Creating power for your home, off grid.
Emphasis on nuts-n-bolts, hands-on projects.
They installed this Sharp SunVista 3.07kW solar system earlier this year.
It's a grid tie system that operates automatically. They call the inverter a power conditioner and it has a control and info panel near the utility breaker panel. It lights up different colours during the day to indicate the power level. Blue means the system is generating a surplus and is selling electricity to the grid and yellow means it is generating but grid power is being used as well.
The panels are mounted on both sides of the roof but the slopes face sort of east and west so one half of the array is always sub-optimal. The sun doesn't make such a low angle in winter here in Tokyo when compared to the south of the UK so the variation of day hours are less extreme and Japanese Autumns and Winters are characterised by clear sunny days (very unlike the UK). In the summer the sun goes mostly directly overhead so it's not such a problem.
Their house is the one at the back of the white one - you can just see the panels on the roof. The houses are terraced back to back.
The installers mounted the inverter on the outside wall and then ran a wire to the remote control panel inside.
The mains is fed to two meters outside that the utility company installed. The digital one on the left measures grid power drawn and the old school mechanical one on the right measures solar power sold to the grid.
The remote panel in the house displays an estimate of power being generated as well as the proportion being used or sold and the lifetime kWh. Flicking through the menus you can pull up generating history graphs for the last hour, day, week, or month.
It's about 11am in this shot and it's just started to make a surplus now that we are done with breakfast and have stopped using the kettle. The sun is a bit hazy today.
They tend to sell a lot of power during the weekdays when they are out at work but then buy it back at the weekends when they use the air conditioning and clothes dryer...
The whole system is a kit made by Sharp but a local installation company fitted it.
Next week we're visiting my father-in-law who installed a bigger 5kW system.
- Dennis The Bus Dweller
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It's a bit misleading looking at their house as this street was all specially designed to a Swedish pattern for the houses so they aren't typical at all of most Japanese houses. My sister-in-law is an editor of a hair & beauty magazine here and loves visiting Europe so they especially wanted a western style house.
Ikea just opened up here last year and she's a big fan...
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. Each panel has 72 cells and so would appear to be about 39.6V nominal. The array with the 18 panels makes sense as that could be 2x9 panels at 356V nominal. The other array with 13 panels is a bit of a mystery as it is a prime number so could only be either an odd mis-matched pair of 9 and 4 or one group of 13 but that would exceed the 380V nominal rating of the system converters...
Anyway, all the conversion kit is made by Sanyo and it's a grid tie system.
The two arrays DC feeds meet at a junction box outside that also seems to be some kind of 380V DC-DC up-convertor.
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.
As it appears to be putting out 200V rather than the house 100V, either it is 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 was generating a net surplus to the household requirements but now that it's November it isn't quite making enough to completely offset their usage. On a clear sunny day like today, 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 an air-water heat exchanger made by Sanyo that extracts 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 refridgerant 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.
While out sightseeing at the dammed lake reservoir near Miharu, we stopped at a hotel spa place that has a very good tofu cafe that sells all sorts of yummy food entirely (almost) made from tofu or derivatives (even the donuts!).
Anyway, while walking about I noticed that somehow they had also built an observatory (it gets very dark up here in the mountains away from any town).
Next to the observatory was what at first glance appeared to be a bus shelter (err.. because it had busses parked under it). In fact it was a sizeable solar array!
It consists of 8 rows of 14 x 167W 48 cell (23.2V MPP) Kyocera panels (I could read the info plates on the undersides). From the date stamps on the panels it seems to have been in operation since 2002. The nominal output is 18.7kW - maybe enough to offset most of the power used by the small hotel, observatory and cafe.
The electronics were all in a sort of phone box shaped hut next to the back row.
Travelling from the remote town of Takayama through the mountains to Matsumoto I saw quite a few new looking home based PV systems but many more old looking solar hot water systems. These types of evacuated tube or flat plate collectors have been popular for decades with the Japanese.
I've got some catching up to do! My experimental solar array is just 204W and cobbled together in true mad inventor style. Luckily, the electronics store I bought all my panels from has just announced on their web shop that they've got another load of those cheap 15W amorphous panels in stock again... My garage roof is calling out to them
I could make a wisecrack about a "solar powered observatory" being short on power after the sun goes down, but so few restaurants here have attached research laboratories, the joke would fall flat.
At the moment they offer a grant to pay for part of the installation of a home PV system but it's a feeble attempt as the process for getting the grant is complicated and there are a limited number of grants per year. If they turned it around and said "We want to install a PV system on every suitable roof in the UK and we or the utility company are going to pay you to have it installed" then we'd be moving in the right direction.
Sounds a bit mad but mobile phone companies have been doing it for years... They pay all sorts of businesses and even homes to have a mobile phone transmitter installed on their property (on office and appartment blocks, farmers fields, petrol stations, schools, etc.) If my utility company said to me that they wanted to install a PV system on my roof and would either pay me rent for the roofspace or give me a discount on my bills in perpetuity for generating credits (or have the government give me a green tax break) then I'd sign up.
Expecting home-owners to make the infrastructure investment in renewable power generation is the wrong way to do it. Most don't have that kind of capital sitting around even if over 20 years it pays a dividend. Most wouldn't consider it as they don't tend to stay in the same house for that long. Only governments and major utility companies can invest like that.
Utility companies also have a problem... They just don't have the scope in the UK to go building big solar farms all over the countryside
a) because it's used for growing food
b) because the parts that aren't covered in food are either covered in roads, houses or trees (national parks)
Building arrays on houses also would mean that the total array area would be spread over a very wide geography, limiting the effect of our typically part cloudy weather. Even with patchy cloud, an array spread over a whole city would experience less shading dropouts than one concentrated in a single field. If a network of arrays were spread over a whole county then the effects would be even lower, solving one of the problems of solar generation in the UK - an almost complete lack of clear sunny days that results in erratic generation from any geographically concentrated high power array. It's not uncommon for it to be raining buckets in one part of town and be sunny just a kilometer away.
Generating the power in the cities where the energy is used would also reduce transmission losses from remote power stations to the homes. With inverter technology now 95-97% efficient, it should be better than the losses on a high tension transmission line from far away stations.
Having solved the UK's power generation problems this morning, it's time for a spot of lunch and then I'll sort out that nonsense in Afghanistan before tea.
Much too cheap and simple. That's why they want to put the arrays in Africa and build a high voltage DC line to Europe. Local arrays means lower profits for people with more money than they know what to do with. Politically impossible.AccordGuy wrote: Generating the power in the cities where the energy is used would also reduce transmission losses from remote power stations to the homes. With inverter technology now 95-97% efficient, it should be better than the losses on a high tension transmission line from far away stations.
I said I'd solved the UK's generating problem... Whether they choose to adopt the solution is up to them
I'm just building an off-grid PV system to annoy the utility company (as if they care). Actually, a guy came round from them to change my meter to a digital one and was very interested in my solar array (either that or he was just humouring the madman).
Here's one for you - The average utility electricity meter consumes 3W of energy just to do its job (you can check the info plate on the meter). That means for the UK with 24.7 million households (almost all on the grid), they had to build a 74MW power station just to run the electricity meters. If you want to reduce CO2 emissions - ban electricity meters!
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