For years, standard EVA was good enough for most solar modules. Then TOPCon arrived, and the rules changed. Researchers at UNSW found that EVA-encapsulated TOPCon modules lost output under damp heat mainly because of acetic acid from the EVA, which corroded the cell contacts (pv magazine). Suppliers have answered with three main options: low-acid EVA, anti acid EVA encapsulant, and EPE. Each one claims to solve the acid problem. But they work in very different ways, and they don’t cost the same.
At Raynex Solar, we manufacture both EVA and EPE encapsulant, and module makers ask us this question every week. Most of what you will find online comes from launch news and supplier promotions. This guide takes a neutral, test-based view instead. We explain how each option controls acid, where each one falls short, and how to check a supplier’s claims. Then we give you a simple guide to choose the right one for your cell type, module build, and climate.
To pick the right fix, you first need to understand the problem. Acetic acid is the same acid found in vinegar. Inside a solar module, it slowly eats away at the metal parts that carry current out of the cells. The damage is quiet at first, but it grows with every year of heat and humidity. That is why acid control has become one of the main topics in encapsulant selection.
EVA stands for ethylene vinyl acetate, and the “acetate” part is the source of the acid. Under water and UV exposure, EVA breaks down and releases acetic acid, which lowers the pH inside the module and speeds up corrosion (NREL). Heat makes the reaction faster, so hot, humid sites suffer most. The acid attacks silver contacts, solder joints, and ribbons. It also adds to yellowing and can weaken the bond between layers, which leads to delamination. Our post on why EVA turns yellow in solar modules covers the yellowing side in more detail.
Older PERC modules tolerated some acid without major losses. TOPCon cells are less forgiving because of the metal pastes used on their contacts. In the UNSW study, front contacts made with standard silver-aluminum paste corroded badly, while rear contacts also showed corrosion and delamination (pv magazine). Modules with low-aluminum paste held up better, but EVA still added to their losses. Module build matters too. A glass-glass module seals acid inside, while a breathable backsheet lets some of it escape. So a TOPCon glass-glass module is the toughest case for any EVA-based encapsulant.
Low-acid EVA is an EVA encapsulant made to release much less acetic acid than standard EVA as it ages. It looks and laminates like normal EVA, so module makers can use it on the same lines with the same recipes. Its main goal is to slow corrosion while keeping EVA’s low cost. Several large suppliers now sell it, which makes it the most widely available of the three options. For many module makers, it is the first step up from standard EVA.
Low-acid EVA tackles the problem at the source by using a formulation that forms less acid in the first place. Suppliers keep their exact recipes private, but the aim is the same: cut the amount of acid the film can release over its life. Some suppliers now even use acid-resistant EVA as the outer layers of their EPE films (TaiyangNews). In HIUV’s accelerated stress tests, standard EVA modules showed dark areas on EL images from acid reactions, while low-acid EVA modules stayed bright and uniform. That is a strong sign the approach works. Still, low-acid EVA reduces acid; it does not remove it.
Acid levels are usually reported in parts per million (ppm). As one example, Alishan reports an initial acid value of 4 to 6 ppm for its low-acid EVA, rising to under 10 ppm after 1,000 hours of damp heat (SolarQuarter). Numbers like these are useful, but only if you know how they were measured. Test method, sample prep, and aging time can all change the result. So always ask suppliers for the full test conditions behind any acid value. We cover what to ask for later in this guide.
Anti-acid EVA encapsulant is an EVA film that contains additives which trap or neutralize acetic acid inside the module, so less acid reaches the cell contacts. Instead of only forming less acid, it actively deals with the acid that does form. In India, RenewSys has promoted it as an option that beats low-acid EVA and costs less than EPE (pv magazine India). Like low-acid EVA, it runs on standard EVA lamination lines. It is a newer category, so long-term field data is still limited.
The key ingredient in anti-acid EVA is an acid acceptor, sometimes called an acid scavenger. These are fine particles mixed into the film that react with acetic acid and lock it away. Patent filings in this field name materials such as hydrotalcite, magnesium oxide, and magnesium hydroxide as acid acceptors (USPTO). Suppliers don’t always disclose which ones they use. The idea has been around for years, but recent TOPCon problems have brought it into the spotlight. Getting the right additive and dose is the hard part, as the trade-offs below show.
