The work presented in this paper analyzes the use of storage solutions by comparing different scenarios in which a Power wall can be used. These scenarios compare different states of the United States of America and Portugal, considering the electricity prices and billing system in each of the regions. The potential savings provided by using the Powerwall result mainly from different hourly tariffs, and in California, it can be of 0.21€/kWh in the summer and 0.12€/kWh in the winter; in Hawaii, it can be of 0.26€/kWh plus approximately 800€/year on fixed bill savings. In Alabama, it can be of 0.10€/kWh, and finally, in Portugal, it can be up to 0.19€/kWh, since all the cities or states practice different electricity prices and grid injection schemes. The scenarios considered for this work involve a 100% self-consumption regime in which grid injection is not considered even though it is allowed in some cities or states. To evaluate the economic impact of the Power wall, different economic methods are used, such as the Profitability Index, the Internal Return Rate, and the Discounted Payback Period of the Investment. Other base economical parameters include interest rate, maintenance, operations rate, inverter replacement rate, Powerwall Battery replacement, VAT tax rate, electricity evolution rate, electricity price, prices for a PV system connected to a Powerwall system, and PV degradation rate are also considered. The overall results show that Portugal is not attractive in any scenario while in several scenarios for the United States, considering the different states, the investment can be doubled or tripled, including using the Powerwall without a PV system.

1. “Tesla Powerwall,” Retrieved from https://en.wikipedia.org/wiki/Tesla_Powerwall [Accessed: February 15, 2015].
2. T. Motors. (n.d). Powerwall; Tesla home battery. [Online], Avaliable: https://www.teslamotors.com/powerwall [Accessed: May 2, 2015].
3. S. R., Abreu, M., Leça, X., Chen and F. Morgado-Dias, “On the current payback time for small investors in the photovoltaic systems in the region of Madeira,” In CONTROLO’2014–Proceedings of the 11th Portuguese Conference on Automatic Control, Springer International Publishing, pp. 375-384, 2015.
4. Venables, M., Energy Retail Association, & Gilbert, R. (2008). PORTUGAL, Ministry of Economy and Innovation, Decree-Law n. No. 172/2006 of23 August, Article 58 th. Researched in.World Wide Web.
5. Decree Law 153/2014, Distributed Energy Production.. 2014, pp. 5298–5311.
6. S. Rodrigues, F. Faria, N. Cafôfo and X. Chen, “The Current situation of the residential and commercial PV system self-consumption market in Portugal,” Int. Renew. Energy Environ. Conf., pp. 1–13, 2015.
7. J. L. Bernal-Agustín and R. Dufo-López, “Economical and environmental analysis of grid connected photovoltaic systems in Spain,” Renewable Energy, vol. 31, no. 8, pp. 1107-1128, 2006. https://dx.doi.org/10.1016/j.renene.2005.06.004
8. A. Audenaert, L. De Boeck, S. De Cleyn, S. Lizin and J. F. Adam, “An economic evaluation of photovoltaic grid connected systems (PVGCS) in Flanders for companies: A generic model,” Renewable Energy, vol. 35, no. 12, pp. 2674-2682, 2010. https://dx.doi.org/10.1016/j.renene.2010.04.013
9. A. Campoccia, L. Dusonchet, E. Telaretti and G. Zizzo, “An analysis of feed’in tariffs for solar PV in six representative countries of the European Union,” Solar Energy, vol. 107, pp. 530-542, 2014. https://dx.doi.org/10.1016/j.solener.2014.05.047
10. T. Lang, E. Gloerfeld and B. Girod, “Don׳ t just follow the sun–A global assessment of economic performance for residential building photovoltaics,” Renewable and Sustainable Energy Reviews, vol. 42, pp. 932-951, 2015. https://dx.doi.org/10.1016/j.rser.2014.10.077
11. J. Obaidullah. “Profitability Index,” (2013). Available: https://goo.gl/3sIepE, [Accessed: February 01, 2015].
12. Edision International Electricity Company Southern California, “SCE Introduces a New Residential Time-Of-Use Rate Plan,” 2015. [Online]. Available: https://goo.gl/DmJi4t
13. ERSE, “Cycle Time,” [Online]. Available: https://goo.gl/yBVC2A [Accessed: 02-Feb-2015].
14. EIA, “Electric Power Monthly,” The U.S. Energy Information Administration (EIA), 2015. [Online]. Available: https://goo.gl/qGgXka [Accessed: 15-May-2015].
15. ERSE, “Prices transitional sales to customers in portugal continental final in 2015,” [Online].Available: https://goo.gl/EkaBV0 [Accessed: 02-Feb-2015].
