Saving with DC Lighting and Infrastructure

In SON-T luminaires, alternating current (AC) is converted to direct current (DC). The centralization of the conversion, instead of seperate conversions in each fixture, is more energy efficient and can result in savings for greenhouse growers of almost € 10,000 to € 20,000 per ha per year. The three significant results are:

1 - DC-powered SON-T luminaires consume per fixture 1.6 to 1.9% less electrical energy (VA) relative to the best-performing AC ballast on the market. Per exposed hectare the savings per year is € 2,000 (84 μMol/m²) to € 3,400 (175 μMol/m²) per year. This is based on 2357 hours and a cost of € 0.10 per kVA / kWh. It is expected that there are also savings on infrastructure by lower copper costs.

2 - DC powered SON-T fixtures will, at sufficient scale, be cheaper to produce and install than AC powered SON-T fixtures. Therefore, the initial investment will be lower, which lead to less interest payments and a lower write-off. Price per fixture is expected to retail for the grower at € 37.50 (600W) to € 45,- less than the current best-of-market AC fixture. This results in an annual saving of € 3,900 to € 5,700 per hectare per year. This includes lower interest payment and lower write-off combined.

3 - DC powered fixtures offer at component-level a longer lifetime. In AC fixtures the conversions of AC to DC determines the lifetime of the luminaire. If this conversion is not taking place inside the fixture, the lifetime can increase. 7 years, is now considered as plausible, and with DC the lifetime of the luminaire can be 10 years or longer. This means that the write-off is 30 to 40 percent lower. Per acre may result in a lower depreciation of € 8,000 to € 14,000 per year. The duration of the project itself has been too short to also demonstrate in practice this extended lifetime.

Before growers can apply DC lighting and infrastructure, there are two major obstacles to overcome. First, the electrical infrastructure must be developed for greenhouses. Without this infrastructure the DC luminaires have no value and do not even operate. Secondly, to actually achieve saving is also dependent on the chosen strategy and price positioning of the vendor(s). For the technology to succeed, a rapid deployment with an attractive price level is desirable, which need not necessarily be successful for the supplier(s).

This project is funded under the program 'Greenhouse as energy source'. Partners of the project are: Direct Current BV, Joulz, Rabobank, The Hague University, Agrolux, Gavita Netherlands and grower Vreeken Floriculture BV (Bouvardia).