What Can Solar Panels Power in My Home ?
Whether a solar electric system can entirely replace the utility grid and meet your daily energy needs depends on your daily consumption.
If your home is already connected to the utility grid, replacing completely the utility with a PV system might NOT be cost-effective.
Offsetting a part of your electrical bills through a solar system however could be the best way to save money on electricity.
While you take your connection to the local utility grid for granted, solar produced electricity is more expensive because your costs for solar electricity production are higher than the costs of your utility grid for producing electricity.
Therefore before implementing a solar system you should try to reduce your daily electrical consumption. You should start with increasing energy efficiency of your home or office. Achieving energy efficiency means reducing electrical consumption and your monthly electricity bills respectively.
Yes, saving energy is less expensive than producing energy. By improving energy efficiency the cost of the photovoltaic system you are going to install will be reduced.
Electrical heating appliances (dishwashers, washing machines, electrical boilers, tumble driers) are not recommended to be powered by photovoltaic systems.
For each heating appliance you should find a proper both energy-efficient and cost-effective alternative. As a matter of fact, heat is always an expensive source.
Actually you could power all those devices by solar electricity. You will rarely see anyone do that however since heating devices are known as ‘power-hungry’. This means that powering heating devices by photovoltaics turns out to be very expensive.
Calculating your daily consumption
Calculating your daily electricity consumption is a step to both reaching energy efficiency and implementing a solar electric system.
Since an off-grid is not connected to the grid, it is irrelevant to talk about offsetting a part of your energy consumption to the PV system. The PV system should be able to meet all of your daily energy needs.
Calculating your daily electrical consumption means performing a load analysis – determining your daily electrical energy consumption in Wh (or kWh).
Performing a load analysis is very important since your PV system should be neither oversized (=waste of time and money) nor undersized (=useless for you).
By looking at the list of devices and consumed energy, you will get the idea which of them consume the most energy and either think about ways for reducing the consumption or discuss possible alternatives.
Example: AC loads table for a summer house:
Total power = Rating x Qty
Average daily use = (Total power x Hours use per day x Days of use per week) ? 7 days per week
If we assume a value of 0.92 for inverter efficiency, and the total average daily load is 0 (i.e. no DC devices are used), the daily energy target is calculated by the formula: Daily energy target = = (Total average AC load ? Inverter efficiency) + Total average DC load = = (1,646 ? 0.92) + 0 = 1,789 Wh = 1.789 kWh
Instead of doing these calculations this manually, you could automate the process by our Load Analysis Tool. Click Here to Learn More About this Tool
The Load Analysis Tool performs all the above calculations. Thus you can directly use the values obtained in off-grid system basic evaluation.
What to do if your daily consumption is too high?
If your daily consumption of electricity is more than 2.5 kWh or if you live in a region with poor sunlight for long periods, a purely photovoltaic off-grid system cannot meet your energy needs. In such a case hybrid systems are recommended.
A backup power generator modifies a stand-alone (that is, purely photovoltaic) system into a hybrid one.
You could actually do without a backup generator in a photovoltaic-only system but at higher cost – by oversizing your stand-alone PV system and choosing a battery bank with very large capacity.
Such a strategy however is highly impractical for two reasons:
• Extremely high initial cost on batteries
• Such a system will work with maximum performance just a few months a year (probably in winter) while in the rest of the time it will work far below its maximum efficiency. Therefore the value of the electricity produced will be probably not enough to cover the expenses needed for maintenance support of the battery bank.
A hybrid system is a combination of photovoltaic generator and alternative power generator operating by wind or fuel. Such a generator charges the batteries upon lack of sunlight and is used either as backup or in case the PV system alone cannot meet specific energy demands.
Here is a simplified view of a hybrid system:
Here are the advantages of a hybrid system:
- Electricity is available at an acceptable cost during long periods of cloudy/rainy weather or in winter
- You can power some of the power-hungry devices (not all however!) in your house
- You could buy smaller (less expensive) battery bank and inverter
What about the disadvantages of a hybrid system:
- Additional costs required for fuel and maintenance
- Higher costs for buying fuel generator and bigger battery charger
So, when you should buy a hybrid system rather that a purely solar electric one:
- When sun is not enough during some months of the year, so a PV system cannot cope alone with your energy needs
- When you want to lower your initial costs
- When the access to your house is difficult and/or expensive
- When maintenance costs are not a problem
- When you demand that electricity must be available all the time
So, if you live away enough from a utility grid, and you consider buying a stand-alone PV system, first of all you should answer the following questions:
- What applications do I need to power?
Above all you should mind that a PV system is not economically beneficial to be used for powering heating appliances. Therefore you should find a good alternative solution for heating, cooking and refrigeration.
- Have I already made your building energy-efficient? Are my loads as efficient as possible?
- Do I live in my house during all the year, or just during certain seasons?
If you live in your building in winter and your energy consumption is as much as in summer, a more cost-effective solution would be a hybrid system.
It will reduce your initial costs on batteries and, most probably, PV modules.