Solar Hydrogen Production: PV Electrolyzer Sizing

Last updated: November 2026

A 10 MWp solar plant cannot make hydrogen on its own. It needs an electrolyzer, water, gas handling and storage. This guide sizes that chain from sun to hydrogen and shows what drives cost per kg.

The 10 MWp, 18,000 MWh case in the quick answer is an example. It assumes 1,800 kWh per kWp a year (10,000 kWp × 1,800 kWh). The 327 tonnes is 18,000,000 kWh ÷ 55 kWh/kg = 327,273 kg. It counts energy only and assumes the electrolyzer can use every kWh.

For a solar developer, the practical question is how much hydrogen a plant can deliver, at what cost, and under which rules. This guide shows the chain from sun to hydrogen, compares electrolyzer types and walks through sizing and cost sums. A hydrogen process team must design the process, storage, electrical protection and start-up.

Sizing Example: 1 Tonne of Hydrogen a Day

This table starts from the target and works back. It uses 55 kWh/kg for the whole electrolysis system (DOE PEM status) and an example PV yield of 1,800 kWh per kWp a year.

A solar plant only makes power in daylight, so the electrolyzer is sized for fewer hours, not 24. That moves the answer toward the larger electrolyzer number. A time-by-time model of your site decides the real size.

For comparison, the EU’s PVGIS tool gives about 1,750 kWh per kWp a year for Los Angeles at a 20° tilt (south-facing, 14% system loss, version 5.3, run 28 October 2026). Use a PV yield prediction for your own site. See solar yield prediction.

How PV Electrolysis Works

The overall reaction is:

2 H2O → 2 H2 + O2

PV makes electricity. Electrolysis uses electricity to split water. Hydrogen is a way to carry and store energy, and a raw material for industry. It is not free energy. The US Department of Energy electrolysis overview describes the reaction and the main electrolyzer types.

The plant is more than the stack. These are the stages to define:

A stack efficiency number does not cover every row. Ask each supplier for a boundary drawing and a list of what the quote includes.

Electrolyzer Technologies Compared

DOE groups electrolyzers by the electrolyte: PEM (proton exchange membrane), liquid alkaline and solid oxide. The table shows status values from Table 2 of DOE’s Hydrogen Shot Water Electrolysis Technology Assessment. These are reference values, not a guarantee for any one product.

Notes on the table:

• For solid oxide, the system figure counts both electricity and heat. It is not an electricity-only number.
• DOE says most liquid alkaline systems fall in the $500 to $750 per kW range uninstalled. Costs run from $500 to over $1,500 per kW between makers.
• DOE lists PEM uninstalled system cost at $700 to $1,100 per kW at today’s manufacturing volumes in another section. The table shows $1,000 per kW as the status value.
• DOE gives no status values for AEM (anion exchange membrane) electrolyzers. It says AEM aims at targets like PEM.

Use these numbers as a first screen. For a real project, ask each supplier for the load range, ramp rate, start-up time, water quality, output purity and guarantees for your duty cycle. Compare the output quality, availability and service terms, not only efficiency.

Efficiency: Know What Is Counted

Electrical efficiency, solar-to-hydrogen (STH) efficiency and cost per kg measure different things. State what each one counts.

The DOE Alternative Fuels Data Center lists the lower heating value (LHV) of hydrogen as 33.3 kWh/kg. The higher heating value (HHV) is about 39.4 kWh/kg, using the listed 61,013 Btu/lb. These are energy per kg of hydrogen, not per kg of water. LHV and HHV differ in how they treat the water formed when hydrogen burns.

Electrical efficiency (LHV) = hydrogen output (kg) × 33.3 kWh/kg
                              ÷ electrical input (kWh)

Example. A system uses 55 kWh to make 1 kg. LHV efficiency is 33.3 ÷ 55 = 60.55%. DOE’s PEM table lists 61% for the same 55 kWh/kg. On an HHV basis, the same machine is 39.4 ÷ 55 = 71.64%. The number changes with the convention. The kilograms do not.

Solar-to-Hydrogen Efficiency

Say 5 kWh/m² of sunlight falls in a day on 50 m². That is 250 kWh of incoming solar energy. If 1 kg of hydrogen were made, that would be 33.3 ÷ 250 = 13.32% on an LHV basis. This is only a worked example of the ratio. It does not predict what a real array would make.

Research papers may use a different energy convention. Check the formula, the light source, the area and what extra energy is counted before you compare a paper with a plant estimate. Do not multiply a module’s rated efficiency by an electrolyzer’s efficiency and call it a yearly plant result.

Pilot-Scale and Research Highlights

Here are two reference projects. They show what has been done. Neither is a price or a sizing rule.

