The inverter is one of the most important and most complex components of an independent system. Luckily, you don’t have to understand the inner workings of an inverter, but you should understand some basic functions, capabilities and limitations.

This buying guide gives you the basic information so that you can choose the right inverter, and use it wisely.

Why You Need an Inverter

An independent electric power system is one that is untethered from the electrical utility grid. Such systems vary in size from tiny yard lights to remote site homes, villages, national parks, or medical and military facilities. They also include mobile, portable, and emergency backup systems. Their common bond is the storage battery, which absorbs and releases power in the form of direct current (DC). In contrast, the utility grid supplies consumers with alternating current (AC) power. AC is the standard form of electricity for anything that “plugs in” to utility power (it is more practical for long distance transmission).

The inverter converts DC power to AC power, and also changes the voltage. In other words, it is a power adapter. It can allow a battery-based independent power system to run conventional appliances through conventional home wiring. There are many ways to use DC power directly, but if your electrical needs are beyond the simplest “cabin” level, you will need an inverter for many, if not all, of your loads (devices that use power).

DC flows in a single direction. AC alternates its direction many times per second. The standard DC voltages for home- size systems are 12, 24 and 48 volts. The standard for AC utility service in USA is 120 and 240 volts at 60 Hertz (cycles per second). In Europe and some countries in Latin America, Asia and Africa, it’s 220V or 230V at 50 Hertz. The inverter is used to reconcile these differences.

An Inverter is Not a Simple Device

Outwardly, an inverter looks like a box with one or two switches on it, but inside is a small universe of dynamic activity. A modern home inverter must cope with input voltage that varies as much as 35% (with varying battery state and activity), and also with huge variations in output demand (from a single night-light to a big surge required to start a well pump or a power tool). Through all, it must regulate its output quality within narrow constraints, with a minimum of power loss. This is no easy task. In addition, some inverters provide battery backup charging, and can even feed excess power into the grid.

What to Consider When Comparing Inverters Before Purchasing

Where is the Inverter to be Used?

Home – directly tied to the utility grid (grid-tie inverter)

Cabin – standalone, completely off grid (off-grid inverter)

Backup/emergency backup (hybrid inverter)

Recreational vehicle

Marine (marine inverter)


Electrical Standards

DC input voltage

AC output voltage and frequency

Power capacity (Watts) – How much power can the inverter put out?

Continuous rating

Limited duration ratings

Surge rating (for starting motors/pumps)

Expandability (modularity, stackability)

Power quality (waveform)

Some inverters produce “cleaner” power than others.

Pure sine wave inverters

Ideal, smoothly alternating AC (like swing of a pendulum)

Equivalent (or superior) to grid power relatively expensive

Modified sine wave inverters

Inferior waveform, choppy alternation (like pendulum forced by hammers)


Adequate for many homes with simple needs, but about 5% of loads malfunction

May confuse digital timing devices in some appliances

May overheat power converters in some appliances/computers

May overheat surge protectors (don’t use them) causes some devices to buzz (some fluorescent lights, ceiling fans, transformers)

Reduces energy efficiency of motors and transformers by 10% or more, causes motors and transformers to run hotter

Generally reduces the reliability of appliances

Internal protection – How much abuse can it tolerate?

Overload and surge protection

Low voltage shutoff

Inductive load capability – Some loads accept the AC wave with a slight time delay. These are call inductive loads. Motors are the most severely inductive loads.

Starting large motors (well pump, washing machine, power tools, etc.)

Inverters’ Physical Attributes

There are two ways that inverters are built:

Transformer type inverters

Heavy, expensive

High surge capacity

Historically the most reliable

Makes buzzing noise

High frequency switching type inverters

Light weight, inexpensive

Less reliable in cases of cheap consumer units

No audible buzz

Inverter Efficiency

It is not possible to convert power without losing some of it (think of “friction”). Efficiency is the ratio of power out to power in, expressed as a percent. If the efficiency is 90%, that means 10% of the power is lost in the inverter. Lost power manifests as heat. Efficiency of an inverter varies with the load. Typically, it will be highest at about 2/3 of the inverter’s capacity. This is called its “peak efficiency”. The inverter requires some power just to run itself, so the efficiency of a large inverter may be low when running very small loads.

In a typical home, there are many hours of the day when electrical load is very low. Under these conditions, an inverter’s efficiency may be around 50% or far lower. The full story is told by a graph of efficiency vs. load, as published by the inverter manufacturer. This is called the “efficiency curve”. Watch out. Some manufacturers cheat by drawing the curve only down to 100 Watts or so, not down to zero!

Because the efficiency varies with load, don’t assume that an inverter with 93% peak efficiency is better than one with 85% peak efficiency. The 85% efficient unit may be more efficient at low power levels, for example.

