Monday, May 31, 2010

Made in Japan (part 2)

This time we're in Miharu in the prefecture of Fukushima to the NNE of Tokyo by some 200km.

If you keep hitting (+) on the map it will zoom in and show Miharu (eventually!).

My father-in-law's house has two arrays on the South and West facing roof slopes and luckily even though it is in a quite steep valley, the valley runs East to West and his house is on the North side so it gets a fair bit of sun even in the winter.

The panels are made by Hitachi and are their newest hybrid crystalline amorphous type that have layers that give excellent wide spectrum responsiveness on cloudy days but the high output of crystalline panels on sunny days. The Sharp ones used on the house in Tokyo were a common crystalline type. On the South roof there are 18 panels and another 13 on the West roof.
All the power conversion kit is made by Sanyo.

As the array is split into unequal strings of 18 and 13 panels, they work at two different DC voltages. So outside on the wall is a voltage converter / combiner that converts the two different DC supplies into one at a common voltage that then goes into the inverter indoors.
A single DC cable goes to the power conditioner in the house where it is converted to mains. It's a less elaborate unit than the Sharp one and just has a single display that toggles between current kW output and the lifetime kWh generated. The information plate says it is rated for 70-380V DC input and 5.5kW output at 200VAC with an efficiency of 95%.
Outside, the utility company has fitted two digital electric meters, again one for power used and another for surplus power sold to the grid.
The inverter appears to be putting out 200V rather than the house 100V, so either it's designed to be split phase (100-0-100) relative to earth or it actually doesn't feed the house directly but just the grid through the separate meter so that the household usage bill is offset by the generating credits.

My father-in-law said that in the summer and up until September it generates a net surplus to the household requirements but by November it doesn't quite make enough to completely offset their usage.  On the clear sunny day shown here, the inverter reported making 3.0kW for a short while around mid-day but 2.1 to 2.6kW for the bulk of the day. The sun was quite low in the sky even at noon and as it moved round to the West, the output declined a bit.  In summer it was probably ok with the sun much higher in the sky and on cloudy days it probably doesn't make much difference either having part of the array facing west.

Another novel feature of their house is a Sanyo air source heat pump (ASHP) that heats water by extracting heat from the outside air (usually hot and humid). Using a sort of reverse air conditioner it pumps the heat into an insulated hot water tank. 

It uses about 60-70% less electricity than a resistive heater. The Japanese call it an Eco-Cute. It doesn't mean "cute" though... "kyu" is a kanji in Japanese than means "to heat water". The difference between an ordinary air conditioner compressor and these water heaters is that the refrigerant is at a much higher pressure in this system to more efficiently extract heat and it's only in recent years that they've been made small enough and cheaply enough for home use.

Inside the house is the large hot water tank and compressor. A digital display shows the water temperature and how "full" the hot tank is as a bar graph.
The system also controls the heating of the bath to a constant temperature - very important for Japanese.  You take a shower and wash and then sit in the tub just to relax and get warm while the system cycles the water.  You could sit in it all evening.

He also had the kitchen refitted and they changed from a gas hob for cooking to electric induction.  This wastes a lot less energy (95% of the energy goes into heating the pan rather than the hob or the air) but did have the drawback that they had to replace most of their cookware.  Induction hobs only work on ferrous metal pans, so the typical aluminium or stainless steel with copper bottoms don't work well.  As they generate quite a large surplus of electricity, it made sense to change from gas to electric for cooking.

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