Do-it-yourself DIY solar panels are said to be the lowest cost option for installing solar panels.
Making solar panels at home is simply not as easy as described in books and articles. While you may have watched YouTube videos and read all sorts of how-to guides, the construction of solar panels does require a certain level of skill to create a high quality, effective, and safe product. Homemade solar panels are NOT recommended for use in systems that require high wattage/voltage/current, including those for powering an entire household. Here are the reasons:
1) Shorter lifespan and much faster efficiency degradation than manufactured solar panels. Unless you are able to encapsulate your solar cells effectively, water will infiltrate the product and over time, the panel will degrade. This means that your DIY solar panel could have a lifespan of only a few years.
Just compare this to the common 25-year lifespan of factory-made panels, combined with a 25-year performance guarantee! What is more, the possibility of a hailstorm damaging a branded solar panel is rather low.
This, however, is not true for a DIY solar panel. Manufactured panels have been designed to withstand the various elements whether it is hail or snow — DIY products simply do not have the same level of detail.
2) Could be a fire hazard resulting from poor quality soldering, especially when combined with the high voltages that occur when connecting several panels together in a string. Many of the DIY solar panel systems fail to address safety. Homemade solar panels should not be made using wood and/or plastic due to the potential for electrical short and resulting fire hazard.
3) Lack of proper certifications. This means that:
- You cannot connect your house to the grid, since homemade solar panels are not compliant with the applicable electrical codes.
- You cannot apply for a government rebate or incentive.
- If a DIY solar panel ignites, and this results to fire damage to your house, your insurance company will not pay up an indemnity for a fire caused by a solar panel with no UL certification (for the US).
- Furthermore, since DIY panels are not certified, mounting them on any insured structure will void the insurance policy on that structure.
DIY panels are NOT a viable alternative to factory-made solar panels when it comes to:
- Having a safe and reliable solar electric system
- Cutting your electricity bills
- Qualifying for rebates and government incentives
There are countless green websites and DIY books full of stuff that seems to work. The question is, how long will such a solar panel system last when exposed to the weather? If you’ve never done DIY before and you’re now taking your first exciting steps in photovoltaics, solar panel assembly is not a great place to learn electrical wiring and soldering. Above all, you need some real practice, rather than starting out by damaging your solar cells with an idea to make a cost-effective, working solution!
Evaluating a solar panel system based on DIY solar panels
On the next pages, you will learn how to estimate whether it is worth investing in DIY solar panels and a DIY solar panel system.
We are going to calculate:
- The price of building the DIY solar panels yourself
- Overall system cost including the solar panels and the rest of the solar panel system building blocks needed
- Annual maintenance cost of your solar panel system.
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Let’s consider the following example of a PV system built of DIY solar panels. The solar panel system should provide 200Wh daily for area of PSH (Peak Sun Hours)=3. Peak Sun Hours (PSH) is a measure of the available daily solar resource. PSH are also known as ‘insolation’ and depend on the specific geographic location. Please, do not mistake Peak Sun Hours with available sunny hours!
For example, 6 available sunny hours on a bright sunny day might only translate into 4 PSH for that day.
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The system is comprised of the following components:
- Solar panel
- Charge controller
- Wires to connect the solar panel to the charge controller, the battery and the loads. The system voltage is 12V.
A solar electric system with DC loads We are interested in and we are going to calculate the following key values:
- Installed peak power required, Wp
- Minimum capacity of the battery bank required, Ah.
The installed peak power is calculated as follows : Installed peak power, W = = Daily energy consumption, Wh ÷ PSH ÷ System efficiency Where: — Daily energy consumption is the daily averaged or daily peak electricity consumption in Wh, — PSH is the Peak Sunny Hours value at the system location in hours, — System efficiency is the efficiency of the solar panel system. For a stand-alone PV system, the system efficiency is usually evaluated at about 0.6–0.67. If the daily energy target is 200Wh and PSH=3 (see above), then: Installed peak power, Wp = 200Wh ÷ 3 ÷ 0.67 = 100Wp The minimum required battery bank capacity is :
Battery bank minimum capacity, Ah = = (Daily energy consumption, Wh x Days of Autonomy) ÷ Depth of Discharge ÷ Cable Losses correction factor ÷ System voltage, V Where: — Daily energy consumption is the daily averaged or daily peak electricity consumption in Wh; — Days of Autonomy (DoA) is the desired number of consecutive days that we would like the battery bank to power the load in case of a complete lack of sunshine; — Depth of Discharge (DoD) defines up to how much percentage the battery bank should be discharged, i.e., 100%=empty battery bank and 0%=full battery bank); in the formula the decimal value rather than the percentage should be used; — Cable Losses correction Factor is the overall system losses due to cable resistance in %; in the formula, the decimal value rather than the percentage should be used. — — — — So, if we assume: › Days of autonomy = 3 › Depth of discharge = 0.8 › Cable Losses correction factor = 0.97, then for daily energy consumption 200Wh and system voltage 12V, the minimum required battery bank capacity would be: Battery bank minimum required capacity = = (200Wh * 3) ÷ 0.8 ÷ 0.97 ÷ 12V = 64Ah So the system should comprise: a 100Wp solar panel for system voltage of 12V, a charge controller and a 64-Ah battery bank of 12V.
