Solar Pool Covers: How They Work and What They Actually Save
Updated: Aug 25
Heat leaves a pool through the surface, and most of it leaves overnight. A solar cover is the cheapest thing you can put on a pool that changes that.
It's a sheet of UV-stabilised polyethylene made up of thousands of small sealed air pockets — closer to heavy-duty bubble wrap than to a tarpaulin — and it floats directly on the water. It does three jobs at once: adds heat, holds heat, and cuts the water and chemicals lost from the surface.
This guide covers how it works, how to work out what it's worth on your own power bill, how to use it through the season, and the mistakes that destroy a cover early.
Solar pool cover and reel installed on an Auckland pool.
How a solar cover works
The design does one job during the day and a different one at night.
Daytime: the air pockets transmit and trap solar energy and pass it into the water below.
Night: the same sheet becomes a barrier across the surface. That stops evaporation and insulates the water against the overnight temperature drop.
The night job is the one most pool owners underestimate. Every litre that evaporates takes energy with it, which is why an uncovered pool is cooler in the morning after a warm day, and why a heat pump on an uncovered pool spends much of its running time replacing heat that escaped a few hours earlier.
What a solar cover saves
We're not going to quote a percentage at you. Here's the physics instead, because it's the part that doesn't vary by supplier or by marketing budget.
Evaporation is the main way a pool loses heat. Not the air temperature, not the walls — the surface. Every litre of water that evaporates carries roughly 0.63 kWh of heat out of the pool with it. That's the latent heat of vaporisation of water, a physical constant. It's the same in Kerikeri as it is in Invercargill.
Run the number and it lands hard. A pool losing 100 litres a day to evaporation is losing about 63 kWh a day in heat. At the national average residential electricity price of around 39c/kWh (MBIE Quarterly Survey of Domestic Electricity Prices, February 2026), that's real money leaving through the surface every night, and it's what your heater is working to replace.
A solar cover puts a physical barrier across that surface. That's the whole mechanism:
What happens | Why |
Water loss drops | The surface is sealed, so evaporation largely stops while the cover is on |
Heat loss drops | Heat leaves with evaporating water, so stopping one stops the other |
Water gains heat during the day | The air pockets transmit and trap solar energy into the water below |
Chemical use drops | Sanitiser degrades in UV and leaves with evaporating water — the cover slows both |
Cleaning drops | Dust, pollen and leaf litter stay out while the cover is on |
On published percentages. No New Zealand agency — EECA, MBIE, NIWA, Consumer NZ — publishes independent performance testing on pool covers. Every "cut heating costs by 50%" and "reduce evaporation by 90%" you'll find on a New Zealand pool website is that supplier's own marketing number with no study behind it. We're not repeating those, and we're not borrowing overseas ones either. What we'll give you instead is a way to measure it on your own pool.
Measure it on your own pool
This is the only figure that's actually about your pool, your region and your power rate. It takes two weeks of doing nothing.
Week one — uncovered. Mark the waterline on the skimmer with a piece of tape. Don't top up. After seven days, measure the drop in millimetres. Note any rainfall — a wet week invalidates the test, so run it again.
Week two — covered. Reset the tape to the same starting level, keep the cover on whenever you're not swimming, and measure the drop again.
Convert to litres. Water surface area in m² × drop in mm = litres lost. An 8 × 4m pool is 32 m², so a 5mm drop is 160 litres.
Convert to heat. Litres saved × 0.63 = kWh of heat you didn't lose.
Convert to dollars. kWh × your power rate. Use the rate on your own bill — regional variation across New Zealand is wide, so the national average is a starting point, not your number.
That gives you a weekly figure you can defend, multiply across a season, and check against what you paid for the cover. It's your pool's number, not an industry average.
If you don't heat your pool at all, the saving isn't on power. It's water, chemicals, cleaning time, and swimming weeks at either end of summer.
Bubbles down, always
Lay the cover on the pool with the bubble side facing the water.
Two reasons. Heat transfer into the water is better with the bubbles in contact with it, and the bubbles are protected when submerged rather than exposed to direct sun.
This is the most common installation error and it costs you both performance and cover life.
Sizing, trimming and first fit
A solar cover should sit edge to edge across the water surface. Any gap around the perimeter is where evaporation and heat loss carry on.
Ours are cut to the measurements you enter, with a 150mm allowance added to each dimension so the edge sits slightly up the pool wall. For rectangular pools, first fit is usually nothing more than checking the edge. For oval and round pools the cover is cut to the shape rather than trimmed down from a rectangle.
First fit: float the cover on the pool for a few hours before trimming anything. It will relax and settle into the true shape of the water surface. Trim with sharp scissors, following the waterline with a small overlap onto the coping, then let it settle again before cutting closer. You can always take more off.
Enter your pool shape and dimensions and you'll see a price for a cover made to those measurements — no quote form, no callback.
Not sure how to measure? Read How to measure your pool first.
Handling it: why you want a reel
A full-size solar cover is large, wet and awkward. Getting it on and off single-handed is the reason most solar covers end up folded in a corner of the shed by January.
A reel fixes that. It also keeps the cover rolled and off the ground when it's not on the pool, which protects it from grit and tearing. A rolled cover still needs shade — see storage below.
We stock a manual stainless reel with a telescopic tube, in two sizes: 4.6m and 5.5m. It's hand-wound, needs no power, and can be fitted with castors. Motorised and bench-concealed reels aren't stocked here and are handled by enquiry.
Full detail: Pool cover reels.
