There are several components to designing a Solar Powered stand alone power system and thus there are several ways to minimize the cost of the system! This article will talk about each component how it is sized and what your options are in each case.The average solar powered stand alone power system consists of the following components:
- Solar Panels
- Solar Controller
- DC / AC Appliances
Each of these can be optimized to the resource available (the amount of energy seen by the panel) and if the resource is not enough things like maximum power point trackers and generators can be added to the system. This will add further complexities however in some cases can lead to reduction in the number of solar panels and size of battery if one has access to petrol/diesel for a generator.
Starting with the DC/AC Appliances:
It helps to buy products with low surge factors, this is something that you should be able to ask about when you purchase the product from a store. If not, it is an answer that companies have to give consumers. Having low surge factor products in a home can allow you to have more appliances on at the same time or allow you to use a lower rated inverter. Using appliances that consume less electricity or have higher energy efficiency standards also allows you to save money on the battery bank and the array of solar panels because now you don’t need as much energy to be stored or generated.
Buying a bigger inverter allows you to leave room for new appliances that you might not have thought you needed at the time of installation. Usually there is a safety factor that designers and installers use but it is not very large and contracts will usually suggest what items they have accounted for in their design thus it might be useful in the long run to chose a bigger inverter.
The battery pack:
A common piece of advice not followed in industry is the use of parallel battery banks. Unlike parallel solar module arrays this is a bad idea given the irregular charge and discharge cycles that residential usage forces on batteries. This means there is a greater decrease in the lifespan of the battery pack and increases in the cost of wiring the batteries, and if the wiring is not done correctly it increases the system losses and might be the reason for the installer adding one or two more batteries ‘just incase’.
This is a tricky one to talk about without going into specific case studies and results. For the point of this article I can suggest that using a maximum power point tracker allows you to produce more power from your panels in low light conditions and in varying temperature. Thus using an MPPT can theoretically suggest the use of a lower number of modules but because the MPPT role is to regulate the charge flowing between the Solar Panel and the battery it would make more sense to down size the battery bank than to down size the modules, ensuring that your batteries are able to go back to full charge more often, a state of charge which is preferred in order to prolong the battery lifespan (especially because in most cases parallel battery banks are cheaper upfront than series battery banks).
There are two options here. Either oversize your modules so you won’t need a generator (usually in industry this is 1.3 times the load that needs to be provided based on the users consumption habits) or down size your panels and use a generator to charge the batteries for a certain number of hours a day, where a certain number of hours every month must be reserved for ‘equalizing’ the batteries.
Written by Prateek Chourdia
MEngSc – Photovoltaics and Solar Energy, UNSW
Solar Energy Analyst
© 2010 Solar Choice Pty Ltd