Solar power

Solar power is the leading renewable energy source for sunny countries including Australia and Spain. Wind is the big competitor in less sunny locations including Scandinavia. what are the options for Solar and where is the future?

Summer in Sydney, Australia, brings high solar power from 10:00 am through to 4:00 pm. Winter in Sydney produces high solar power from 11:00 am through to 2:00 pm. There are lower power levels from sunrise until the peak period and from the end of the peak period until sunset. Your local solar power levels will depend on your distance from the equator and other factors including trees, other buildings, and the amount of smoke in the atmosphere. There are some critical questions to ask about the use of solar power and some of the answers are described on this page.

• How do you use solar power during the low power periods?
• How do you use solar power during the peak power periods?
• How do you access solar power overnight?

The following list shows the main ways to use solar energy direct and are discussed in detail. Hydroelectric power is an example of indirect use of solar energy with the sun providing the energy to evaporate the water that falls as rain in the hydroelectric power collection area.

• Photovoltaic
• Concentrating Solar Power

How do you use solar power during the low power periods?

The lowest power morning period may coincide with your breakfast but not provide enough power to cook breakfast. The power level will run your radio, Internet connection, and some fans. The fans could be blowing the room air around to cool you in summer or blowing the room air over over heat bank storage to warm your house in winter. Instead of fans, you could have small pumps circulating hot or cold water to control the room temperature. The stored water can be heated or cooled at other times of the day.

After you head off to work, the increasing solar power can run a washing machine and start heating water. The water can run direct into solar heating panels without conversion to electricity. Solar hot water is popular on the Australian mainland. Tasmania is the southernmost part of Australia and is too far from the equator for easy solar heating of water. For a comparison in Europe, Tasmania would be the equivalent of northern France. In a warm area you could use a washing machine with a time delay and cold water. In cold areas, you can use the time delay plus the first warm water from your water heating system.

The low power is enough to run tiny motors and could open or close sun shades to let in the sun during winter and keep out the sun over summer.

The afternoon low power period still produces enough power to run your refrigerator, to switch on and run a microwave oven to cook dinner, and perform lots of other little tasks. The power could continue to open and close sun shades as the sun moves across your house. In hot weather you might pump a little rainwater from your tank onto your vegetable patch.

Note that this description has not mentioned batteries. You would need a small rechargeable battery system to run the computer controlling the solar connection during the early hours of the day. A battery system could keep your clocks, Internet access, and alarm systems functioning overnight. For larger overnight power requirements, you would buy back the power you supplied to the grid during the peak power period of the day. In hot weather you might use electricity to cool the water in your heat bank then use the cool water to cool your house during the day.

How do you use solar power during the peak power periods?

The peak power period should run all the high load activities plus store excess energy for use overnight. If you have a time delay electric oven, the oven could be set to bake a cake or roast dinner. A time delay operated clothes dryer could switch on to dry clothes in humid climates. You could switch on a reverse cycle air-conditioner to heat a cold house, using both the peak solar power and the warm middle of the day air. You could switch on a reverse cycle water heater to heat the water in a heat bank and use the hot water from the heat bank to heat the house overnight.

Excess power during the day can be sold onto the electricity grid. The grid operators can use excess power to pump water up a hill into a hydroelectric system. Overnight, when solar power is not available, the water in the hydroelectric system would gush back down to supply electricity for street lights, hospitals, whatever is needed.

How do you access solar power overnight?

Think about your power usage overnight. You want some power for lighting, to browse the Internet, and to let your youngest child use TuxPaint on the old dell computer you scavenged off the scrap heap at your office. A small battery system will easily run these devices. You want hot water for the bathroom and the water was heated by the sun during the day. In winter you can heat your house using water heated during the day. In summer you can cool your house using fans operated by the battery system.

On very hot humid nights you need more power to run air-conditioning and that would come from the grid because a battery system would be too expensive. The grid gets the power from the hydroelectric system filled up by excess peak power during the day.

Photovoltaic

Photovoltaic (PV) power is generated from arrays of Photovoltaic cells. The cells might be mounted on machines to tract the sun. The cells are expensive and the cost is falling. The cells have a low level of efficiency but they have a long life and no moving parts to break. PV is the most flexible approach to power generation and works only during the day which means you have to couple PV with a storage technology for overnight power.

Concentrating Solar Power

Concentrating Solar Power (CSP) is the name given to systems where the sunlight is reflected into a central point to create intense heat, enough to boil water to run a steam power generation plant. CSP systems fail to product power overnight and have one of four backup power systems.

Gas operated backup systems burn unnatural gas or coal seam gas to produce electricity and carbon dioxide pollution. This is the stupid system selected by Australia's current stupid/insane/bent federal government to demonstrate CSP.

Superheated hot water is water heated to the point where it should turn to steam but is held back by extreme pressure. You superheat water in your CSP during the day then release it as steam during the night to generate your overnight electricity. This system has a long history and one real disadvantage, the superheated water/steam erodes the storage containers fast enough to create significant ongoing maintenance costs.

Salt will melt at 500&degs;C and can be stored in a similar way to superheated water but without requiring the extreme pressure and should not have significant ongoing maintenance costs. Salt systems are new and the only really big salt based systems are in Spain, where one is in effective operation and several more are under construction.

Hydroelectric power backup is the obvious choice if you have water and a hill to pump the water up. Spain has large flat areas with mountains around the edge of the country. The salt based CSP systems could be the best choice in the large flat areas. Hydroelectric backup would be better for CSPs near the mountains.

PV or CSP?

The best choice for your city depends on your geography. In Sydney we have massive areas suitable for PV systems on house and factory roofs. We have mountains nearby for hydroelectric backup. if we attempted to use CSP, we would have to destroy hundreds of acres of houses to fit the CSP system or destroy one of our few remaining food farms. Sydney is already a huge importer of food because we destroyed most of the farms a long time ago. Destroying our few remaining fresh food farms for a CSP seems stupid.

There are cities with large waste areas near the city that could fit a CSP. There are cities without the hills or water for a hydroelectric backup and a salt based CSP sounds like a good choice.

Wind power?

Wind has a different performance profile compared to solar energy. Wind can help supplement solar power but still needs backup storage. Wind can blow for a few days then stop for a few days. The only storage system with enough power backup for wind is hydroelectricity. If you have wind but no hills or no water, wind power has to be backed up by expensive battery systems or non renewable power sources.

The one advantage of wind coupled with solar power and a really big hydroelectric backup is the immense power reserve you can build up in cold weather. Using Sydney as the example, we get most of our wind power in the winter when the cold southerly winds chill Sydney. Wind power would help heat Sydney homes during the coldest part of the year.

Wind power is not as stable as solar power and would require a far bigger backup power system.