Automatic on/off

As stated above, an inverter takes some power just to run itself. This “idling” can be a substantial load on a small power system. Cheap portable inverters usually have a manual on/off switch. If you forget to turn the inverter off, you may surprised by a discharged battery bank after a few days. Most inverters made for home power systems have an automatic load-sensing system. The inverter puts out a brief pulse of power about every second (more or less). When you switch on an AC load, it senses the current draw and turns itself on. Manufacturers have various names for this feature, like “load demand”, “sleep mode”, “power saver”, or “standby”.

This feature can make life a bit awkward because a tiny load may not trigger the inverter to turn on. For example, you start your washing machine and after the first cycle, it pauses with only the timer running. The timer may draw less than 10 Watts.

The inverter’s turn-on “threshold” may be 10 or 15 Watts. The inverter shuts off and doesn’t come back on until it sees additional load from some other appliance. Some people solve this problem by leaving a small light on while running the washer.

Some system users cannot adapt to this situation. Therefore, inverters with automatic on/off also have an “always on” setting. That way, you can run your low- power night lights (they won’t flash on/off) and your clocks and other tiny loads without losing continuity. A good system designer will then add the inverter’s idle current into the load calculation (24 hours per day), and the cost of the power system will be correspondingly higher.

Battery Charging Features

Some inverters have a built-in battery charger that will recharge the battery bank whenever power is applied from an AC generator or from the utility grid (if the batteries are not already charged). This function is essential to most renewable energy systems because there are likely to be occasions when the energy supply is insufficient. It also makes an inverter into a complete emergency backup system for on-grid power needs (just add batteries).

Here is a list of specifications that relate to battery charger function:

Maximum charging rate (amps)

Generator size and voltage requirements

Charge control features, including accommodation of different battery types (flooded or sealed), temperature compensation, and other refinements

Be careful when sizing a generator to meet the requirements of an inverter/charger. Some inverters require that the generator be oversized. Be sure to get experienced advice on this, or you may be disappointed by the result.

Expansion Options

Some inverters can be “stacked” to expand a system’s capacity.

Laboratory Certification

Inverters should be certified by an independent testing laboratory such as UL, ETL, CSA, etc., and stamped accordingly. There are different design and rating standards for various applications, such as use in buildings, vehicles, boats, etc. These also vary from one nation to another. An inverter used for a home power system must be appropriately rated for the system to pass an electrical inspection.

Phantom Loads

High tech consumers are stuck with gadgets that draw power all of the time that they are plugged in. These little demons are called “phantom loads” because their power draw is unexpected, unseen, and easily forgotten. An example is a TV with remote control. Its electric eye is on all the time, watching for your signal to turn the screen on. Other examples include any devices with an external wall-plug transformer or a built-in clock, plus smoke detectors, alarm systems, motion detector lights, fax machines, answering machines, and all cordless (rechargeable) appliances. Central heating systems have a transformer in their thermostat circuit that stays on all the time. How many phantom loads do you have?

There are several ways to cope with phantom loads. (1) You can avoid them (easy for a small cabin or other simple- living situation). (2) You can minimize their presence and disconnect them when not needed, using external switches. (3) You can work around them by modifying certain equipment to shut off completely. (4) You can substitute devices that use DC power instead of AC. (5) You can pay the additional cost for a large enough power system to handle the extra loads plus the inverter’s idle current (often over $1000 added). Be very careful and honest when considering avoiding all phantom loads.

You cannot always anticipate future needs or human behavior. All it takes is one phantom load to mess up your perfect plan.

Powering a Water Well or Pressure Pump

At a remote site, a water supply pump is often the largest electrical load. It warrants special consideration for several reasons. (1) Most pumps draw a very high surge of current during startup. The inverter must have sufficient surge capacity to handle it while running any other loads that may be on. (2) Most pumps are used for automatic pressurizing. In that case, the pump will start unexpectedly, several times per day. (3) In North America, most pumps (especially submersibles) run on 230 volt power while smaller appliances and lights use the 115 volt standard. (4) AC water pumps are not very energy-efficient.

The power system (as well as the inverter) may need to be substantially larger to handle the load.

It is important to size an inverter sufficiently, especially to handle the starting surge. Oversize it still further if you want it to start the pump without causing lights to dim or blink. Ask us for help doing this because inverter manufacturers have not been supplying sufficient data for sizing in relation to pumps. To obtain 230 volts from a 115 volt inverter, either use two inverters “stacked” (if they are designed for that) or use a transformer to step up the voltage. (The pressure switch should be wired in before the transformer, so the transformer will not be a phantom load.)

