Reduce Your Electrical Bill – Solar and Battery Calculations for Residential Use

It’s that time of month again. You open your mailbox (or for the more progressive, your email) and find the most dreaded of bills – your Hydro bill.

For many home owners they accept the fact that they will have to continue to pay for this utility. Yet there is another group that is quietly exploring alternatives. These people are looking at ways they can generate their own power and reduce – or in some cases eliminate – their reliance upon the electrical grid.

The solution this article explores is the combination of solar PV (photovoltaic) and small scale battery storage to generate and store the power that the household needs. To be upfront, there is a cost of exploring this alternative – however it is one that will benefit you and your family long into the future. By installing a solar array on (or if you have the ability) near your house you can generate power. This power is then stored in a series of batteries that can be ‘drawn on’ when needed. Through inverter technology your array can prioritize demand to draw from batteries before the grid is utilized.

Depending upon the amount of power you use, and the number of solar panels and batteries you install your payback can come as quickly as 6 years by using equipment that will operate for well over 20 years (meaning approximately 14 years of ‘free’ power through the installation of a system). Sounds interesting, doesn’t it? But where do you start?

If you are trying to calculate how much ‘solar’ you will need there is some simple math you can perform. If you look at your utility bill you’ll see an amount of power that you used. This is shown in kWh. Your bill may also show you your usage in kWh for the last year.

There are two ways to look at this. Firstly is the average of your usage over the twelve months. Using this method will result in designing a system that will result in periods where the power generated will not provide enough to power your entire home but it will average out over the year. The second way is to design for your ‘peak’ usage – in most residences this will be during the summer when air conditioners and pools are driving up electrical costs. In this case you may produce too much power and end up ‘giving back’ some power to the utility once your batteries are fully charged. In both cases you want to calculate the average daily usage in kWh. For illustration purposes let’s assume you need to produce an average of 30 kWh per day.

To determine the number of panels we need to take the daily kWh usage and divide it by the number of hours of sunlight. If we use seven hours for the purpose of calculation we would have 30 kWh divided by 7 hours or 4.29 kW from your solar array. If you are using 250 w panels in your array, the following formula would apply: 4.29 (kW) divided by 250/1000 (kW) or 17.1 panels would be needed to offset 30 kWh per day in *ideal* conditions.

At this point you need to be sure your roof or ‘area’ can accommodate 18 (you can’t have 17.1) panels and that it would receive seven hours of sunlight a day and there are no obstacles blocking the panels.

Your best bet after performing these simple calculations is to locate someone that can assist you with the engineering and calculations as well as the implementation of your project. Completed properly this solution could remove – or at the least drastically reduce – your power bill.