I can answer most of your questions, see below:
Charles Dolci wrote:
> David:
> Interesting ...
> Just curious though. How much space do these things take up?
> I know the common figure for solar energy striking the earth at sea
> level is about 1000 watts per sq. meter.
Correct
Most current, affordable
> photovoltaics are at about 12 - 14% efficiency, tops (although a
> subsidiary of Cypress Semi issued a press release last year saying they
> had developed a cell that "approached 17% efficiency" - but they didn't
> put any pricing data in the release).
The rule-of-thumb for modern panels is 150 W/m², with normal light
incidence at 25°C
> Of course, that is under optimum conditions. But let's be generous and
> assume 16% efficiency, so that means you need 37 sq. meters or 403.6 sq.
> feet of space to generate 6kw.
> One company
> (http://www.wattsun.com/products/wattsun_trackers/Wattsun_Tracker_Price_Sheet.html)
>
> actually selling systems has a 300 watt system (11.48% efficiency) that
> takes up 26 sq. feet. so to get 6kw means you need about 520 sq. ft.
At my figure, 6 kW nominal is obviously 40 m² = 430 ft²
>
> Is the power output DC or is it converted to AC? I am no expert but
> isn't there a 10-15% loss of energy during conversion?
The output is low-voltage DC. The panels are put in series/parallel to
give something like 18 - 24 V. The inverters are very efficient with a
resistive load, like 96% at loads exceeding 30% of maximum. The
efficiency will drop somewhat (by 2-3%) with very reactive loads.
> Of course, these are theoretical numbers. Are you able to orient the
> cells to enjoy maximum efficiency?
Large installations usually have trackers, so that the light incidence
is normal. The cheaper trackers are just horizontal, but there are
azimuthal trackers, as well. However, tracking errors of ±45° do not
drop the output very significantly, because the cells have a ceiling
output, with saturation occurring at light levels considerably less than
normal sunlight incidence.
Do dust and dirt affect efficiency?
Obviously, thick deposits will, but thin deposits don't, for the same
ceiling reason. Routine maintenance should include occasional cleaning,
typically once per year in rural locations.
> Is there a tracking system that moves the cell panels to keep them
> oriented to the sun or do you lose efficiency as the sun "travels"
> across the sky?
See above.
If these cells are located on your roof does house
> orientation and roof pitch affect efficiency?
Obviously, for a non-tracking system, the ideal would be to have a
S-facing roof with a pitch so that the light incidence is normal at the
midday equinox. However, the pitch can be adjusted because most panels
are not laid flat on the roof but are held in an aluminium frame system;
it is therefore possible to have the panels at an angle different from
the roof.
>
> Not that it matters since it is your property, but what do your
> neighbors say about the solar cells?
Who the hell cares what the neighbours think, provided that the planning
authorities give their OK?
Are they on the roof or are they
> free standing in your back yard?
Whatever!
Does shade from trees or adjoining
> structures impact output?
Very much so: just one single cell, a fraction of a panel, in the shade
and the output drops very significantly.
These may work in Arizona, but will they work
> in Minnesota?
If the sun is shining, they will work better in MN than in AZ. This is
because there is a negative temperature coefficient of about -2%/°C over
25°C. As a guess, I would say that you would probably get more watts on
a clear winter's day in MN than on a summer's day in the middle of the
desert.
>
> I suspect that photovoltaics are not yet cost effective otherwise
> taxpayers and ratepayers would not be asked to pick up part of the cost.
At the current (no pun intended) costings, an average domestic
installation with sell-back to the power utility of surplus production
at the same rate as the purchase cost will take ~30 years to amortise
(typical panel life), including interest on the capital. However, this
is expected to improve, because the purchase cost of electricity is
forecast to double or triple in the next decade.