As an alternative, you may consider using a DC powered pump. It will be completely independent from the inverter. Efficient DC pumps have been developed especially for renewable energy systems. They can pump water using 1/3 to 1/2 the energy of an AC pump. DC pumps are specialized and therefore more expensive than AC pumps, but an extra $1000 spent on a DC pump can save $2000 in total system cost.

Inverter Quality – You Get What You Pay For

A good inverter is reliable and able to handle a wide variety of loads without wasting lots of energy. It is well protected from surges from nearby lightning and static, and from surges that bounce back from motors under overload conditions. A good inverter is an industrial quality device that is proven and certified for safety, and can last for decades. A cheap inverter may soon end up in the junk pile, and can even be a fire hazard. Consider an inverter to be a foundation component. Buy a good one that allows for future expansion of your needs.


Pumped hydro dams are prominently used as energy storage in East Africa, but that is changing with the increase in renewable energy and battery energy storage systems. The Eastern Africa countries have announced a total of more than 2,000 MW in new solar PV and wind power projects over the next three years. Battery systems in both Front Of The Meter (FOTM) and Behind The Meter (BTM) applications provide for energy access leading to rural electrification, diesel generator replacement, and support grid systems.


Countries such as Libya, Egypt, Sudan, and the Democratic Republic of Congo (DRC), Ethiopia, Kenya, Rwanda, Tanzania, and Uganda are in Eastern Africa Power Pool (EAPP). In East Africa, pumped hydro dams are usually the main source of energy storage. In essence, a scan across most countries in the region shows that reliance on hydroelectricity is significant. Lately, other sources of generation, namely wind and solar, are starting to be built at utility-scale, and that has driven the conversation towards deployment of battery energy storage. This storage interest is particularly strong in Kenya, where variable renewable energy generation now accounts for 14% of installed generation capacity.

The Eastern Africa countries have announced more than 2,000 MW in new solar PV and wind power projects. These new projects are estimated to start online over the next three years. On the commercial and industrial front, Battery Energy Storage System (BESS) technologies have made headway, especially in both Front Of The Meter (FOTM) and Behind The Meter (BTM) applications.

The use cases lend themselves to three broad categories:

Energy Access Projects / Rural Electrification

Diesel Abatement / Replacement

Weak Grid Mitigation.

Energy access / Rural electrification

Various rural electrification programs and private sector-led investments across Kenya, Uganda, Tanzania, Rwanda, Ethiopia, South Sudan have deployed dozens of hybrid micro-grids (solar plus BESS plus generator). These represent the most common and only FOTM BESS applications in the region. Lead-acid batteries have dominated the market space due to lower capital expenditures (Capex), but Lithium BESS installations are making their mark.

Energy access projects are designed to provide towns and villages with reliable and cost-effective renewable energy, often displacing diesel generators and the darkness.

Some projects include:

A 2.3 MWh BESS coupled with a 450KWp solar PV site in Eritrea

A 1.9 MWh BESS coupled with a 400KWp solar PV at another site in Eritrea

A 2 MWh BESS coupled with a 1.5MWp solar PV site in DRC

Ethiopian Government pilot program with 6.5 MWh of BESS spread across 12 rural electrification sites

Kenyan Government pilot program with 11.2 MWh of BESS spread across 7 rural electrification sites.

Diesel abatement

This market segment has seen several hybrid mini-grids deployed to supplant thermal generation as the primary power source in commercial facilities that are situated away from the reach of the main grid. With the prices of the primary fuel source, diesel in the region of USD $1.00/liter, which translates into a Levelized Cost of Energy (LCOE) of USD $0.35/kWh, a combined solar + BESS LCOE in the region of USD $0.18-$0.25 has proven very competitive. Adoption has, however, been slowed down by the high initial Capex associated with switching. More is needed to provide well-matched financing to spur uptake.

Notable diesel abatement projects include:

A 1.3MWh BESS paired with a 660KWp at a game lodge in Kenya

A 500kWh BESS at an off-grid lodge in Tanzania

A 700kWh BESS at an office complex in South Sudan

Weak grid mitigation

In industrial hubs, most activity in Eastern Africa is concentrated, which is well supplied by the national grid. However, you do come across agricultural-processing facilities that are located relatively far from these industrial parks. Often, they happen to be situated at the end of a long distribution line with brownouts. Brownouts are voltage and frequency fluctuations leading to equipment at the factory sites being damaged or rendered unusable. By combining on-site generation (Solar PV) and BESS, grid-interactive mini-grids solve the brownouts problem. The advanced BESS controls enable these sites to monitor grid conditions and island the site when there is a grid outage or severe deterioration on power quality.

A notable weak grid mitigation project is a 4 MWh BESS co-located with a 1.5MW Solar PV + grid at a Tea Plantation and factory in Kenya.