Resource Evaluation: 43 Hectare Property
Naranjitos de Quepos, Costa Rica
For: --------------------
By: Paul Collar
September 25, 2005
Introduction
A resource evaluation field survey was undertaken on July 23 on a 42.6 hectare property outside of Naranjitos de Quepos. Field investigators included the author of this report, Paul Collar, the property owner, David Bauduin, and the previous owner, Omar Quirros. The objectives of the field survey were to collect information necessary to determine the suitability of property resources for the development of hydroelectric power as well as potable water supply for a modest tourism development to include a caretaker house and an owner’s house in the near term (Phase I) and in the long term a handful of additional remote, fully-anointed residences (Phase II). This report summarizes the anticipated power and water demand and how much of this demand the property is capable of sustaining through its intrinsic resources.
Property and Project Overview
The Naranjitos-area property (Figure 1) is located about six kilometers from the small town of Naranjitos, itself about 15 km from the coastal tourism center of Quepos, Costa Rica. Access to the property is by a stretch of gravel road and by a final trajectory of dozer-cut track in steep forested terrain. Access is by 4WD only, and no municipal services (water, energy, phone, etc.) extend to the property. The terrain is mostly forested and steep, though there are a number of building sites along a ridgeline with spectacular views of the ocean and the Quepos-area lowlands and foothills. There is one modest stream that forms a large waterfall at the boundary of the property, though the owner has indicated a prior interest in negotiating the purchase the portion of the adjoining property containing the waterfall. The stream in question is formed from the confluence of two smaller streams about 200 meters upstream from the property boundary. The Right and Left Forks are reported by Mr. Quirros to be perennial. Above the location where water is currently being extracted for water supply, Quirros reports that the smaller Right Fork dries up in the dry season months but that the Left Fork carries more water and remains perennial even higher up in the watershed than the Right Fork.
Figure 1: Blue shows the approximate trajectories of the two streams on the property, green the trajectory taken during field survey of the property. The maroon oval is the approximate area contemplated for Phase II facility development and Building Sites I is the area considered for Phase I deployment of the owner’s home and the watchman’s house.
There are two stages of anticipated development. Initially, two houses are planned, a caretaker’s house and an owner’s house, both planned for 2006. Thereafter a series of up to four well-anointed homes will be built sequentially and are intended for the
Quepos-area vacation rental market. For the purposes of this report, I have assumed the eventual deployment of five fully-equipped American-style homes with a peak occupancy of eight persons per residence and a guard house with an occupancy of two.
Water Demand. At peak occupancy, the facility would have as many as 42 people. Using the American water-demand design parameter of 100 gallons per person per day, an occupancy of 42 people presupposes a peak water demand of 4,200 gallons per day, which corresponds to a flow rate of only 2.9 gpm, presuming adequately sized water storage tanks.
Power Demand. The table below summarizes a list of appliance power requirements in order to compile anticipated power demands for each house. The table employs a series of assumptions to arrive at a reasonable peak demand expectation for each house.
Table 1. Approximate power demands of appliances considered to typify an American-style home.
If we assume that everything is running at the same time, each house equipped with the appliances above would have a power demand of 9 kw. For rational design, a 50% simultaneity factor and 25% safety margin are reasonable design criteria. Application of these factors leads to a rational anticipation of a 6 kw peak demand for each house. Because refrigerators operate around the clock, a 16% power demand reduction can be achieved by using fossil-fuel refrigeration, like propane or kerosene. Even a 12-Volt regrigeration system will lead to reduced power requirements. While alternative energy appliances are considerably more expensive than off-the-shelf AC appliances, it may be appropriate to consider such energy conservation appliances. However, for the purposes of this analysis, the houses are assumed to include a 16 cubic foot side-by-side off-the-shelf refrigerator/freezer.
Five identical houses presume a peak power demand, therefore, of 30.25 kw. If we add in 3 kw for the anticipated watchman house power demands and an additional 5 kw for power consumption anticipated from a workshop/guardhouse or comparable facility, we come up with a facility demand on the order of 38 kw.
Water Supply
Using volume displacement in a tank of known capacity and an existing water intake, a Right Fork flow rate of 40 gpm was measured. Losses were approximated at somewhat more than 100%. The total capturable water was therefore on the order of 100 gpm. Quirros reports that in the dry season, flow falls to one third of the observed flow, or around 35 gpm.
