Comparison of Biomass and Solar Energy Yields
These are very important calculations. More below.
On Fri, Aug 1, 2008 at 1:07 AM, Greg Walker <greg@rtd.gb.com> wrote:
> We were talking about energy yield from biomass. These are some of the > figures that I have:- > > If we start with 1 cubic metre of fresh cut timber, its cellulose content > will yield 1476 kilowatt hours of fire power. Moisture content will lower > the temperature at which that can be delivered. Cellulose content would be > about 450 Kg. > > Convert that material to charcoal, & you get 94 Kg, which will give you 803 > kilowatt hours of fire power. > > Convert it to Pyrolysis Oil and you get 315 Kg (25% moisture content), > giving 1480 kilowatt hours of fire power.
That is an amazing yield. Is this proven technology, or are you talking of a theoretical value? Please reference this if you can.
> If we take woodland growing at yield class 15, it will deliver 15 m3 of > timber per hectare, per annum – on average.
Tell me more about growing classes. I heard from sustainable forestry people back in Wisconsin, where I lived before, that the sustainable yield is about 2000 lb/year/acre - or about 4 cubic meters/hectare/year. Is your value for heavy-input plantations, or natural, integrated forests?
> So 1 hectare should give us say 22,000 KWH of fire power per annum, about > 2.5 KWH per hour, or an average output from burning the biomass created, of > 2.5KW. > > That’s 2.5 KW per 10,000 sq metres – or about ¼ watt per square metre > > Compare that with peak sun power of 1 KW per square metre. A factor of > 4000:1
> I guess the bottom line is “Solar power conversion doesn’t have a lot of > competition from biomass”
Right.
> I’m not sure what public utilities charge for electricity in the US, but in > the UK it’s about $0.20US per KWH – or it was until a few months ago, I > think. It might have moved quite a lot since then. That puts biomass cash > flow at $4,400 per Ha per annum.
Ok, but you are forgetting about the conversion to electricity here - which puts that figure at 10 times lower. In the US, it's about 10 cents/kWhr - so you'd make $200/ha/yr on that biomass.
> If you can get 5KW from 40 m2 of solar (it is actually 30 m2) > collector, peak – that’s 0.125 KW/ m2 peak, say (one third of this, or:) 0.04 averaged over 24 hours. > $700,000 per Ha per annum! or $70 per square metre per annum. Wow.
I'd consider one quarter, or .03 kW/m2 average, or $500,000 per Ha per annum.
The cost for that amount of concentrator will be $1.2M based on linear extrapolation of our present system cost - which excludes labor cost because of DIY construction. this means 2-3 year payback.
Now to reality. For the first prototype with straight steam generation and no heat recovery, we're expecting 500W (2% overall efficiency) of usable power - based on Mike Brown's 1 hp steam engine and required steam flow rate. That's a start, and I think, at that scale, we can reach 15% overall efficiency if we are good - or 3.5 kW of usable peak power.
At that rate, the payback time will be 4 years.
Overall, on economic terms - the harnessing of solar energy is viable. On ecological terms, it is absolutely essential.