Charles Weems, Chairperson, Residential Wind Power Subcommittee. Response to Council Referral in the Viability of Residential Wind Power in Berkeley

Transcription

1 Energy Commission To: Energy Commission From: Submitted by: Charles Weems, Chairperson, Residential Wind Power Subcommittee Subject: Response to Council Referral in the Viability of Residential Wind Power in Berkeley SUMMARY The Residential Wind Power Subcommittee investigated the potential of vertical axis wind turbines as a renewable power generation in Berkeley. After conducting an analysis of wind resources in Berkeley, the subcommittee concludes that wind speeds are generally inadequate to make residential wind power viable in the city. RECOMMENDATION No further action required. FISCAL IMPACTS OF RECOMMENDATION None. BACKGROUND Vertical axis wind turbines (VAWTs) are touted as a simple and cost effective way to generate sustainable power for homes. A VAWT generates power through the rotation of airfoils around a vertical drive shaft connected to a generator [see attachment 1]. Advances in materials and aerodynamics have made it possible to create lightweight and durable blades for VAWTs that function at lower wind speeds. VAWTs have several potential advantages over other sources of renewable energy in that they are relatively inexpensive, simple to install, and are easy to maintain. In keeping with its commitment to reduce greenhouse gas emissions through renewable energy, the Berkeley Energy Commission formed the Residential Wind Power Subcommittee to in response from a referral by City Council to research the viability of emerging residential wind turbine technology Milvia Street, Berkeley, CA Tel: (510) TDD: (510) Fax: (510) manager@cityofberkeley.info Website:

2 TYPES OF TURBINES AVAILABLE The Residential Wind Power Subcommittee found only three commercially available VAWTs that could be applied for residential use: The Semtive Nemoi M, Semtive Nemoi S, and the Visionair3. Model Height Minimum Wind Speed Cost Visionair ft. 9 mph (4 m/s) Not advertised. Semtive Nemoi M ft. 3.1 mph $4,695 Semtive Nemoi S ft. 3.1 mph Not advertised. For the purposes of our research into residential wind power, our subcommittee focused on the Semtive Nemoi M, as it offered the best performance in low wind conditions of the three options available. WIND RESOURCES A crucial consideration for the viability of VAWTs in Berkeley is whether adequate wind resources are available. One major challenge that residential wind faces is that wind speeds are reduced near the surface of the earth due to obstructions such as trees and buildings. The U.S. Department of Energy s 30-meter wind resources map indicates that Berkeley has poor conditions for wind power, with average wind speeds modeled at less than 4 m/s (9 mph). 4 Given that this estimate is for 30-meters above ground level, conditions at rooftop level are likely to experience an even lower speed. However, the Semtive Nemoi M claims to be able to generate power at speeds as low as 3.1 mph. 5 This low cut-in speed means that the Nemoi M and future residential wind turbines could be performant even in Berkeley s light wind conditions

3 Initial Power Output Simulation The subcommittee began by using wind data from Alameda Naval Air Station to simulate the performance of the Semtive Nemoi M. This data set was considered a best case scenario. Alameda NAS is an open field with close proximity to winds from the San Francisco Bay, making it a better location to capture wind power. The subcommittee used the power output curve provided by Semtive to find the Nemoi M s output at a given wind speed [see Attachment 2]. This initial simulation [see Attachment 3] found that over the course of a year, the Semtive Nemoi M s output would range between 53.6 kwh and 91.6 kwh per month. Given an average household consumption of 897 kwh per month, the Nemoi M would have supplied between 5.76% and 10.44% of a household s energy needs. On average for the entire year, the Semtive Nemoi M would have provided energy for 8.5% of a household s needs. According to the subcommittee s analysis, the Semtive Nemoi M would have a 33.7 year pay-back period with these light wind conditions. This estimate is based on an initial cost of $4,695 and a kwh value of $0.152, and an installation at Alameda NAS. This initial analysis suggests that a residential VAWT like the Semtive Nemoi M may not make a substantial contribution to a household s sustainable energy production. However, one of the major drawbacks of the wind data used was the low resolution of the wind measurements. Monthly averages do not fully capture the distribution of wind speeds, meaning that the analysis may be missing peaks in wind speed that a VAWT could capture. High Resolution Wind Data for Berkeley To gain a higher-resolution analysis of how a VAWT like the Semtive Nemoi M would perform in Berkeley, the Residential Wind Power Subcommittee collected publicly available wind data from two amateur weather stations in Berkeley. The data consists of 185,247 measurements from two weather stations since January The wind speed measurements occur in 5-10 minute increments. While not every area of Berkeley is covered by the data-set, it forms a basis for calculating the effectiveness of a VAWT in a residential context. Weather Station ID Location Elevation # Wind Measurements KCABERKE102 Berkeley Hills 571 ft. 92,379 KCABERKE40 Westbrae 85 ft. 92,868

