Energy Unlimited by Victron

8. Micro power generation: thinking different

8.1. Introduction

For the purpose of this book micro power generation is defined as power generation for systems requiring, on average, between a few hundred Watts and up to 10 kW of electric power. Over a period of 24 hours this equates to in between 24 x 0.2 = 4.8 kWh and 24 x 10 = 240 kWh of electric energy per day. As will be shown, 240 kWh is the upper range of the amount of electric energy needed by a few families to live comfortably, be it in a small community of one or a number of houses, in a mobile home or on board a boat.

It is within this range that several recent technical developments make it worthwhile to “rethink” power generation.

A very important characteristic of the application considered here is that the amount of electric power required will at times be nearly zero and at other moments increase to several times the average. When a petrol or diesel fuel powered AC generator is used to supply the required electricity, it has to be sized for the highest power demand that is to be expected, and therefore will run at practically no load during most of the time. Very inefficient in terms of wear and fuel consumption, not to speak about noise, maintenance and pollution. A problem more specific to boats (and motor homes) is shore power. The rating of the shore power outlet is often insufficient to supply a washing machine, an electric stove or air conditioning. And when crossing the Atlantic voltage is different and frequency is 60 Hz instead of 50 Hz, or the other way round.

Of increasing importance on boats is also weight and volume.

In the following sections new technologies and concepts to improve the performance of micro power generation are presented and discussed.

8.2. New technology makes the DC concept more attractive

8.2.1. The DC concept

In the DC concept the battery is the hart of the system. All power generated or taken from a shore power outlet is converted to DC or generated as DC. The sources of electric power are connected to a DC bus, to which the battery is also connected. Likewise, all consumers are either DC or are supplied from the DC bus by an inverter.

In the DC concept the battery is a buffer of electric energy that compensates for any imbalance between energy suppliers and energy consumers.

In fact all smaller boats do use the DC concept:

Power is generated by one or more alternators on the main engine, and often also by alternate sources like solar or wind power, or a water generator. All sources of electric power are connected to a DC bus, to which the house battery is also connected. All consumers, such as navigation equipment, cabin lighting, etc. are supplied from the DC bus.

As electronic power conversion technology improves, more and more household appliances, which do require an AC supply, are also being connected to the DC bus, with an inverter.

In the next sections 2 new developments that substantially increase the attractiveness of the DC concept are presented.