We've been using solar power in one way or another for thousands of years. In the last fifty years, though, we have learnt how to use it to provide hot water and electricity in our homes. Solar power and solar water heating use the sun's energy in different ways.
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Home Solar Hot Water Systems
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Home solar power hot water systems are the most cost-efficient use of solar energy. They can be up to one-fifth the cost of PV solar panels used for generating electricity. Solar hot water systems operate on the simple basis of exposing circulating water to the sun's rays and thereby absorbing the heat. In virtually all cases, an insulated storage tank for the heated water(normally sited inside the home) is required. Many homes will already have these, unless it is a home using an instant hot water system powered by gas or electricity.
There are two main types of solar water heating systems on the market:
- Passive - which relies on gravity circulation of water (on the principle that cold water rises)
- Active - which relies on electric pumps to circulate the water
In regions with severe winter temperatures, it may be necessary to inject non-freezing fluids into the system. (Your supplier or installer can guide you as to what is best for your situation.
For a daily production of 80- 100 gallons of hot water, recent estimates put the cost of system installation at between US$2,500 - $4,000 in the US and GB£2,500 - £4,000 in the UK. (You might well ask why the UK is twice the price of the US!) Prices of systems relying solely on gravity circulation are naturally cheaper.
Payback time really depends on the cost of heating water your water now, that is what your local electricity or gas supplier charges. However, it will be a much shorter time than solar panels for electricity generation. Some estimates suggest payback within five years, but make your own calculations to be certain.
Savings generated by making the switch to a solar hot water system have been estimated between 50% and 85%. (On average, heating hot water is about a quarter of your energy bill.)
The most commonly used equipment for generating domestic hot water is based on the "flat plate collector" technology. A flat plate collector is an insulated metal box with a glass or plastic cover and a dark-coloured absorber plate. The water flows through tubes close to the plate and is gradually heated as it circulates.
A technical description on this and other solar water heating technologies is available.
It is normal practice for the insulated storage tank to be a dual fuel system, that is, if the solar system is unable to meet your needs, say in case of sudden high water usage or longer periods of darkness, it can be supplemented by more conventional methods.
Two roof-mounted flat plate collectors
As part of determining what system is best suited to your needs, you should take advice from local installers. You also need to calculate your normal hot water consumption, such as the number of occupants, the number of appliances using hot water. A married couple, for example,would probably have a different consumption pattern from that of a family of four.
You need to have an area of flat roof, ideally sloping at an appropriate angle towards the position of the midday sun. There should be no likelihood of the collector plate being put in the shade by adjacent buildings or trees (and remember, trees keep growing).
While a competent amateur might be able to install a home solar water heating system, this job is best left to the professional installer who will know what is best for your location. Look for one who is a member of the appropriate trade or regulatory body. If you are looking for a grant to contribute to the cost of a system, it is likely it will be a requirement that you use a qualified installer.
There is currently more excitement about PV solar panels for generating electricity - probably because it seems sexier than the hot water system. However, the technology involved is more complicated, it is currently subject to fairly significant developments and improvements, and, for the present, it is expensive both in up-front costs and its long payback time.
That doesn't mean you should not consider it. The universal rise in the price of energy, the limited supply of non-renewable energy sources, as well as issues over security of supply, means it is increasingly likely to become an economical option.
Learning the terminology is one of the first barriers to overcome in learning about generating electricity from the sun. Here's a beginners guide to some of the key words:
- PV or Photovoltaic - a photovoltaic cell is a device that converts light energy into electrical energy. You really don't need to know how that happens, but if you really do, then click_here.
- Solar cell - normally synonymous with photovoltaic cell
- Solar module - a set of solar or PV cells
- Solar panel - a set of solar modules
- Solar array - a set of solar panels
The list above specifies the component parts of a traditional solar power system that would be found on a house roof.
However, nanotechnology and other research is changing the future of the solar industry, which need be no longer reliant on silicone:
- Organic solar cells - made of plastic which are flexible and could be applied like paint.
- Thin film solar - capable of being mass-produced by the roll and laid on your roof or alternatively, is your roof.
- Dye sensitised solar cells - still in the development phase, but expected to be a tenth the cost of conventional solar panels, with the ability to produce electricity from tinted windows as well as roofs.
