How much energy will a 5kw solar system produce for you?

I grabbed the above table from here.

I thought I'd have a peek at how much these solar systems actually produce, and what they cost.

For example, a $300 million dollar solar plant is being built at Nyngan. It will consists of 300,000 solar panels, manufactured by Suntech. I’m assuming they’ll use the top of the range utility scale panel called the Reliathon.

Interesting thing to note from reading the specs on the Reliathon – it can put out 280 watts, but you have to assume irradiance of 1000W/m2 and a temp of 25 degrees.

This plant is quoted as producing “up to 100MW”. However, if you multiply 300,000 panels by a peak performance of 280 Watts, you only get 84MW. Just a slight discrepancy. But what’s 16Mw between friends? I guess some smart-arse PR person thought they could up the numbers a bit without anyone ever bothering to check. Before I go on, we should note that plenty of "old media" outlets unthinkingly reprinted the press release without ever bothering to spend 5 minutes doing some research and crunching some numbers. For crying out loud - how hard is it to punch this into Excel: =300000*280?

Anyway, let's go back to the table above. It shows the actual expected power output in KW/h in Sydney from a 5000W (or 5KW) solar system.

Now, in a perfect world of eternal sunshine, a 5000 watt system would produce the following amount of kilowatt hours in a month =5*24*30 = 3600kw/h.

Of course the sun doesn't shine all day, and its intensity varies between summer and winter. So let's extract the numbers from the table above and get a monthly average:

=(898+795+713+541+450+413+434+563+723+810+896+907)/12 and you get 679 kw/h. In other words, you're getting 18.8% of the "nameplate" capacity.

OK, so what's a 5000w system likely to cost you?

You can buy one direct from China and bring it in yourself for US49,260. Plus import duties and shipping and installation blah blah blah.

How much does your average Sydney household consume?

Well, this data is from 2004, but let's assume 8,000kw/h per year. Let's also assume it costs 20 cents per kw/h.

Theoretically, a 5KW system will supply enough power for your average household in Sydney, as it will deliver 8143 kw/h over the course of a year. However, you might find yourself shivering a lot in winter when there isn't enough power during the day to run a heater, and there's no power at night. But let's ignore those quibbles for the moment.

At 8,000kw/h per year, at 20 cents per kw/h, this household will be paying $1,600 in power bills.

That means it will take 31 years to pay off the $49,260 system you just bought from China, assuming it costs you nothing to ship, import and install. But you'll have a slight problem in that after 25 years, the system will only be producing 80% of what it was when new.

Oops, there's a fly in the ointment. Most people wouldn't have $49,260 lying around, so they'd have to take out a loan. Assuming a 7 year repayment schedule, you'll also pay $31,400 in interest.

So the full cost of the system will be closer to $80,000 once financing is included, which means a payback period of about 50 years - except the system will probably be dead after about 30 years. And you have this small problem of having no power after the sun goes down, and not enough power in winter to cook and keep warm.

Now I know that the cost of these things is dropping dramatically year on year. They certainly make sense for people who are off the grid (and you also have to remember the cost of battery banks for those systems, and replacing those batteries every few years). But I just can't see how they stack up economically for city slickers like me.