Those trade-offs matter. One patent notes that metal oxides such as MgO or ZnO can trap acid but may reduce the film’s transparency (EPO). Another found that hydrotalcite can lower the film’s electrical insulation, because the charged particles allow ions to move (Justia Patents). Lower insulation can raise PID risk, and lower transparency can cut output. So a good anti-acid EVA must balance acid control against clarity and insulation. Always check transmittance and volume resistivity data alongside the acid claims.
The simplest way to see the difference is to think of a leaking pipe. Low-acid EVA is like a better pipe that leaks less. Anti-acid EVA is like a pipe with a sponge around it that soaks up what leaks. The best products may combine both ideas: a low-acid base with an acid acceptor added. Neither approach changes EVA’s core weak points, though. Both are still EVA, so their moisture barrier and PID resistance stay close to standard EVA.
EPE takes a different route from both EVA options. It is a three-layer film with a polyolefin (POE) core between two thin EVA skins. The POE core forms no acetic acid at all, so EPE contains far less acid-forming material than a full EVA sheet. But the skins are still EVA, and in commercial films EVA makes up about 42% to 64% of the total volume . So EPE lowers acid risk without removing it completely. That is why many suppliers now use low-acid or acid-resistant EVA for the outer layers of their EPE.
Where EPE clearly pulls ahead is protection beyond acid. Its POE core is a much stronger moisture barrier than EVA. Commercial EPE films measured 3.1 to 11.7 g/m²/day per 100 µm for water vapor, compared with about 35 for EVA. Less moisture means less fuel for acid formation in the first place, since EVA needs water to break down. EPE also offers much stronger PID resistance than any EVA variant. Anti-acid and low-acid EVA treat one symptom; EPE treats both moisture and acid. You can see the specs on our EPE encapsulant product page.
Here is how the three options stack up on the factors module makers care about most. We have added standard EVA as a baseline, so you can see how far each option moves from it. Ratings are general, because results vary a lot between brands and grades. Use this table to narrow your choice, then confirm with test data from your shortlisted suppliers.
| Factor | Standard EVA | Low-Acid EVA | Anti-Acid EVA | EPE (EVA-POE-EVA) |
|---|---|---|---|---|
| How it controls acid | None | Forms less acid | Traps or neutralizes acid | Less acid-forming material; POE core forms none |
| Acid risk | High | Low | Low | Low (lowest with low-acid skins) |
| Moisture barrier | Baseline (about 35 g/m²/day per 100 µm) | Similar to EVA | Similar to EVA | Much better (about 3 to 12) |
| PID resistance | Baseline | Similar to EVA | Similar to EVA; can drop if additives lower insulation | High |
| Transparency risk | Low | Low | Depends on additive type and dose | Low for most grades |
| Lamination | Standard | Same as EVA | Same as EVA | Close to EVA |
| Relative cost | Lowest | Low | Low to mid | Mid |
| Field history | Decades | Several years | Limited (newer) | Growing fast |
| Best fit | PERC, glass-backsheet, mild climates | Cost-led TOPCon glass-backsheet | Cost-led TOPCon where acid is the main risk | TOPCon glass-glass, bifacial, humid or high-voltage sites |
The big takeaway: both EVA variants target acid only. EPE targets acid, moisture, and PID together. If acid is your only worry, a good EVA variant may be enough. If moisture or PID also matter, EPE is usually the safer choice.
There is no industry standard that defines these terms. One supplier’s “low-acid” can release more acid than another’s standard grade. “Anti-acid” can mean anything from a strong acid acceptor to a small additive dose. And “acid-free” is rarely true for any product that contains EVA. Even launch coverage of anti-acid EVA describes the product as leaving a small acid residue, not zero (pv magazine India).
This is not unique to EVA. In POE, a UNSW study found that some POE formulations can trigger metal corrosion in TOPCon modules (pv magazine). Industry reviews of that research point to the additive package as the cause, in films whose data sheets looked nearly the same (Couleenergy). Labels describe intent, not results. The only reliable way to compare products is to look at measured data under the same test conditions. Our rule is simple: if a supplier can’t show you the numbers, treat the label as marketing.