Solar, thermal or debris — which one you actually need
Solar cover | Thermal cover | Debris cover | |
Main job | Add and hold heat | Hold heat | Keep debris out |
Sits | Floating on water | Floating on water | Above water, on fixings |
Solar gain | Yes | Minimal | No |
Heat retention | Good | Highest | Limited |
Best for | Extending the swim season | Heated pools, cooler regions | Winter shutdown, heavy leaf fall |
In our range | Yes — 600 micron | Yes — 3mm foam | No |
Plenty of pools use two: a solar cover through the swim season and a debris cover over winter. Debris covers aren't part of our range, so that's a separate purchase. Full comparison in How to choose a pool cover.
Using a solar cover through the season
Spring (Sep–Nov). The highest-value period of the year. The cover is holding the day's gain overnight at exactly the point in the season when nights are still cold and the water is trying to come up to temperature.
Summer (Dec–Feb). On whenever the pool isn't being used. In the warmer northern regions a heated pool with good sun exposure can occasionally run warmer than you want in midsummer — if that happens, pull the cover off overnight to let heat go rather than dropping it from your routine.
Autumn (Mar–May). The second high-value period, and the one most people waste. Autumn days stay warm well into April across most of the country while nights cool off fast. The cover is what holds the day's gain overnight.
Winter (Jun–Aug). A solar cover is not a winter cover. If you're shutting the pool down or dealing with leaf fall, that's a debris cover. Clean, dry and store the solar cover properly rather than leaving it on through winter.
Water restrictions. Several councils apply restrictions during dry summers. Covering the pool when it isn't in use is the most effective single thing you can do to reduce top-up water.
Wind, rain and water level
Rain is not a problem for a floating solar cover — it sits on the water, so there's nothing to pool in. Watch your water level after heavy rain and drain to the middle of the skimmer if the pool comes up too high.
Wind is the risk. A solar cover lifts when the water level drops below the coping or when the cover is left partly rolled. Keep the water level up, and take the cover off and secure it before forecast severe wind rather than after.
Water chemistry is what actually kills solar covers
The most common cause of early failure isn't sun or wear. It's water chemistry — specifically low pH and high sanitiser levels.
Balance before you cover. Test regularly and keep pH and sanitiser in range. Testing takes two minutes and is the difference between a cover that reaches its service life and one that goes brittle in a season.
Never cover straight after dosing. After adding any water balancer or chlorine shock, run the pump for at least a few hours, then test before putting the cover back on. Covering a freshly dosed pool traps concentrated sanitiser against the underside of the material. The plastic goes weak and brittle and the bubbles start breaking down.
Don't let sanitiser drop just because it's covered. A covered pool in midsummer is warm, and warm water with low chlorine grows algae faster, not slower. The cover reduces how much sanitiser you lose — it doesn't remove the need for it.
Chemistry damage isn't covered by any solar cover warranty, ours included. This is the one habit worth building. Test strips and pool chemicals are stocked by any pool retailer; we make covers, not chemicals.
Storage, cleaning and cover life
Off the pool, keep it out of the sun. Prolonged direct sun on a cover that isn't on the water is one of the fastest ways to destroy it. Rolled or heaped, it overheats and the bubbles deform and delaminate. Cover the roll, park the reel in shade, or fit a reel overcover. Heat damage sustained off the pool is not a manufacturing fault and is not covered under warranty.
Rinse it with fresh water before long storage. No solvents, no harsh cleaners, no pressure washer.
Dry it fully before rolling it away for winter, and store it rolled rather than folded, in shade, off the ground and away from rodents.
Cover life comes down almost entirely to those two things — chemistry and UV exposure off the pool. Manage both and the cover reaches its full service life.
Covers carry a 10-year pro rata warranty. Pro rata means replacement cost is shared on a published schedule rather than free for the full term — the schedule is set out on our Warranty page.
Safety
A solar cover is a thermal product, not a safety device. It floats on the surface, will not support the weight of a child or a pet, and is not a substitute for compliant pool fencing. Never let anyone walk or stand on a solar cover, and keep children away from the pool while the cover is being put on or taken off. Your pool barrier obligations under New Zealand law are unchanged by fitting any cover.
Frequently asked questions
Bubbles up or down? Down, against the water. Bubbles up reduces heat transfer and exposes the bubbles to direct sun.
Do I need a reel? Not technically, but a cover you can't easily remove is a cover you stop using. If you're the only person handling it, a reel is the difference between daily use and no use.
Can I swim with the cover on? No. It comes off before anyone gets in, every time.
Will a solar cover heat my pool on its own? It adds solar gain and cuts heat loss, so a covered and an uncovered pool in identical conditions won't sit at the same temperature. How much gain you get depends on your region, sun exposure, shading and pool size, which is why we don't publish a single temperature figure — and why we'd treat any supplier who does with suspicion. Run the two-week test above and you'll have your own number.
Does it work on a salt-chlorinated pool? Yes. The same chemistry rules apply — keep pH and sanitiser in range, and don't cover immediately after shocking.
Can it be trimmed? Yes. Ours are made to your measurements with a 150mm allowance on each dimension, so trimming is minor adjustment at first fit only.
Do I still need to run the pump the same amount? A covered pool takes in less debris, so cleaning and filter workload drop. Don't cut filtration or sanitiser back on the assumption the cover is doing that job — it isn't.
How thick should it be? Both our bubble covers are 600 micron. Thinner grades are sold elsewhere as budget options and generally need replacing sooner.
How long does it take to arrive? 14 working days from payment. Free delivery to North Island addresses, $50 flat to the South Island.
Get a price for your pool
No quote form, no callback, no waiting. Enter your pool shape and measurements and see the price for a cover made to fit it.
Comments