nothing - a perfect resource to tap in to!

By using a suitable bi-directional grid-interactive inverter, the electric car, and a suitable control system, it certainly is possible to do many interesting things.

Technically, it is relatively easy to set up such an inverter system to run in conjunction with the grid - and even to make such a system run independently from the grid. Most grid-interactive inverters, due to regulations, are designed/programmed to shut down when the grid connection is lost. However, most of the inverters are technically capable of running stand-alone (i.e. without a grid connection) but this functionality is inhibited or locked out.

I suppose what I'm saying in a long-winded manner, is that there are no real technical barriers to the ideas proposed - most of the barriers are purely regulatory.

[Draffa]

Woops - Draffa, connecting 6V batteries to get 240V doesn't change their current capacity. That's done with a parallel connection, which doesn't improve the voltage (but does double the number of batteries each time). Worth mentioning I thought.Indeed. I don't know exactly what Steffen595 wants to do with his power/battery capacity, but it sounds like he wants to keep his house running at minimum power useage (fridge, freezer, a few lights). Depending on his current draw, that's what he would size the battery pack for (various combinations of Series/Parallel strings). Maybe even wire the Fridge/Freezer to a dedicated circuit (which is the only one energized off the backup when the Grid fails).

What does a typical fridge draw?

[Bruiser]

I'd say about 200W, but being a compressor, and given that it's recovery from blackout, they tend to have a big inrush. The problem with getting rooftop pv to run off grid ('island') is stability - it needs a battery to maintain the dc link in the inverter. Batteries have a tendency to kill the payback - every 5 years or so the investment to replace them knocks the payback down to near zero. The benefit of rooftop pv is really a fuel/generation saving. I totally agree that, to run a fridge, the cheapest approach is a 400 dollar genset and an extension lead, and that 4 hours without power is no problem. A fridge is, after all, still an esky of sorts.

[Oldneweng]

I have read about people who have found old but still usable batteries for very little cost (scrap). Electric powered vehicles that regularly have batteries replaced are a good source. There is also the method of revitalising old batteries using a welder to zap off the dendrites (I think) which cause dead batteries. Depends on whether you want to do a bit of playing around. I agree that buying batteries is not viable.

Dean

[265chemic]

PV during a blackout is definitely possible - IF (big if) the sun stays out and is providing more than the wattage you are using. The 'brownouts' when the sun goes behind a cloud is what kills things - and this is why when there is no backup A/C the PV must switch off - all or none - to protect appliances.

[Bloss]

PV during a blackout is definitely possible - IF (big if) the sun stays out and is providing more than the wattage you are using. The 'brownouts' when the sun goes behind a cloud is what kills things - and this is why when there is no backup A/C the PV must switch off - all or none - to protect appliances.

It's a pretty old post - gotta watch the dates.

But this is not possible (other than technically being able to be configured to do so - with lots of changes and additions and so far as I am aware only when installed off-grid in Australia, in which case the system is likely to have batteries etc) when wired to current Australian Standards and grid-connected.

[265chemic]

That was generally my point - possible yes, sensible or legal - no. Just pointing out with no battery you'll get brownouts which don't do electrical items any good!

[Wombat2]

Just saying my 2c's - we lived on a wind generator and batteries for 3 years with a 2kva inverter feeding the power points. If another appliance was going the fridge start would trip the inverter but if the fridge was already running we could have up to 3 appliances start and run without hassle.

[Bloss]

Just saying my 2c's - we lived on a wind generator and batteries for 3 years with a 2kva inverter feeding the power points. If another appliance was going the fridge start would trip the inverter but if the fridge was already running we could have up to 3 appliances start and run without hassle.

Off-grid works fine with a variety of power inputs (micro-hydro, wind, PV) and a range of newer soft-start appliances etc help add stability too as do the newer smart inverters and power supply/ battery management systems, but as per the heading, the OP was asking about using a grid-connected PV in a blackout which is a whole different ball-game.