d-Lumen: A Proposed System for Cost-Effective Water Heating From Solar PV

This is an idea I had a few months ago. After lots of research I’ve decided not to develop it, at least for the moment. However, I will share the proposal in case it might be useful for somebody else. Perhaps you’ll build on the idea or adapt it idea for a better use. Click on the “Download” button below to download a PDF which outlines the idea.

Problems With the d-Lumen System

Initially I thought that, because of the low voltage, the d-Lumen would be intrinsically safer and subject to fewer regulations than AC electrical systems. I thought this would lead to opportunities for cost savings. However, after more research I found out that the system would come under the standard definition of “electrical installation” (see the National Rules for Electrical Installations, 4th Edition; ETCI, 2008). This means that a RECI cert would be required for every installation, adding to the cost.

Another problem I ran into was the issue of live DC wires inside the building. Solar PV systems are required to automatically isolate any DC wires in the event of a power outage. This is a safety feature to protect fire fighters. This would add complication because the DC cut-off switch would have to somehow be connected to the AC mains in order to detect power outages.

Having considered these issues, I came to the conclusion that a grid-tied solar PV system with a power diverter would be just as cost effective as the d-Lumen system and with better performance. This would have made the d-Lumen system obsolete for most people.

Opportunities to Adapt the Idea for Other Uses

The d-Lumen might still be worth considering for people who need a lot of hot water in off-grid locations. In this situation, the cost-comparison with on-grid systems is irrelevant. However, there is already a product called the DMMPT450 that will probably cover most peoples’ needs in this case. Perhaps the d-Lumen could be useful for campers, people who live on boats, or some other group who I haven’t even thought of. Let me know if you know of some use for a d-Lumen type system that I haven’t thought of.

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Installers generally don't offer quotes for timeframes longer than 6 months. So here are guide prices (before grants):

  • 2kW (S): ~€5,500
  • 4kW (M) + myEddi: ~€8,500
  • 6kW (L) + battery: ~€12,500