If you want to produce renewable and free electrical power using solar energy, here’s a list of things you absolutely need.
1. Solar radiation
It’s obvious, right? No, it’s not! Not for many people!
Solar radiation is everywhere, but not everywhere it’s enough to produce electricity using solar photovoltaic module. All the modules are described by one most important parameter — output power, for example 200 Wp — 200 watts (peak). The peak subscript is used to specify that the solar module won’t produce that power at all time, but only in specific conditions. Those conditions are:
- solar radiation intensity — 1 kW/m²,
- radiation spectrum similar to the one reaching ground at 35°N lattitude in summer,
- temperature of solar panels equal to 25°C (77°F).
Without using solartracks you won’t have that solar radiation intensity except for a very brief moment during the day. So you shouldn’t expect your solar module to produce the peak power during the whole day.
If you live in Europe and want to see whether solar photovoltaics is a good idea for you, check this great PV potential estimation tool, prepared by the European Commission.
2. Solar photovoltaic panel (module)
The core of solar photovoltaic system is the panel, consisting of several solar cells. The cells are connected in series and in parallel to attain the desired voltage and power. Connecting cells in series increases the voltage, while connecting them in parallel increases the current the module may produce.
Most solar moduls are said to produce 12V electricity, but to be more specific, they produce slightly higher voltage. It’s because they are used to charge 12V lead-acid (in most cases) batteries, and the voltage required to charge those batteries is above 14V. This voltage is the most popular because most batteries are produced for that voltage as well, and some systems are at this voltage. For example, your car has probably 12V battery and all the electrical devices, most RVs and campers have 12V as well.
The lower the voltage, the higher the current to produce the same electrical power. The higher the current, the higher the power losses in all the cables. And because of that if you don’t have a good cause to use 12V systems, use 24V or 48V systems. It’s easy to make 48V system — you just buy four photovoltaic panels and connect them in series, as well as four batteries, also in series.
Solar modules produce electricity when the sun’s shining. But you need the electricity mostly when it’s not — for example most people watch tv in the evenings. So you need to store it somehow.
There are many different methods for energy storage, but in small systems only one is feasible — batteries.
Batteries need to store energy not only during one day, but also for longer periods. It’s posible to have several days with no sunlight, especially in winter, so if you want to rely only on solar photovoltaics, you need to have large battery bank.
The capacity of batteries is measured in Ah, ampere-hours. 1 Ah is the capacity that allows the battery to produce 1 A current for the one hour, till it’s discharged completely. 1 Ah for 12V battery means 12 Wh — the amount of energy used by 12 W lightbulb during an hour. If you plan to purchase a battery bank, you need to convert Wh to Ah and back.
For example, if you use 1 000 Wh daily, and have 48V system, you would need total battery capacity of 1 000 / 48 = 20,8 Ah. But note that this battery bank would consist of four 12 V batteries, so you would have to buy four 12V / 20,8 Ah batteries, and not four 12V / 5,2 Ah batteries! The capacity of batteries is added up only when the batteries are connected in parallel.
If you’d like to extend your battery storage to, say, seven days, you would have to multiply the capacity calculated above by 7. And I must note here that it’s not healthy for the batteries to be completely discharged — their lifespan is highly increased if they’re not discharged much during the entire cycle, so I suggest to increase the capacity by the factor of 2-3 at least!
4. Charge controller
Solar charge controller is a small electronic device that does several very important things:
- protects the batteries from overcharging,
- also protects them from being discharged below the safe level,
- disconnects the solar modules at night (when they would drain current from the batteries).
Solar charge controllers are produced for specific voltage and current. So pick one that is suitable for your system.
Inverter is not absolutely necessary, but very useful. It transforms the DC (direct current) produced by solar system and stored in batteries to AC (alternating current) used in most household appliances. The electricity in the power grid is AC, so if you want to substitute the grid with your solar system, you should use the inverter.
It’s not absolutely necessary, because you can buy many appliances (lights, microvawes, TVs, etc.) prepared for DC. But since there’s at least three different voltage levels for popular DC systems (12V in cars, 24V in trucks, 48V popular in some stationary systems), you need to choose the appliance that would work with your system.
If you build your system from the scratch, it’s probably a good idea to use DC appliances, because the DC→AC transformation is not done with 100% efficiency. On the other hand, the DC has always lower voltage and thus higher losses than AC system. It’s important especially in Europe, where we have 230V AC grid, and less important in USA and Canada, as they have 110V in their sockets.
I will describe all the parts of the solar photovoltaic system in future posts.