Primary Design Specification

 

Energy and Power Assessment

MyEcoFuture is a ‘Turnkey Solar Solutions Company’ doing custom solutions accurately addressing the requirements of our customers. To do an acurate design we need to know your power and energy requirements…we need a design specification. There can be many components to a complete design specification, but we require at least the 3 primary parameters.

 

  • The energy used per 24-hour day indicates to us the amount of energy the solar panels are required to harvest per day. This defines the quantity of solar panels that will be required.
  • Total energy used during night-time indicates to us the amount of energy the battery needs to store. This defines the size of the battery required.
  • The Peak Power demand defines the maximum capacity/size of the inverter.



 

Each of the primary design parameters enable us to accurately select the correct size and quantity of components for your custom designed solutions. Many inexperienced solar installers simply assess your Eskom utility bill and do a design on the average energy used per day. This shortcut ignores assessing the size of the battery (expensive!) and the size of the inverter(s) required. Two of the primary and most expensive components of a solar solution, the battery and the inverter, are sized with no more than guesswork!

The 3 Primary Design Specifications

 

Param 1

24 Hour Energy

Param 2

Night-Time Energy

Param 3

Peak Power Demand

There are a few approaces to the ’24-hour’ energy parameter. Is this 24-hour energy for the entire household (Grid Independent), or only a selected few (Backup) items?
Off Grid (Grid Independent) Backup
The term ‘off-grid’ is loosely used, and can have different meanings. We prefer to use the term ‘Grid independent’ when referring to residential solutions where Eskom/Grid power is available. These solutions are usually more expensive and requires the solar solution to power all the electrical power users in a house. This includes a stove, geyser(s), heaters etc which use large amounts of energy. The easiest and most accurate way to determine the 24-hour energy consumption of a building is to install an energy monitor and record actual data over a period of time (usually 7 days). This recorded data must then be analyzed to calculate the average energy demand in 24 hours. If a backup solution is required, it usually involves separating the “essential items” from the not-so-essential items in your house. Typically, the essential items will include all your lights, a fridge, microwave oven and maybe a TV. The remaining ‘heavy’ energy hungry appliances (stove, geyser, tumble-dryer, under-floor heating etc) are excluded from the backup solution. The only way to determine the 24-hour energy requirement of this backup solution is to mathematically calculate the energy need. We will complete a comprehensive list of items/appliances and the duration each is to be used, in consultation with you, to calculate the 24-hour energy need of your house.
The only way to determine the size of the battery which will get you through the night, is to quantify the required energy. The battery will probably contribute between 20% and 50% of the total cost of your solar solution, and it is also the only component that is a consumable item (it is ‘used up’ in a relatively short life), so it makes good sense to accurately determine the size of it! Fortunately, if the procedure for the 24-hour Energy is followed as outlined in column 1 to the left, this data is readily available. Important to note, is that ‘night-time’ could be from 16h00 to 08h00 in Gauteng during winter months. Be careful to plan for winter too! Peak Power demand is a function of ‘how many things are on at the same time’? The more appliances that are used concurrently, the more power the inverter needs to be able provide at any one time. An example will be the concurrent use of the dishwasher, tumble dryer, washing machine and electrical iron. This scenario will require an inverter that can deliver 8kW. Fortunately, most energy monitors are capable of recording peak power, and the mathematical model referred to in column 1 will reveal this parameter.