The water supply exceeds that required for potable water by many times over and is situated at an elevation above the Phase I area homes, thus permitting gravity delivery to Phase I facilities, but not above the Phase II homes, implying that without the improbable discovery of supplemental spring sources high on the mountain, these homes will require water supply through pumping. Because the current water source is within a few hundred meters of the uppermost springs and the location is itself a dry season spring, it is expected that this water will be of relatively high quality and require only particulate filtration and ultraviolet disinfection to ensure potability.
Power Supply
Based on an anticipated dry season flow of 35 gpm, the present water intake, located at an elevation 150 feet higher than the property entrance terrace, has a hydroelectric potential at the terrace surface that can be approximated using the empirical hydroelectric potential formula
P = H * Q * 0.18 * E
Where P = Watts per hour, H = head (ft), Q = flow in gallons per minute, 0.18, a units conversion coefficient, and E, efficiency: 50% for micro-, 65% for mini-hydro turbines.
The summertime flow rate corresponds to a hydroelectric potential of 472.5 watts per hour at the terrace, enough to run nearly five 100 watt bulbs continuously. However, this modest output adds up to 11.3 kw per day. This is enough power, if a propane fridge is substituted in the appliance list given earlier, to fully operate the owner’s home presuming DC power generation and associated battery banks. The wintertime flow rate of 100 gpm corresponds to 1.35 kw/hour, or 32.4 kw per day, enough for nearly three houses with fossil fuel refrigeration.
However, if both tributaries are captured at the same elevation, this makes for more water and therefore more power. The Left Fork was not hiked on the fields survey but was clearly a larger stream by at least 50% and is reported by Quirros to be perennial farther uphill than the Right Fork. It appears reasonable therefore to assume a dry season hydroelectric combined water supply rate of 90 gpm, if the two streams are both harvested. Generation at the plateau would under this flow rate have a hydroelectric potential of 29 kw/day. If the adjoining property containing the waterfall is acquired, however, an additional 100 feet of head is achieved over a short geographical distance, and the hydroelectric power generation potential rises to 49 kw/day. This amount of energy would be expected to provide for the full electrical requirements of a Phase I owner’s house, a watchman’s house and leave residual potential for electrifying a workshop area.
However, the total hydroelectric potential at the waterfall base is during the dry season capable of supplying only 28% of the power needs of five similarly anointed homes operating at peak capacity, which means that during summer months significant additional charging sources (solar panels and/or backup generator) will be required to sustain operational power demands. During the months of May to December, the expected hydroelectric potential of 135 kw per day (presuming a combined flow rate of 250 gpm) is expected to satisfy 80% of the energy demands of the five houses at peak usage. If propane refrigerators are used, wintertime base-flow rates are expected to satisfy 96% of the peak facility power demand.
Because DC-power generation can tolerate variable flow rates, it is possible to achieve modest overages in generation from the much larger flow rates associated with storm runoff. Under such hydrologic circumstances, flow rates are not limited by the water supply but rather by the intake and piping capacity. Presuming a reasonable upper boundary of 250 gpm based on the practical limits of two inch pipe and intake constraints, the combined storm flow of 500 gpm has a hydroelectric potential two times that of winter time base flow. While additional equipment downstream (another Pelton wheel and the expanded manifold capacity to handle it) is required to take full advantage of storm flow, this is likely to be competitive economically with the alternative of the fossil fuel cost of generator makeup power.
Discussion
The AC power generation potential of the property is insufficient during dry season flow rates to sustain even a single house, and during the winter season would be expected to satisfy the needs of only a single home adequately. However, the resources are capable through DC power generation and the use of batteries and AC Invertors, to provide attractive returns in power. However, peak operations of five homes will require supplemental charging sources even in the wet season months. Current-generation digital sin-wave AC invertors are designed to process a variety of charging sources simultaneously, making it seamless to provide additional energy through a complimentary solar array. A large diesel or propane generator rounds out the complementary/redundant energy sources and is handy to top off batteries as needed or for welding and other short-term energy consumptive applications.
Unless and until the lower waterfall property are acquired by the ownership, it appears reasonable to predicate recommendations on the basis of power generation within existing property boundaries. Nevertheless, the acquisition of the waterfall base area would nearly double the property hydroelectric potential, and if the ownership seriously pursues acquisition of the adjoining property, then design and development would most logically be undertaken so as to include the possibility of generation at the waterfall base.
