 |
|
|
||||||||||
|
||||||||||||
 |
||||||||||||
|
|
 |
|
|
||||||||
|
Is solar pond generated power and water feasible? For the purposes of this calculation we will work on a pond size of 0.3ha which is well documented with functioning examples in Australia and the USA. In a sunny location, a 0.3ha solar pond can reliably produce at 15kWe day and night, summer and winter. 15kWe is sufficient to drive a reverse osmosis plant producing 15kLitre /day of fresh water from sea water. This is enough for a small town of around 20 people.
The solar pond As noted above, several smaller units would be easier to manage than one large unit and, at this stage we only have experience at managing solar ponds of around 0.5ha. A 0.3ha pond would be needed to generate the 15kWe. If there is not a local supply of hypersaline water, a (shallow, unshaped) lake of similar area to the solar pond will be needed to produce a supply of hypersaline water (or salt) for maintenance of the saline gradient in the main pond.
Hence the total cost of the dam and hot water extraction system is $108,000.
Return to top............. ...........Return to home page The Organic Rankine Cycle Engine and Electric Power Generation White Refrigeration recently quoted for a 15kWe unit delivered to Victoria and commissioned for $160,000 as a one off production. (Note that this power rating is nett of power used in the ORC engine itself). This plant required 7.5litre/sec of water at 75 degree C (or more) and 12Litre/s of cool water at 20 degree C (or less) to meet its full power output. Such output is easily within the capability of a 0.3ha solar pond in a climate such as the SA riverland or northern Eyre Peninsula. (The cool water requirement can come from saline groundwater or the sea - depending on location) There would be additional on site installation costs of the order of $50,000 Hence the total cost of the hot water to electricity conversion system is $210,000. What will the electricity cost the consumers? Like most solar production methods, there is no 'consumables' or fuel required for a solar pond. However, a solar pond does need to be managed to keep the temperature gradient right and to keep it free of algae which reduce its efficiency. The easiest form of management is to add salt to the deepest layer from time to time (a weekly test is advisable) and to grow artemia (brine shrimp) to prevent algae blooms. With few running costs, the cost of power and water from these systems is determined by the interest rate - the 'cost of capital'. It is common to amortise the capital cost of industrial plant of this type over a 35 year period - values below are calculated at 6% interest - the current government bond rate. The ORC engine, like any mechanical device, requires inspection and maintenance from time to time. However, like any refrigerator, it is reasonable to expect it to operate for long periods without skilled attention. Capital invested in the solar pond is $108,000 and the ORC engine is $210,000 to produce 15kWe. A total of $318,000. Over a year this unit would produce 131,400 kWh of electricity Payments on the 'loan' would be $21,758 per year @ 6% interest. As this system is producing quantities of 'green' power it will generate 131 greenhouse gas certificates (one certificate per MWh) which can be sold on the open market. At the moment the price of a certificate is around $60 but it is expected that this price will drop to $45 in the longer term (the penalty charged to power producers if they cannot buy certificates). So 131 certificates could be sold annually for $5895. This makes the annual cost of the system $15,863/year If this power was 'sold' to consumers they would need to pay 12c per kWh (this compares with 15c/kWh to Adelaide retail consumers). Distribution costs are assumed to be negligible for a small community In windy locations, wind power may be a more economic alternative at 6 c/kWh - but remember if there is no wind there is no power. Ideal wind locations are expected to produce full power only 60% of the time. Remote diesel power for backup of a wind system costs more than 35c/kWh
Return to top............. ...........Return to home page Reverse osmosis - converting power into fresh water Several manufacturers produce reverse osmosis plants at a range of sizes. For example, Pall Rochem (of Hamburg, Germany) produce a unit to purify 15klitre/day of fresh water from sea water requiring 15kWe for $150,000 plus installation (around $50,000). The reverse osmosis unit is semi automated and similarly would be expected to run without continuous attention. There is however more need to maintain such a system than the pond. There is also some running cost, mainly to cover cleaning and replacement of the 'filters' - approx $7,000 per year. Cost to consumers If all the power from the pond was used to produce fresh water then the unit would produce 5500 k litres in a year. The cost of the reverse osmosis unit and installation is $200,000 in addition to the above costs of the solar pond and ORC engine of $318,000. This is a total investment of $518,000 which can be amortised over 35 years at 6% by an annual payment of $35,440. There is a good case to suggest this system also should attract Greenhouse gas certificates which would reduce this by $5895 annually (at least) but the running cost of the RO unit would add $7000 making the annual cost $36,540. The price of water to consumers would therefore be $6.64 /klitre Note 1 the retail cost of water to Adelaide consumers is 95c/kLitre Note 2 the cost of filters decreases markedly as the size of the unit increases. Note 3 the cost of diesel produced power is 35c/kWh Producing power AND water. Both the above calculations have been done as if the objective is to produce EITHER power OR water. In a normal small town situation, the RO unit would (most likely) only operate when power was not all being used directly by consumers. In practice, the ORC engine and solar pond would work at full power all the time with surplus power being used to produce water when power demand was small. If the RO unit was not run at full capacity, the apparent price of water would increase proportionately (because the annual payment is still the same)
Summary
Return to top............. ...........Return to home page Scaling up to bigger systems.Larger power or water outputs could be achieved by building a series of similar units. However, there are a number of economies of scale which are known or seem likely. The solar pond cost has a substantial 'start up' cost (~10%) which is the same for any size pond. The cost of moving soil and the cost of the liner are based on area and will not change with the scale of the project. On the other hand, it seems likely that a pond of more than 1ha may be difficult to manage and scaling to greater sizes (in a single unit) would present management challenges. The critical component of the ORC engine is the 'turbine' - actually a screw compressor manufactured for the commercial air conditioning industry. These come in a range of sizes appropriate for 20kWe, 100kWe or 375kWe units. While there is (considerable) cost advantages to scale up to 375kWe, it may be advantageous to use multiple 375kWe units in tandem, rather than building larger units. Reverse osmosis plants already come in many sizes. The above unit is close to the small end of the scale. There are both capital and running cost advantages in scaling up to the 150kLitre/day size. Over that limit, it is comon to use multiple units in tandem.
Soil Water Solutions45a Ormond Avenue, Daw Park, South Australia 5041 ABN 43 610 650 060 Phone 61 (08) 8276 7706 (all hours) (no fax) emailcliff.hignett@soilwater.com.au Return to top............. ...........Return to home page |
|||||||||
|
|
|
[index] [solarlinks] [compare] [HISTORY] [saline] [ro] [moreinfo] [history] [costs] |