Obviously, subsidies are a thorny subject and vary enormously from
place-to-place. Here, for example, the subsidy is 55% of the capital
cost for domestic installations and the buy-back price for every kWh
generated (not just the surplus) is twice the purchase price, so
amortisation is possible in 8 years, which is reasonable. However, it is
not the taxpayer who pays for this, it is the electricity consumer, with
a 0.2% levy on all electricity bills.
You should be aware that there is a limit to the number of installations
in a region. The rule-of-thumb is that variable renewables (solar, wind,
wave etc.) should never exceed about 20% of peak demand. If, for
example, you had 30% of power in AZ coming from solar and a heavy
weather front passes quickly over the whole state on a hot summer's day
with every aircon working full blast in the SW, it will send the grid
into a tizzy and would probably cause a chain of black-outs over the
whole area from Oregon to Louisiana. A sudden change of up to 20% is
acceptable, provided that you have idling back-up power that can come on
line within about 15 minutes, which is standard practice.
In other words, those who think that variable renewables are the answer
to climate change need to put a milder weed in their pipes. At the best,
they can serve a useful purpose by reducing fuel consumption of
conventional power generators by a few percent. As coal, oil and natural
gas must be targeted heavily if we are to avoid the worst of climate
change, this leaves us little choice:
- firstly, reduce consumption by more efficient appliances and user
awareness. Houses should be mandatorily made more fuel-efficient and
solar water-heating is economically viable, even up to 55° from the equator.
- maximise generation from waste (in urban areas, 10% of electricity
requirements can be met by household waste incineration in suitable
plants) and biomass, where it is practicable. Also fixed renewables,
such as tide and hydro, provided there is no severe environmental or
biotopic impact.
- where feasible, install wind/wave generation up to the "magic" 20% of
peak, possibly solar if costs are reduced by economy of scale.
- that leaves the major fixed generation and we have only one way
forward here with present technology: nuclear fission. There is a
growing awareness of this with planning going forward in a number of
countries, even the USA (a major utility in S. Carolina is seeking
approval to increase its nuclear facilities quite significantly).
Hope this helps.
Brian
>
> Just curious.
>
> Chuck Dolci
>
>
> David Douthit wrote:
>
>> Joe,
>>
>> I am currently installing a 6kw photo voltaic system and I have already
>> installed a solar hot water heater.
>>
>> I am also trying to "spread the word" here but I am beginning to get
>> strange looks. I am borrowing money, while it is cheap, (inflation
>> spiral) to pay for these items. It is strange that I live in a "desert"
>> in Arizona and so little effort is being put into solar energy.
>>
>> People simply don't believe or want to here you. Classic "denial"
>> symptoms.
>>
>> Only 2 companies in the Phoenix area are licensed and bonded to install
>> solar cell power systems.
>> Only 4 in the entire state! This is incredible.
>> None of the hardware they are installing is built in the USA. We may get
>> so far
>> "behind the power curve", literally, that we can not afford the hardware
>> needed to reduce energy consumption (inflation and unemployement
>> spirals!).
>>
>> I am very worried for my children!!
>>
>> David A. Douthit
>> Manager
>> LoCan LLC
>>
>> Joe Fjelstad wrote:
>>
>>> Thanks Dave,
>>>
>>> I agree that it is not No..1. I forwarded another's message for
>>> consideration and it was their choice for No. 1 but it is a matter
>>> of significant
>>> concern.
>>>
>>> Thanks also for the link. Interesting reading and there are a number of
>>> counter points that I have heard but the indisputable fact is that
>>> there will be
>>> an end to cheap oil and we are seeing the start of that day now.
>>>
>>> Humans are very selfish creatures but we are also capable of great
>>> sacrifice
>>> for our progeny if we see and understand threat. The question is,
>>> drawing on
>>> the word's of Lincoln, can we summon " the better angels of our
>>> nature" in
>>> advance of the threat becoming overwhelming?
>>>
>>> Kind regards,
>>> Joe
>>>
>>>
>>>
>>>
>>
>
|
