Batteries

National Electrical Code (NEC) articles 480 and 690.71 address battery installation and containment, and should be referenced prior to specifying or building your battery enclosure. In most instances, residential battery systems are limited to 50 VDC nominal. (Requirements for battery packs operating at over 50 VDC nominal are not addressed here.)
Regardless of battery type (sealed or flooded), adequate ventilation is required to “prevent the accumulation of an explosive mixture.” While ventilation specifics are not clearly outlined in the NEC, some important considerations are identified. Article 480.9 (A) states that, “hydrogen disperses rapidly and requires little air movement to prevent accumulation. Unrestricted natural air movement in the vicinity of the battery, together with normal air changes for occupied spaces or for heat removal, will normally be sufficient. If the space is confined, mechanical ventilation may be required in the vicinity of the battery.”
Because hydrogen is “lighter than air and will tend to concentrate at ceiling level,” the NEC states that “some form of ventilation should be provided at the upper portion of the structure. Ventilation can be a fan, roof ridge vent, or louvered area.” A common approach used to meet these requirements, especially when flooded batteries are used, is the inclusion of one or more air intake vents installed low on the battery enclosure, used in conjunction with a pipe-connected exhaust vent that routes gases to the outdoors.
All live parts of battery systems, including terminals and cable lugs, are required to be guarded, or covered, to protect against the possibility of an electrical short if a tool or other metal object is inadvertently dropped across the batteries. In addition, access to the battery bank should be limited, either by locking the battery room or enclosure, or restricting access with some other permanent means (Article 110.27).
The battery enclosure cover or doors should allow adequate and convenient access to the battery bank for qualified people, and adequate working clearances should be provided (Article 110.26).
Finally, the NEC Handbook includes the following reference to flooded versus sealed battery types: “Although valve-regulated batteries are often referred to as ‘sealed,’ they actually emit very small quantities of hydrogen gas under normal operation, and are capable of liberating large quantities of explosive gases if overcharged. These batteries therefore require the same amount of ventilation as their vented counterparts.” (Article 480.9)

Evaluation of global wind power

The goal of this study is to quantify the world's wind power potential for the first time. Wind speeds are calculated at 80 m, the hub height of modern, 77-m diameter, 1500 kW turbines. Since relatively few observations are available at 80 m, the Least Square extrapolation technique is utilized and revised here to obtain estimates of wind speeds at 80 m given observed wind speeds at 10 m (widely available) and a network of sounding stations. Tower data from the Kennedy Space Center (Florida) were used to validate the results. Globally, ~13% of all reporting stations experience annual mean wind speeds ≥ 6.9 m/s at 80 m (i.e., wind power class 3 or greater) and can therefore be considered suitable for low-cost wind power generation. This estimate is believed to be conservative. Of all continents, North America has the largest number of stations in class ≥ 3 (453) and Antarctica has the largest percent (60%). Areas with great potential are found in Northern Europe along the North Sea, the southern tip of the South American continent, the island of Tasmania in Australia, the Great Lakes region, and the northeastern and northwestern coasts of North America. The global average 10-m wind speed over the ocean from measurements is 6.64 m/s (class 6); that over land was 3.28 m/s (class 1). The calculated 80-m values are 8.60 m/s (class 6) and 4.54 m/s (class 1) over ocean and land, respectively. Over land, daytime wind speed averages obtained from soundings (4.96 m/s) are slightly larger than nighttime ones (4.85 m/s); nighttime wind speeds increase, on average, above daytime speeds above 120 m. Assuming that statistics generated from all stations analyzed here are representative of the global distribution of winds, global wind power generated at locations with mean annual wind speeds ≥ 6.9 m/s at 80 m is found to be ~72 TW (~54,000 Mtoe) for the year 2000. Even if only ~20% of this power could be captured, it could satisfy 100% of the world?s energy demand for all purposes (6995-10177 Mtoe) and over seven times the world?s electricity needs (1.6-1.8 TW). Several practical barriers need to be overcome to fully realize this potential.