• Research cell, 30% STH. A 2016 Nature Communications study reported a 48-hour average solar-to-hydrogen efficiency of 30%. It used one triple-junction solar cell with an active area of 0.316 cm², driving two PEM electrolyzers in series under simulated concentrated light. It is a lab result. It is not a silicon PV plant result and not an alkaline result.
• Fukushima FH2R, 10 MW class. Toshiba’s March 2020 announcement describes 20 MW of solar facilities on a 180,000 m² site, plus grid power, feeding a 10 MW-class hydrogen unit. It can produce up to 1,200 Nm³ of hydrogen per hour at rated power. Nm³ is a “normal” cubic meter. Record the reference pressure and temperature before you convert it to kilograms. The 180,000 m² ÷ 20 MW works out to 9,000 m² per MW, but the site holds more than the solar field.

When you read a pilot report or a paper, note the device area, test length, light source, how the parts are connected, how the hydrogen was measured, and what extra energy is counted.

Size with Time-Matched Electricity and Hydrogen Demand

There is no fixed best ratio of solar to electrolyzer size. PV size is usually in DC MWp. Electrolyzer power may be stated at an AC or a DC point. Define both before you form a ratio.

For each time step in your model:

1. Work out the electricity available after other site loads and conversion losses.
2. Apply the electrolyzer’s operating curve, minimum load, start-up needs and power limit.
3. Add auxiliary loads and any storage use.
4. Turn the electricity the electrolyzer accepts into hydrogen.
5. Check the storage and the buyer’s demand.

Try several ratios and control rules. More PV can raise utilization, but it can also waste more energy or raise cost. A smaller electrolyzer runs closer to its rating, but that does not mean more hydrogen in total. Compare yearly output and cost per kg.

DOE notes that systems with a low capacity factor need more hydrogen storage to cover the gaps.

Annual Energy Screening Example

Say the target is 1,000 kg a day on average, and the whole system uses 55 kWh/kg:

• Yearly target: 1,000 × 365 = 365,000 kg.
• Yearly electricity: 365,000 × 55 = 20,075,000 kWh (20.075 GWh).
• Assume the PV plant gives 1,800 kWh per kWp a year at the electrolyzer input.
• PV size, energy only: 20,075,000 ÷ 1,800 = 11,152.78 kWp, about 11.15 MWp.

This ignores solar energy the electrolyzer cannot take when it is produced. It does not show daily delivery, and it does not pick an electrolyzer size. Use a time-series model for that.

A second check shows why ratings alone are not enough. A 10 MW electrical-input system at a 50% capacity factor takes 10 × 8,760 × 0.5 = 43,800 MWh a year. At 55 kWh/kg that gives about 796,364 kg a year, or 2,182 kg a day on average.

Plant Layouts and Their Trade-Offs

A DC link can skip some conversion stages. It does not remove all conversion losses. The grid is not an unlimited buffer: connection size, tariffs and permission apply. A battery needs enough usable energy to run the electrolyzer overnight. Keep battery assumptions separate from hydrogen storage. They buffer different things.

DOE says the solar and wind cases in its cost study do not include battery or hydrogen storage as a way to handle changing output.

Water, Storage and Plant Layout

The reaction uses about 9 kg of water per kg of hydrogen. The molecular masses give 36.03 g of water for 4.03 g of hydrogen, which is 8.94 kg per kg. For 1,000 kg of hydrogen a day, that is about 9,000 kg (9 m³) of water a day.

That is not the full water need. The DOE Hydrogen Shot assessment says:

• Direct water use during electrolysis, without cooling water, is about 4 gallons per kg of hydrogen. For 1,000 kg a day that is about 4,000 gallons, or 15 m³.
• Water for purification and for making the electricity adds 3 to 65 gallons per kg, depending on the power source.
• As little as 7 gallons per kg is needed in total for electrolyzers on solar or wind power. For 1,000 kg a day that is 7,000 gallons, or about 26.5 m³.

Ask your supplier for feed water quality and water use. Then draw a site water balance. Cooling and treatment waste are part of it.

Agree the hydrogen purity, pressure and delivery condition with the buyer. Drying, compression, liquefaction or turning hydrogen into another carrier adds equipment, energy and losses. Do not assume a storage pressure of 350 or 700 bar for every project. Do not treat ammonia as hydrogen without counting the conversion steps.

Your layout needs space for process equipment, access, water treatment, storage and safety. A qualified hydrogen process team must set the permits, spacing, ventilation, gas detection, pressure rules and emergency steps for your site. A land-per-MW figure from another project does not replace that design. For industrial sites, see the factory solar system design guide for the PV side.

