I live in Florida, the "Sunshine State", and I also work for the Pinellas County Building Department, so I see and hear a lot about solar.
Even here in Florida, solar does not work well if the panels are not able to be oriented in the right directions. Your roof design plays an important part about this, the slope and direction your roof surfaces face.
Direction is important because the panels must be able to collect direct (and some scatter) sunlight during the most parts of the day. East and West facing roof surfaces will not get near the direct exposure as North or South facing roofs, depending on you latitude. The general rule of thumb is to have the panels facing within 30 degrees of North or South, but no more than 45 degrees. The farther out, the less efficient. A panel facing West will only receive direct exposure 1/4 to 1/3 of the day, while the panels that face North or South get exposure all day, with the best exposure between 10:00 and 3:00.
Roof slope is also important because you want the panels to be as perpendicular to the suns rays as possible. An angled mounting system can adjust for this. But just as we here in Florida must deal with, so do you in Okinawa, high winds become a major concern. We both have hurricanes, although you seem to get far more than anyone else. Not only must they be mounted well enough to survive hurricane force winds, the roof must be strong enough to do the same with the added resistance of the collectors.
Dead load is not as big an issue, as most roofs in high wind zones are capable of resisting uplift, so they can resist gravity loads just as well, and every year the panels get more efficient and lighter, especially photo-electric panels.
Since you are looking at photo-electric, you will probably need a lot of panels to provide sufficient power to make it worth while. Most places allow you to sell you power back to the electric company during periods when your system is making more power than you are using, but not everywhere. If you cannot do this, it may make a big difference in how fast your system will pay for itself in years, especially if you install a large or very efficient set of collectors which adds to the cost.
Solar pool heaters are very common here in Florida, as they extend the swimming season by about 2 months in each direction, and are far less expensive to run than gas or electric pool heaters. They are also more expensive to install than the other systems. During the summer months, the sun is so hot swimming pools can get in the high 80's to low 90's, which is not really that nice for swimming. The most use I find here in Florida for pool solar systems is when people run their systems at night during the summer to actually cool their pools when the temps drop overnight.
As far as the actual design, most photo-electric systems I see are either direct use or have an optional bank of storage batteries. The batteries are a definite purchasing and maintenance expense and are not commonly found here. The most common is the solar panels tied to a converter which converts the DC to AC at the correct voltage and frequency. There are also solar tracking devices which will keep the panels aimed at the best angle with the son, but these are also very expensive, and in Florida, do not usually improve the efficiency enough to compensate for the cost. Up north is a different story. Some use a timer that you set to move the panels a certain distance every few hours and another uses a device that casts a shadow onto a receiver, and when Sun hits the device (like a ball), the device casts a shadow onto a receiver. As the Sun moves across the sky, the shadow cast by the device moves outside of it's target area, then a mechanism turns the collectors to position the device's shadow back to the center of the target area. Every evening, they move the entire collector back to the starting location for the next day. Both systems are very efficient, and very costly and not normally used or needed on the average residential installation where the sun's rays are plentiful. Also, it is more used on solar water systems as they require far less collectors than photo-electric. You would need a device on each collector.
Most systems here have the collectors mounted in a fixed position and angle on the roof and send the generated power to a DC to AC inverter. The Inverter is directly connected to your Circuit Breaker panel where power can go to your household circuits. If optional batteries are used to store excess power for later use, they are also tied through the circuit breaker panel. Remember, if you are using 120 volts, you need ten 12 volt batteries connected in series to get 120 volts. If you are not using batteries and your system produces more power than you are using, the excess power can actually back-feed the electric meter and feed the electric company.
I'm not real sure how this part works, but I imagine your meter will go backwards, and if you show a lower meter reading than the month before, they know how much power your system has provided to them and they pay you for that amount of kilowatts. You again need to check with your power company to see how that works and if they do buy your excess power.
Also, most system s have a device to sense if the power company has lost power to your house, and prevents back-feeding electricity which can electrocute a repair technician working on the power lines, thinking it is de-energized when it is still being powered by your system.
I have not yet heard of any maintenance problems or panel failures, but that does not mean that hasn't happened.
The general rule is to examine your monthly electric bill, determine how much power you use seasonally and annually, determine how much power your system will generate, determine from that how much you will save on your electric bill, factor in if you are able to generate and sell any power back to the power company, then divide that into the installation cost to see how many years it will take to pay for itself.
Here in Florida, it seems the average payback time is between 4-10 years, depending on the above factors.
Also, do yourself a big favor in the long run and replace your roof covering before installing the solar system unless it has very recently been replaced, as you will need to remove the collectors to replace the shingles later.
That's my 2 cents, or actually about 3.78 cents!