A conceptual diagram for a de-centralized energy system, involving hydroelectric power generation at the plateau, is shown in Figure 2. Figure 3 shows a diagram for a centralized energy system, in which hydroelectric power is generated at the base of the waterfall. The two different generation points presuppose radically different philosophies to facility power supply. If power is generated at the terrace, the power will be sufficient only for Phase I facilities, and Phase II houses must be energized by solar or generator power.
If the base of the waterfall is used as a generation point, however, it becomes reasonable to concentrate all power generation at this point (including supplemental solar and fossil-fuel generator) and to transmit power from this central power center to all of the homes by either buried copper or aerial aluminum electrical cable. This would enable the use of a single, large, backup generator (as opposed to five smaller ones), and a single battery bank, rather than five sets of smaller banks. Modest invertors would still be required for all five houses, and transmission cabling would also be required, a minor capital cost in a decentralized power generation model. A central power unit presents the option of including solar panels or eliminating them completely and depending on a beefy generator for make-up facility power during summer months.
For both configurations, a dual-fork hydro pipeline is proposed, consisting of infiltration gallery water intakes installed on both forks at the same elevation as the existing Right Fork water intake, and two-inch pipelines along the forks, merging into a three inch pipeline for the remainder of the run to either the terrace or the base of the waterfall.
Both configurations provide for Phase I potable water supply by gravity and Phase II potable water supply by pumping up from a separate stream-water collection system to connected tanks supplying individual houses. A solar pump and panels will be
Figure 2. Conceptual diagram; power generation at the plateau.
Figure 3. Conceptual diagram; power generation at the waterfall base.
Figure 4. Photograph of stream confluence area
used to convey water from the stream to the top tank. Lower tanks would be charged by overflow, controlled by float valves on all tanks.
Costs
In a forthcoming addendum to this report cost estimates for both the decentralized and centralized power alternatives will be presented. For both alternatives an additional site survey and detailed engineering will necessarily precede the elaboration of actual installation bids. However, a close estimate is essential in the very nearterm for comparison with running ICE lines to the property. I expect it to take as much as one more week for me to compile supplemental drawings and a preliminary work plan necessary to prepare as accurate an estimate of final costs as possible. Also I am still on hold for costs of some of the system components and have some more legwork on the fossil-fuel generation options.
Conclusions
The Naranjito property has micro-hydroelectric resources capable of sustaining 80% of the power needs of five American-style homes at peak capacity from May through December. From January through April hydroelectric resources are capable of sustaining only about 30% of peak capacity power demand. AC-direct power generation has an absolute output ceiling far beneath anticipated facility power demand and is therefore discarded from additional consideration. A battery-based micro-hydropower system offers a robust latitude of operational and delivery capacities, ideal for the seasonal variability of the water source flow rate. However, a full stand-alone power system for peak capacity of the anticipated installations will require both fossil fuel generator and solar panels, and the full complement whether centralized or decentralized will be costly.
If the waterfall is not acquired, then the dry season water supply will sustain Phase I electrical demands adequately. Power demands of Phase II facilities, however, would necessarily require stand-alone solar systems or generators.
Gravity fed water is implicit for the Phase I installations, but water for Phase II facilities must be pumped from the stream, via a separate infiltration gallery and collection tank beneath the confluence of the two tributaries.
A reasonable sequence of steps in weighing and pursuing a hybrid alternative energy solution for the Naranjitos property is given below
1) On the basis of preliminary cost estimates tendered in a forthcoming addendum to this report, an economic analysis would be appropriate comparing capital and operational costs of an alternative power solution for the Naranjitos property versus capitalizing the installation of ICE grid lines to the property.
2) If alternative energy is a reasonable solution economically and aesthetically, then the ownership must make a final disposition regarding whether to acquire the waterfall property or constrain system design to the existing property boundaries.
3) A second site visit will be required for final engineering and design for siting, measurement of distances, dimensions, elevations and other characterizations, ideally timed in the dry season to pin down base flow.
4) Compile work plan, timeline, and budget.
5) Construction / Installation
6) Commissioning / Testing / Training
7) Comprehensive written and illustrated Owner’s Manual.