4 Findings of Detailed Analysis Based on the 185,247 wind speed data points combined with the Semtive Nemoi M s power generation curve, the subcommittee modeled the Nemoi M s output in kwh since January 1st, 2017 (year-to-date). Of the two amateur weather stations included in the survey, neither demonstrated that a VAWT like the Semtive Nemoi M would produce a significant amount of power. Monthly output ranged between 42.1 kwh and 3.6 kwh, with a median output of 16.5 kwh. At its peak output, the Nemoi M would have generated 4.7% of a household s monthly electricity demand, and at its lowest it would have generated 0.4% of a household s demand. The median amount generated would be 1.8%. The Residential Wind Power Subcommittee interprets these results to indicate that Berkeley s wind resources are not adequate to make residential wind a major source of renewable energy for Berkeley. NOISE CONSIDERATIONS VAWTs are generally very quiet. For example, in a 25 mph mile an hour wind, the Semtive Nemoi M produces only 38 decibels of noise, which is less than the ambient noise created by the wind. IMPACT ON BIRDS The commission was unable to find any comprehensive data on the impact of small VAWTs on bird life. However, one advantage of small VAWTs is that they rotate at a

5 slower speed than horizontal wind turbines such that the blades remain visible at high wind speeds. PERMITTING CONSIDERATIONS The Semtive Nemoi M stands 9.8 feet tall, and is designed to be mounted on a roof or deck. According to the manufacturer, the permitting process is identical to that of a solar installation. RATIONALE FOR RECOMMENDATION Given the lack of wind resources in Berkeley, the Residential Wind Power Subcommittee concludes that no broader action to promote VAWTs is needed. For Berkeley residents intent on reducing their carbon footprint, the investment made towards a VAWT could be better spent on the installation of solar panels, improvement of home insulation, or on purchasing wind-power from East Bay Community Choice Energy. CITY MANAGER The City Manager [TYPE ONE] concurs with / takes no position on the content and recommendations of the Commission s Report. [OR] Refer to the budget process. Note: If the City Manager does not (a) concur, (b) takes any other position, or (c) refer to the budget process, a council action report must be prepared. Indicate under the CITY MANAGER heading, See companion report. Any time a companion report is submitted, both the commission report AND the companion report are Action reports. CONTACT PERSON Attachments: [Delete if there are NO Attachments] 1: Figure: How a Darrieus Rotor Works

6 2: Figure: The Power Generation Curve of the Semtive Nemoi M Semtive provides the following power generation curve for the Nemoi M:

7 Based on this curve, the subcommittee plotted a series of points from the curve: M/s kwh/day Based on these points, the a polynomial function was derived to fit the power generation curve. While wind speed is greater than 1.4 m/s (3.1 mph, the Nemoi M s cut-in speed) and less than 29 mph (13 m/s, the maximum on the power generation curve): kwh/day = * w * w * w * w * w * w Since this equation produces number of kwh produced by day, the result was divided by 1440 (the number of minutes per day) and then multiplied by the duration (in minutes) of the wind speed reading. 3: Table: Simulated Output of the Semtive Nemoi M at Alameda Naval Air Station Month Avg. Wind Speed (mph) Wind Speed (m/s) Semtive Nemoi Average Daily Output (kwh) Monthly Output (kwh) Energy Value (@ $0.152/kWh) % of monthly energy usage January $ %

8 February $ % March $ % April $ % May $ % June $ % July $ % August $ % September $ % October $ % November $ % December $ % 4: Table: Simulated Output of Semtive Nemoi M at Two Amateur Weather Stations Month KCABERKE40 Output (kwh) KCABERKE109 Output (kwh) January February March April May June July August September October November