Solar Packages

Package prices below are predicated on a few common sets of assumptions, enumerated below:

1)  Pricing is based on wholesale US pricing plus 20% importation profit margin and 5% maritime and domestic shipping costs.

2)  Includes 13% Costa Rican sales tax on imported items.

3)  Presumes seven hours of average daily insolation.

4)  All package designs are presumed to be roof-mounted with aluminum panel racks.

5)  Travel, room and board, and associated logistics costs for an installation crew are not included in any of these packages and would vary as a function of location and other site-specific details.

6)  Battery bank sizing in all cases has been done to provide six hours of stand-alone capacity at 50% battery drawdown.

7)  A modest cable budget is included in all cases for the battery saddles and for connection of the panels; this will vary somewhat according to variations in configuration and the distance between the panels and control system.

8)  All package estimates include ancillary non-conventional appliances that are assumed as part of the design, including DC-refrigerator and solar hot water heater

9)  Water pumping is not included in any of these system designs.  For more information on costing and system requirements for water supply, refer to the section on water pumping. 

10) No volume discounts are factored into the price estimations.  With larger systems, unit pricing is discounted commensurate with the size of the system.

11)  Until this caveat is removed from the online content, some of the pricing should be considered as a ballpark estimate, particularly for the largest system described.

Cabin in the Woods (no hot water):  $4850

For the most basic of power supplies, it is entirely reasonable to plan for a 12- or 24-volt system capable of power DC-lighting, fans, and refrigeration.  An inexpensive portable inverter can be included to power a television set, radio, a computer to charge batteries, and other small alternating current appliances as needed, though the charging source (panel sizing) is predicated primarily on basic functionality, not for regular power supply for such miscellaneous additional electrical appliances.

Table 1-A below summarizes the lighting, fan, and general electrical anointment of the system.  Two totals columns at the bottom of Table 1-A summarize the total daily power demand as well as the instantaneous peak power demand.  Table 1-B provides a list of the equipment required to satisfy the electrical power demand summarized in Table 1-A, and Table 1-C provides an itemized estimation of the project costs plus installation fees.

In Table A, a daily power demand of 2080 watts was calculated.  Over seven hours, this is satisfied by a charging source of 297 watts.  I recommend in nearly all cases to use only the current generation largest solar panels to accommodate for optimal expandability.  In the case of a cabin in the woods, however, expandability may not be a virtue, and the 224-watt current generation panel does not fit will with the calculated power demand.  One such panel would be insufficient, and two such panels would be overkill.  In this case, an exception is made, and two panels of 160 watts are recommended.

In order to determine the battery bank required for this application, we have assumed that this system will be configured in 12 volts.  Therefore, the ability to independently supply the peak demand of 165 watts for a total of 6 hours is equal to 165 * 6 / 12 / 0.5 = 165 amp-hour.  Since this is relatively small, I am including a single 12-volt, 225 amp-hour battery in the system design recommendations. 

Starter Home:  $22,400

The second package system is one that includes a full range of household appliances and utilities that are likely to be considered as basic necessities for a comfortable lifestyle.  Still, the power demands are estimated modestly, and the starter home estimate is predicated on a two-bedroom home and occupancy by a family of four.  For this alternative, no 220 volt appliances are considered, and the system is designed as a 24 volt system with top-shelf 6-Volt Rolls-Surrette batteries.

Assuming a seven-hour average insolation, the daily power demand is satisfied by a charging source of 1712 watts.  This is equal to 7.64 224-watt panels.  To sustain a 3073 watt peak demand six hours with no more than 50% battery draw down, assuming a 90% inversion efficiency requires a battery bank capable of supplying 1708 amp-hours.  Typical first time solar shoppers are likely to examine the battery costs and decide that they are willing to settle for less independent capacity to save capital investment.  If we strip the peak power to exclude the coffemaker and miscellaneous from the load (which are only projected for two hours of daily use rather than six, anyway(, that leaves 872 watts of peak power demand.  To independently provide this amount for six hours requires a battery bank of only 484 amp-hours,  For this design a battery bank composed of four 6-volt 820 amp-hour Rolls surette batt

Fully Anointed:  $51,000

The fully anointed home below has a few extras and more lighting and fans in general.  Still, it assumes natural gas for cooking, supplemental water heating, and hybrid clothes drying.  A daily power demand of 28.01 kw-hrs, over seven hours average insolation, is achieved with a 4001 watt charging source, corresponding to 18 panels.  The peak power demand exceeds the 3600 watt maximum capacity of Outback inverters, so two stacked inverters are required to provide peak power.  While no 220- volt appliances are included in the list of appliances given, a system of two stacked inverters has the capacity to provide up to 3.6 kilowatts at 220 volts.  Using our same criteria for independent battery capacity, a 4000 watt demand sustained over 6 hours will require a battery bank capacity of 1111 amp-hours assuming a 48-volt system.  In this case the battery deployment shown below provides 1000 amp-hours, so there isa sacrifice of 10% of independent capacity in order to constrain the facility design to battery ratings easily available without overdesigning dramatically.  Panel wiring is assumed to consist of two series of 9 panels, presupposing two 90-amp charge controllers.  Two stacked inverters are presumed for this system, and flexware assembly hardware is included for aesthetics and ease of assembly.  Accessories not included in prior packages are presumed for this package to increase the user's flexibility to control and monitor the system.

Fully Anointed Carbon Neutral:  $120,000

This final option is included mostly for illustrative purposes on the costliness of eliminating a residential carbon footprint.  So far in our design calculations we have presumed that all cooking, supplemental water heating, and clothes drying is achieved using natural gas.  In order to eliminate this fossil fuel and provide these household functions using climate-friendly solar power requires a dramatic boost in two limiting design criteria:  charging source and power inversion.  In order to understand how dramatic this effect is, let us consider the electric dryer.  A conventional electric dryer requires 4500 watts at 220 volts.  Therefore to run a single load of laundry per day and dry those clothes for one hour, requires 4500 watt hours of power.  In a seven hour solar day this is a 642 watt charging source, which is equivalent to THREE 224 watt panels.  To operate 4500 watts at 220 volts requires FOUR inverters.  Therefore, not even counting boosted battery bank capacity, the addition of a conventional clothes dryer to the "fully anointed" option just described adds the capital cost of three panels and two additional inverters, or the equivalent in equipment alone of $9200 !!!  And that is to operate the clothes dryer a single hour per day.

Likewise, to eliminate a carbon footprint requires conversion to an electric stove and supplemental hot water to augment the solar hot water heater in periods of reduced solar insolation. 

The calculations below show the same fully anointed option just described, but replacing the fossil fuel appliances with clean solar power.

To satisfy a 46.4 kw-hour daily power demand in seven hours of average daily insolation requires a charging source of 6630 watts, equal to 30 224-watt solar panels.  For parallelism, in order to configure a 96-volt charging source however, it makes more sense to plan for 32 panels in order to wire them in four sets of 8 panels.  If we assume that our peak power supply includes use of the 220 volt stove and oven but not the hot water heater nor dryer, then we need a peak of 5000 kilowatts of 220 volt power and 4380 watts of 110 volt power, which requires a minimum of SIX stacked Outback 3648 inverters.  A six hour independent battery backup, assuming 9400 instantaneous watts, 9400 x 6 / 48 / 0.5 / 0.9, of 2600 amp-hours, presupposes 24 2-volt 3000-amp-hour batteries.  Four 90-amp charge controllers, a full set of linkage hardware, and a 12 kilowatt backup diesel generator (can't get completely away from fossil fuels without dramatically boosting the charging source to cover for extended periods of rainy days) rounds out the components required for this system.

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