= Microgrid
{wiki}
A <microgrid> is a bounded group of interconnected <electrical loads> and <distributed energy resources> that can be controlled as one entity. Its defining boundary and coordinated operation matter: a collection of nearby generators is not sufficient by itself. A <microgrid> may exchange <power> with an external <electric power system>, while <islanded microgrid operation> supplies its connected <electrical loads> without that external connection. The DOE overview identifies generation, storage, and the controller as interacting equipment, rather than treating storage capacity alone as a guarantee of service.<Microgrid Overview by the U.S. Department of Energy>[Printed pp. 1–2, definition, main components, and Figure 1]{ref}
For a worked operating point, suppose a <microgrid> must supply $100\,\mathrm{kW}$ of <electrical load> plus $5\,\mathrm{kW}$ of losses. Its solar supply delivers $40\,\mathrm{kW}$ and an <electrical generator> supplies $30\,\mathrm{kW}$. Storage must deliver
$$
P_{\rm storage}=100+5-40-30=35\,\mathrm{kW}.
$$
If the storage system can continuously deliver $40\,\mathrm{kW}$ and has $70\,\mathrm{kWh}$ of usable output <energy>, it can support this unchanged operating point for $70/35=2\,\mathrm h$. Here usable output <energy> already accounts for the chosen discharge convention; no further conversion loss is silently subtracted.
Now let a cloud reduce the solar supply to $10\,\mathrm{kW}$. The storage demand becomes $65\,\mathrm{kW}$, above its $40\,\mathrm{kW}$ rating even with a full store. The controller must obtain more generation or reduce <electrical load>. This <power-rating limit versus energy autonomy in a microgrid> explains why an <energy> budget and an instantaneous <power> constraint must both be checked. A test of <islanded microgrid operation> therefore records the external connection state, generation and storage <power>, and the response of the connected <electrical loads>, rather than merely checking that a battery is present.
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