16. R. Naam, “Why Energy Storage is About to Get Big – and Cheap,” 2015. [Online]. Available: https://goo.gl/ZDq7Xx [Accessed: 15-May-2015].
17. D. Hahn and D. Llorens, “2015 United States Solar Power Rankings,” Solar Power Rocks, 2015. [Online]. Available: https://goo.gl/lsfqpl [Accessed: 15-May-2015].
18. Retscreen International, “Renewable energy project analysis software.” 2014.
19. P. Stackhouse and J. Kusterer, “Surface meteorology and Solar Energy,” 2014. [Online]. Available: https://eosweb.larc.nasa.gov/sse/ [Accessed: 14-Mar-2014].
20. Hawai’i Public Utilities Commission, “Effective Rate Summaries.” 2015. Avaliable: https://goo.gl/SnDjEV
21. P. Magazine, “Tested: Solar World Sunmodule Plus SW 245 poly,” 2013. Avaliable: https://goo.gl/57cn3E
22. G. Granata, F. Pagnanelli, E. Moscardini, T. Havlik and L. Toro, “Recycling of photovoltaic panels by physical operations,” Sol. Energy Mater. Sol. Cells, vol. 123, pp. 239-248, 2014. https://dx.doi.org/10.1016/j.solmat.2014.01.012
23. K. Zweibel, “Should solar photovoltaics be deployed sooner because of long operating life at low, predictable cost?,” Energy policy, vol. 38, no. 11, pp. 7519-7530, 2010. https://dx.doi.org/10.1016/j.enpol.2010.07.040
24. J. Lu. L. Peng and H. Yang, “Review on life cycle assessment of energy payback and greenhouse gas emission of solar photovoltaic systems,” Renewable and Sustainable Energy Reviews, vol. 19, pp. 255-274, 2013. https://dx.doi.org/10.1016/j.rser.2012.11.035
25. M., Mani and R. Pillai, “Impact of dust on solar photovoltaic (PV) performance: Research status, challenges and recommendations,” Renewable and Sustainable Energy Reviews, vol. 14, no. 9, pp. 3124-3131, 2010. https://dx.doi.org/10.1016/j.rser.2010.07.065
26. V. Fthenakis, R. Frischknecht, M. Raugei, H. C. Kim, E. Alsema, M. Held and M. De Wild-Scholten, “Methodology guidelines on life cycle assessment of photovoltaic electricity,” IEA PVPS Task, vol. 12, 2011.
27. “Electricity prices by type of user – Eurostat”, Ec.europa.eu, 2015. [Online]. Available: https://goo.gl/Ez96Lf [Accessed: 02- Feb- 2015].
28. “US Average Retail Price of Electricity”, Ycharts.com, 2015. [Online]. Available: https://goo.gl/cGCiTR [Accessed: 02-Feb- 2015].
29. “Trading Economics | 300.000 Indicators from 196 Countries”, Tradingeconomics.com, 2015. [Online]. Available: https://goo.gl/ZPnegw [Accessed: 02- Feb- 2015].
30. A. Campoccia, L. Dusonchet, E. Telaretti, and G. Zizzo, “Comparative analysis of different supporting measures for the production of electrical energy by solar PV and wind systems: Four representative European cases,” Solar Energy, vol. 83, no. 3, pp. 287-297, 2009. https://dx.doi.org/10.1016/j.solener.2008.08.001
31. P. K. Koner, V. Dutta and K. L. Chopra, “A comparative life cycle energy cost analysis of photovoltaic and fuel generator for load shedding application,” Sol. Energy Mater. Sol. Cells, vol. 60, no. 4, pp. 309-322, 2000. https://dx.doi.org/10.1016/S0927-0248(99)00050-1
32. F. Sick and T. Erge, Photovoltaics in Buildings: A Design Handbook for Architects and Engineers. Earthscan, 1996.
33. “Retscreen Software Help,” 2014. [Online]. Retscreen developers, Available: https://www.retscreen.net/
34. S. Rodrigues, F. Faria, A. Ivaki, N. Cafôfo, X. Chen and F. Morgado-Dias, “The current situation of the residential and commercial PV system self-consumption market in Portugal,” In International Renewable Energy and Environment Conference (IREEC), 2015. Sol. Energy Mater. Sol. Cells.

S. Rodrigues, F. Faria, A. Ivaki, N. Cafôfo, X. Chen and F. Morgado-Dias “Tesla powerwall in the United States and Portugal–A comparative analysis on the use of storage with small scale photovoltaic systems,” International Journal of Technology and Engineering Studies, vol. 2, no. 1, pp. 5-12, 2016.