Good test data turns a sales pitch into a fair comparison. The goal is to see how much acid each film forms, how it ages, and what that does to a real module. Ask every supplier for the same set of results, measured the same way. If possible, run your own module tests on top of the supplier data. Here are the checks we recommend:
For a full supplier review process, see our guide on what to check before approving a solar encapsulant supplier. Our article on EVA gel content explains how to run that test on your own line.
There is no single best encapsulant for every module. The right choice depends on four things: your cell type, your module build, the climate where modules will be installed, and your cost target. The table below shows where we would start in common cases. Treat it as a starting point, then confirm with your own damp-heat and PID tests.
| Your Situation | Our Starting Pick | Why |
|---|---|---|
| PERC, glass-backsheet, mild or dry climate | Standard or low-acid EVA | PERC tolerates some acid, and the backsheet lets acid escape |
| TOPCon, glass-backsheet, cost-led project | Low-acid or anti-acid EVA | Cuts acid corrosion while keeping EVA cost and processing |
| TOPCon, glass-glass or bifacial | EPE | Glass-glass traps acid and moisture; EPE limits both |
| Any cell type, 1,500 V utility plants | EPE | Strong PID resistance on top of acid control |
| Humid, coastal, or very hot sites | EPE (with low-acid skins if possible) | Moisture fuels acid formation, so a better barrier helps twice |
| HJT modules | EPE | EVA skins bond to the cell coating; POE core blocks moisture |
A few rules of thumb sit behind these picks. If acid is your only real risk, an EVA variant is a sensible, lower-cost upgrade. If moisture or PID are also risks, an EVA variant only solves part of the problem, and EPE is the safer bet. Glass-glass is the clearest case for EPE, since nothing inside can escape. For more on TOPCon specifically, read our guide on encapsulants for TOPCon solar modules.
Acetic acid from EVA has become a real threat to modern modules, especially TOPCon. Low-acid EVA reduces how much acid forms. Anti-acid EVA traps or neutralizes the acid that does form. EPE cuts the amount of acid-forming material and adds a far stronger moisture barrier and PID resistance. Both EVA variants are sensible, lower-cost upgrades when acid is the main risk. When moisture, PID, or glass-glass builds are also in play, EPE is usually the safer long-term choice. Whatever you pick, judge it on test data, not on the name printed on the roll.
At Raynex Solar, we manufacture EVA and EPE encapsulant sheets in India for module makers who need reliable, well-tested materials. If you are comparing acid-control options for a new bill of materials, our team can share test data and help you plan trials on your own line. Explore our EVA encapsulant and EPE encapsulant ranges, or request a quote to get samples.
Anti-acid EVA is an EVA encapsulant that contains acid acceptors, which trap or neutralize acetic acid inside the module. This lowers the amount of acid that can reach and corrode the cell contacts. It laminates like standard EVA, so it fits existing production lines. It is a newer product type, so long-term field data is still building up.
Low-acid EVA uses a formulation that forms less acetic acid in the first place. Anti-acid EVA adds materials that trap or neutralize acid after it forms. Some products combine both approaches. Both remain EVA, so neither improves the moisture barrier or PID resistance much beyond standard EVA.
For acid control alone, a good anti-acid EVA can come close. But EPE also has a much stronger moisture barrier and better PID resistance, thanks to its POE core. Anti-acid EVA is usually cheaper, which makes it attractive for cost-led glass-backsheet modules. For glass-glass, bifacial, or high-voltage modules, EPE is usually the safer choice.
No EVA-based film is completely acid-free, because the vinyl acetate in EVA is the source of the acid. Low-acid and anti-acid grades can reduce acid to very low levels. Even EPE contains some EVA in its outer layers. Only non-EVA films like pure POE avoid acetic acid entirely, though their additives still need checking for other acid sources.
Yes, many module makers use them for TOPCon, especially in glass-backsheet designs. They are a clear step up from standard EVA, which research has linked to contact corrosion in TOPCon. For glass-glass TOPCon modules, the trapped moisture and acid make EPE the stronger option. Always run damp-heat tests on your exact cell and paste combination before you commit.
They can if the formulation is not well balanced. Some acid acceptors can reduce film clarity, and others can lower electrical insulation. Lower clarity cuts output, and lower insulation can raise PID risk. That is why you should check transmittance and volume resistivity data along with acid values.
