Oil from algae

Heh, okay, there's a big difference between the efficiency of an open pond vs. that of a photobioreactor. The 25/m2/day figure was for a PBR. For an open pond, it's about the same, BUT, the density of the biomass is much lower. So, you're calculating the hard way, we could just leave it at the areal figure, but if you want to double check the volume figure, one open pond's highest productivity was 0.18g/L/day.

A good reason to do this calculation is to give you an idea as to how much culture media you will need to make each day. You have 25000L of culture over 100m2 of open pond. Then you harvest half (a healthy culture will double about once a day), and replace the other half with fresh media. So, you need to add 12500L of media each day, and dewater/filter 12500L of culture each day. The return? 2.5kg by area, or 2.25kg by volume. This is vs a photobioreactor, which you will need to replace only 750L in the same area, if that. I haven't yet designed this rooftop PBR, so I can't give you exact dimensions.

As a disclaimer, these calculations are just based on experimental data, so it's really up to multiple factors, in the end, as to what you actually come up with. For 100m2, it's not a lot, though. Most people calculate for an acre, or a little over 4000m2. That's when yield figures for fuel become more reasonable, but the cost of covering an acre in PBRs or even ponds is something that's being worked on by some of the brightest in the industry.

Still.. Assuming the experimental data is correct, do you agree with my efficiency calculation of about 17% ?

Does that mean that it is not photosynthesis itself that is the limiting factor but more if the "farm" is closed or open and how much you manage to circulate the algae?

We got a few things working in our advantage:

* Exponential growth
* Future reprap technology to build ponds

On the bad side:

* Converting the algae soup to useful oil and then into plastic means a lot of techically advanced processing steps, some which contain dangerous chemicals?

Hi mimarob,

... recently i read a tech-article, where someone managed to 'clean' carbonize any organic stuff as vegetables or household-droppings.

He simply used a pressure-cooker filled with the vegetables, some water and citric acid as catalysator and heated this for 12 hours or so up to 120

Photosynthesis is indeed a very limiting factor in this biological system. Algae grow about 10x slower than bacteria, because they have to produce their own food.

mimarob Wrote:
-------------------------------------------------------
> Am I right to assume that people doing ponds that
> are 25 cm deep could expect to get 1.6g/liter/day
> which means that in "my" pond structure I could
> get
> 100 x 0.25 x 1000 x 1.6g = 40000 g = 40 kg of
> green goo a day?

It's more like 2.5kg, the rationale for that figure is in the post above. This changes all your calculations.

> Assuming I would live near the equator take [40
> kg/day] x 365 = 14600 kg
> which would be almost 15 tons of the stuff in a
> year?

912.5kg, as you said in one of your posts earlier in this thread... "My rooftop example would then give about 900 kg of biomass for a year."
That much algae can yield 365kg of oil at an extraction efficiency of 40%; or about a hundred gallons of oil per year.

> Energy content of the oil would be about 10kwh/kg
> (just a wild approximation)

Just double-checking your numbers, biodiesel has 35.7MJ/L, or 135MJ/gallon worth of energy. Your approximation was spot on, that's 9.9kWh/L.

Thus, energy content of 100 gallons of biodiesel is 13.5GJ, or 3,750kWh.

> In one year we "produce" 70000 kwh (sorry for
> being to lazy to convert to Joules)
> Assuming again in the equator example a sun influx
> of about 1kw/m^2 we would end up with about 4000
> sun hours under ideal conditions.
>
> The energy input would be 1 x 4000 x 100 =
> 400000 kwh

There are a few solar insolation maps from NREL that show that 5kWh/m2/day in the south-western United States, for example, is a good figure for this, averaged throughout the year. Let's say we get 2000kWh per square meter per year, and, as you did, multiply that by 100... 200,000kWh/year.

> Now with this calculation we end up with an
> efficiency fo 70000/400000 = 17.5 % which is way
> to high by an order of magnitude!

Now we have an efficiency of almost 2%.

Have you guys seen this video?
[www.youtube.com]


You could make a lot more oil a lot cheaper if you just grew plants to make sugar on a wide area and fed the sugar to the algae to get a 1000x greater yield than with sunlight alone. Your bioreactors could be incredibly small for the output they would produce.