Cost per Kilogram

A fair levelized cost of hydrogen (LCOH) divides lifetime costs by the kilograms delivered, both discounted, at a stated point. Write down the currency year, financing, electricity, install cost, operations, wear, replacement, water, storage and delivery scope. Do not count the PV plant’s capital cost and its full electricity price twice.

Electricity cost per kg

At 55 kWh/kg, the electricity part of the cost is 55 times your price per kWh:

Each $0.01/kWh adds $0.55 per kg. These figures leave out electrolyzer cost, water, service, compression, financing and delivery.

Equipment cost per kg and running hours

The electrolyzer’s cost is spread over the kilograms it makes. A plant that runs fewer hours makes fewer kilograms per kW. This example uses DOE’s PEM uninstalled system cost of $1,000/kW, 55 kWh/kg and a simple 10-year life. It leaves out installation, financing, replacement and service.

A solar-only plant has a low capacity factor, so equipment cost per kg rises. That is why storage, wind or grid power matter for cost.

What DOE’s cost study found

DOE’s modeling (2020 US dollars) with grid electricity at $0.06 to $0.10 per kWh and a 97% capacity factor gives about $5.80/kg for alkaline, $6.70/kg for PEM and $7.60/kg for solid oxide at today’s technology and cost. DOE’s future target scenarios use much lower electricity costs, such as $0.012/kWh for a hybrid solar and wind case with tax credits and a 74% capacity factor. DOE’s PEM table lists a 2022 status production cost above $3/kg and targets of $2/kg for 2026 and $1/kg for 2031. They are goals, not selling prices.

Get supplier quotes and apply current local policy separately. Show any subsidy as its own scenario. Compare making hydrogen with other uses of the same electricity, such as selling it to the grid or using it directly in industry.

What to Hand Over

Give the buyer the weather and electricity data, model boundaries, equipment assumptions, dispatch rules, hydrogen mass and delivery profile, water balance, storage limits, costs and sensitivity results. Mark which items are forecasts, supplier guarantees, past demonstrations or policy targets.

DOE says all upstream emissions must be counted. A solar-connected electrolyzer is not automatically certified as zero-emission, and it does not automatically qualify for every “green hydrogen” scheme. Check the accounting, metering and certification rules with specialists.

SurgePV supports 3D roof modeling, array layout, shading analysis, energy-yield modeling and financial modeling. Use it for the PV side of a project. The electrolyzer and the hydrogen process need separate engineering tools. A guided demo shows how the PV design workflow and the generation and financial tool work.

Frequently Asked Questions

What is solar hydrogen production via PV electrolysis?

Solar panels make electricity. An electrolyzer uses that electricity to split water into hydrogen and oxygen. The plant also needs power conversion, water supply, gas drying and cleaning, storage and safety systems.

How much electricity does 1 kg of hydrogen need?

About 51 to 55 kWh. The US Department of Energy lists 51 kWh/kg for a PEM stack and 55 kWh/kg for the whole PEM system (2022 status). Alkaline systems are listed at the same 51 and 55 kWh/kg. Solid oxide systems need less electricity (47 kWh/kg for the system) because they also use heat.

How much solar do I need to make 1 tonne of hydrogen a day?

At 55 kWh/kg, 1 tonne a day needs 55 MWh of electricity a day. If your PV plant gives 1,800 kWh per kWp a year, that is about 11.15 MWp, counting energy only. A real design needs more, because the electrolyzer cannot use every kWh at the moment it is made.

How should I compare solar-to-hydrogen efficiency?

Ask what energy is counted, what area is counted, how long the test ran and what equipment is included. Research papers may count reaction energy instead of hydrogen’s lower heating value. A short lab result is not a yearly result for a commercial plant.

How much does solar hydrogen cost per kilogram?

No single price applies. Electricity alone adds 55 kWh/kg times your price per kWh, such as $1.65/kg at $0.03/kWh. Equipment cost per kg falls as the electrolyzer runs more hours. DOE’s cost model with grid electricity (2020 USD) gives about $5.80/kg for alkaline, $6.70/kg for PEM and $7.60/kg for solid oxide. Get project quotes for your own case.

Which electrolyzer technology is best for solar?

DOE says PEM electrolyzers respond quickly and have shown they can follow variable power, while alkaline designs have generally not suited variable operation. Alkaline systems cost less per kW. Ask each supplier for guaranteed operating data at your solar duty cycle.

How much water does a solar hydrogen plant need?

The reaction itself uses about 9 kg of water per kg of hydrogen. DOE says direct water use in the electrolyzer is about 4 gallons per kg (about 15 liters), and a system on solar or wind power needs as little as 7 gallons per kg (about 26 liters) in total, counting upstream use. Get the supplier’s water needs and make a site water balance.