Summary We report on the development of non‐tracking solar concentrator troughs designed subject to the condition that they operate efficiently for diffuse irradiation from all angles during daylight hours. Troughs of the usual compound parabolic form were considered initially. Remarkably however, the most efficient shape for the above requirement turns out to be a trough of simple semi‐circular cross‐section incorporating a tube of height equal to the circle radius and with a planar absorber plate placed vertically. This trough has a limited concentration ratio of exactly 2.0 but an intercept factor for incident radiation of 100% for all angles of incidence. This desirable feature is explained from the properties of caustics arising from reflection of incident light at the semi‐circular trough (SCT) surface. This very simplest of trough design has the clear advantages of small size and low‐cost of manufacture. Experimental tests conducted under varying solar irradiation conditions, demonstrate that the simple step of placing an evacuated tube in a SCT can lead to a power output gain of a factor of at least 1.7 on average.

Smart-grid rooftop solar electricity (SG rooftop PV) is an alternative sustainable energy resource. This research was conducted in the Central Highlands of Vietnam (CHV) in light of the different levels of retail electricity pricing, the sunshine duration, and the implementation of a feed-in-tariff system, in order to calculate the financial indicators (FIs) of SG rooftop PV, which would supply investors, companies supplying SG rooftop PV, and policymakers with useful information. The FI values were calculated based on the net present value, the payback period, and the internal return rate. The results show that the electricity retail price level affects the FI of SG rooftop PV. SG rooftop PV is installed to satisfy higher electricity consumption levels, which attracts a higher retail electricity price. As a result of the greater benefits, especially if SG rooftop PV is installed and the highest level of electricity (exceeds 400 kWh) is used to satisfy domestic consumption, users will recoup their investment in only four years and after that will enjoy free electricity. All the FI values derived from this research show that people in the CHV can derive benefits from installing SG rooftop PV.

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Abstract Background: There are many constraints on the use of fossil fuels and, many countries have, therefore, conducted research relating to alternative energy resources to replace conventional fuels. On 31 January 2019, the Vietnamese Ministry of Finance enacted a preferential policy relating to the installation of under-50kWp rooftop solar projects. The Central Highlands of Vietnam has a high potential for solar power generation due to the duration of sunshine it enjoys, and the development of both rooftops solar and solar farms is appropriate for the region. The study reported investigated the economic efficiency of smart-grid rooftop solar electricity systems (SG rooftop PV) in the Central Highlands of Vietnam in light of the different levels of retail electricity pricing in Vietnam and the implementation of a feed-in-tariff system. The research reported in this paper will be useful for many groups of stakeholders, including electricity consumers who intend to install rooftop solar panels on their houses, companies who supply SG rooftop PV, and policymakers, who can use the findings relating to SG rooftop PV to adjust the retail price of electricity during different periods.Method: Financial indicators were calculated based on the net present value, payback period, internal rate of return, and the number of hours of sunshine in the Central Highlands of VietnamResult: The study’s results show that the electricity price level affects the economic efficiency of SG rooftop PV. In particular, SG rooftop PV installed to satisfy higher levels of electricity consumption, which attract a higher retail electricity price, result in greater benefits, especially when domestic electricity consumption exceeds 400 kWh, at which level the retail electricity price is at the highest level. In this case, people who install SG rooftop PV and use all the electricity to satisfy domestic consumption will recoup their investment in only 4 years and thereafter will enjoy free electricity. Conclusion: All the financial indicators derived from this research show that people in the Central Highlands of Vietnam can derive benefit from installing SG rooftop PV, whether they sell all the electricity output to the grid or use the power output to satisfy their domestic demand.