In order to ensure that your energy needs are met, it is important to recognize that the components of a system have to work together. As a follow up to the previous post on solar system design, brief introductions to the following components are provided below:
Loads
At the beginning of the system design process, it is necessary to examine the various items that will require energy from the future system and to determine their total consumption. Understanding your energy consumption will be essential in designing a system of an appropriate size. Loads may include anything from lights and stereos to water pumps and microwave ovens. When exploring each of your loads, consider the following:
Does the item require AC or DC power?
The nature of the loads should be explored to make sure that power of the necessary type (AC or DC) is available in sufficient quantity.
What is the total consumption of the item?
Determine the watts consumed by each load. Then, estimate the number of hours per week that each load will need to run. For each load, multiply the watts consumed by the hours run per week. This calculation will provide you with watt hours per week for that load. Find the total weekly energy required from the system by determining the sum of all of the weekly consumptions for the individual loads.
Power Source
(i.e. Solar Photovoltaic Panels, Wind Turbines, Fuel Generators, Etc.)
The mix of power sources that is ideal for you will depend upon your needs, but also upon the resources available to you.
After analyzing loads and usage patterns, knowledge of the amount and intensity of wind and sunshine at your location will allow you determine the appropriate type and capacity of your ideal power source. At Glenergy, we generally design so that the daily production calculated is about 1.5 times the estimated daily consumption. This factor covers the various inefficiencies in the system. In residential systems, we definitely recommend the inclusion of a fuel-fired generator to provide power when the batteries are depleted from an extended period without renewable energy availability.
Energy Storage (Batteries)
Most alternative energy systems require batteries to store energy. For the most part, lead acid deep cycle batteries provide the best price/performance among the batteries available on the market today. These batteries come in a number of varieties including: flooded, sealed, gel or Absorbed Glass Mat (AGM).
Size really does matter! Batteries are the heart of the system so it is important to make sure that they are big enough. A reasonable “rule of thumb” is to provide rated capacity equal to a week’s consumption. For example, if your total weekly consumption is 1200 Wh/week, then a battery of at least 100 Ah at 12 V (W = A x V / Wh = Ah x V) would be required. A battery bank of this size should provide approximately 3 to 4 days of reserve capacity. In order to keep batteries in top condition, we design systems such that the batteries will not need to be brought below 50% of their capacity.
Power conversion and distribution systems
In the alternative energy world, it is often necessary to convert direct current (DC) from batteries into alternating current (AC) to run appliances. The tool used to achieve this conversion is called an inverter.
While some appliances require the very high quality AC power provided by sine wave inverters, many devices can function very well with less expensive square wave or modified sine-wave inverters. Less expensive inverters tend also to be less efficient and generally do not offer additional features such as automatic generator starting, load transfer or battery charging.
In some cases, it is possible to meet energy needs without an inverter by switching smaller loads to DC. A 12V DC system, particularly for lighting, can help you to avoid the relative inefficiency or expense of an inverter.
Charge controllers
Charge controllers are used to manage the charging of batteries and, sometimes, the discharge of batteries by the loads. Charge controllers vary widely in effectiveness, options and price. Many models include metering systems to display such things as current from the solar panels, current to the loads, battery voltage, etc. There are versions that include technologies such as Pulse-Width Modulation (PWM) or Maximum Power Point Tracking (MPPT) that optimize the charging of batteries from solar panels. Some models can manage both wind and solar charging. At Glenergy, we carry a number of different charge controllers to suit the diverse needs of our customers.
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