- Polymers - another potentially cheaper and more simple alternative to silicon cells. Also still in the development phase, but offering the option of applying solar cells through printing or painting techniques
Thin Film Solar Cell
Excluding the systems using nanotechnology, there are two variants of PV solar systems on the market:
- Stand alone - Some of the earlier pioneers in the application of PV solar power systems for home use were people, usually living in country areas, who were not linked to a local grid. Because they wanted much of their power for the time when the sun wasn't shining, it was necessary to store the power in batteries, on the same principle as a car starter battery. However, these were, and still are, very large batteries and are probably not compatible with the urban environments, where the push for renewable energy is now coming from.
- Grid linked - The alternative is to have a system that is linked to your local grid. This means that during the day, when your power consumption is probably less than the amount you are generating, you can sell power to the grid. In the evening, you can buy power from the grid.
The efficiency of solar cells to convert light energy to electrical energy is constantly being improved. Because they are converting light, not heat, they are suitable for use in all climates. While the light may be stronger the nearer you are to the equator, if you enjoy long summer evenings where you live, you can be generating electricity up to 18 hours a day!
The cost of a home solar power PV system is very dependent on how independent you want to be, how much power you use on a daily basis and how much roof space you have sited at the correct angle. Systems can meet varying amounts of your average daily needs
Recent estimates of grid linked systems that would meet up to 60% of the average home's electricity needs are US$15,000 - $40,000 in the US and UK£10,000 - £25,000 in the UK.
Payback time is often quoted as being around 20 years. This will depend on your level of consumption and level of generation.
Savings generated are difficult to calculate as there are many variables, such as the cost of electricity you have to buy from the grid and the price the grid will pay you for electricity you sell back. What no one knows is the long-term price of electricity, but if that continues to rise, then you will make savings. For many, it may continue to be cheaper to be supplied solely from your local grid in the short to medium term.
PV modules can be supplied in a solar array fitted to the house roof or erected in the yard. They can also be supplied in the form of roof tiles. Watch also for new developments arising (see above under nanotechnology).
You will also require an inverter and mew meter (if linking to the local grid) and a solar power monitor.
As part of determining what system is best suited to your needs, you should take advice from local installers. You also need to calculate your average electricity consumption.
You need to have an area of flat roof, ideally sloping at an appropriate angle towards the position of the midday sun. There should be no likelihood of the solar array being put in the shade by adjacent buildings or trees (and remember, trees keep growing).
While a competent amateur might be able to install a home PV solar power system, this job is best left to the professional installer who will know what is best for your location. Look for one who is a member of the appropriate trade or regulatory body. If you are looking for a grant to contribute to the cost of a system, it is likely it will be a requirement that you use a qualified installer.
Heating a swimming pool uses the same general principles as heating your domestic hot water supply. If your plot is big enough for a pool, it may be big enough for a separate free-standing system which need not be on the roof of your house.
As a guide for calculation purposes, the area of solar panels should equate to between 30 - 50% of the pool surface area, more if the pool is in an especially exposed location. They should be installed in a sunny position the midday sun.
In a typical system the solar panels are linked into the filtration circuit, making use of the filter pump. Filtered water passes through the panels ahead of any heater, allowing free solar energy to be used first with back up heating only cutting in when a further boost is needed. For solar panels to achieve optimum efficiency there should be some form of automatic control to ensure that pool water only passes through the panels when there is a solar gain available.
Austria and Switzerland have already outlawed any other means of heating outdoor pools and Americans use solar energy for heating pools more than anything else. Payback time can be as short as two to four years (pools being expensive to heat by conventional means) and can extend the swimming season by several weeks.
A range of products are now on the market which enable you to use solar energy to power battery-driven external lighting and security installations. Next time you are installing or replacing these items, consider the viability of a solar-powered version instead. Check out some products or suppliers here.
The good news is that you don't have to invest in your own solar systems to power your home. In some industrialised countries, energy suppliers now have to produce a percentage of their output from renewable sources. In Canada, the US, Spain, Portugal and above all Germany, some ambitious projects are in place or under development to produce electricity from the sun.
If your electricity supplier is not involved in this yet, you should ask them "Why not?". In the UK, some suppliers are already producing 100% of their supply from renewables, but so far, developments there are low scale compared to continental Europe.
Check for Articles on this topic.
A solar energy complex in Bavaria, southern Germany,
run by Berkeley's PowerLight Corp
If you've not read them already, we suggest going to these pages on this website as well:
How much does it cost?
Can I get a grant to help pay for it?
How do I sell surplus power back to the grid?
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Updated 24 August 2007