[LINK] Solar cells

[Adam Todd]

At 10:13 AM 20/01/2007, Stewart Fist wrote:
>Glen writes:
> >
> > I'm not so sure about that. Large solar panels are expensive. But
> > I'm increasingly impressed by the small ones -- the sort of thing
> > that runs your garden lights or changes your phone.  I think
> > solar is now at the stage where its superceeded technology is
> > itself efficient enough to be useful.
>
>Glen's Big vs, Little point is important
>
>We can also ask, are they:
>
>Useful?      Definitely Yes.

Very.

>Cheap?       Probably No

I've been buying 100-400 Watt panels as that's what I can "afford" to buy, 
rather than being the best price per Watt.

>Efficient?   Definitely not

In Australia, at least in Sydney, yes.  My panels constantly, especially in 
summer, exceed their power ratings.  Most of the time the volts are higher 
than rated and the current is between 15-30% greater.

Capturing that extra source has made my panels perhaps a better bang per 
buck overall.

>Fragile?     I haven't been able to find any useful information.

I've had mine on my roof now for up to 8 years.  They are all still working 
individually and collectively very well.  None have been damaged by hail 
storms, tree branches or other weird events.

>Long-lasting?  No one really knows, and it must depend on the type.

Some are 8 years, some are 4 years.  Not bad really.

My whole office is run from Solar power.  I don't have enough juice to run 
a Large Family Fridge but then that's hardly a critical resource most of 
the time.

>The last time I looked the combined 'energy cost' of manufacturing
>large-panel solar cells and the electrical storage unit to make them useful,
>was marginally higher (according to some sources) than the energy they would
>generate over a life-time.  Other sources said it was lower.

It seems to vary.  Although BP Solar have a good process.

>Either way, the margin is not too great if you are considering solar as an
>alternative to conventional energy sources -- unless you've got no
>alternative.

Our payback was calculated over five years.  As we've put more resources 
onto the system than we had anticipated, our payback was brought down to 
3.8 years.  Hence my expansion at 4 years.  Which is just now coming to the 
end of it's "cost" period and into a savings period.

Strangely over the same time, the electricity bill has only INCREASED by 
about 20-30% even though we use less most of the time.

I'd have thought a CPI increase of a few percent was barely acceptable, but 
it's been far greater than that.

And with Integral upping it's fees in the last 12 months, I'm now looking 
at putting more solar in to take general lighting off the grid, as well as 
a lot of the kitchen appliances we use.

They don't use a lot of power, but still.  It adds up.

I've already prepared a "temporary" conversion to 12 volt energy saver 
styled lights.  They are equally as bright as 240volt lights, but use even 
less power overall.  Adding photo cells so they can come on and off 
depending on the light ambience in areas of the house will help too.


>If you can bring in a power-cable from some distant grid, for a reasonable
>multiple of the cost of a solar unit, it will probably be justified very
>quickly.

Maybe in the short term, but not the long term, and not as the quality of 
power degrades and the load increases.

We already have regular blackouts in our area on hot days caused by the 
excessive number of air conditioners.  We don't have one, even if we did, 
we'd use it sparingly.

My UPS's trip regularly, several times a day because of brownouts, too much 
noise on the input or over voltage.

Only the oldest of the TV's in the house aren't on a UPS.  (Those I picked 
up in council cleanups!)  The few CRT's that are left here are also on the 
mains power, but via filters.

Sometimes you can see the power shifting during the day!

>Of course, it also depends on what the solar cell promoters mean by a
>lifetime.  Are large panels of solar cells able to withstand the occasional
>heavy hailstorm?

We had a carpeting of hail in the last year and the first thing I did was, 
during the storm, rescue my panels.  I think my efforts were less than 
useful as I was only able to cover a couple of the panels during the storm 
itself.  There was no damage.


>Most sites just ignore this question, although one promotional site says:
>
>"Most are tested for hail damage, but the reality is that hail tends to
>glance off the module¹s surface because of the angle that most arrays are
>installed at. However, given a strong enough impact, modules could break. If
>a module is shattered or punctured, it would eventually fail due to water
>getting into the solar cells and causing corrosion. "

That's correct.  I check for seepage every 6 months anyway, just in 
case.  So far none have shown any "wear and tear" so I'm pretty pleased.


>After seeing the damage to tiled roofs in Sydney a few years ago, I don't
>find that reassuring, and even less so when it comes to costing the energy
>efficiency.

You know there are options. You can install over your panels a perspex 
sheeting.  Costly yes, but it does solve the problem for the longer term, 
probably adding about 2 months to your payback costing.

As the panels I've purchased have been "reasonably" cheap and I've put the 
difference in spending aside for new panels, I'd just replace any that 
break either with the same type if it was less than 2 years old, or a 
larger, lower cost per watt panel if it's outside the four year mark.

I'm now looking at more portable solutions.

>The collector-type systems which use curved metal mirrors to bounce the
>energy back to smaller high-temperature silicon cells are protected against
>hail but they require motors, etc. to track the sun.  Then they require
>technicians on hand.

Nope, don't have anything like that, but I have considered it.

I already have a sun tracker I designed and built out of old dot matrix 
printer motors and parts.  I was starting to develop a panel tilt and 
movement system, with a "vertical rise" in case of storm mode.

But so far only the tracking of the sun has been achieved :)  The motors do 
follow the sun with pin point accurate :)

I was going to install a telescope and CCD camera on the tracker to follow 
the sun and web cam it, but haven't had time :)

Incidentally I use the same tracking system for my Motion camera rig for 
tracking human and object movement :)

>The claim that a solar panel can last 25 years, is also one that I'd take
>with a grain of salt.

I'll tell you in about 15 :)

>And, if we really are seeing rapid advancements in the technology, then 
>most installed today would be obsolete long before this.

Yes the technology seems to improve every 3-5 years and the cost seems to 
be fairly stable.  Maybe down a few points every year.

The problem is with the Governments 50% rebate, the prices just doubled, so 
we're paying too much.

And the rebate is only available for "professionally" installed systems on 
a fixed premises.  So if you wanted to move and take your solar with you, 
you can't.  Which is stupid really.  Because the system is designed for 
YOUR needs, not the next person.

If we left our system here, most people would have an excess of power they 
were unable to store.

My system has been designed to run 24x7 power needs, unlike most homes that 
have 8 hours of darkness, less the fridge, but it cycles less over 
night.  I can't imagine there are too many people that have to have 1.5 
KVA/hr of power available 24 x 7 continuously day and night.

We only use 1.27KVA/hr

And don't forget in most cases, the night isn't the only dark time in a 
house, most people go to work leaving houses dark during the day too.  I 
had to compensate for the fact that our house is active all day, using the 
power all day, because we have 6+ people here every day of the week.  If we 
all went to work and left the house empty, the batteries would charge 
during the day and supply us with power during the night.  That's not our case.

I have computers, monitors, security, online and powered 24 x 7.  Then we 
have regular use of fridge, hot water and lighting all day and night.

The office in my home is permanently lit with energy savers because it gets 
very little natural light - not enough to work by.  There is no natural 
light in the garage :)

>Has anyone got any trustworthy figures on costs, returns, etc in terms of
>energy as well as money?

I'd not want to offer my figures for the obvious reasons described above:

1.  Not a typical installation.  It's a 24x7 minimum load that is "high"
     by most households use.
2.  Has been grown and added.
3.  Didn't intend to compare supplied power vs solar
4.  Supply costs have gone up, seemingly proportional to the saving
     However, we use less supply than we otherwise would.
5.  We don't use solar for fridges and hot water (sigh)