In addition, we need a 7m-long wire of a 4-mm² cross section for connecting the solar panel to the charge controller. The next step: what kind of charge controller to choose? Since we are building a low-power low-cost system, we are going to use a PWM controller. We have a 100Wp solar panel for a 12V solar panel system. Therefore, we need a PWM controller with rated current of 100 W ÷ 12 V = 8.33 A We should enter a safety margin of 25% to account for the changing solar panel output depending on the temperature. Therefore, we need a 12V PWM controller with rated current not less than 1.25 * 8.33 A = 10.4 A If you want to conform to the National Electric Code (NEC) standard, you have to “de-rate” once again the received value by 25%. Therefore, the current should be modified as follows: 1.25 * 10.4 = 13A You should, however, take into account that some of the established brands, e.g., Morningstar, give for a PWM controller’s rated current the de-rated value, which accounts for a 25% additional increase.
Please, carefully check this in advance because in such a case you should only multiply the rated current by 1.25, in order to adhere to the NEC standard applicable for the USA. Furthermore, the standard recommends performing such calculations by using the solar panel’s short circuit current (Isc), rather than by using the presupposed working current we’ve calculated in our example so far.
For such a purpose, you should have a solar panel’s datasheet at your disposal. If you do not have such a datasheet available, you could use the method described above to determine the charge controller current, by dividing the solar panel rated wattage to the system voltage.
Also, don’t forget that in case of several solar panels being connected in parallel into a solar array, the resulting current of the array is a sum of the currents provided by each solar panel. So, if you consider our example, in a case of such ‘already de-rated’ charge controller, its current rating must be greater or equal to 10A. Why do you need two de-rating coefficients of 25%? The first de-rating coefficient ensures that the charge controller will withstand any instantaneous changes in the solar panel’s current because of constantly changing ambient temperature and solar irradiation. The second de-rating coefficient ensures that the charge controller will withstand the continuous load of the increased solar panel current for three hours or longer.
Therefore, you have to multiply the solar panel’s current by 1.25*1.25=1.56. Don’t forget, however, that in the case of an already de-rated branded charge controller, you should only multiply the solar panels current by 1.25, in order to comply with the NEC standard. What is more, in such calculations it is recommended to use the short circuit current (Isc) of the solar panel or the solar array, instead of forecasted solar panel’s nominal operating current.
Now, let’s summarize. In our example, if you choose to use a brand charge controller whose current has already been “de-rated,” you need a PWM charge controller with rated current greater or equal to 10A. Otherwise, you need a charge controller with rated current greater than or equal to 13A. The price of such a branded PWM controller is about $40. Actually, on eBay, you can find a cheaper PWM controller from a less reputable brand for around $15, but this will be at the expense of non-guaranteed performance characteristics and eventually shorter battery life. The choice is yours.
Now, let’s calculate the materials needed for building the solar panel.
If you are aiming at the lowest cost solution, you have to build your panel out of polycrystalline cells. One polycrystalline cell typically gives 0.56V and about 6 to 8 Amps of current, depending on the cell grade/quality. Mind that the higher the quality, the higher the current. Therefore, if you connect 36 cells in a series, you will receive a panel of voltage about 20V and current of about 6A, which translates into about 120Wp of power. The 20V panel output will guarantee that under all operating conditions, the panel output voltage will be high enough to charge the battery bank. To assemble that solar panel we need:
- 36 polycrystalline cells — $40 (on eBay)
- Wiring kit — $25 (includes a tab wire, a bus wire, a flux pen, a junction box with Schottky diodes) — sometimes is provided as a bonus, if you are lucky.
- Clear Plexiglas or low iron solar glass — $40
- Plywood panel — $25
- Paint, stainless screws, wood for frame — $10
- Your dollar time value to assemble this panel (this is your hourly pay rate from your employer) — $X. Total cost = $140, excluding your dollar time value, plus the price of additional cells you need in case of breaking some cells while assembling them. If you are inexperienced, you’ll inevitably break some of them — don’t fool yourself! You can, however, find similar first-hand panels for $160-$180 with 25 years of warranty. This information is just for your records.
Therefore, the total price of the system is $3.9 per installed Wp. Let’s assume a lifecycle of 25 years of operation. We are going to calculate the system’s annual maintenance costs . The system contains a battery and a charge controller, so we need to calculate: › The battery’s annual maintenance costs ›
The charge controller’s annual maintenance costs. A lead-acid battery has to be replaced every 5 years of operation. Let’s assume that the battery bank cost, stated by the solar vendor, is $3 per Ah. In addition, the battery cost for the first 5 years is included in the system’s cost. If the stated battery cost were $3, then for the next 20 years of the system lifecycle, the costs for a battery bank of 64 Ah would be: 64 Ah * (20 years ÷ 5) * $3/Ah = $768 Such a cost, distributed over the remaining 20 years of operation, will result in average battery maintenance costs per year as follows: $768 ÷ 20 years = $38.4/year
Furthermore, for a PWM charge controller of $40, which is not likely to be replaced during these 25 years, the annual maintenance costs would be: $40 ÷ 25 years = $1.6/year Therefore, the total annual maintenance costs would be : $38.4/year + $1.6/year = $40/year
Consequently, the estimates show that annual maintenance cost of this system is about $40, upon assumed 25 years of operation.
And that’s all you need to know what you are making DIY solar panels !