The planning of your solar system. Every solar installation should have a few guidelines and results are the best if these are followed.
- How to get enough power
- How to store that power
- How to use that power
How to get enough power ?
The so-called PV (Photo-Voltaic) panels come with a lot of specifications that might seem difficult, so we’ll just start on the most common, the rated power. That value is sometimes called “Watts” but it actually is “Watt-peak” also addressed as Wp.
So a 200Wp panel gives 200 Watts, but … the trick is into peak. The panel gives the rated power only at certain standard conditions. Another widely used value is efficiency. This is very nice but also only at certain conditions.
The best way to “calculate” actual output of your solar panel is finding out how many sun-hours you location gets annually and how muchs difference there is each month. The latter is only important is you plan to use your solar fully offgrid.
US averages can be found here:
On the top of that list it says Atlanta, Georgia with 2738 sunshine hours annually. As a guideline we calculate by dividing this number by 1950 and we get an easy to use number for future calculations. It’s 2738 / 1950 = approx. 1.4
This number, multiplied by our solar panel output of 200Wp gives the annual output in kWh (kilo Watt hours) like you find on you electricity bill. So 200 x 1.4 = 280Kwh Annually. This is not a set number, weather is not constant, but as an average this is pretty good handle.
The next thing that might be important is the ratio in sunshine hours in your a between summer and winter. In the summer you might have 8 hours of sun and in the winter just 2 depending on your location. So during the winter month you generate less power. The output of panels at colder temperatures is actually higher so that helps a bit.
How to store that power ?
Power is usually stored in one or more batteries. This only applies to offgrid systems of course. A good balance between the solar panels and the battaries is important. To much energy from the panels can cause damage to the battery. Not enough power from the panels might never fully charge the batteries. As a guideline please try to have a maximum current between 1/12 and 1/8 of the batteries Ah-value (Amphours). So a 100Ah battery should be charged between 8.3A and 12.5A max. Some batteries (dedicated solar batteries) can handle higher current so please check this in advance.
A few other very important things are:
- Maximum battery discharge
- Know that you need to put 50% more energy in than you take out.
Discharge, try to keep this under 20% a day (). That will ensure longer battery life, the lifespan is in cycles (charge and discharge) and will become rapidly less if discharge occurs to very low levels. Besides that, if you have a day with no sunshine the battery can still last you a few more days.
How to use that power ?
Power in the batteries can be used as low voltage DC of as regular grid-like 110V AC to use regular products. Low DC voltage, for example 12 Volts can be used to power anything that you can also use in a car or a motorhome. Daily stuff like lighting, laptops, USB-chargers for telephones and every other accessoiry you can think of.