Solar power for homes: sizing residential solar energy systems.

Residential Solar power is increasingly becoming a preferred solution towards green living and utilizing renewable energy for homes. Whilst purchase and installation costs continue to remain at high levels, various national subsidy schemes, such as investment subsidy funds, electricity feed-in tariffs and tax incentives, aim at promoting such applications by reducing their investment costs.Through these financial incentives and with cost-reductions achieved by technological progress, solar power systems are gradually becoming economically viable for homes.

Residential Solar Power Systems

Residential solar power systems can help reduce running energy costs by providing “free” solar energy in place of “paid” energy bought from the electricity grid (electricity bill); thus solar generated energy can cover a portion of your residence’s energy needs. Sources of solar power include solar thermal systems (using solar radiation to provide hot water for either hot-water-consumption or household-heating), or photovoltaic systems (converting solar energy (sunlight) to electricity for either directly powering electrical appliances or ‘selling’ electricity to the electrical power grid – feed-in-tariffs). In this article we focus on photovoltaic systems for houses.

Before attempting on any residential solar installation it is important to address certain issues such as assessing your household energy needs, establishing location-environmental data (solar radiation) and estimating the appropriate size the solar system.

Checklist to home solar panels

In general, the following steps can act as a guideline:

  1. Assess your energy needs: You can estimate your energy needs by referring to your energy bills. It is advisable to gather data of at least 12 consecutive months, or more, (on an annual basis) so as to have a good representation of your actual needs throughout the year (covering all seasons).
  2. Monthly energy consumption:  From observing your electricity bills you can keep a clear, easily accessible record of your monthly consumption figures (in kilowatt-hours Kwh).
  3. Average monthly consumption: From recorded monthly figures you can derive your average energy needs per month (which is total consumption, i.e. sum for 12 months, divided by 12.  It is always a good idea to also keep a record of your lowest and highest consumption figures (Kwh and month) so that you develop an understanding of your energy demand and a sensitivity towards reducing them over time.
  4. Location Solar Radiation Data: Find the typical duration of sunlight (in hrs) at your location (country and town) over a period of 30 days.   This number is normally expressed in hours of sunlight over a period of 30 days (e.g. 150 hrs of sunlight in 30 days). Alternatively, you can find this figure expressed as Mean Solar Radiation or Daily Average Solar Radiation. Such information can be found from National Environmental or Meteorological Agencies or Solar Radiation Resource Maps.
  5. Appropriate size of Solar system: By dividing your average monthly consumption (Kwh) by the average monthly sunlight hours (hrs) at your location you get an estimate of the size of solar panels (kw) you should be looking for.  Similarly this can be computed on daily-figures instead of monthly-figures, provided that you keep a common basis (monthly or daily). For example, a house with monthly average consumption of 350KWh in a location with Mean Solar Radiation of 150 hrs per month would require a system of 2,33 (say 2.4) kilo-watts (i.e. 350/150). However, it is essential to understand that these figures are derived on an “average-basis” over a period of 12 months. Thus, the capacity of 2.4 kw surely will not be adequate, at all times, to cover for energy demand spikes or during cloudy days of limited sunlight. To compensate for this fluctuation one needs to consider increasing the power potential and/or installing energy storage (batteries).
  6. Number of Solar Panels: Once you have established your power capacity needs (kw) you can start looking at different solar (photovoltaic) panels; note that different brands or technologies exhibit different solar behavior.   In evaluating potential solutions you should consider various factors such as: installation and other costs, solar panel efficiency and rating, system connectivity (e.g. for storing energy), estimated (or guaranteed) product life etc. For example, if you are looking at 100-watt solar panels, it means that you will need 24 panels to build a capacity of 2.4 Kw (2400W/100W – you may wish to refer to our article “Solar Market: Chinese solar imports Vs US solar industry“).

In general, one should decide on what percentage of household’s energy demands (Kw h) is aiming to cover by solar energy panels and adjust these energy figures accordingly.

Finally, it should be made clear that the above steps are given as a brief guide and that numbers used are ‘simplistic numbers’ to illustrate the general idea.  Hopefully, they will provide a better understanding in assessing potential solutions and for discussing with energy contractors.